Gansu and Qinghai provinces, located in high altitude of the northwest of China with high-intensity ultraviolet (UV) radiation, are important oversummering and high-frequency virulence-variation areas for Puccinia striiformis f. sp. tritici (Pst) in China. To explore the effects of UV radiation on the survival and virulence variation of Pst, the UV-B sensitivity of 21 Pst isolates collected from some regions of Gansu and Qinghai provinces was investigated based on relative germination rates of the urediospores and the LT₅₀ (lethal time 50%, i.e., radiation time required to obtain a lethal rate of 50% for the Pst urediospores under certain UV-B radiation intensity) values for all the Pst isolates. The results showed that the relative germination rates of urediospores of Pst isolates from Gansu and Qinghai were extremely negatively correlated with the time length of UV-B radiation under each of the three UV-B radiation intensities (150, 200, and 250 μw·cm^-2) (P<0.000 1). The comparison results of relative germination rates and LT₅₀ values among all the isolates under the three UV-B intensities demonstrated that there were differences in sensitivity to UV-B radiation among all the Pst isolates and that the difference in sensitivity to UV-B radiation among the Pst isolates from Qinghai Province was higher than that among the Pst isolates from Gansu Province. In this study, a theoretical basis was provided for further studying virulence variation of Pst, and for monitoring, resistance breeding, and management of wheat stripe rust caused by Pst.

Microbial communities within plant root systems play significant roles in host growth and development, nutrient absorption, and disease resistance. To investigate the correlation between changes in the wheat root microbiome and the occurrence of wheat yellow mosaic, and consequently seek biological control methods for wheat yellow mosaic, this study collected wheat root samples that are healthy (H), moderately infected (M), and severely infected (S). The bacterial community structures within the wheat roots under varying degrees of infection and their environmental driving mechanisms were studied. Results revealed that as the degree of infection increased, the richness of bacterial communities within the wheat roots showed a declining trend. Bacterial community structures significantly differentiated among varying degrees of infection and were related to changes in the nutrient content of rhizosphere soil. Specifically, the genera Curtobacterium, Rhizobium, Mesorhizobium, Sphingomonas, and Luteibacter were enriched in infected wheat roots, and their relative abundance was positively correlated with the nitrate nitrogen (NO^-₃-N), available phosphorus (AP), organic carbon (SOC), total phosphorus (TP), total potassium (TK), and plant carbon (PC) content in the rhizosphere soil, but negatively correlated with ammonium nitrogen (NH⁺₄-N) and magnesium (Mg) content. The genus Pantoea was enriched in healthy wheat roots, and its relative abundance was positively correlated with plant nitrogen (PN) content. These findings indicate that changes in the bacterial community structure within wheat roots are related to the occurrence of wheat yellow mosaic and the increase in nutrient content in the rhizosphere soil.

Stripe rust (yellow rust) caused by Puccinia striiformis f. sp. tritici, leaf rust caused by P. triticina, and powdery mildew caused by Blumeria graminis f. sp. tritici are important wheat leaf diseases, which seriously affect the yield and quality of wheat. Timely identification and diagnosis of the diseases are very important for their effective management. Now it is more convenient to acquire plant disease images, but it is difficult to unify image sources in actual disease identification, thus it is very important to explore the effects of images from different sources on image-based plant disease identification. In this study, a total of 1 354 images of wheat stripe rust, wheat leaf rust and wheat powdery mildew (including individual disease images and mixed-infected leaf images) were obtained in the field by using three different image acquisition devices including a smartphone iPhone 5s, a smartphone iPhone 11, and a digital camera Nikon D700. The single lesion images of wheat stripe rust were obtained by using the lasso tool in the software Adobe Photoshop CS6 in combination with the slice tool, and the single lesion images of wheat leaf rust and wheat powdery mildew were obtained by using the slice tool in combination with the K-means clustering algorithm. A total of 9 479 segmented single lesion images were obtained, and then from them, 164 color, shape, and texture features were extracted. By using ReliefF and clustering feature selection methods, a feature combination consisting of 36 features was determined for building disease recognition models. Four training sets, three composed of the images from the three individual sources, respectively, and one composed of the images from the three different sources, were constructed. Based on each training set, disease recognition models were built by using six modeling methods including support vector machine (SVM), K-nearest neighbor (KNN), Gussian naive Bayesian, multilayer perceptron (MLP), label propagation algorithm, and self-training semi-supervised algorithm, with the optimal parameter/parameter combination obtained by using the random search method. Accuracy, precision, recall, and F1 score were used to evaluate the disease recognition performance of the built models. The results showed that, for the SVM, MLP, and self-training semi-supervised models built based on each training set consisting of the individual-source images, high accuracies, precisions, recalls, and F1 scores were achieved on both the training set used for modeling and the testing set with the same image source as the training set used for modeling, however, the corresponding values achieved on the two other testing sets with the different image sources as the training set used for mode-ling reduced, except that the accuracy, precision, recall, and F1 score of the testing set with the same image source as the training set used for modeling and the corresponding values of the testing set consisting of the images acquired by using the smartphone iPhone 11 were not much different for the self-training semi-supervised model built based on the training set consisting of the images acquired by using the smartphone iPhone 5s. Based on the training set consisting of the images from the three different sources, satisfactory recognition performances were achieved by using the built SVM, MLP, and self-training semi-supervised models; acceptable recognition performance was achieved by using the built KNN model; and the built SVM model was optimal, with the accuracies, precisions, recalls and F1 scores not less than 91.31% on all the testing sets. The results indicated that different image sources can affect image-based disease recognition and demonstrated that satisfactory recognition performance on multi-source images can be achieved by using the model built based on the training set consisting of images from different sources. In this study, some basis was provided for further studies on the automatic and intelligent recognition of wheat diseases.

Wheat stripe rust caused by Puccinia striiformis f. sp. tritici (Pst), is an epidemic disease which seriously affects wheat production and food security in China. Qinghai Province is a frequent epidemic region and an important part of the northwest over-summering region of wheat stripe rust in China. The eastern agricultural region is the main wheat production region in Qinghai Province. Understanding the population genetic structure of Pst in this region is helpful to elucidate the origin and relationship of wheat stripe rust and provide scientific basis for the control of wheat stripe rust. The population genetic structure of 185 Pst isolates in 9 Counties (Districts) of eastern Qinghai Province were analyzed using 13 pairs of SSR primers. The results showed that the genetic variation mainly comes from individuals within the subpopulations. Huzhu County subpopulation had the highest genetic diversity, and Hualong County subpopulation had the highest genotype diversity. It was speculated that Huzhu County and Hualong County might be the genetic diversity center of Pst population in eastern Qinghai Province. The Fst value showed that the genetic differentiation of Pst populations in eastern Qinghai Province was distinct. Bayesian clustering, DAPC, PCoA and phylogenetic clustering reflected that there were three population groups. The shared genotypes were distributed among the subpopulations in Hualong County, Huzhu County, Datong County and Huangzhong District, indicating that there was close Pst inoculum exchange among them; The discovery of a large number of exclusive genotypes suggested that there were relatively independent genetic populations. The results of linkage disequilibrium analysis showed that sexual reproduction signals were detected in the subpopulation of Jianzha County, and no sexual reproduction signals were detected in the subpopulation of other Counties (Districts). On the whole, the Pst population in the eastern Qinghai Pro-vince showed mixed reproductive characteristics of both sexual and asexual reproduction. In conclusion, it was confirmed that the Pst population in eastern Qinghai Province has both long-distance transmission and relatively independent characteristics, and is an important over-summering and variation base of Pst in China.

In recent years, resistance of Magnaporthe oryzae, which causes rice blast, to isoprothiolane has been reported in several provinces, such as Shandong, Heilongjiang, and Liaoning Province. In the current study, 101 M. oryzae isolates were collected from rice field in Jiangsu Province in 2019, and 13 isolates were consi-dered as isoprothiolane-resistant isolates. The resistance frequency was 12.9% in Jiangsu Province while resistance frequencies were 40.0%, 33.3%, 11.5%, 5.0% and 5.9% in Xuzhou, Huai’an, Lianyungang, Dongtai, and Yixing city, respectively. However, no isoprothiolane-resistant isolate was detected in Yizheng city. The EC₅₀ values of all 13 isoprothiolane-resistant isolates were ranged from 15.0 to 20.6 mg·L^-1, and were lowly resistant to isoprothiolane with resistance factors (RF) less than 5.0. Only 2 isolates (2019-33 and 2019-45) from the 13 isoprothiolane-resistant isolates showed reduced fitness. Furthermore, all the 13 isoprothiolane-resistant isolates had no cross-resistance with pyrimethanil, imidazamine and ricinamide, and there was no mutation in the gene MoIRR which was reported to be related with the isoprothiolane resistance in M. oryzae.

The objective of this work was to analyze the distribution of Streptomyces scabies on potato plants and its population dynamics in the field. The plant samples from different growing environments, and the soil samples at different plant growth stages were collected. Two molecular techniques, regular PCR and quantitative PCR (qPCR), were used for the qualitative and quantitative analysis of the pathogens. The scab-pathogen-specific amplified band (184 bp) was detected in all diseased tissue samples including roots, stolons, tubers, stems and leaves from diseased field, greenhouse potted plants and minituber seedbeds. However, there were no such bands in the corresponding tissues of healthy plants. The qPCR detection results showed that the spore equivalents per gram of different tissue samples (diseased field/pot plants/minituber seedbed) were: leaves (7.63/8.06/20.49)×10³, stems (2.67/4.75/73.35)×10⁴, stolons (56.84/3.78/79.88)×10⁵, tubers (1.67/2.60/43.47)×10⁷, roots (2.51/51.79/8.31)×10⁵. During the different growth periods of potato in the diseased field, the spore equivalents of pathogens per gram of free soils and rhizosphere soils were (2.12-9.18)×10⁴ and (2.31-14.03)×10⁴ respectively, and the tuber swelling stage was higher than others. Further tracking by quantitative detection was conducted in order to reveal the relative amount of pathogens in different parts of diseased plants. The testing results showed that the range of spore equivalents per gram were leaves (4.62-23.76)×10³, stems (6.12-77.08)×10³, stolons (2.75-4.57)×10⁴, roots (1.41-2.36)×10⁵, tubers 3.43×10⁴-2.04×10⁷ at four stages of seedling, tuber forming, tuber swelling and harvest respectively. This study preliminarily investigated the distribution of Streptomyces scabies on potato plants and its population dynamics in the field. It laid a foundation for further study on the infection mechanism and occurrence regularity of the common scab disease.

Zucchini green mottle mosaic virus (ZGMMV), belonging to the genus Tobamovirus, was newly reported from China in 2018. In this study, we purified ZGMMV from field-grown bottle gourd sample, and inoculated bottle gourd (Lagenaria siceraria), watermelon (Citrullus lanatus), muskmelon (Cucumis melo), cucumber (C. sativus), zucchini (Cucurbita pepo), pumpkin (Cucurbita moschata), luffa (Luffa cylindrica), Nicotiana benthamiana, N. glutinosa and N. occidentalis at the seedling stage. Through the symptom observation, serological and molecular detection, the host symptoms and range were investigated. The results showed that ZGMMV could infect all tested plants. The symptoms were mosaic, mottle and chlorotic spots on the leaves of all inoculated plants. In addition, necrotic spots on stem and flesh decay were observed in watermelon, and chlorotic spots appeared on the fruit surface of muskmelon. We studied the transmission modes through pruning, drip irrigation and seeds. Results showed that ZGMMV can be transmitted by mechanical pruning, drip irrigation water and seeds. It was confirmed that one percent of seed transmission occurred in bottle gourd, watermelon and muskmelon. These results will help us to design effective prevention and control strategy for the virus.

In order to clarify the virulence change of Blumeria graminis f.sp. tritici population in Anhui Pro-vince in recent years, forty-one differential hosts were used to monitor and analyze the virulence of Blumeria graminis population in Anhui Province in 2010, 2015 and 2019. The results showed that the average virulence frequencies of the pathogen population to the resistance genes or combinations Pm3c, Pm5a, Pm7, Pm19, Pm3d, Pm17, Pm6, Pm1a, Pm3a, Pm3f, Pm8, Pm1+2+9 and Pm3e were higher than 70%, indicating that these genes or combinations had lost their resistance in wheat production in Anhui Province and could not be used in wheat breeding for disease resistance. The virulence frequencies of Pm12, Pm21, Pm16, Pm1c, Pm35, Pm13 and Pm2+MLD were lower than 20%, indicating that these genes or combinations had good resistance and could be used in wheat breeding for disease resistance. The results of principal component analysis of the virulence data of Blumeria graminis showed that the virulence structures of the populations in 2010, 2015 and 2019 could be regarded as a group on a whole, but there were some differences among the populations in the three years. So the continuous monitoring of the pathogen population virulence in Anhui Province should be strengthened. It will be helpful for the prediction of wheat powdery mildew, wheat breeding for disease resistance and the rational distribution of wheat varieties in Anhui Province.

Longnan, located in southern Gansu, is a virulence variable region (hotspot) for the wheat stripe rust pathogen Puccinia striiformis f. sp. tritici (Pst), a frequent epidemic region for wheat stripe rust, and an important area for management of the disease in China. Determination of the role of barberry (Berberis) as alternate host for Pst in occurrence of wheat stipe rust in Longnan will be beneficial for understanding origin of new races of the pathogen and guiding integrated management of the disease. In the present study, Pst isolates were recovered from naturally rusted barberry (B. aggregata) and wheat plants in field adjacent to the diseased barberry bushes in spring respectively. Nineteen Pst single-uredinium (SU) isolates from the rusted barberry produced 5 virulence patterns (VPs) of VP1-VP5 based on tests on the routine classical differential hosts that are used to differentiating Chinese Pst races, indicating that all of the 19 Pst SU isolates of 5 VPs were new. The 19 Pst SU isolates generated 17 various VPs on a set of combined differentials consisting of near isogenic lines (NILs) and wheat genotypes carrying Yr genes. Twenty nine SU Pst isolates from wheat fields gave rise to 10 VPs of VP1-VP10, identifying that all of them were new races. The 29 SU Pst isolates showed 24 different VPs on the set of the same combined differentials as mentioned the above. Comparisons between the two Pst populations showed that the shared pathotypes VP1-VP5 were shared, and that virulence patterns of some of Pst isolates from the diseased barberry were different from those from wheat fields. Analyses using principal coordinate analysis and clustering of phenotypes based on virulence on the combined differentials indicated the existence of gene flow between both populations from the naturally rusted barberry and wheat fields close to the diseased barberry bushes. Altogether, the results indicated that under natural conditions occurrence of Pst sexual reproduction on wild susceptible Berberis species in Longnan is routine, and that susceptible Berberis species play in a role in providing aeciospores-derived from barberry plants as inocula to cause stripe rust infection on wheat in this area. Therefore, treatment of barberry bushes should be considered in integrated management of wheat stripe rust in Longnan. This strategy will be apt to reduce rates of generating new races of Pst and breakdown of the resistance of wheat cultivars against stripe rust, extending utilization of stripe rust-resistant wheat cultivars and decreasing spread of new races to wheat production areas in eastern China for ensuring safe production of wheat.

An outbreak of sesame bacterial wilt caused by Ralatonia solanacearum was observed after first interplanting of citrus-sesame in an 11-years old orange orchard. To investigate the original infection pathogen, a strain JXRs02 was screened from the tissues of sesame infected with Ralstonia solanacearum. By morphology, molecular biology, and cluster analysis, JXRs02 was identified as R. solanacearum phylotypeⅠ. Four kinds of weeds including Amaranthus blitum, Alligator alternanthera, Feather cockscomb and Erigeron canadensis appeared in the orange orchard were inoculated with strain JXRs02 by pin prick. The results showed that JXRs02 could infect and cause wilt symptoms in Am. blitum. And the pathogen in the infected tissues of Am. blitum was identified as R. solanacearum by Loop-mediated isothermal amplification (LAMP). According to Koch’s postulates, the molecular biological methods were applied to verify that the pathogenic strains which are pathogenic to the Am. blitum or the pathogen causing the symptoms of sesame wilt are the R. solanacearum strains of phylotype I. Meanwhile, the results also showed that R. solanacearum isolated from the infected tissues of sesame could multiply in the rhizospheric soil of Am. blitum, Al. alternanthera, F. cockscomb and E. canadensis. These results indicated that Am. blitum, Al. alternanthera, F. cockscomb and E. canadensis may be the intermediate host of R. solanacearum, and the pathogen accumulated in its rhizospheric soil may be the primary source of R. solanacearum after citrus trees were interplanted with sesame cultivars. These data could provide scientific guidance on disease control strategies of bacterial wilt disease on crops.

Sugarcane white leaf (SCWL) is a devastating disease caused by phytoplasmas, which is extremely harmful to sugarcane production. In order to clarify the occurrence regularity of SCWL in different cultivars and different crop cycles, in 2018, we conducted field investigation and nested PCR detection of SCWL in cane-planting areas of Mangweng and Hepai in Gengma, where SCWL was the most serious in China. The results of field investigation showed that the natural incidence rate of different varieties was different. The average disease incidence rate in Yuetang60 was the highest (73.50%) while Liucheng05-136 had the lowest (13.67%). The na-tural incidence rate in newly planted sugarcane was the lowest (32.38%), whereas, in the three-year ratoon sugarcane it was the highest (64.33%). The results of pathogen detection showed that the positive detection rate in all varieties was above 90%. The positive detection rate of Yingyu91-59 was the lowest (90.95%) and Liucheng05-136 was the highest (96.67%), the positive detection rate of asymptomatic samples was 81.53%, and the two and three-year ratoon sugarcane had the highest positive detection rate (96.67%). The results of this study showed that the incidence of SCWL increased with the increase of crop cycle, and the field investigation based on white leaf symptoms could not accurately reflect the actual occurrence of SCWL.

Necrotic lesion is one class of important diseases on bagged apple fruits, which causes 3%~10% loss every year, and black spot is one kind disease of necrotic lesion. In order to understand the pathogen, pathogenic mechanism and conditions causing black spot on bagged apple fruit and provide the bases for disease control, we conducted several experiments, including pathogen isolation, inoculation, and disease induction assays. The results showed that Trichothecium roseum was the pathogen of black spot disease. A large number of T. roseum were colonized on younger fruit surface 30 days after apple bloom. Younger apple fruits collected from orchard without fungicides spraying began to produce black spot after 3 days of incubation at 20℃~30℃ and 100% relative humidity (RH), and the black spot number was increased with prolongation of incubation period within 2 weeks. Suberinization of the pulp cells was induced when the pathogen penetrated into the host tissue, which in turn prevented the growth and expansion of the pathogen. The young apple fruit sampled in late May can produced black spots, while the lesion size is limited. The Fuji apple fruit were susceptible to black spot pathogens in early July, and black spot lesions induced at 25℃ and 100% RH were large in number. The resistance of fruit against the disease increased significantly in August. All the 9 tested fungicides can effectively inhibit development of the black spot disease and reduce the disease incidence, but none of which can completely prevent the formation of black spots. Therefore, it is important for disease control by spraying fungicides to decrease pathogen content of the fruit before bagging.

Barley yellow striate mosaic virus (BYSMV) is a newly identified virus causing disease in wheat-growing regions in China. Investigation of the transmission pattern and characteristics of the BYSMV by the insect vector is important to determine the periodicity of this disease so as to develop effective preventive methods. Preliminary results revealed that BYSMV could only be transmitted by Laodelphax striatellus Fallén. In Laodelphax striatellus Fallén, the minimum virus circulative periods was 6 days. Both the minimum viral acquisition periods of second- and third-instar nymphs and the inoculation feeding time were 1 min. For wheat seedlings, the minimum latent period of BYSMV was 5 days. These results indicated that Laodelphax striatellus Fallén has a high capacity for acquisition and transmission of BYSMV. This study provides the experimental basis for further study of the host range and disease circle of BYSMV, and also was helpful for the development of effective antiviral strategies.

For earlier and more accurate assessment efficacy of three kinds of fungicides on wheat stripe rust, the molecular disease index (MDI) of latent period obtained by real-time PCR and field actual disease were analyzed in this study. The induction centers among wheat cultivars Mingxian 169 and Jing 0045 experimental plots were inoculated with urediniospore of Puccinia striiformis f. sp. tritici (Pst) during the returning green-jointing stage and eradicated when these plants showed disease fully. Seed treatment with 2% Tebuconazole was conducted before sowed. 25% Azoxystrobin and 30% difenoconazole propiconazole were sprayed at 21 and 28 d after inoculation, respectively. Disease incidence and severity of different treatments were assessed, and disease index (DI), area under disease development curve (AUDPC) were calculated. The results revealed that plots treated with azoxystrobin and difenoconazole·propiconazole showed light symptoms of wheat stripe rust and disease development was restricted within certain ranges, while Tebuconazole treated plots showed severe symptoms with larger ranges. Samples of wheat cultivar Jing 0045 were collected at 24 and 33 d after the induction centers inoculation, respectively. Duplex real-time PCR was applied to quantify and MDI was obtained. The results indicated that the regressions between MDI and AUDPC were significant; Azoxystrobin and difenoconazole propiconazole had continued inhibition effect to Pst in latent period, while seed treatment of Tebuconazole showed inhibition effect just at the beginning of latent period.

Daily sporec on centration of Blumeria graminis f. sp. tritici were monitored using Burkard volumetric spore samplers in the air of moderately susceptible variety Zhongmai2 and highly susceptible variety Jingshuang16 wheat fields in 2014 and 2015.Daily meteorological factors were recorded by meteorological station in the fields. The correlations were analyzed between spore concentration and meteorological factors, such as air temperature, humidity, rainfall, wind speed and solar radiation. The results showed that spore concentration was mainly positively and significantly correlated to air temperature(r>0.348 3,P<0.05). Then the correlations were calculated between disease index (DI)and four kind of accumulated spore concentrations, which were the accumulated spore concentration before the day of disease measuring, and the accumulated spore concentration before the current week of disease measuring, and the accumulated spore concentration in the previous week of disease measuring, and the accumulated spore concentration in the current week of disease measuring respectively. The data showed that there were exponential relationships between DI and the accumulated spore concentration in mo-derately susceptible variety Zhongmai2 wheat fields in 2014 and 2015, and the best DI estimating model was based on the accumulated spore concentration before the day of disease measuring or on the accumulated spore concentration before the current week of disease measuring; there were mainly logarithmic relationships between DI and the accumulated spore concentration in highly susceptible variety Jingshuang16 wheat fields in 2014 and 2015, and the best DI estimating model was based on the accumulated spore concentration before the current week of disease measuring.

In order to predict the dynamic variation of Puccinia striiformis f. sp. tritici in the northwest of Hubei province, the parasitic fitness of the most prevalent isolates CYR32, CYR33 were estimated through testing resistant components on wheat cultivars, Zhengmai 9023, Emai 352, Xiangmai 55, Xiaoyan 22 and Mingxian169. The results showed that the infectivity was the most important component of parasitic fitness, and then spread capacity and sporulation capacity. The mathematical models had been developed to estimate three principal components of pathogen parasitic fitness. In all, the relative parasitic fitness of isolates CYR32, CYR33 was high,and CYR32 was little higher than that of CYR33. The relative parasitic fitness on wheat cultivars,E-mai352, Xiang-mai55, was lower than that of other hosts.

Wheat stripe rust is one of the most destructive wheat diseases in China and frequently resulted in serious yield loss in wheat production. Growing resistant wheat cultivars is considered as the most economic, effective, and environmental-friendly approach for controlling the disease. However, the resistance of wheat cultivars was overcome by emergence of new races of Puccinia striiformis f. sp. tritici (Pst), the causal fungus of wheat stripe rust, within a few years after release of the resistant cultivars. Previous studies demonstrated that the loss of resistance of wheat cultivars resulted from emergence of new rust races due to virulence variation of the pathogen. In recent years, as the discovery of barberry (Berberis spp.) serving as alternate host for Pst, we firstly reported that Pst completes its sexual reproduction on wild barberry under natural conditions in China. Our objectives in this study were therefore to isolate Pst samples from naturally infected Berberis, establish their single-uredium populations, test their virulence based on the differential set, and analyze virulence characteristics of their single-uredium populations. We isolated 8 Pst samples from 3 Berberis spp. collected from Gansu and Shaanxi provinces in 2015. Based on their virulence tests and analyses, only one Pst sample was matched to the known Pst race Su11-126 in virulence patterns, and the remaining 7 were new races. Out of 93 isolated single-uredium populations that produced 47 virulence patterns including 14 known race types and 33 new race types, fifty-six were matched with the known Pst races in virulence patterns and 37 were new. In this study, we obtained more evidences for supporting the existence of sexual reproduction of Pst on Berberis spp. under natural conditions in China, which led to the generation of new races of the pathogen. Our results confirmed that wild Berberis spp. play a role in completion of the whole life cycle of Pst and in disease cycle of wheat stripe rust in China.

Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is one of the most important wheat diseases worldwide. However, the relationship of latent PST in overwinter wheat leaves and the disease index (DI) of the next spring remains obscure. To address this issue, a systemic study with the combination of field sampling and DI investigation, molecular PST detection and correlation analysis was performed. Specially, in winter, sampling of wheat leaves was conducted simultaneously with GPS positioning in Xiangyang, Yicheng and Zaoyang, the overwinter regions of PST. Duplex real-time PCR was used to quantify the latent PST in the sampled leaves. In spring, disease investigations were conducted simultaneously in the same sampling positions. Sampling areas were divided into different districts based on town/suburb district. The MDI and DI of each district were obtained by calculating the average of all sampling and investigation points within the district. Each MDI of a district was converted to risk index (RI) by a formula, and then RI was calculated for correlation with DI. Meanwhile, spatial analyses were conducted based on coordinate data. The results showed that the quantities of PST in latent were significantly correlated with the disease in spring, and their distributions and degree of disease were highly correlated with the distance to the Han river.

The epidemic processes of grape downy mildew were investigated and analyzed systematically in the field plots, Shenyang, 2012-2014. The correlation between epidemic dynamic of the disease and meteorological factors were analyzed in different years. The results were shown that the seasonal epidemic curve of grape downy mildew in Shenyang was a typical single peak S curve. The logistic model could reflect the temporal dynamic of grape downy mildew well by using SPSS19.0, and the epidemic periods were derived. The exponential phase was from early-July to late-July, which was the most effective period for chemical control. The logistic phase was from late-July to late-August, and the degenerating phase was from late-August to the end of grape growing season. Days of the disease occurrence, every epidemic phase’s days and the maximum disease index in different growing seasons were different significantly, but the trend was basically consistent with the logistic model. The apparent infection rate of the disease in each epidemic stage was shown: exponential phase＞logistic phase＞degenerating phase, exponential phase and logistic phase were the key periods of epidemic decision of grape downy mildew in the different growing seasons. Meteorological factors had significant effect on the epidemic degree of grape downy mildew. The apparent infection rate was a significant positive correlation with relative humidity, rainfall and leaf wetness duration before 7 days respectively, but was a significant negative correlation with temperature before 7 days. It was shown that the four meteorological factors were the key factors affecting grape downy mildew in Shenyang.

In order to predict and control wheat powdery mildew ( Blumeria graminis f. sp. tritici) , we studied the sensitivity to temperature on pathogen isolates and the relationship between temperature-sensitivity and their virulences. In 2013, a total of 90 isolates were sampled from 5 provinces (cities)，including Yunnan, Sichuan, Beijing, Henan and Shaanxi. The isolates were tested on their sensitivity to temperature by using the detached leaf segment method and their virulences were determined by 32 wheat varieties or lines with known powdery mildew resistant genes. The results showed that the mean ET50 of tested isolates was 23.22℃. The highest and the lowest ET50 of the isolates were 25.15℃ and 19.78℃, respectively. The ET50 value of 73.34% of isolates ranged from 22.0℃ to 24.0℃, and 10% of isolates below 22℃, 16.67% of isolates above 24℃. The virulence gene diversity index of the 90 B. graminis f. sp. tritici isolates was 0.237 0. The highest index was recorded on isolates from Sichuan Province with H = 0.221 2 while the lowest index was recorded on isolates from Henan Province with H = 0.197 5. The results showed that there was a significant negative correlation between temperature-sensitivity and virulence diversity of B. graminis f. sp. tritici populations.

Epidemic processes and yield losses of early leaf spot (Cercospora arachidicola) and web blotch (Phoma arachidicola) of peanut were analyzed in the field plots. The results showed that there were no significant correlations between the two diseases at the early stage when they occurred together, but the negative correlation between the two diseases gradually increased with the development of the disease. This phenomenon showed that there was an inhibitory effect between the two diseases. Disease severity was different when C. arachidicola and P. arachidicola were inoculated in the different growth stage, early leaf spot and web blotch were more serious when C. arachidicola and P. arachidicola were inoculated in the early flowering stage and the flowering stage than in the late flowering stage, and the results demonstrated the inhibitory effect. The yield loss when two diseases occurred together was less than the sum of that caused by each individual disease. Yield loss of Baisha1016 caused by the two diseases occurring together was about 77.2%-85.7% of the sum of yield loss that caused by the corresponding individual disease. Yield loss of Silihong caused by the two diseases occurring together was about 76.1%-79.6% of the sum of yield loss that caused by the corresponding individual disease. The yield losses of two cultivars were both reduced gradually with the delay of inoculation period at the different growth stage.

Tibet Province is an independent epidemic area for wheat stripe rust in China. The wheat stripe rust is one of the most destructive diseases on wheat, affecting safe production of wheat in Tibet. Linzhi prefecture has been considered an area where wheat stripe rust occurs frequently and is serious epidemic. It was verified recently that Berberis spp. serve as alternate host for Puccinia striiformis f. sp. tritici (the causal fungus of wheat stripe rust, Pst), playing a role in resulting in variation in pathogenicity to produce new Pst races and in occurrence of the disease in China. Linzhi has a distribution of plenty of Berberis spp., however, it is lack of studies on Berberis spp. severing as alternate host for Pst in Linzhi prefecture so far. In this study, whether Berberis spp can serve as alternate host for Pst were identified based on investigations on Berberis spp. in Linzhi, Tibet where wheat stripe rust occurs frequently. The results showed that six Berberis spp. are very general in geographic distribution, and were identified to serve as alternate host for Pst. This provides a basis for further studying on occurrence and epidemics of wheat stripe rust, pathogenic variation of Pst, and perfecting integrated control of the disease in Tibet.

Conidia of Blumeria graminis f. sp. tritici(Bgt)in the air were monitored by Burkard volumetric spore samplers in 2012 and 2013. Conidia concentration of Bgt within the canopy was positively correlated with above the canopy and was significantly higher than that above the canopy. Conidia concentration raised along with time, reached the maximum concentration at filling stage of wheat, and then declined. Time series analysis showed that conidia concentration in the fields was fitted with ARIMA (1, 1, 0) models. A model was constructed based on the significant correlation between conidia concentrations in the air and temperature. Two models for prediction of disease index were established by inoculum variable only, and by both inoculum and weather va-riables, resprctively. The model based on inoculum only has more universal applicability to predicting disease index in comparison with the model based on both inoculum and weather variables.

Fourty-three isolates of Colletotrichum spp. were isolated from diseased Hevea brasiliensis collected from 4 different counties in Hainan Province, China. The isolates were identified and the sensitivity of these isolates to carbendazim and prochloraz was determined by mycelium growth rate method. The results indicated that 23 isolates were C. gloesporioides and 20 isolates were C. acutatum. The EC₅₀ values of 43 isolates ranged from (0.332 3-7.425 6) and (0.009 1-0.113 3) mg·L^-1, respectively, with an average value of (1.714 1±1.684 7) and (0.036 8±0.023 8) mg·L^-1, respectively. The average EC₅₀ value of C. acutatum to carbendazim was significantly higher than C. gloesporioides, with an average value of (2.922 7±1.556 3) and (0.663 2±0.194 4) mg·L^-1, respectively. There were no significant difference between the average EC₅₀ value of C. acutatum and C. gloesporioides to prochloraz, with an average value of (0.038 3±0.015 2) and (0.035 5±0.020 1) mg·L^-1, respectively. There was no significant correlation between the EC₅₀ values of the tested isolates to carbendazim and prochloraz, which indicated that these two fungicides can be alternative use in disease control.

Glomerella leaf spot (GLP) caused by Glomerella cingulata is a new kind of apple disease in China. To understand the requirements and developments of sporulation by the pathogen, and provide information for developing methods to forecast and control the disease, effect of temperature, moisture and illumination on sporulation of conidia and ascospores were investigated under artificially controlled environment. Results showed that when wetted disease leaves were cultivated in the environment at 15℃-30℃ with RH=100% for 2-6 days, a large amount of acervuli and conidia were produced on diseased leaves. The largest amount of conidia was observed at 30℃ among all the temperature treatments and only 2 days were required for conidial formation. Perithecia and ascospores were also produced on the diseased leaves when cultured at 15℃ to 30℃ for 20-30 days. The optimum temperature for G. cingulate to produce perithecia was 25℃ and formation of perithecia required saturated relative humidity or wetted environment. Perithecia and ascospores were also produced by the single-spore isolates of G. cingulata after cultivated on PDA at the optimum temperature (25℃) for 20-30 days. Result also showed that UV light (254 nm), black light (365 nm) and sunlight can promote the sporulation of the pathogen.

To understand the virulences of Puccinia triticina from Yunnan, Sichuan, Qinghai, Shanxi, Gansu and Henan in 2011-2012 crop season, 31 differential lines were used to identify the virulence phenotype and frequency of the 180 P. triticina collected from the six provinces. In total, 62 virulence phenotypes were detected mainly including SHJ(10%)、THT(8.9%)、PHK(6.1%)、SHN(5%)、PHT(4.4%)、SHD(4.4%)、PCH(3.9%)、THP(3.3%)and THK(3.3%). Virulence frequency to Lr2c, Lr10, Lr14a, Lr14b, Lr33 and Lr36 were all above 75% in the six populations indicating the loss of resistance of corresponding resistant genes. Virulence frequency to Lr9, Lr19, Lr24, Lr25, Lr28, Lr29, Lr38 and Lr42 were all below 30% in the six populations suggesting the effectiveness of these resistance genes. Virulence frequency to Lr2a, Lr3, Lr3bg, Lr20, Lr30 and Lr32 were variable in the six populations. Virulence diversity in Yunnan and Sichuan populations were the highest, followed by Henan, Gansu and Shanxi populations, Qinghai population was the lowest.

Host resistance and fungicides are two of the main approaches used to control plant diseases in conventional agriculture. The widespread use of host resistance and fungicides selects for pathogen individuals or populations that can overcome the host defense systems or that are resistant to the applied fungicides. One hundred and twenty nine isolates of Blumeria graminis f. sp. tritici were collected from 9 provinces/cities in 2012, and inoculated onto 31 differential wheat lines of powdery mildew to test the virulence. The sensitivity of the isolates to triadimefon was tested by seed treatment and detached leaf segment methods. The correlation between virulence diversity and triadimefon-resistance was carried out by SAS software. The results showed that median EC₅₀ of isolates to triadimefon was 109.97 mg/L,the coeffective of EC₅₀ was 107.2,the mean resistance factor (RF) was 52.62.The resistant frequency of all isolates to triadimefon was up to 99.22%. The mean resistant factors of B. graminis f. sp. tritici isolates from Beijing was higher compared to the other eight provinces. Virulence diversity of B. graminis f. sp. tritici isolates from Sichuan Province was highest with the index of virulence gene diversity 0.224 1. The virulence gene diversity of isolates from Zhejiang was lowest with the index 0.096 8. The association between triadimefon-sensitivity and virulence diversity of B. graminis f. sp. tritici isolates showed that there was no significant correlation among EC₅₀, variation coefficient of EC₅₀ and virulence diversity. However, there is a logarithmic (r=0.240 4, P=0.009 6) relationship between EC₅₀ and numbers of virulence genes of 129 B. graminis f. sp. tritici isolates. These results may provide a reference for reasonable utilization of wheat resistance varieties, as well as the use of triazole fungicides.

One thousand and three hundred ninety one wheat stripe rust samples were collected from 29 counties in Gansu, Sichuan, Shaanxi, and Tibet, China during spring of 2009-2010. Nine hundred and sixty one isolates of Puccinia striiformis f. sp. tritici were recovered from those samples. Population genetic diversity of the P. striiformis f. sp. tritici population containing 961 isolates was investigated with SSR technique. The results demonstrated that the genetic diversity of Tianshui, Pingliang and Longnan populations in Gansu, and Aba, Guangyuan populations in Sichuan was much higher than that in other regions. However, the genetic diversity of Yibin, Liangshan in Sichuan, and Linzhi in Tibet was lower than that in other regions. AMOVA of SSR was carried out using Arlequin software. Results showed that main genetic variation presented mainly within populations. Populations in inland (Gansu, Shaanxi, and Sichuan) had extensive gene exchange (Nm>4), and little gene exchange was found between Tibet and inland (Nm<1). The Structure and cluster analysis also indicated that there was almost no gene exchange between Tibet and inland populations. The frequent gene exchange was found between populations of Baoji in Shaanxi and Pingliang in Gansu, among populations of Hanzhong in Shaanxi, Longnan and Tianshui in Gansu, and Guangyuan in Sichuan. There was a certain gene exchange among populations of Yibin and Liangshan in Sichuan with Aba in Sichuan, Hanzhong in Shaanxi, and Longnan in Gansu. We preliminary argue that the population of P. striiformis f. sp. tritici in Tibet may be an independent from other populations under study.

The quantity of airborne conidia of Alternaria solani (Ell. & G. Martin) in potato canopy, the severity of potato early blight and the correlation between them as well as the influence factor were investigated and analyzed systematically during the growing season. The results showed that from potato emergence to harvest (June-August), the quantity of airborne conidia of A. solani in the canopy had significant linear correlation with the disease progress of potato early blight when the disease index below 4, and the correlation declines as the disease index increasing. The weather conditions had significant effect on the quantity of airborne conidia of A. solani in potato canopy. Generally, a peak of airborne conidia of A. solani could appear in 2 days after rain. The airborne conidia were remarkably reduced when the daily average temperature (2 m above ground) was below 18℃. The quantity of airborne conidia of A. solani in the canopy was also different at the different time in a day, there were more conidia in the air from 6∶00 am to 16∶00 pm, and fewer during 17∶00 pm to 5∶00 am the following day, which count 60.95% and 39.05% of the total conidia were trapped during the whole day, respectively. The proportion of conidia of A. solani dispersed in to the air at each hour in a day had a significant negative correlation with relative air humidity and positive correlation with air temperature.

To understand the virulence dynamics and the molecular genetic structure of the wheat powdery mildew population (Blumeria graminis f.sp. tritici) in Southern Gansu, virulence and multigene genealogy of 49 powdery mildew isolates collected from Southern Gansu were analyzed. It was shown that the virulence frequency of wheat powdery mildew to resistance genes Pm12, Pm16, Pm18 and Pm21 was less than 10%, indicating that these genes could be used for resistance breeding. The virulence frequencies of Pm23, Pm25, Pm30, Pm34 and Pm35 were high (35%-95%), with difference in Longnan and Tianshui, which indicated that we should be very cautious in using these genes. The virulence frequency of Pm4b increased sharply. The powdery mildew isolates were divided into four groups except isolate 11, with a similarity index of 0.752. Gene fragment from alternative oxidase (AOX), elongation factor-1α (EFA), protein kinase A (PKA), protein phosphatase type 2A (PPA) and β-tublin (TUB) were used for multigene genealogical analysis. The result showed that the isolates could be grouped into two knots. The pathogen dispersal existed between the two cities. There was independent evolution although interchanges existed between in the two cities.

Citrus tristeza virus (CTV), Citrus tatter leaf virus (CTLV), Citrus exocortis viroid (CEVd), and Candidatus Liberibacter asiaticus (Ca. L. asiaticus) associated with Huanglongbing (HLB) are important graft\|transmissible pathogens of citrus. A rapid multiplex PCR protocol with an internal control was developed for the detection of these citrus pathogens using a timesaving two\|temperature cycling for PCR amplification. The assay was applied for rapid detection of those pathogens in field\|grown trees. The results indicated that 89.3%, 10.7%, 17.9% and 28.6% of the 28 field\|grown citrus samples were infected with CTV, CTLV, CEVd and Ca. L. asiaticus, respectively, and approximately half of the samples were co\|infected with more than one pathogen. In addition, the absence of multiple pathogens in shoot\|tip grafted budlings was evaluated with the multiplex PCR assay.

College of Plant Protection, Henan Agricultural University, Zhengzhou 450002, China)
Abstract:The cereal cyst nematode has become one of the serious diseases of wheat in recent years in China. The basic work for disease control is to clarify the infection dynamics of pest nematodes. In this study, the infection dynamics of two species of cereal cyst nematode, Heterodera avenae and H.filipjevi were assessed under field conditions in Zhengzhou of Henan. The results indicated that the wheat roots were infected by the second stage juveniles (J2s) two weeks after planting. A few of J2s developed into J3 subsequently. The first infection peak of J2s appeared at the sixth weeks after planting, and a few of the fourth stage juveniles were found in wheat roots at the same time. As the temperature decreased after 60 days of planting in the winter, the number of juvenile at different stages remained stable. As the temperature increased in the spring at 120 days after planting, the number of the second stage juveniles in roots started to increase and reached the second peak in late March and early April (150 days after planting), with fewer nematodes than those in the first infection peak. Duration of the second peak is also much shorter than the first one. Finally the larva gradually developed into white females and cysts. The infection dynamics of two CCN species are almost same, but J3, J4 and white female of H.filipjevi appeared one week earlier than H.avenae. These results provided the essential information for the control of cereal cyst nematode of wheat.

An allele specific oligonucleotide-PCR (ASO-PCR) with mismatches at the 3′ terminal of the primer was set up to detect moderately carbendazim (MBC)-resistant genotype (Codon²⁰⁰ TTC→TAC) of Fusarium asiaticum. The results showed that a pair of probe, NT-7 R1/NT-7 Err5 F with mismatches was deve-loped to successfully detect moderately MBC-resistant isolates (Codon²⁰⁰ TTC→TAC). The ASO-PCR amplification by MBCRF/MBCRR3 was conducted with the following parameters: an initial pre-heat at 94℃ for 5 min, following by 35 cycles of denaturation at 94℃ for 60 s, annealing at 56℃ for 60 s, extension at 72℃ for 60 s and terminated with a final extension at 72℃ for 15 min. 26 important plant fungi were used to test the amplification specificity of the primer pair. This method is simple,accurate and time-saving.The result was obtained within 6 h.

To provide a theoretical basis for the use of cultivar diversity on wheat powdery mildew control, the effects of cultivar diversity on wheat powdery mildew, the yield and the protein content of wheat were studied. The genetic relationship of five wheat cultivars was studied by SSR. Mixtures of two, three, four or five winter wheat cultivars and their pure stands were exposed to mixed powdery mildew races in 2007-2008 and 2008-2009. The changes of AUDPC value, yield and protein content were investigated. The results showed that relative relation of the tested five wheat cultivars was close, which might decreased the effect of the diversity. R-S mixtures were affected significantly in combinations of two winter wheat cultivars. Efficiency was strengthened along with proportion of resistance cultivar increased. The number of cultivars had no relations with disease control effect. The effect of mixture was influenced by genetic background.The effect of cultivar mixture was decreased when there are exotic pathogen. Therefore, if the mixtures were proper, cultivar mixtures have some effect on wheat powdery mildew and no effect on yield and grain protein content. So cultivar mixtures can be a measurement for powdery mildew control.

Bacterial strain L5 was isolated from soil in Yangzhou and showed inhibitory effect to many pathogenic fungi in dual-culture tests. This strain produced pyrrolnitrin and siderphore, and showed 72% efficiency to control grey mould caused by Botrytis cinerea on detached tomato leaves. The strain L5 was identified as Serratia odorifera based on sequence analysis of 16S rDNA and 16S-23S rDNA intergenic spacers (IGS), physiological and biochemical characterization. The analysis of IGS sequence found two different types of IGS in strain L5. One included the tRNA^Glu , and the other contained a cluster of tRNA^Ile and tRNA^Ala.