Jiahui Wang, Junjuan Wang, Hongsheng Shang, Xianming Chen, Xiangming Xu, and Xiaoping Hu 1 State ... more Jiahui Wang, Junjuan Wang, Hongsheng Shang, Xianming Chen, Xiangming Xu, and Xiaoping Hu 1 State Key Laboratory of Crop Stress Biology for Arid Areas and College of Plant Protection, Northwest A&F University, Taicheng Road 3, Yangling, Shaanxi 712100, China 2 Agricultural Research Service, United States Department of Agriculture and Department of Plant Pathology, Washington State University, Pullman, WA 99164-6430, U.S.A. 3 NIAB East Malling Research, New Road, East Malling, ME19 6BJ, Kent, U.K.
Crown rot (CR) and Fusarium head blight (FHB) are two serious wheat diseases caused by Fusarium p... more Crown rot (CR) and Fusarium head blight (FHB) are two serious wheat diseases caused by Fusarium pathogens in China. To identify new resistant sources for CR and FHB, 205 Chinese wheat cultivars collected from Huang-Huai wheat-growing region in China were screened for resistance. Cunmai633, LS4607, Pubing01, and Hongyun2 showed seedling resistance to CR with disease index (DI) less than 0.25. Sixteen cultivars showed adult-plant resistance to CR with DI lower than 0.10. Twenty-six cultivars showed moderate resistance to CR at seedling stage with DI from 0.26 to 0.35, and 63 cultivars showed moderate adult-plant resistance with DI from 0.11 to 0.20. Among them, Cunmai633, LS4607, Pubing01, Xinong916, Zhengda161, Xumai14017, Zhengpinmai30, Bainong8822, Jimai216, Huacheng865, Fengyumai5, and Tianmin319 showed resistance or moderate resistance to CR at both seedling and adult plant stages, with Cunmai633 showing the best resistance. Most of the cultivars (>76%) were susceptible to FHB...
Fusarium redolens was previously reported as a plant pathogen or an endophyte that is closely rel... more Fusarium redolens was previously reported as a plant pathogen or an endophyte that is closely related to F. oxysporum, a notoriously significant soilborne phytopathogen. Subsequent studies demonstrated the unique nature of F. redolens, which was considered a distinct species that causes multiple symptoms on multiple hosts. It was recently identified as a pathogen that causes root rot of American ginseng. Currently, few high-quality F. redolens genome sequences exist in the public database. Here, we report the whole-genome sequence of F. redolens strain YP04, based on a hybrid assembly of long- and short-read sequencing with PacBio and Illumina platforms, respectively. The assembly consists of 40 configs with a total length of 52.8 Mb nuclear genomic DNA and 49.6 kb complete mitochondrial genomic DNA, and encodes a total of 18,985 genes, including 18,517 protein-coding genes and 469 RNA genes which were functionally annotated. In total, 4,606 proteins were identified in the pathogen–...
Plants sense various pathogens and activate immunity responses through receptor like kinases (RLK... more Plants sense various pathogens and activate immunity responses through receptor like kinases (RLKs). Cysteine-rich receptor-like kinases (CRKs) are involved in massive transduction pathways upon perception of a pathogen. However, the roles of CRKs in response to stripe rust are unclear. In the present study, we identified a CRK gene (designated TaCRK10) from wheat variety Xiaoyan 6 (XY6), which harbors high-temperature seedling-plant (HTSP) resistance to stripe rust caused by fungal pathogen Puccinia striiformis f. sp. tritici (Pst). The expression level of TaCRK10 was induced by Pst inoculation and high temperature treatment. Knock-down of TaCRK10 by virus induced gene silencing resulted in attenuated wheat HTSP resistance to Pst, while has no effect on Pst development and host responses under normal temperatures. Notably, overexpression of TaCRK10 in susceptible variety Fielder provided resistance just under normal temperatures at fourteen days with reactive oxygen species (ROS) accumulation and defense-related gene expression of the salicylic acid (SA) pathway. Moreover, TaCRK10 physically interacted with and phosphorylated a histone variant TaH2A.1, which belongs to the H2A.W group. Silencing of TaH2A.1 suppressed wheat resistance to Pst, indicating that TaH2A.1 plays a positive role in wheat resistance to Pst. Thus, TaCRK10 serves as an important sensor of Pst infection and high temperatures, and it activates wheat resistance to Pst through regulating nuclear processes. This knowledge helps elucidate the molecular mechanism of wheat HTSP resistance to Pst and promotes efforts in developing wheat varieties with resistance to stripe rust.
American ginseng is an important herbal medicinal crop in China. In recent years, there has been ... more American ginseng is an important herbal medicinal crop in China. In recent years, there has been an increasing market demand for ginseng, but the production area has been shrinking due to problems associated with continuous monocropping. We analyzed the microbiome in bulk soils to assess whether and, if so, what changes in the bulk soil microbiome are associated with continuous American ginseng cropping. The alpha diversity of fungi and bacteria was significantly lower in the soils planted with American ginseng than the virgin (non-planted) land. The relative abundance of Fusarium spp. and Ilyonectria spp., known plant root pathogens, was much higher in the soils cropped with American ginseng than the non-planted. On the other hand, a number of bacteria with biodegradation function, such as Methylibium spp., Sphingomonas spp., Variovorax spp., and Rubrivivax spp., had lower abundance in the soils cropped with American ginseng than the non-cropped. In addition, soil pH was lower in t...
Stripe rust, caused by Puccinia striiformis f. sp. tritici Erikss., is an important disease of wh... more Stripe rust, caused by Puccinia striiformis f. sp. tritici Erikss., is an important disease of wheat worldwide. Identification of pathogen survival hot spots is important for predicting disease onset and subsequent spread to other regions, and such understanding is essential for developing integrated management strategies. We conducted field studies to determine the relationship of P. striiformis f. sp. tritici overwintering potential to winter temperatures in 10 sites in the northwest of China in three growing seasons (2011–12, 2012–13, and 2013–14). The fungus survived better in wheat cultivars with stronger winter hardiness than in those with weaker winter hardiness. Windowpane analysis suggested that P. striiformis f. sp. tritici winter survival is related to temperatures in the coldest period from mid-December to late January. β Regression showed that P. striiformis f. sp. tritici winter survival was negatively related to the number of days with daily average temperature
Potato (Solanum tuberosum L.) is one of the most important staple foods in many parts of the worl... more Potato (Solanum tuberosum L.) is one of the most important staple foods in many parts of the world including China. In recent years, Verticillium wilt has become a severe threat to potato production in China. During 2015 to 2016, 287 samples of symptomatic potato plants were collected from 15 counties in five provinces from northern China. One hundred and eighty-seven Verticillium-like colonies were isolated from these samples and identified to species based on cultural and morphological characteristics, and multigene phylogeny based on the partial sequences of actin (ACT), elongation factor 1-alpha (EF1α), glyceraldehyde-3-phosphate dehydrogenase (GPD), and tryptophan synthase (TS) genes. A consensus-rooted most parsimonious phylogenetic tree was generated from the data. One hundred and fifteen isolates comprising 61.5% of the total were identified as Verticillium dahliae, and the remaining 38.5% of the isolates were identified as V. nonalfalfae. V. dahliae was widely distributed i...
Received 6 April 2018; Accepted 6 April 2018 Author affiliations: College of Forestry, Beijing Fo... more Received 6 April 2018; Accepted 6 April 2018 Author affiliations: College of Forestry, Beijing Forestry University, Beijing, PR China; Department of Plant Pathology, College of Plant Protection, Northwest A&F University, Yangling, PR China; United States Department of Agriculture, Agricultural Research Service, 1636 E. Alisal St., Salinas, CA 93905, USA. *Correspondence: Steven J. Klosterman, Steve.Klosterman@ars.usda.gov
Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is an important disease o... more Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is an important disease of wheat worldwide. Understanding the survival of Pst during the winter is critical for predicting Pst epidemics in the spring. We used a real-time quantitative PCR (qPCR) method to quantify Pst CYR32 biomass in infected wheat seedlings under several fluctuating temperature regimes (three average temperatures 0, −5 and −10 °C, each with two daily fluctuating amplitudes 8 and 13 °C). The survival of Pst CYR32 increased with increasing average temperature but also varied greatly with the amplitude – larger amplitude led to lower survival, particularly at 0 and −5 °C. Nevertheless the survival at both amplitudes was still significantly greater than under the corresponding constant temperatures. There were small, albeit statistically significant, differences between the two cultivars (Xiaoyan 22, low winter-hardiness; Lantian 15, high winter-hardiness) in Pst CYR32 survival. This study indicated potential errors that could result from using daily average temperatures to predict Pst survival during the winter.
Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is an important disease o... more Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is an important disease on wheat, seriously threatening wheat production worldwide. China is one of the largest stripe rust epidemic regions in the world. The pathogen sexual reproduction and migration routes between Tibet and the other regions in China are still unknown. In this study, we obtained 961 Pst isolates from 1,391 wheat leaf samples from Gansu (277), Shaanxi (253), Sichuan (172), and Tibet (259), comprising 13 natural populations, and genotyped them with simple sequence repeat (SSR) markers. The isolates can be divided into two distinct clusters based on DAPC and STRUCTURE analyses. The genetic diversity of Longnan (in Gansu) and Yibin (in Sichuan) populations was the highest and lowest among the 13 populations, respectively. The hypothesis of multilocus linkage disequilibrium was rejected for the populations from Linzhi in the Himalayan, Longnan, Hanzhong, Guangyuan, Mianyang, Liangshan, and Chendu ...
Using biological control agents (BCAs) is an essential component of integrated pest and diseases ... more Using biological control agents (BCAs) is an essential component of integrated pest and diseases management. Despite much research on biocontrol of plant diseases, success in field crops has been limited with most successes being achieved in greenhouse cultivation. This lack of success is often attributed to the complex ecological processes involved in biocontrol. We used next generation sequencing (NGS) technology to study environmental fate of Bacillus subtilis, a widely used BCA, focusing on its dispersal aspect in open field and under protection. The dispersal of B. subtilis was very limited, particularly under protection. The reduction in the BCA population size was relatively small within 8 days; indeed, no overall reduction in the relative abundance was observed under the protected condition. These results suggested that limited dispersal is probably the main reason for its variable (and often low) control efficacy under field conditions. Thus to increase biocontrol efficacy,...
Alfalfa (Medicago sativa Linn.), widely grown throughout the world, is an important perennial for... more Alfalfa (Medicago sativa Linn.), widely grown throughout the world, is an important perennial forage crop. It is high in protein and digestible fiber and is an excellent source of several vitamins (A, D, E, and K) and minerals for beef cattle, horses, sheep, goats, and even humans (2). Wilt symptoms on alfalfa were observed during a disease survey in Yangling, Shaanxi, China in 2009. Symptoms included discoloration, shortened internode, and plant death. However, the vascular tissue of diseased alfalfa plants did not exhibit discoloration and typical “V” symptoms of Verticillium albo-atrum infection. Eleven fungal isolates were obtained from diseased alfalfa plants in Yangling by a tissue isolation method (1). Isolates were cultured on Czapek Dox Agar (CDA; pH 7.2) slants at 22 ± 1°C in darkness. Colonies on CDA plates were whitish and cream-white when viewed from the underside, later becoming dark gray due to the formation of gray or dark brown chlamydospores in single or in short c...
Wheat stripe rust (yellow rust), caused by Puccinia striiformis Westend f. sp. tritici Eriks. (PS... more Wheat stripe rust (yellow rust), caused by Puccinia striiformis Westend f. sp. tritici Eriks. (PST), is one of the most destructive diseases in many wheat-growing regions worldwide, including China (Chen, 2005). The yield losses caused by PST were 6.00, 3.20, 2.65, and 1.40 million metric tons, when the severe epidemics occurred in 1950, 1964, 1990, and 2002 in China, respectively (Chen et al., 2009). It seriously threatens the wheat’s production in China. Overwintering of PST is the important stage of the wheat stripe rust epidemic. The amount of overwintering PST decides the spring epidemic degree of the disease. In the natural condition, PST begins to overwinter in hypha (mycelia) in host plant when the temperature is 1~2°C. When temperature declines to -6~-7°C, it is difficult to survive for PST (Li and Zeng, 2002). But, all the studies were based on the results of field investigation. There has been lack of research on the overwintering biology at molecular level, which limited...
Verticillium dahliae kleb. is a soilborne plant pathogen which infects more than 200 plant specie... more Verticillium dahliae kleb. is a soilborne plant pathogen which infects more than 200 plant species. Microsclerotia, the main survival structures of V. dahliae and primary causal inoculum agent of host plants, may remain viable in soil more than 10 years with the lack of hosts. The quantification of microsclerotia of V. dahliae is the base for monitoring and prediction of Verticillium wilt. The number of microsclerotia in soil is usually estimated by colonies recovered from plating of soil samples in semi-selective medium and microscopic analysis. But it takes 6 to 8 weeks to complete. Hence, an alternative method to test 10-g soil samples using wet-sieving extraction of microsclerotia followed by quantification real-time PCR (qRT-PCR) assay was developed. The standard curve for quantification of V. dahliae microsclerotia was established using 10-fold dilutions for DNA of 10 000 microsclerotia. A high correlation was observed in regression analysis (R2=0.93) between qRT-PCR results a...
Verticillium wilt caused by Verticillium dahliae Kleb. is a soilborne wilt disease of many crops ... more Verticillium wilt caused by Verticillium dahliae Kleb. is a soilborne wilt disease of many crops all over the world and is difficult to control. Microsclerotia are the main resting structure of V. dahliae in soil and can survive for more than 10 years whether associated with or without debris. They are composed of compact masses of thick-walled, pigmented cells which originate from swollen, septate hyphae by a process of budding. The quantity of viable microsclerotium determines the severity of Verticillium wilt, e.g. on cotton and on strawberry. Surveys in the past 5 decades showed that the diseased area of Verticillium wilt of cotton kept expanding. In 2012, diseased area of Verticillium wilt of cotton was about 3000,000 acres in China. Current control measures, including chemical control, biofumigation, bio-control, crop rotation, failed to control this kind of disease. Easton and Nagle (1986) claimed that Verticillium wilt was efficient controlled through cropping to a green pea...
Spatial patterns of pathogen inoculum in field soils and the resulting patterns of disease may re... more Spatial patterns of pathogen inoculum in field soils and the resulting patterns of disease may reflect the underlying mechanisms of pathogen dispersal. This knowledge can be used to design more efficient sampling schemes for assessing diseases. Spatial patterns of Verticillium dahliae microsclerotia were characterized in commercial cotton fields through quadrat and point sampling in 1994 and 2013, respectively. Furthermore, cotton plants with wilt symptoms, caused by V. dahliae, were assessed in six commercial cotton fields in 2013. Soil samples were assayed for the density of microsclerotia (expressed as CFU g-1 of soil) using a wet-sieving plating method and a real-time quantitative PCR method for the 1994 and 2013 study, respectively. The estimated inoculum threshold for causing wilt development on individual plants varied with the three fields: ca. 1.6 CFU g-1 of soil for one field, and 7.2 CFU g-1 of soil for the other two. Both quadrat and point sampling spatial analyses showe...
Jiahui Wang, Junjuan Wang, Hongsheng Shang, Xianming Chen, Xiangming Xu, and Xiaoping Hu 1 State ... more Jiahui Wang, Junjuan Wang, Hongsheng Shang, Xianming Chen, Xiangming Xu, and Xiaoping Hu 1 State Key Laboratory of Crop Stress Biology for Arid Areas and College of Plant Protection, Northwest A&F University, Taicheng Road 3, Yangling, Shaanxi 712100, China 2 Agricultural Research Service, United States Department of Agriculture and Department of Plant Pathology, Washington State University, Pullman, WA 99164-6430, U.S.A. 3 NIAB East Malling Research, New Road, East Malling, ME19 6BJ, Kent, U.K.
Crown rot (CR) and Fusarium head blight (FHB) are two serious wheat diseases caused by Fusarium p... more Crown rot (CR) and Fusarium head blight (FHB) are two serious wheat diseases caused by Fusarium pathogens in China. To identify new resistant sources for CR and FHB, 205 Chinese wheat cultivars collected from Huang-Huai wheat-growing region in China were screened for resistance. Cunmai633, LS4607, Pubing01, and Hongyun2 showed seedling resistance to CR with disease index (DI) less than 0.25. Sixteen cultivars showed adult-plant resistance to CR with DI lower than 0.10. Twenty-six cultivars showed moderate resistance to CR at seedling stage with DI from 0.26 to 0.35, and 63 cultivars showed moderate adult-plant resistance with DI from 0.11 to 0.20. Among them, Cunmai633, LS4607, Pubing01, Xinong916, Zhengda161, Xumai14017, Zhengpinmai30, Bainong8822, Jimai216, Huacheng865, Fengyumai5, and Tianmin319 showed resistance or moderate resistance to CR at both seedling and adult plant stages, with Cunmai633 showing the best resistance. Most of the cultivars (>76%) were susceptible to FHB...
Fusarium redolens was previously reported as a plant pathogen or an endophyte that is closely rel... more Fusarium redolens was previously reported as a plant pathogen or an endophyte that is closely related to F. oxysporum, a notoriously significant soilborne phytopathogen. Subsequent studies demonstrated the unique nature of F. redolens, which was considered a distinct species that causes multiple symptoms on multiple hosts. It was recently identified as a pathogen that causes root rot of American ginseng. Currently, few high-quality F. redolens genome sequences exist in the public database. Here, we report the whole-genome sequence of F. redolens strain YP04, based on a hybrid assembly of long- and short-read sequencing with PacBio and Illumina platforms, respectively. The assembly consists of 40 configs with a total length of 52.8 Mb nuclear genomic DNA and 49.6 kb complete mitochondrial genomic DNA, and encodes a total of 18,985 genes, including 18,517 protein-coding genes and 469 RNA genes which were functionally annotated. In total, 4,606 proteins were identified in the pathogen–...
Plants sense various pathogens and activate immunity responses through receptor like kinases (RLK... more Plants sense various pathogens and activate immunity responses through receptor like kinases (RLKs). Cysteine-rich receptor-like kinases (CRKs) are involved in massive transduction pathways upon perception of a pathogen. However, the roles of CRKs in response to stripe rust are unclear. In the present study, we identified a CRK gene (designated TaCRK10) from wheat variety Xiaoyan 6 (XY6), which harbors high-temperature seedling-plant (HTSP) resistance to stripe rust caused by fungal pathogen Puccinia striiformis f. sp. tritici (Pst). The expression level of TaCRK10 was induced by Pst inoculation and high temperature treatment. Knock-down of TaCRK10 by virus induced gene silencing resulted in attenuated wheat HTSP resistance to Pst, while has no effect on Pst development and host responses under normal temperatures. Notably, overexpression of TaCRK10 in susceptible variety Fielder provided resistance just under normal temperatures at fourteen days with reactive oxygen species (ROS) accumulation and defense-related gene expression of the salicylic acid (SA) pathway. Moreover, TaCRK10 physically interacted with and phosphorylated a histone variant TaH2A.1, which belongs to the H2A.W group. Silencing of TaH2A.1 suppressed wheat resistance to Pst, indicating that TaH2A.1 plays a positive role in wheat resistance to Pst. Thus, TaCRK10 serves as an important sensor of Pst infection and high temperatures, and it activates wheat resistance to Pst through regulating nuclear processes. This knowledge helps elucidate the molecular mechanism of wheat HTSP resistance to Pst and promotes efforts in developing wheat varieties with resistance to stripe rust.
American ginseng is an important herbal medicinal crop in China. In recent years, there has been ... more American ginseng is an important herbal medicinal crop in China. In recent years, there has been an increasing market demand for ginseng, but the production area has been shrinking due to problems associated with continuous monocropping. We analyzed the microbiome in bulk soils to assess whether and, if so, what changes in the bulk soil microbiome are associated with continuous American ginseng cropping. The alpha diversity of fungi and bacteria was significantly lower in the soils planted with American ginseng than the virgin (non-planted) land. The relative abundance of Fusarium spp. and Ilyonectria spp., known plant root pathogens, was much higher in the soils cropped with American ginseng than the non-planted. On the other hand, a number of bacteria with biodegradation function, such as Methylibium spp., Sphingomonas spp., Variovorax spp., and Rubrivivax spp., had lower abundance in the soils cropped with American ginseng than the non-cropped. In addition, soil pH was lower in t...
Stripe rust, caused by Puccinia striiformis f. sp. tritici Erikss., is an important disease of wh... more Stripe rust, caused by Puccinia striiformis f. sp. tritici Erikss., is an important disease of wheat worldwide. Identification of pathogen survival hot spots is important for predicting disease onset and subsequent spread to other regions, and such understanding is essential for developing integrated management strategies. We conducted field studies to determine the relationship of P. striiformis f. sp. tritici overwintering potential to winter temperatures in 10 sites in the northwest of China in three growing seasons (2011–12, 2012–13, and 2013–14). The fungus survived better in wheat cultivars with stronger winter hardiness than in those with weaker winter hardiness. Windowpane analysis suggested that P. striiformis f. sp. tritici winter survival is related to temperatures in the coldest period from mid-December to late January. β Regression showed that P. striiformis f. sp. tritici winter survival was negatively related to the number of days with daily average temperature
Potato (Solanum tuberosum L.) is one of the most important staple foods in many parts of the worl... more Potato (Solanum tuberosum L.) is one of the most important staple foods in many parts of the world including China. In recent years, Verticillium wilt has become a severe threat to potato production in China. During 2015 to 2016, 287 samples of symptomatic potato plants were collected from 15 counties in five provinces from northern China. One hundred and eighty-seven Verticillium-like colonies were isolated from these samples and identified to species based on cultural and morphological characteristics, and multigene phylogeny based on the partial sequences of actin (ACT), elongation factor 1-alpha (EF1α), glyceraldehyde-3-phosphate dehydrogenase (GPD), and tryptophan synthase (TS) genes. A consensus-rooted most parsimonious phylogenetic tree was generated from the data. One hundred and fifteen isolates comprising 61.5% of the total were identified as Verticillium dahliae, and the remaining 38.5% of the isolates were identified as V. nonalfalfae. V. dahliae was widely distributed i...
Received 6 April 2018; Accepted 6 April 2018 Author affiliations: College of Forestry, Beijing Fo... more Received 6 April 2018; Accepted 6 April 2018 Author affiliations: College of Forestry, Beijing Forestry University, Beijing, PR China; Department of Plant Pathology, College of Plant Protection, Northwest A&F University, Yangling, PR China; United States Department of Agriculture, Agricultural Research Service, 1636 E. Alisal St., Salinas, CA 93905, USA. *Correspondence: Steven J. Klosterman, Steve.Klosterman@ars.usda.gov
Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is an important disease o... more Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is an important disease of wheat worldwide. Understanding the survival of Pst during the winter is critical for predicting Pst epidemics in the spring. We used a real-time quantitative PCR (qPCR) method to quantify Pst CYR32 biomass in infected wheat seedlings under several fluctuating temperature regimes (three average temperatures 0, −5 and −10 °C, each with two daily fluctuating amplitudes 8 and 13 °C). The survival of Pst CYR32 increased with increasing average temperature but also varied greatly with the amplitude – larger amplitude led to lower survival, particularly at 0 and −5 °C. Nevertheless the survival at both amplitudes was still significantly greater than under the corresponding constant temperatures. There were small, albeit statistically significant, differences between the two cultivars (Xiaoyan 22, low winter-hardiness; Lantian 15, high winter-hardiness) in Pst CYR32 survival. This study indicated potential errors that could result from using daily average temperatures to predict Pst survival during the winter.
Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is an important disease o... more Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is an important disease on wheat, seriously threatening wheat production worldwide. China is one of the largest stripe rust epidemic regions in the world. The pathogen sexual reproduction and migration routes between Tibet and the other regions in China are still unknown. In this study, we obtained 961 Pst isolates from 1,391 wheat leaf samples from Gansu (277), Shaanxi (253), Sichuan (172), and Tibet (259), comprising 13 natural populations, and genotyped them with simple sequence repeat (SSR) markers. The isolates can be divided into two distinct clusters based on DAPC and STRUCTURE analyses. The genetic diversity of Longnan (in Gansu) and Yibin (in Sichuan) populations was the highest and lowest among the 13 populations, respectively. The hypothesis of multilocus linkage disequilibrium was rejected for the populations from Linzhi in the Himalayan, Longnan, Hanzhong, Guangyuan, Mianyang, Liangshan, and Chendu ...
Using biological control agents (BCAs) is an essential component of integrated pest and diseases ... more Using biological control agents (BCAs) is an essential component of integrated pest and diseases management. Despite much research on biocontrol of plant diseases, success in field crops has been limited with most successes being achieved in greenhouse cultivation. This lack of success is often attributed to the complex ecological processes involved in biocontrol. We used next generation sequencing (NGS) technology to study environmental fate of Bacillus subtilis, a widely used BCA, focusing on its dispersal aspect in open field and under protection. The dispersal of B. subtilis was very limited, particularly under protection. The reduction in the BCA population size was relatively small within 8 days; indeed, no overall reduction in the relative abundance was observed under the protected condition. These results suggested that limited dispersal is probably the main reason for its variable (and often low) control efficacy under field conditions. Thus to increase biocontrol efficacy,...
Alfalfa (Medicago sativa Linn.), widely grown throughout the world, is an important perennial for... more Alfalfa (Medicago sativa Linn.), widely grown throughout the world, is an important perennial forage crop. It is high in protein and digestible fiber and is an excellent source of several vitamins (A, D, E, and K) and minerals for beef cattle, horses, sheep, goats, and even humans (2). Wilt symptoms on alfalfa were observed during a disease survey in Yangling, Shaanxi, China in 2009. Symptoms included discoloration, shortened internode, and plant death. However, the vascular tissue of diseased alfalfa plants did not exhibit discoloration and typical “V” symptoms of Verticillium albo-atrum infection. Eleven fungal isolates were obtained from diseased alfalfa plants in Yangling by a tissue isolation method (1). Isolates were cultured on Czapek Dox Agar (CDA; pH 7.2) slants at 22 ± 1°C in darkness. Colonies on CDA plates were whitish and cream-white when viewed from the underside, later becoming dark gray due to the formation of gray or dark brown chlamydospores in single or in short c...
Wheat stripe rust (yellow rust), caused by Puccinia striiformis Westend f. sp. tritici Eriks. (PS... more Wheat stripe rust (yellow rust), caused by Puccinia striiformis Westend f. sp. tritici Eriks. (PST), is one of the most destructive diseases in many wheat-growing regions worldwide, including China (Chen, 2005). The yield losses caused by PST were 6.00, 3.20, 2.65, and 1.40 million metric tons, when the severe epidemics occurred in 1950, 1964, 1990, and 2002 in China, respectively (Chen et al., 2009). It seriously threatens the wheat’s production in China. Overwintering of PST is the important stage of the wheat stripe rust epidemic. The amount of overwintering PST decides the spring epidemic degree of the disease. In the natural condition, PST begins to overwinter in hypha (mycelia) in host plant when the temperature is 1~2°C. When temperature declines to -6~-7°C, it is difficult to survive for PST (Li and Zeng, 2002). But, all the studies were based on the results of field investigation. There has been lack of research on the overwintering biology at molecular level, which limited...
Verticillium dahliae kleb. is a soilborne plant pathogen which infects more than 200 plant specie... more Verticillium dahliae kleb. is a soilborne plant pathogen which infects more than 200 plant species. Microsclerotia, the main survival structures of V. dahliae and primary causal inoculum agent of host plants, may remain viable in soil more than 10 years with the lack of hosts. The quantification of microsclerotia of V. dahliae is the base for monitoring and prediction of Verticillium wilt. The number of microsclerotia in soil is usually estimated by colonies recovered from plating of soil samples in semi-selective medium and microscopic analysis. But it takes 6 to 8 weeks to complete. Hence, an alternative method to test 10-g soil samples using wet-sieving extraction of microsclerotia followed by quantification real-time PCR (qRT-PCR) assay was developed. The standard curve for quantification of V. dahliae microsclerotia was established using 10-fold dilutions for DNA of 10 000 microsclerotia. A high correlation was observed in regression analysis (R2=0.93) between qRT-PCR results a...
Verticillium wilt caused by Verticillium dahliae Kleb. is a soilborne wilt disease of many crops ... more Verticillium wilt caused by Verticillium dahliae Kleb. is a soilborne wilt disease of many crops all over the world and is difficult to control. Microsclerotia are the main resting structure of V. dahliae in soil and can survive for more than 10 years whether associated with or without debris. They are composed of compact masses of thick-walled, pigmented cells which originate from swollen, septate hyphae by a process of budding. The quantity of viable microsclerotium determines the severity of Verticillium wilt, e.g. on cotton and on strawberry. Surveys in the past 5 decades showed that the diseased area of Verticillium wilt of cotton kept expanding. In 2012, diseased area of Verticillium wilt of cotton was about 3000,000 acres in China. Current control measures, including chemical control, biofumigation, bio-control, crop rotation, failed to control this kind of disease. Easton and Nagle (1986) claimed that Verticillium wilt was efficient controlled through cropping to a green pea...
Spatial patterns of pathogen inoculum in field soils and the resulting patterns of disease may re... more Spatial patterns of pathogen inoculum in field soils and the resulting patterns of disease may reflect the underlying mechanisms of pathogen dispersal. This knowledge can be used to design more efficient sampling schemes for assessing diseases. Spatial patterns of Verticillium dahliae microsclerotia were characterized in commercial cotton fields through quadrat and point sampling in 1994 and 2013, respectively. Furthermore, cotton plants with wilt symptoms, caused by V. dahliae, were assessed in six commercial cotton fields in 2013. Soil samples were assayed for the density of microsclerotia (expressed as CFU g-1 of soil) using a wet-sieving plating method and a real-time quantitative PCR method for the 1994 and 2013 study, respectively. The estimated inoculum threshold for causing wilt development on individual plants varied with the three fields: ca. 1.6 CFU g-1 of soil for one field, and 7.2 CFU g-1 of soil for the other two. Both quadrat and point sampling spatial analyses showe...
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