| Wheat yellow mosaic disease is widespread in winter wheat in China, covering the area of almost 50% of winter wheat planting regions along Huanghuai, and Yangzi River basin as well as Eastern Shandong and Sichuan basin. The causal agents are Wheat yellow mosaic virus (WYMV)and Chinese wheat mosaic virus (CWMV), which are transmitted by plasmodiophorids vector, Polymaxa graminis, a worldwidely spread biotrophic parasite of many plants. Both WYMV and CWMV cause yellow mosaic symptom on wheat, leading to serious yield loss under condition favorable for the disease development. This plasmodiophorids vector is an obligate soil-borne parasite which can survive in soil as resting spores for many years in the absence of the host. Concerning the economic and ecological reasons, currently there are no effective or acceptable chemical for control of virus vector. Therefore, wheat yellow mosaic disease is very difficult to control. Up to now, the only an available way to control this disease is by growing resistant wheat varieties in the field infested with viruliferous vector.In this study, to gain the more detail information on the epidemiology of wheat yellow mosaic disease in winter wheat in China, we examined the prevalence and molecular diversity of viruses in winter wheat growing area. The structure of WYMV population and responses of wheat cultivars to different virus isolates were also analyzed. First, to examine the prevalence of the viruses in winter wheat growing area, we prepared WYMV or CWMV specific antiserum for immunoassay of field samples. From 2007 to 2010, we carried out field survey for wheat yellow mosaic disease in winter wheat growing regions. The results show that the disease had expanded to wider wheat planting area in China during the last 10 years. In several places such as Taian (Shandong province), Shangqiu (Henan province), Danjiangkou, Xiangfan and Suizhou (Hubei province) WYMV occurrence was newly found. Co-infection of WYMV and CWMV had become more serious in Jiangsu province. Neijiang was the only area with disease in Sichuan province whereas wheat yellow mosaic disease was not detected in Zhejiang province.Analysis of genetic variability of viruses can provide important information that leads to understanding of viral pathogenicity and evolutionary process. In this study, the sequences of the CP gene from about 30 independent clones of WYMV from each of a total of 11 different locations in 5 provinces in China were determined. Sequences of the VPg gene from three of these locations were also determined. The CP was generally more variable than the VPg. At some sites, populations appeared relatively uniform, but there was evidence of two or three major subpopulations at three amino acid sites in their CP sequences. Most differences in the VPg were silent but in the CP striking co-variation at amino acid positions 112 and 115 enabled the division of all known WYMV sequences into three types. Based on the consensus sequence of CP gene, WYMV isolates were divided into 3 subgroups. The distribution of these groups is probably correlated with their geographical locations. Almost isolates collected from Jiangsu province belong to A subgroup, whereas isolates from northern and eastern of winter wheat growing area belong to B subgroup.Plant virus commonly breaks host resistances by genetic variation or mutation resulting in big epidemic in the field. To evaluate the resistance of wheat cultivars to WYMV, about 600 wheat cultivars were planted in a infested field at Xiping(Henan province), Yangzhou(Jiangsu province), Yantai and Rongcheng (Shandong province)during 2008 to 2011. The result shows that Huaimai 20,Zhengmai 366,Fengkang 1,0488,Xiaoyan 5,Shaanmai 150,Xinong 2208,Hengguan 111,Lantian 23 and Zhongmai 9 are resistant to Yantai WYMV isolates;Yannong 23 for Rongcheng; Keyou 1,Gaoyou 503,Gaoyou 505, Huapei 2 ect. are resistant to Yangzhou isolates; Fumai 936, Gaoyou 503, Hankang 4118,Xinmai 208, Yumai 70, Yumai 70-36, Zhengmai 366, Zhengmai 902 ect. are resistant to Xiping isolates. This result suggests that those resistant cultivars are potential as germplasmic resources for the breeding of resistant wheat cultivar against WYMV infection.To evaluate resistance of winter wheat cultivars currently grown in Henan Province, China to WYMV, the resistance of 62 commercial wheat cultivars was tested in a infested nursery at Xiping, Henan Province in the years 2006 to 2010. Of the 62 cultivars, only Xinmai 208 was immune to WYMV and nine cultivars (14%) were resistant: Yumai 70-36, Fanmai 5, Fumai 936, Shandong 95519, Yumai 70, Gaoyou 503, Yumai 9676, Zhengmai 366 and Shaanmai 229. Thirteen cultivars (21%) were moderately resistant (Puyou 938, Lankaoaizao 8, Xinyuan 958, Huapei 2, Wenyou 1, Yumai 18, Zhengmai 9023, Yumai 47, Yunong 201, Yanzhan 4110, Yumai 36, Bainong 878 and Yumai 49-198) and the remaining 39 cultivars (63%) were susceptible. Moreover, the effects of disease severity on wheat yield and grain quality were also investigated. The results showed that the average of grain yields, spike numbers and 1000-grain weights are decreased if disease severity was increased. 9.6% of yield was lost when disease severity was grade 1, and 30.3% and 33.5% yield was lost when the disease severity was grade 2 and 3, respectively.Some wheat cultivars were randomly sampled for further analysis of virus distribution in the plants by Western- and tissue blotting. The results showed that WYMV accumulation and movement was inhibited in resistant cultivars differently. In some cultivars, such as Ningzimai 32 and Linmai 7, virus accumulation was not detected in whole plant. In other cultivars such as XK0106-108D6,Yumai 70-36 and Fumai 936, viral replication and spread in the roots were inhibited. Transportation of virus from the root to stem was restricted, in cultivar Shaan 8242-1,Xinong 889,Zhongmai 12, while virus accumulation in leaves was suppressed in cultivar Youmaibai 15,Xiangmai 81,Xiannong 151. The virus content in susceptible wheat cultivar was also different. Some cultivars contained large amount of virus in all tissue, such as Guan 0014,Yang 06-(NX)-71,Yang 06-129 and Yangmai 11. Other cultivars contained more virus in roots and leaves than in stems, such as Shaan 159, Yunong 202, Mianmai 185 and Yannong 22. Some cultivars contained more virus in roots and stems than in leaves, such as 0448 and Wangmai 15.To investigate the intra-viral protein interaction among WYMV-encoded proteins, Bimolecular fluorescence complementation (BiFC) and Yeast two-hybrid system(YTH) assays were carried out to examine the interaction of WYMV CP with other viral-encoded proteins. The results showed that in addition to its self interaction, CP interacted with P1. Analysis of sub-cellular localization indicated that CP was capable to form vesicles which move along microfilament-like structure and endoplasmic reticulum in Nicotiana benthamiana epidermal cell. |
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