Evaluation Of Cross-Protection Between Different Strains Of Soybean Mosaic Virus And Analysis On Sequences Of HC-Pro Gene

Soybean mosaic virus(SMV) is one of the most broadly distributed diseases worldwide. It causes yield loss and seed quality deficiency in soybean(Glycine max(L.)Merr.) seriously. Cross protection between different SMV strains have been conducted at home and domestic. In this study, different SMV strains from four soybean production regions in China were utilized to prove the broad existence of cross protection in SMV, to detect the difference of cross protection between combinations of SMV strains and soybean cultivars, to study effects of challenged inoculation time and inoculation treatments of cross protection, and to analysis effects of cross protection on some characters of soybean cultivar. The main results obtained are as follows:1. Reactions of seven soybean cultivars to fifty-four SMV strains were identified. The results showed that different symptom reactions appeared when different soybean cultivars were infected by the same SMV strains, or the same soybean cultivars were infected by different SMV strains. The stability of reactions may be caused by interactions between viruses and hosts. Eleven strains appeared stable symptom reactions on the five cultivars respectively.2. Eight combinations of SMV strains and soybean cultivars were used to study cross protection. The results were as follows: different challenged-inoculation time effected cross protection. Higher protection ratio was detected challenged inoculation after seven days protected inoculation than after three, five, nine and eleven days. Cross protection were also effected by different inoculation treatments. Obvious protections were observed when cultivars were inoculated one strain after another, whereas no protection appeared when cultivars were inoculated by inoculum from mixture of two strains or each unifoliolate inoculated by different strains respectively. Cross protection exsited between different strains. A mosaic strain used as protected inoculation strain exhibited better protection to challenged inoculation. Cross protection can decrease disease index, and affect soybean on leaf area, root dry weight, plant height, chlorophyll content and nodule fresh weight in different soybean cultivars.3. Six SMV HC-Pro genes have been cloned and sequenced. The results showed that the complete HC-Pro gene had 1371 nucleotides encoding 457 amino acids. The protein HC-Pro had functional domains as follows: the CCC motif related to virus movement and the PTK motif combined with DAG motif of coat protein. Homologies of their nucleotides were 89.2%～99.9% and amino acids were 95.4%~99.8%. HC-Pro gene of TS216 had closest genetic relationship with 4434, which had only one different nucleotide with TS216. Between six sequences obtained in this study and other seven reported sequences, HC-Pro gene of HZ1 had the lowest similarities with other twelve SMV strains. Furthermore, homology of the same species of HC-Pro was obviously higher than between different species.