Analysis Of The Key Factor Mediating Pathogenesis In Sclerotinia Sclerotiorum

Sclerotinia sclerotiorum (Lib) de Bary is an important pathogen, responsible for leaf blight, stem rot and pod rot of oilseed rape (Brassica napus L.), resulting in the great losses to this crop, especially in the canola-growing areas along the Yangtze River Region. In recent years, it causes serious damage to rapeseed production, both on yield and on quality. The infection of mycovirus on S. sclerotiorum alters many of the characteristics of the fungus, including reduced virulence (hypovirulence), slow growth and abnormal colony. Those changes may involve in interference of pathogenic elements in S. sclerotiorum. We hypothesized that these abnormal strains can be used to disclose pathogenesis mechanisms of the fungus.Firstly, the pathogenicity, culture characteristics and dsRNA molecules of 18 strains of 5. sclerotiorum were compared. The results showed that the pathogenicity of these strains differed significantly, 7 strains including Ep-1PNA5 were strong pathogenic type (SPT), 3 strains including Ep-1PA were intermediate pathogenic type (IPT), and 8 strains including Ep-1PN belonged to weak pathogenic type (WPT). The SPT strains and IPT strains grew rapidly (0.9-1.8cm) and formed normal colonies. No dsRNA or only one species dsRNA (7.4kb) was detected in mycelia of these strains. Among the 8 WPT strains, 7 grew very slowly (0.2-0.7cm) and formed abnormal colonies, the other strain designated as Ep-1PB grew rapidly (1.8cm) and formed normal colonies. In mycelia of the 6 abnormal strains, two species of dsRNA (6.4 and 7.4 kb) were detected and in mycelia of the other abnormal strain, only one species of dsRNA (6.4 kb) was detected. In mycelia of Ep-IPB, one species of dsRNA (7.4 kb) was detected. These results suggest that the 6.4 kb-sized dsRNA may be more important to the weak pathogenic phenomenon in 5. sclerotiorum.Secondly, production of oxalic acid (OA), polygalacturonase (PG), laccase, protease and amylase between S. sclerotiorum strains Ep-IPN (WPT) and Ep-1PNA5 (SPT) was compared. The results showed that Ep-IPN could normally produce OA and the extra-cellular enzymes mentioned above. Production of PG by Ep-IPN, Ep-PNA5 and SHTNA5-7 (WPT) was confirmed by the technique of reverse transcription PCR. From these results, a hypothesis was suggested that the vigor of the mycelial growth (VMG) was important for pathogenicity of S. sclerotiorum.