Identification Of Sclerotinia Minor And Genetic Diversity Of Sclerotinia Minor And Sclerotinia Sclerotiorum In Sunflower

Sclerotinia sclerotiorum (Lib) de Bary(S. sclerotiorum) is a main disease in sunflower, which causes loss of yield in sunflower planting region over the world. In our research we isolated, purified and identified the pathogen in the samples of stem-rotted sunflower plants collected from wulanchabu in Inner Mongolia. Sclerotinia minor was identified as the causal of this disease. And we studied the genetic diversity and pathogenicity of isolates of Sclerotinia sclerotiorum from Xinjiang and Sclerotinia minor from Wulanchabu.1. Sclerotinia minor was identified as the pathogen of the rotted sunflower collected from wulanchabu.2. By comparing biological characteristics of isolates of Sclerotinia sclerotiorum from Xinjiang and Sclerotinia minor from Wulanchabu, we found that OA secretion level, PG activity, diameter of disease lesion, growth rate and weight of sclerotia were significantly higher or larger in Sclerotinia sclerotiorum from Xinjiang than that in Sclerotinia minor from Wulanchabu. Significance analysis showed that all factors had significant difference in P<0.05 level except for PG activity’s. The pathogenicity analysis showed that Sclerotinia sclerotiorum from Xinjiang were more pathogenic than Sclerotinia minor from Wulanchabu.3. By studying Sclerotinia minor from the same sunflower field, the OA secretion ability、PG enzymes activity、pathogenicity and the fungicide sensitivity test suggested:the difference on the OA secretion ability. PG enzymes activity and pathogenicity of tested isolates within the same MCG do observe; average level of aboved factors between two biggested MCGs is not different; carbendazim and dimethachlon have different degree of inhibition for Sclerotinia minor, however, the dimethachlon has the higher degree of inhibition than carbendazim for Sclerotinia minor, that is to say, the Sclerotinia minor is more sensitive to dimethachlon compared with the sensitivity to carbendazim.4. We grouped isolates of Sclerotinia minor collected from Wulanchabu in Inner Mongolia by mycelial compatibility groups (MCGs). The results showed that:Eleven MCGs were identified in 52 Sclerotinia minor isolates collected from Wulanchabu,5 MCGs contained 1 isolates, taking 45% of all the MCGs, the largest MCGs is MCG1 which contained 16 isolates, taking 30.8% of all the tested samples, MCG2 contained 12 isolates taking 23.1% of all the tested samples, and others contained 4 to 6 isolates. From the same sunflower field collected 17 Sclerotinia minor isolates in Xigedan,Bayinxiang, Chayouzhongqi of Wulanchabu City, Inner Mongolia, except the 10th isolate was not identified, another 16 isolates obtained from Xigedan in Wulanchabu grouped in 6 MCGs, 4 isolates identified in MCG2,3 isolates grouped in MCG1 and MCG4 respectively and 2 isolates grouped in other 3 MCGs. Interestingly, the 7th and 8th isolates which obtained from two infected sunflower in the same hole were grouped in different MCGs. The same result was also found in the pair of the 11th and 12th isolates and the pair of the 13th and 14th isolates. Isolates of Sclerotinia minor obtained from Xigedan, Jubaolong, Tuchengz in Wulachabu were grouped in different MCGs.5.90 isolates from the same sunflower field in Wenquan, Xinjiang region, can be grouped into 15 MCGs. MCG1 is the biggest one which contained 34 smaples,37.8% of all the tested samples; 6 MCGs only contain a single isolate; the other MCGs included 2 to 13 isolates. Meanwhile, the difference on the OA secretion ability、PG enzymes activity, and pathogenicity of tested isolates within the same MCG do observe; average level of aboved factors between two biggested MCGs is also different. The distribution of two mating type within the same MCG was identified also, the 1:1 ratio of Inversion-minus and Inversion-plus type was observed in MCG1, the biggest group among all the MCGs; however, the inversion-plus is the dominant mating type in MCG2、MCG4and MCG6. The fungicide sensitivity test data of the isolates within MCG1 and MCG2 suggested 84% sample is more sensitive to carbendazim compared with the sensitivity to dimethachlon.7 isolates (3 from MCG1 and 4 from MCG2) showed the opposite tendency.3 isolates (one from MCG1 and 2 from MCG2) have the same sensitivity to both tested fungicide.