Resistance Evaluation Of Sweet Potato And Fungicides Screening Against Sweet Potato Southern Blight

Sclerotium rolfsii Sacc. is a soil-borne plant pathogenic fungus with a wide hostrange about600kinds of plants and worldwide distribution.It was reported thatsouthern blight had been a new important disease in sweet potato growing areas inChina in recent years. The screening of strong pathogenicity strains, resistanceevaluation methods,indoor resistance evaluation of different sweet potatocultivars(lines) and fungicides screening about sweet potato southern blight had beenstudied systematically in this paper.These studies would provide theoretical basis forthe effective control and resistance evaluation to sweet potato southern blight.The pathogenicity of15Sclerotium rolfsii Sacc. isolates collected from sweetpotato had been test on tubers of4sweet potato cultivars(lines). The result showedthat all15isolates could infect the all kinds of tubers with the same diseasesymptoms, white silk-like hyphae and rapeseed-like sclerotium gradually turningform white to yellow to brown. In addition,there was significant difference amongisolates by identifying the pathogenecity. The strongest was No.14, the weakest wasSR36on the pathogenecity. Susceptibility and Disease spot color were differentbetween the4tested sweet potato cultivars(lines) and G182showed the highestsusceptibility.The research for the disease conditions of sweet potato southern blight showedthat the mycelium of Sclerotium rolfsii Sacc. infected sweet potato stem throughepidermal tissue or wound which favored the infecting. The average temperature fordisease development ranged from15~30℃with an optimum at30℃. Sweet potatostem could be infect under3types of light conditions—12h alternating lightand dark,0h light and24h light, however, the disease incidence and lesion growth rate was notsignificantly different.In this paper, sweet potato stems were evaluated with agar disk containingmycelium by two ways of plastic film fixation and micro pipette tip fixation.Thestudy result indicated that plastic film fixation had haven more moisture retention andfixation effect, and it was closer to the natural incidence,so Therefore,this way appliedeven more to the resistance evaluation of sweet patato southern blight.The resistanceevaluation of sweet potato southern blight was test on the stem of93sweet potato cultivars(lines) by the way of plastic film fixation, the results showed that there wasno one immune variety and4high resistance such as972,1254, Zhanjiang pearl red,and10-098,furtherly,the resistance distributed as a tendency of Two head less, andmiddle more.Fungicide testing on NA plates revealed that five pesticides,250g/Lpyrazole-kresoxim-methyl400g/L flusilazole,10%difenoconazole,50%boscalid and50%azoxystrobin, showed the greatest inhibition of hyphal growth and sclerotiaproduction of Sclerotium rolfsii Sacc. on sweet potato,so they could be considered asthe main pesticides for preventing and controling sweet potato southern blight.