Fungicide sensitivity of Corynespora cassiicola strains with different phenotypes isolated from cucumber in Baiyin of Gansu

Abstract:

[Objective] Via researches on phenotypic features (optimal growth temperatures, sporulation quantity, etc.) and fungicide sensibility of five strains of Corynespora cassiicola with different phenotypes isolated from cucumber in Gansu Province, to provide technical support for control of cucumber Corynespora leaf spot and stem blight. [Methods] The optimal growth temperatures were evaluated by temperature gradient method; The sporulation quantity was assessed by conidia yields per unit area on PDA plate; Fungicide sensitivity of Corynespora cassiicola strains was assessed by amendment plate method, autoclaved PDA media were amended prior to pouring with 8 different fungicides. [Results] The optimal growth temperatures of all the five strains were among 25?30 °C; Conidia amounts of the strains with scanty aerial hyphae were significantly more than the strains with luxuriant aerial hyphae on PDA plate (cultured 5 d at 25 °C); Under test concentrations, the sensitivity of the five tested strains of Corynespora cassiicola to eight fungicides successively were: mancozeb>flusilazole>tebuconazole>difenoconazole>procymidone>chlorothaloni>azoxystrobin>carbendazim. [Conclusion] Different phenotypic strains of Corynespora cassiicola isolated from cucumber were different in optimal colonial growth temperatures, growth speeds, sporulation quantity and fungicide sensitivity. At the tested concentrations, the strains showed very low sensitivity to carbendazim and azoxystrobin (inhibition rates<40%), which implied that the two kinds of fungicides had lost its effect on control of cucumber Corynespora leaf spot and stem blight in the region.