Occurrence and Damage and Pathogene of Potato Early Blight in Winter in Yunnan Province, China

[Objectives] The paper was to understand the species and pathogenicity of the pathogen causing potato early blight in winter. [Methods] The occurrence of potato early blight was investigated in 5 winter potato growing areas in Yunnan Province. The disease samples were collected from two locations (Zhutang Village and Zhanai Village, Pu’er City) where the occurrence of early blight was severe. The pathogen was isolated and purified in laboratory and identified by morphological characteristics and phylogenetic analysis of ITS gene sequence. And it was further verified via re-inoculation by Koch’s rules. The growth characteristics and pathogenicity of isolates in different seasons were analyzed with 4 strains of Alternaria isolated in spring (EYZ, EYAX, TA1 and TAC) as controls. [Results] Early blight occurred in varying degrees in the 5 winter potato growing areas, and the incidence of early blight was up to 100% in some plots in Lancang County, Pu’er City. A total of 35 strains of Alternaria were isolated from plots with high incidence, which were divided into two types according to colony morphology. The first type was round colonies with smooth edges and gray white fronts, and the second type was round colonies with rough edges and gray black fronts. Three strains LC1, LC2, LC3 of the first type and two strains ZT3 and ZT8 of the second type were selected and identified as Alternaria alternata through morphological and molecular identification. Re-inoculation test further confirmed that the pathogen was A. alternata. Meantime, it was found that the growth rate of colonies isolated in winter was relatively slow, and there was no significant difference between the pathogenicity of LC1 and TA1, but the pathogenicity of strains isolated in winter was generally higher than that isolated in spring. [Conclusions] It is confirmed that the pathogen causing potato early blight in winter is A. alternata in Yunnan Province. The results will lay a foundation for the research of pathogenesis, occurrence regularity and disease control of A. alternata in winter potato.