Abstract：In the condition of natural powdery mildew，resistance evaluation experiments of 263 core collections of cucumber（Cucumis sativus L.）germplasm resources to powdery mildew were conducted at adult stage in spring and autumn，respectively．Results revealed that 52 germplasm resources，accounting for 19.8% of all resources，expressed 3 resistant grade including I（immunity），HR（high resistance）and R（resistance），and 183 germplasm representing 69.6% of all collections exhibited S（susceptibility）or HS（high susceptibility）in spring．The germplasm number of these 2 groups showed above in autumn was 75 and 125，accounting for 28.5% and 47.5%，respectively．With comparison of evaluation results in different seasons，it indicated that 83 germplasm were classified to same resistance level and the percentage of resistance stability was 31.6%．140 germplasm resources expressed higher resistance grade in autumn than in spring，while 40 germplasm showed the opposite trend．Results of variance analysis revealed that the resistance difference of both different germplasm and the same germplasm in 2 seasons reached extremely significant level．Through repeat resistance evaluations in different seasons，14 homozygous cucumber germplasm resources with high resistance to powdery mildew were screened out．The above results could be useful for exploiting elite resistant genes to powdery mildew and applied in cucumber resistance breeding.
