Phytophthora melonis is one of the most destructive cucumber disease, causing severe economic losses in the globe. Despite intense research efforts made in the past years, no permanent cure currently exists for this disease. With the aim to understand the molecular mechanisms of defense against P. melonis, root collars and leaves of four cucumber genotypes consisting of resistant Ramezz; moderately resistant Baby, and very susceptible Mini 6-23 and Extrem, were monitored for quantitative gene expression analysis of the five antifungal and/or anti-oomycete genes (CsWRKY20, CsLecRK6.1, PR3, PR1-1a and LOX1), at three points after inoculation with P. melonis. The gene expression analysis indicated, P. melonis strongly enhanced the expression of these genes after inoculation, in both the leaves and root collars. Further, not only the transcript levels of these genes were significantly higher in resistant and moderately resistance genotypes, but also the time point of the highest relative expression ratio for the five genes was different in the four cucumber genotypes. CsWRKY20 and PR3 showed the maximum expression in Ramezz at 48 h post inoculation (hpi) while CsLecRK6.1, and LOX1 showed the highest expression at 72 hpi. In addition, PR1-1a showed the maximum expression in the Baby at 72 hpi. Root collars responded faster than leaves, and some responses were more strongly up-regulated in root collars than in leaves. The genes found to be involved in disease resistance in two different organs of cucumber after pathogen infection. The results suggest that increased expression of these genes led to activation of defense pathways, and could be responsible for a reduced P. melonis colonization capacity in Ramezz and Baby. Overall, this work represents a valuable resource for future functional genomics studies to unravel molecular mechanisms of Cucumis sativus–P. melonis interaction.

疫霉菌是最具破坏性的黄瓜病之一，在全球范围内造成了严重的经济损失。尽管在过去的几年中进行了大量的研究，但是目前尚无永久治愈该疾病的方法。为了了解防御由抗性Ramezz组成的四种基因型的瓜对P. melonis，根环和叶片的防御的分子机制；对三个抵抗力和/或抗卵菌基因（CsWRKY20，CsLecRK6.1，PR3，PR1-1a和LOX1）的三个抗真菌和/或极易感的Mini 6-23和Extrem进行了定量基因表达分析接种哈密​​瓜假单胞菌后。基因表达分析表明，在接种后，甜瓜强烈增强了这些基因在叶和根领中的表达。此外，不仅在抗性和中度抗性基因型中这些基因的转录水平显着更高，而且在四种黄瓜基因型中五个基因的最高相对表达率的时间点也不同。接种后48 h（hpi）CsWRKY20和PR3在Ramezz中表达最高，而CsLecRK6.1和LOX1在72 hpi时表达最高。另外，PR1-1a在72 hpi的婴儿中表现出最大的表达。根领的反应快于叶片，根领的反应比叶更强烈地上调。发现该基因与病原体感染后黄瓜的两个不同器官中的抗病性有关。结果表明，这些基因的表达增加导致防御途径的激活，并可能导致Ramezz和Baby的瓜病假单胞菌定植能力降低。总的来说，这项工作为将来的功能基因组学研究提供了宝贵的资源，以阐明黄瓜（Cucumis sativus） –甜瓜（P. melonis）相互作用的分子机制。