The paucity of research pertaining to the heterosis, combining ability, nature of gene action and proportional contribution of lines, testers and their interactions for insect-pest and disease resistance in cucumber motivated us to undertake this study. The experimental material comprised 48 F 1 hybrids, developed by crossing 16 lines (eight gynoecious) with three testers during the year 2011. Parents (16 lines and three testers) and their F 1 48 hybrids, along with two standard checks ("KH-1"

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... nd "Pusa Sanyog"), were planted in a Randomized Complete Block Design (RCBD) during the year 2012 for screening against different insect-pest and diseases under natural field conditions. In the present studies, genotypes LC-1-1, LC-2-2, LC-15-5, CGN-20969, CGN-20953, Poinsette and K-75 and crosses LC-1-1 × K-75, LC-15-5 × K-75, LC-3-3 × K-75, CGN-20969 × Japanese Long Green, and CGN-20953 × K-75 were found superior in response to insect-pest and disease incidence. Gene action studies indicated predominant role of non-additive gene action governing all the traits except fruit fly incidence, thereby, indicating usefulness of heterosis for disease resistance breeding in cucumber. Further, proportional contribution of lines was recorded highest for severity of powdery mildew and angular leaf spot, whereas testers were found superlative for fruit fly incidence and severity of downy mildew. Therefore, selection of parents should be done depending upon the trait of interest for resistant hybrid development in cucumber.