Growth Regulators Improve the Intercrossing Rate of Cucumber Families for Recurrent Selection

Cucumber ( Cucumis sativus L.) populations for recurrent selection often are intercrossed after each cycle using bees ( Apis mellifera ) in isolation blocks to save the expense of hand labor. This experiment was conducted to determine whether the rate of natural outcrossing could be increased using growth regulators, plot size management, and node of fruit position for seed harvest. The experiment was a factorial in a randomized complete block design with 2 yr (1997 and 1998), two growth regulators (treated and none), two plot sizes (single plant hills and small plots), two nodes of harvest (crown and top), and four replications (six in 1998). Plots or hills were planted to white‐spined ‘Sumter’ and were surrounded by rows of black‐spined ‘Wisconsin SMR 18’ pollenizer. Plots or hills of Sumter were treated with ethrel to induce gynoecy, and pollenizer rows were treated with silver nitrate to induce androecy. Untreated isolation blocks remained monoecious. Progeny of the harvested white‐spined plants were planted the following year to evaluate spine color, with black‐spined plants indicating an outcross. Results showed that node of harvest had no effect on outcrossing rate. However, growth regulators and plot size had a significant effect. Treated small plots, treated hills, and untreated hills had high outcrossing rates (54%) relative to untreated plots (30%). Therefore, if families are to be intercrossed in isolation blocks, they should be treated with growth regulators for maximum outcrossing.