031 Rate of Natural Outcrossing in Cucumber Isolation Blocks

Cucumber ( Cucumis sativus L.) populations often are intercrossed after each selection cycle using bees in isolation blocks. Previous research showed the rate of natural outcrossing in monoecious cucumber inbreds was 36%. The objective of this experiment was to determine whether the rate of natural outcrossing could be increased using hormones, plot size, and node of fruit for seed harvest. The experiment was run with 2 years (1997, 1998), two hormones (treated, none), two plot sizes (hills, small plots), two nodes of harvest (2, 8), and four replications. Each treatment combination consisted of four plots or hills planted in 1.5-m rows in one isolation block. Plots or hills were planted to white-spined `Sumter', and were surrounded by rows of black-spined `Wis. SMR 18'. Treatment combinations receiving hormones were sprayed at the cotyledon stage and 1 week later. Plots or hills received ethrel to make them gynoecious, and surrounding rows received silver nitrate to make them androecious. Unsprayed isolation blocks remained monoecious. At maturity, fruit were harvested from nodes 2 or 8 from the white-spined plants in each isolation block. Node of harvest had no effect on outcrossing rate. However, hormones and plot size had a significant effect. Sprayed plots, sprayed hills, and unsprayed hills had high outcrossing rates relative to unsprayed plots. Therefore, if families are to be intercrossed in isolation blocks, they should be sprayed with hormones for maximum outcrossing among families.