Cucurbit Genetics Cooperative Report 1:18 (article 18) 1978
Regulation of Sex Expression in Gynomonoecious Muskmelon for Hybrid Seed Production
J. B. Loy
University of New Hampshire, Durham, NH 03824
Several approaches for obtaining hybrid seed in muskmelon without hand pollination have been suggested, but all the methods to date have serious limitations. It has been difficult to obtain stable, true-breeding lines of gynoecious muskmelon, and until recently, there were not easy methods for inducing large numbers of male flowers on female strains The use of ethephon on monoecious lines suffers from the drawback that the induced pistillate stage is of short duration.
Gynomonoecious muskmelon plants are those which produce a flush of pistillate flowers, followed by development of both pistillate flowers and perfect flowers exhibiting various degrees of ovary development. We have found that treatment of gynomonoecious plants with successive foliar applications of 480 ppm ethephon at the 4-leaf stage and one week later, extends the pistillate stage to 16 to 20 days. This assures adequate pollen control for at least the major crown set of the plants.
We have also found that field application of 100 ppm of an ethylene inhibitor (aminoethoxyvinylglycine - AVG) promotes the formation of perfect flowers and some male flowers on the gynomonoecious strain. The results of a greenhouse study indicate that 3 successive weekly applications of 50 to 100 ppm AVG will give excellent results in enhancing perfect and/or male flower formation.
In backcross populations from gynomonoecious x andromonoecious crosses we have been recovering about 3% gynomonoecious plants which have an extended pistillate stage in the field. These plants may or may not be heterozygous for some genes governing the flowering pattern. If the gynomonoecious sex type is easily fixed, then it can be easily adapted for commercial hybrid seed production through the use of ethephon and AVG to further control flowering The elongate fruit character associated with these plants remains a problem. We have selected a round-fruited monoecious strain, but have had difficulties recovering it in segregating populations.