Disparity of Cotton Pollen Dispersal by Honey Bees Visiting Upland and Pima Pollen Parents1

Abstract

In 1982 and 1983, experimental plantings of a genetic‐cytoplasmic male sterile and a pollen fertile upland cotton (Gossypium hirsutum L.) as well as a pollen fertile Pima cotton (G. barbadense L.) were established near Safford in southeast Arizona to study cross‐pollination using honey bees (Apis mellifera L.). The objective of these studies was to determine whether poor yields in previous interspecific crossing blocks were caused by a lack of pollen transfer, poor bee visitation, or because of plant factors such as poor bloom synchrony. Observations and data on blooming rates, honey bee visitation, pollen deposition (pollen grains/stigma), nectar volume and sugar concentration, boll samples and hybrid progeny ratios were obtained. Flowering of the Pima R line started later than the upland cottons and the early Pima bloom was approximately 40% cleistogamous. Thus, during the first 2 weeks of A‐line bloom, Pima pollen availability was minimal. For 5 consecutive weeks in 1982 when honey bee visitation to the A line was adequate (−1.3%), pollen deposition on A‐line stigmas adjacent to the Pima R line ranged from 11.8 to 42.4% (x = 25) of the pollen deposition on A‐line stigmas adjacent to upland B line. Progeny rows grown from F1 seed of the A × R cross averaged 20.2% Pima hybrids, showing that isolation from B‐line pollen was inadequate. In the 1983 study, pollen deposition on the A line adjacent to Pima was low also. The results are documentation of some of the problems of pollen transfer in producing hybrid cotton seed using a G. hirsutum A line and G. barbadense R. line.