Inheritance and Characterization of a Glabrous Trait in Summer Squash

Abstract

This study was undertaken to determine the inheritance of a glabrous trait discovered in yellow straightneck summer squash (Cucurbita pepo L.) in 1992 and to compare trichome distribution and anatomy and morphologic features that relate to productivity in glabrous and nonglabrous genotypes. Inheritance data from 1994, 2003, and 2004 confirm that the glabrous trait is inherited as a single gene recessive, designated gl-2, but that in some segregating F 2 populations with a zucchini or caserta (C. pepo ssp.pepo) background, there is a deficiency of glabrous segregants. Nonglabrous (NG) plants bore numerous trichomes on stems, petioles, leaf blades, and fruit. Trichomes were simple (unbranched), and most were either conical and unicellular or small filiform and multicellular (two to five cells). However, some larger multicellular trichomes with compound feet were found on major leaf blade veins and along vein tracts of petioles. Large, multicellular trichomes with compound feet were only occasionally present on leaf blades and petioles of glabrous (G) plants, and other trichome types were much reduced. This reduction gives fruit and foliage a smooth, waxy feel and largely eliminates trichome damage to fruit and skin irritation to workers during harvesting. Leaf number, staminate to pistillate flower ratios, and fruit size were not significantly different between glabrous (gl-2/gl-2) and nonglabrous (Gl-2/gl-2) backcross (BC) genotypes. In one of two BC populations, pistillate flowering was 2 d earlier in NG as compared with G plants. The glabrous gene reduced the size of leaf blades in two BC populations; however, differences in total leaf areas were not statistically significant at P = 0.05. A comparison of leaf numbers and size among G and NG parental plants and reciprocal F1 hybrids derived from three separate crosses did not reveal a consistent effect of the gl-2 gene on plant morphology. Earliness and productivity of the best glabrous hybrids were similar to that of popular commercial cultivars.