Heterosis in yield, fiber quality, and photosynthesis of okra leaf oriented hybrid cotton (Gossypium hirsutum L.)

Leaf shape is an important factor affecting canopy structure, photosynthetic characteristics, and yield. Introducing okra leaf shape is considered an important strategy in cotton heterosis breeding. The objective of the study was to evaluate the heterosis in okra leaf cotton hybrid F(1)s, which were developed by crossing two sterile near isolines and three restorer near isolines. A normal leaf check hybrid F(1), Zhongza 29, and four newly developed okra leaf oriented hybrid F(1)s, including the super-okra (severely cleft and narrowly lobed leaf), okra (deeply cleft and narrowly lobed leaf), semi-okra (intermediate leaf lobe), and sub-okra (large leaf lobe) hybrids were selected in this experiment. Okra leaf oriented cotton hybrids significantly reduced leaf area index (LAI) (P < 0.0001), thus more light penetrated into the lower canopy. The LAIs for the super-okra and okra hybrids, however, were too small to supply adequate photosynthate, thus resulting in early maturity, short boll filling period, and low yield. As the LAI increases, the semi-okra and sub-okra hybrids showed certain heterosis. The semi-okra hybrid showed 7-12% heterosis over the check hybrid in lint percent, 6-11% in boll weight, 2-147% in canopy light intensity, 1-10% in net photosynthetic rate (Pn), and -3 to 3% in lint yield. As well, all tested okra leaf hybrids improved fiber quality such as micronaire compared with the normal leaf check hybrid. The results suggested that adopting okra leaf parental lines in cotton breeding provided potentials in increasing fiber quality with comparable lint yield.