Drought conditions induce mote formation in interspecific cotton hybrids

Motes are cotton ovules that fail to ripen into mature seeds, developing instead into aborted structures which cause imperfections in ginned fibers and textile products from cotton. Interspecific hybrids (ISHs) of cotton (Gossypium hirsutum L. x G. barbadense L.) tend to produce a high number of motes. The term motes refers to various types and sizes of aborted structures which result from different disorders, may have different effect on lint quality and may be affected differently by various factors. This research was aimed at studying the effect of irrigation regime on the formation of mote of various sizes in ISHs. Five ISHs were examined in 1993 and four ISHs and two control cultivars (G. hirsutum L. and G. barbadense L.) were evaluated in 1994 in the field under both dryland and irrigated treatments. Motes found in seed-cotton samples were sorted into small, medium, and large sizes, and counted. In 1994, flowers were tagged at several stages, and the formation of motes at different reproductive phases was examined. Between 21 and 56% of the total seed potential developed into motes in the ISHs vs. 11 to 28% in the control cultivars. Moreover, when considering mote numbers per gram of fiber, which was previously found to be more closely related to nep (tangled fibers) number, total mote numbers were up sevenfold higher in the ISHs than in the control cultivars. Analyses of motes by size category revealed that numbers of small and medium motes in ISHs were higher than in controls, whereas numbers of large motes were similar. The number of small and large motes from the dryland treatment was 2 to 5 times greater than from the irrigated treatment, whereas medium motes were unaffected by irrigation. The number of small and large motes also increased under dryland conditions as the reproductive process progressed. It was concluded that drought conditions induce the formation of small and large motes, whereas medium motes result from embryo abortion due to genetic disorders.