Cotton responses to shade at different growth stages: Growth, lint yield and fibre quality

Photosynthetic photon Aux density (PPFD) has variable effects on cotton (Go ssypium hirsutum) plant growth, development and lint yield, bur little is k nown about the responses of yield, yield components and fibre quality to lo w PPFD at different developmental stages. Field studies were conducted in 1 993-95 to determine the effects of an 8-d period of shade (63% reduction in PPFD) imposed at different developmental stages (pinhead square (PHS), fir st flower (FF), peak flower IPF) and boil development (BD)) on cotton growt h, lint yield, yield components and fibre quality. Shade for 8 d at the ear ly square stage did nor affect cotton growth and yield. Shade during FF, PF and ED increased fruit abscission, and decreased specific leaf eight, dr) matter accumulation, lint yield, fibre micronaire, and fibre strength compa red with the unshaded control. The detrimental effect of shade on yield inc reased with later growth stages. Shade at the FF, PF and ED stages decrease d lint yield by 18, 34 and 52% in 1993, and by 18, 21 and 29% in 1994 respe ctively compared with the unshaded control. Shade caused the greatest decre ase in the dry weight (DW) of fruits (squares + flowers + bells) and the sm allest decrease in leaf DW among leaves, stems and fruits. Of the three yie ld components (boll number, boil weight and lint percentage), boil number w as the most sensitive to shade. Shade during squaring and early flowering h ad little effect on average boil weight, and did not affect lint percentage . Decreased yield of cotton shaded during FF and PF appeared to be related to decreased boil retention. Shade during ED decreased both boil retention and average boil weight. Under shade conditions, fibre micronaire and fibre strength were decreased, while other fibre properties were unaffected. The se results help explain the yield response of held-grown cotton to low PPFD stress.