Physiological Mechanism of the Caducous Bract of Gossypium harknessii

Physiological Mechanism of the Caducous Bract of Gossypium harknessii

R.E. King, R.J. Wright, and J.R. Gannaway

Texas Tech University and Texas AgriLife Research and Extension

Lubbock, Texas

Bract contamination in cotton lint has been a major problem for the cotton industry for many years. As the bract tissue senesces shortly after the boll opens it becomes entangled in the lint causing 45-55% of botanical trash found in gin trash, especially since bracts are not affected by defoliants that are designed to drop leaves. Reduction of bract tissue could contribute to improved fiber length and length distributions because less lint cleaning procedures would be needed to remove botanical trash during the ginning process. Three species of wild diploid cotton Gossypium armourianum, G. harknessii and G. turneri express the caducous bract trait. This bract sheds completely from the pedicel of the flower before the flower is mature.

Previous studies have used G. armourianum and G. harknessii as parental material to develop a triploid or hexaploid population. The mechanism of the caducous bract was not under consideration in these studies. Preliminary data for this study to determine the physiological mechanism of bract senescence and shed was generated using G. harknessii. Our preliminary data show that there is not an abscission of the bract from the pedicle or involucels, but there is cell death of the soft parenchymal cells of the bract tissue.

Floral form samples from G. harknessii were compared to G. raimondii and G. hirsutum at different time intervals to test when the cell death occurs during flower maturation. Timing of cell death in association to fertilization was determined using both optical and scanning electron microscopes. Comparisons show that cells from G. harknessii are distorted and elongated compared to G. raimondii and G. hirsutum and cell death is initiated at -5 to -3 days post anthesis.