Improving the precision in estimating cotton seed fibre density

Abstract

An increasing demand for lightweight casual garments has driven the need for cotton with lower fibre fineness to facilitate production of finer yarns in the spinning mill. Breeding cottons with finer fibre (lower linear density) to address this target will reduce lint yield unless there is a concomitant change in another yield component. One yield component to consider is seed fibre density (FD) which is the number of fibres per unit seed surface area (SSA). FD can be measured also as the number of fibre initials on the seed coat at fibre initiation by scanning electron microscopy (SEM). In order for a cotton breeder to apply selection during breeding, an accurate measure of FD is required.Micronaire is a common, indirect measurement of cotton fineness but it is confounded by fibre maturity. This paper compares the use of micronaire with a direct measure of fineness in calculating FD. It compares mature seed estimated FD to FD determined by SEM imagery of one day old ovules, and determines the most reliable stage during flowering for quantifying FD. Data from five field experiments provided 1469 samples in which micronaire and fineness were compared for estimating FD. When using fibre fineness for calculation, the average FPS was 17,017, and the average FD was 157mm−2. The average FD by SEM was 5108mm−2, it was higher than FDfin because ovules were ∼4% of the final seed surface area due to growth dilution. Although micronaire and fineness were correlated, there was scatter in that relationship due to differences in fibre maturity. As a result, there were many instances where FD was overestimated when calculated by micronaire, compared with using fineness, such that less than 50% of the top 20% FD measured by fineness were identified by the top 20% of the samples in FD measured by micronaire. Results indicated FD measured by fineness on mature seeds obtained similar ranking to direct measures by SEM of FD on one day old ovules and the mid flowering stage was more reliable than early or late flowering. It was concluded that FD should be estimated by using fineness rather than micronaire because micronaire is not a reliable measure of fineness.