Canopy Architecture and Fiber Quality Variation by Branch Location

T.A. Kerby and G. Ruppenicker


 
ABSTRACT

Previous studies have demonstrated bolls produced at different locations of the plant vary in boll size as well as in fiber development. A good relationship between boll size, percent of fruiting positions setting bolls, and micronaire and/or dye uptake has been established. We presume this variation is the result of a differential carbohydrate supply. Decreased boll size and quality is understandable for bolls set near the end of the season because of severe competition for assimilates. The observation that boll size and fiber quality was also low for some early set bolls was surprising. Apparently, localized carbohydrate deficiencies resulted from additional vegetative development which limited light penetration to leaves which were important to sustained boll development.

Studies were initiated in 1990 with phenotypes with short branches (columnar types) to compare growth and development, light penetration into the canopy over time, distribution of bolls, and fiber quality to standard Acala cottons. Our major interest was to determine if there was an interaction between plant types (columnar or Acala) and quality variation by position on the plant. Columnar 2 (Shafter germplasm) and DPL 895 were compared to GC-510 and SJ-2 in 1990, while DPL 900 replaced DP 895 in the 1991 studies.

Columnar cottons produced a slightly greater percentage of their yield in the premium first position of a fruiting branch compared to standard cultivars. The interaction of plant type and position on the plant was significant for boll size, neps, yarn thick spots, fiber elongation, and micronaire. Dye uptake readings have not been completed to date. Bolls produced on vegetative branches or on fruiting branch positions three or greater have been shown to be of low quality. In the current study where columnar phenotypes were compared to standard Acala cultivars, relative boll size was similar at the first two positions on a fruiting branch. Relative boll size for columnar phenotypes were greater than standard Acala cultivars on vegetative branches and on bolls at the third position of a fruiting branch. When the variation in boll size was compared for all positions of the plant, columnar types had an average standard deviation of 0.63 g boll-1 compared to 0.85 for Acala cultivars.

In a related study, we tried to document positional variation in seed cotton per seed. All bolls on 30 plants for each of three Acala cultivars were harvested and the distribution in seed cotton weight per seed determined for each boll. Each seed (with lint attached) was carefully separated and weighted then placed into weight classes in 10 mg increments from 20 to 300 mg. In this manner, the whole plant distribution in seed cotton weight per seed could be determined. Acala cultivars (Prema, SJ-2, and GC-510) showed similar distributions. Unfortunately, the results did not form a normal distribution, but values were skewed to the low side. These same samples were then forwarded to Cotton Incorporated for collaborative evaluations performed by Mike Watson. Dye uptake of these seed cotton weight classes were determined. Seed cotton weighing 80 mg or less dyed poorly. Seed cotton weighing more than 220 mg dyed uniformly. There was 3.4 percent of the total seed cotton weight which weighed 80 mg or less and 50.0 percent which weighed more than 220 mg. Dye uptake problems declined as seed cotton weight per seed increased between these two intervals.

These results further illustrate that a wide range of fiber quality is produced on the same plant. We hypothesize this variation is primarily the result of variation in carbohydrate supply. Although it is too early to draw firm conclusions, it appears columnar phenotypes have less variation than standard Acala cultivars. Additional studies are required to document these results and to determine how much the variation is diminished by columnar phenotypes, and ascertain if this has any practical value to the mill customer.



Reprinted from 1992 Proceedings Beltwide Cotton Conferences pg. 1069
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998