Project Summaries

07-108  Project Manager: D. C. Jones


Freddie M. Bourland, Derrick M. Oosterhuis and Androniki Bibi, University of Arkansas

Improving the effectiveness and efficiency of selection requires continued development and refinement of breeding techniques.  Modifications made to, and germplasm releases from, the University of Arkansas Cotton Breeding Program were summarized in a paper presented at the 2013 Beltwide Cotton Conference. These modifications include a better understanding and utilization of methods to increase yield efficiency and to improve fiber quality. Yield efficiency has been enhanced by altering yield components and basic plant conformation (how lines achieve yield), and by improving resistance/tolerance to insects, diseases, and stress (how lines protect yield).  Fiber quality has been improved by the development and use of Q-score as a selection index and by evaluation and reduction of marginal bract trichomes. In this project our 2012 work focused on further study of basic yield components by studying the relationships associated with marginal bract trichomes (hairs) and evaluation of the visible true leaf at emergence (VTLE) trait.

Within the UA Cotton Breeding Program, high yielding lines that rely more heavily on increased lint index (lint per seed) rather more seed per acre have been preferred. Dissertation work by Frank Groves (former Cotton Incorporated  Fellow) helped to confirm these relationships and refined a method for estimating fiber density (number of fiber per unit area of seed coat).  This refinement should assist with improving yield components. 

Cotton breeders have long given high priority to reduced trichomes (hairs) on leaves and subsequently have developed many "smooth leaf" varieties.  Cooperative studies with the USDA Gin Laboratory in 2011 and 2012 indicated that both high leaf pubescence and high marginal bract trichome density contribute to high trash in ginned lint.  Surveys of cotton breeding lines and varieties indicate that marginal bract trichome density tends to be lower on smooth leaf genotypes but may vary significantly among genotypes having the same leaf pubescence density.   Some hairy leaf lines have been found to have relatively low bract trichome density and may combine the positive attributes associated with the smooth leaf (lower trash) and hairy (better agronomics) leaf traits.

A total of 43 germplasm lines have been released since 2004.  These lines represent a wide array of genetic backgrounds, host plant resistance, yield and yield component traits, and provide novel breeding material to public and private cotton breeders.   Three conventional varieties ('UA48', 'UA103, and 'UA222') were released in 2010 and 2011. 

Another objective of this project was to develop a rapid method of screening cotton germplasm for heat tolerance.  A variety of techniques were tested to determine and quantify thermotolerance in cotton genotypes. The techniques ranged from controlled environment measurements of fluorescence and membrane leakage to measurement of glutathione reductase and fluorescence-temperature response curves using a leaf thermoelectric cooler heater. The second objective was to compare genotypes for thermo-tolerance. Fluorescence and membrane leakage were determined as the most suitable and practical techniques for determining plant response to elevated temperature. Subsequently, we added a thermoelectric control to the fluorometer to be able to measure plant response to a range of temperatures from 20 to 45C. The fluorometer with thermoelectric control assembly for measuring plant response to a range of temperatures from 20-45C consists of the thermoelectric cooler/heater to rapidly adjust leaf temperature, a digital thermometer with a type K fine wire thermocouple to monitor temperature, and a portable fluorometer to measure actual quantum yield. The fluorescence equipment with the thermoelectric cooler/heater instrumentation was tested for rapid screening of cotton cultivars for heat tolerance under growth chamber and field conditions.
We tested the accuracy and reliability for recording a diurnal trend of leaf fluorescence on two different days, and the diurnal leaf temperature had a similar pattern on each day. We did a number of tests on individual varieties for consistency of results. In these and other similar tests the instrument proved to be sensitive and reliable. The ability of LeafTech to distinguish differences in photosynthetic thermotolerance during cotton leaf expansion was confirmed during the field season.  Very young, expanding leaves were shown to have higher and broader thermal optima when compared with more mature leaf stages on the same plants. This indicated the importance of selecting leaves of similar age. Fluorescence measurements were made on leaves of four contrasting cultivars: DP0912 (sensitive), SiokraL23 (thermo tolerant), Pima (partially tolerant), and a wildtype T1521 (tolerant).  There were some distinct differences between cultivars in their response to increasing temperature. This project will allow us to screen current commercial cultivars grown in Arkansas (for ranking in temperature tolerance) and to start using this new technique in screening new germplasm of Dr. Bourland. The study will continue in 2013 in both growth room and field environments using an increased number of cotton genotypes.


Project Year: 2012

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