Browsing by Author "Longenberger, Polly Suzanne"
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Item Development of a screening method for drought tolerance in cotton seedlings(Texas A&M University, 2007-04-25) Longenberger, Polly SuzanneThe key to an efficient screening method is the ability to screen large amounts of plant material in the shortest time possible. Unfortunately, due to the complexity of drought tolerance, a quick and effective screen for this trait has yet to be established. The research reported herein was designed to evaluate a screening method for drought tolerance in cotton (Gossypium hirsutum L.) seedlings. Twenty-one converted race stocks (CRS) and two cultivars were evaluated for seedling drought tolerance on an individual plant basis. CRS are day-sensitive primitive lines derived from various wild race stocks that were converted to day neutrality for use in temperate region plant improvement programs (McCarty et al., 1993). Genotypes were evaluated October - November 2004 and February - March 2005 under greenhouse conditions at the Norman E. Borlaug Center for Southern Crop Improvement, College Station, TX. Seedlings were subjected to three sequential cycles of drought at 15 days after planting (DAP). Drought cycles consisted of withholding water until the moisture content of "indicator" cone-tainers, containing Deltapine 491 (DP 491), had an average volumetric water content of 0.07. Plants were then watered to field capacity and percent survival was recorded after 48 hours. Genotypes differed in their percent survival following three consecutive drought cycles. Drought cycles 2 and 3 did not contribute to the separation of genotypes. DP 491 was the most tolerant genotype evaluated. None of the CRS were more or less tolerant than Acala 1517-99. CRS M-9044-0165 was the most stable genotype across the two experiments.Item Evaluation of chlorophyll fluorescence as a tool for the identification of drought tolerance in upland cotton(2009-05-15) Longenberger, Polly SuzanneA novel bioassay for the evaluation of plant water status was developed by Burke (2007). The research reported herein was designed to evaluate this new protocol as a tool for use in cotton breeding programs for the identification of drought tolerant genotypes. Twenty genotypes were selected to represent diverse germplasm pools for a two-year field evaluation. Replicated tests were performed in Lubbock, TX and College Station, TX in 2005, 2006, and 2007. Dryland and irrigated treatments were administered in a split plot arrangement of a randomized complete block design. Fluorescence measurements were taken at mid-bloom and late bloom growth stages of growth. Source leaf tissue was harvested at predawn and subjected to high temperature incubation with fluorescence measurements subsequently taken hourly for five hours. Drought stressed plants had not mobilized their carbohydrate reserves from their source leaves overnight and thus maintained cell viability and therefore higher chlorophyll fluorescence values throughout the incubation with the opposite being true for nonstressed plants. Fiber lint yield and fiber properties were measured at the conclusion of the 2005 season in College Station and the 2006 season in College Station and Lubbock for comparison with the fluorescence data. Five genotypes, ?Acala 1517-99?, ?Deltapine 491? (PVP no. 200100159), ?Tamcot CAMD-E?, ?Tamcot 22? and TAM 89E-51, an unreleased breeding line, were selected based on field evaluation results in a preliminary study in 2005 to be included in a diallel analysis to determine the heritability of fluorescence measurements. Genotype x treatment effects complicated the classification of genotypic responses to drought. Few and inconsistent correlations were found among fluorescence values and lint yield or fiber properties. The diallel analysis did not identify general combining ability or specific combining ability effects for chlorophyll fluorescence measurements. Thus this procedure provides little potential in selecting plants for drought tolerance when plants are grown under field culture. Selection among Tamcot 22 and TAM 89E-51 plants for high and low genotypes according to fluorescence values did not yield progeny different from unselected Tamcot 22 and TAM 89E-51.