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Identification of heat tolerant upland cotton (Gossypium hirsutum L.) germplasm utilizing chlorophyll fluorescence measurement




Wu, Tingting

Type of Degree



Agronomy and Soils


Heat stress adversely affects upland cotton (Gossypium hirsutum L.) production in the U.S.. A low level of genetic variability in domesticated upland cotton is one of the major constraints for cotton germplasm improvement. Utilization of exotic accessions through introgression could have potential to improve the heat tolerance of upland cotton. Heat tolerance is difficult to determine, especially when yield and fiber quality are the parameters measured in photoperiodic, non-adapted genotypes. Chlorophyll fluorescence is a widely used technique in abiotic stress studies. My objectives were: (1) to evaluate wild (mostly photoperiodic, non-adapted) genotypes for heat tolerance using a chlorophyll fluorescence assay; (2) to determine the heritability of heat tolerance identified by chlorophyll fluorescence in the segregating generations and select elite lines among advanced populations based on this measurement; (3) and to identify if heat tolerance as measured by chlorophyll fluorescence translates to increased growth and vigor under high temperatures. Forty-four wild accessions of upland cotton were selected as a resource of heat tolerant germplasm for a growth chamber test and a field evaluation. In the growth chamber, six-week old cotton plants were subjected to heat stress at 45oC and 80% relative humidity for 24 hrs. Chlorophyll fluorescence was measured before and after heat treatment. In the field, chlorophyll fluorescence (ΦPSII) was measured between 1200 h and 1400 h on the two youngest fully developed leaves of each plant during the first square stage to the open boll stage. Based on the chlorophyll fluorescence measured in the growth chamber and the field test, three wild accessions (TX 2287, TX 2285 and TX 761) were identified as being heat tolerant. Crosses were made between two elite wild accessions and DP 90. F2:3 lines in these two segregating populations were also evaluated in a growth chamber test and a field evaluation which were in the same manner as wild accessions. The broad-sense heritability of chlorophyll fluorescence on F2:3 lines in the growth chamber was markedly different from that in the field indicating this measurement is sensitive to environmental conditions. Most fiber quality traits of F2:3 lines were comparable to that of adapted cultivars whereas most seed traits of F2:3 were slightly lower than that of adapted cultivars. Furthermore, correlations were found between chlorophyll fluorescence measurement and seed traits as well as between chlorophyll fluorescence measurement and fiber quality traits indicating chlorophyll fluorescence can be used as a selection tool for simultaneous improvement of heat tolerance, seed trait and fiber quality in these introgressed lines.