Five experimental strains and Pima S-6 were grown in nine Regional Tests across the Pima belt in 1987. Experimental strain P70 averaged highest in yield both below and above 2,500 foot elevation. The difference in yield between Pima S-6 and P70 across all locations was 48 pounds of lint per acre. Sequential harvests at Phoenix and Safford, AZ, indicated that P70 was the earliest and Pima S-6 the latest entry in the 1987 Regional Test.

Seed increase of 104 accessions and data collection on 65 accessions were obtained in 1988 to further the maintenance and evaluation of the Gossypium barbadense L. germplasm collection. In a program of conversion of tropical non flowering cottons to a day-neutral flowering habit, 63 accessions were advanced 1 generation by backcross. A systematic screening of the G. barbadense collection for bacterial blight resistance involving 200 accessions from 21 countries yielded 8 accessions resistant to races 1, 2, 7, and 18 of the pathogen. Genetic inheritance and linkage investigations of a male sterile and a foliar mutant progressed. An investigation of the geographic and taxonomic distribution of the ovate leaf trait was concluded with negative results. The frequency of the 2 mutant genes ov₁ and ov₂ proved to be too rare to yield meaningful taxonomic or geographic information about the species. Preliminary results from a performance evaluation of interspecific hybrid cottons conducted at Maricopa and Safford AZ, indicated strong environmental influences on hybrids, but generally favorable yield earliness and plant height data were obtained from the higher -elevation Safford location.

A stain-clearing method, which facilitated the analysis of large numbers of ovules, was developed using methyl salicylate (MS) and azure C, and used with real-time video imaging and image capture. The ability to modulate contrast and illumination intensity using video made it feasible to reduce stain intensity and thus light interference from the specimen. Samples stained and cleared were used as whole mounts which allowed the specimen to be oriented for precise analysis. Of 440 semigamous zygotes examined 439 had one egg and one sperm nucleus resulting from syngamy without karyogamy indicating semigamy is completely expressed. All phenotypes observed in semigamous cotton seedlings appear to arise as products of zygote division. Haploid and tetraploid sectors may result from relative spindle positions, orientation, and the tendency for nearby telophase chromosomes to form a common nucleus. Semigamous endosperm nuclei are triploid, but fusion was never observed. Endosperm may be a result of triple fusion or mitosis-based fusion. A slight delay in endosperm development was observed which could result from failure of the nuclei to fuse. Haploid-diploid ratios of ploidy chimeras were centered on the original 2 : 1, haploid : diploid ratio, but ratios were widely disparate among seedlings. Dispersion resulted from seeds which were chimeric for ploidy in the hypocotyls, but not in the cotyledons. Additionally, departures from the initial ploidy ratio may be a result of normal development. Differences in cell cycling may occur as cells differentiate and specialize. To examine expression of the parents on the leaves of chimeras, crosses were made between three semigamous genotypes, r1r1SeSev7v7, R1R1SeSeV7V7, and r1r1SeSeV7V7. Chimeric plants were scored for leaf color distribution. For cotyledons the average percentage of yellow-green sectors was less than the non-yellow sector, while true leaves exhibited sectoral ratios that were higher for the maternal sectors or, when confounded, for maternal plus hybrid sectors in every cross. Differences between cotyledons and true leaves may result from the differences in development. Chimeric sectors in true leaves were disproportionately derived from the maternal parent. The apparent advantage of the maternal parent may result from initial maternal developmental control.

Drought stress can substantially alter plant metabolism by decreasing plant growth and photosynthesis. The lack of rapid and reliable screening criteria and measurement techniques for determining water use efficiency (WUE) of crop plants has greatly restricted progress in this critical area of crop improvement. In grain sorghum (Sorghum bicolor L.), WUE was associated with the transpiration ratio [CO2 assimilation (A) / transpiration rate (E), A:E] from leaf gas exchange measurements. Research is needed to identify drought effects on plant productivity and to exploit the use of this knowledge in breeding and agronomic efforts. Therefore, the objectives of this study were to determine if differences in A:E and other physiological parameters existed between two selected cotton (Gossypium hirsutum L.) genotypes and to evaluate the response of cotton genotypes experiencing water stress at two different growth stages on biomass production and yield. Two experiments were conducted using two cotton genotypes differing in drought tolerance. Each experiment was repeated three times in a randomized complete block design with six replications. In Experiment I, the water stress treatment was induced by withholding water when the plants reached the 4-node growth stage. The water stress treatment in Experiment II was imposed at early bloom. Gas exchange and chlorophyll fluorescence measurements were collected during dry-down and recovery periods to determine water stress effects on plant physiology. Biomass was partitioned following the recovery period, to examine phenotypic responses of plants exposed to water stress. The results of these experiments indicate that A:E is significantly increased as leaf water potential (ψL) decreases with no differences in A:E between the two genotypes. Gas exchange measurements showed significant decreases with declining ψL and significant increases upon re-watering; yet, no differences were observed between the two genotypes. Chlorophyll fluorescence was not different between genotypes in either light- or dark-adapted leaves. In Experiment I TAM 89E-51 had a significantly greater seedcotton yield; however, in Experiment II TAMCOT 22 had the greater yield. These experiments suggest that the effects of water stress on cotton are a function of the intensity of the stress and the growth stage in which the stress is experienced.

The increased cost of planting transgenic or stacked gene cotton cultivars has stimulated interest in determining the optimal planting density for commercial production. If seeding rates can be reduced without adversely affecting lint yield and fiber quality, producers could regulate initial inputs by fluctuating seeding rates. However, manipulating plant density per unit area can affect the growth and development of the crop. This altered growth throughout the season could potentially affect fiber quality. Fiber properties, which dictate price discounts, are determined by maturity, diameter and length, as well as by physiological activity at the cellular level. These fiber properties are also affected by genetics and environmental conditions, which ultimately can impact lint production as well as the location of bolls set throughout the plant and the maturation period. The objective of this study was to examine the impact of plant density (including high, ideal and low densities) on growth and development of transgenic cotton cultivars. Field experiments were conducted in 2003 and 2004 at the Texas Agricultural Experiment Station in Burleson County, Texas to assess the effects of plant density on lint yield and fiber quality. Experimental design was a spit-plot design with four replications of three cultivars (SG 215 BG/RR, DP 555 BG/RR, ST 4892 BG/RR) in densities ranging from 74 to 222 thousand plants hectare-1. Plant density had no significant effect on lint yield in 2003 or 2004. However, low plant density treatments contained significantly more bolls plant-1 as a result of the plant’s compensatory ability to produce the same number of bolls in a given area. These low density treatments also produced more vegetative biomass plant-1. Due to lower boll numbers and lower ginout percentage, ST 4892 produced the lowest lint yield each year. Lint quality was not significantly affected by density or cultivar treatments either year. However, in 2003 micronaire values were within the discount ranges for ST 4892, and the two lowest density treatments.

A stain-clearing method, which facilitated the analysis of large numbers of ovules, was developed using methyl salicylate (MS) and azure C, and used with real-time video imaging and image capture. The ability to modulate contrast and illumination intensity using video made it feasible to reduce stain intensity and thus light interference from the specimen. Samples stained and cleared were used as whole mounts which allowed the specimen to be oriented for precise analysis. Of 440 semigamous zygotes examined 439 had one egg and one sperm nucleus resulting from syngamy without karyogamy indicating semigamy is completely expressed. All phenotypes observed in semigamous cotton seedlings appear to arise as products of zygote division. Haploid and tetraploid sectors may result from relative spindle positions, orientation, and the tendency for nearby telophase chromosomes to form a common nucleus. Semigamous endosperm nuclei are triploid, but fusion was never observed. Endosperm may be a result of triple fusion or mitosis-based fusion. A slight delay in endosperm development was observed which could result from failure of the nuclei to fuse. Haploid-diploid ratios of ploidy chimeras were centered on the original 2 : 1, haploid : diploid ratio, but ratios were widely disparate among seedlings. Dispersion resulted from seeds which were chimeric for ploidy in the hypocotyls, but not in the cotyledons. Additionally, departures from the initial ploidy ratio may be a result of normal development. Differences in cell cycling may occur as cells differentiate and specialize. To examine expression of the parents on the leaves of chimeras, crosses were made between three semigamous genotypes, r1r1SeSev7v7, R1R1SeSeV7V7, and r1r1SeSeV7V7. Chimeric plants were scored for leaf color distribution. For cotyledons the average percentage of yellow-green sectors was less than the non-yellow sector, while true leaves exhibited sectoral ratios that were higher for the maternal sectors or, when confounded, for maternal plus hybrid sectors in every cross. Differences between cotyledons and true leaves may result from the differences in development. Chimeric sectors in true leaves were disproportionately derived from the maternal parent. The apparent advantage of the maternal parent may result from initial maternal developmental control.

Thesis--Lyon, 1921. / Bibliography: p. [173]-175.

Thesis (M.A.)--University of Hong Kong, 1969. / Typewritten.

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