Traditional plant breeding approaches have not been very effective in the development of higher yielding cotton (Gossypium hirsutum L.) cultivars for growth under water‐deficient field conditions. The purpose of this research was to evaluate the ability of a laboratory technique to identify cotton genotypes with higher growth rates under water stress conditions in the field. The technique consisted of detaching cotton leaves from the plant at sunset and hydrating those leaves overnight. The following day, the leaves were placed under a light‐bank in the laboratory and weighed every 2 min as they dried. From that data, transpiration decline curves were plotted. The curves exhibited stomatal and cuticular transpiration phases. The point where those two linear phases intersected was termed “mean stomatal closure” (MSC), and both time and relative water content (RWC) at that point were estimated. Sixteen entries were evaluated for transpiration decline curve components and growth rates in irrigated and dryland field plots in 1978 at Big Spring, Tex. In 1980, 12 different entries were evaluated for the same traits under dryland conditions at the same location.In 1978, entry differences occurred for all transpiration decline curve components in the irrigated test and for all components, except stomatal transpiration rates, in the dryland test. The interaction between entries and water levels was significant for all components. In 1980, only RWC at MSC and cuticular transpiration rates were different among entries. Growth rates among entries could not be separated statistically within any experiment. However, large negative correlation coefficients were measured between mean RWC at MSC and mean growth rates in the dryland tests in both 1978 and 1980. This relationship indicated that growth rates tended to be higher when the stomates remained open to a lower RWC before closure. The relationship was not significant in the 1978 irrigated test. Transpiration decline curves appear to be useful in screening cotton genotypes for differences in growth rates under conditions of water stress.
As irrigation water becomes more limited and energy costs increase on the Southern Great Plains, more cotton (Gossypium hirsutum L.) acreage will be diverted to dryland production. Because water is the most limiting resource for cotton production in this region, production will be positively related to changes which increase the water supply or make more efficient use of water. The purpose of this study was to evaluate plant (shoot) dry matter accumulation in photoperiodic (exotic) cotton strains under irrigated (water optimal) and dryland (water stressed) field conditions, to estimate their water‐use efficiency under dryland, and to determine the relationship between field growth parameters, laboratory evaluations of heat tolerance, and greenhouse estimates of root growth. Fifteen photoperiodic strains and one commerciacl ultivar were planted in irrigated and dryland field tests at Big Spring, Texas and in acrylic tubes in the greenhouse at Temple, Texas. In the Big Spring test, dry weight harvests from both the irrigated and the dryland plots were made at 44, 58, 72, and 86 days after planting (DAP). Soil‐water use was measured with a neutron probe in the dryland plots, and leaf discs were taken from both the irrigated and the dryland tests to measure heat tolerance. In them Temple test, shoot dry weight, leaf area, taproot length, and the number of major root laterals were measured 35 DAP. Analyses of variance and regression analyses were used to evaluate the data.Significant variability was demonstrated among entries for shoot dry weights under both irrigated and dryland conditions, for water‐use efficiency in the dryland test, for heat tolerance at Big Spring, and for root growth at Temple. The number of lateral roots measured in the greenhouse was positively associated with shoot dry weights in the dryland plots, but not in the irrigated plots. Root morphology and root growth potentials appear to be important traits in the adaptation of cotton to conditions where limited soil‐water availability is a major constraint on plant growth.
Much of the Upland cotton (Gossypium hirsutum L.) acreage growni n the UnitedS tates is producedin environments where lack of moisture and low temperatures frequently limit production. The purpose of the current research was to test the effectiveness of selecting for lint yield in such stress environments as compared with an optimal environment. Random F3 plants from a composite cross population were advanced two generations by self‐pollination. The F4 and F5 progenies were grown at Lubbock, Big Spring, and College Station, Tex. in 1976, and the F5 progenies were grown at the same locations in 1977. In both years, all locations were classified as deficient or adequate in temperature and moisture based on input heat units and available water. Genotype × environmenitn teractions, within‐location herltabifities, and genetic advance for lint yield were estimated.In 1976, Lubbockw as deficient in heat units and adequate in precipitation, Big Spring was adequate in heat units and deficient in precipitation, and College Station was adequate in both heat units and moisture. Entries were not significantly different for lint yield at either Lubbock or Big Spring, although the genotype × environment interaction was significant for these locations. At College Station, entries were significantly different, whereas the genotypes × environment interaction was not significant. We concluded that selection within the stress environments was largely based upon genotype × environment interactions. A significant genetic advance for lint yield was realized at all locations when the selection was made at College Station in an environment considered optimal for the growth of Upland cotton.
Based on their growth habit, 12 cultivars of upland cotton (Gossypium hirsutum L.) were placed in four groups designated as 1) High Plains‐determinate, 2) High Plains.moderately determinate, 3) High Plains‐indeterminate, and 4) non High Plains‐indeterminate. These cultivar groups were grown at three moisture levels at Lubbock, Texas, and evaluated for their degree of indeterminate growth habit, earliness of crop maturity, lint yield, and irrigation water‐use efficiency. The purpose of our study was to determine the relationships between indeterminacy, lint yield, and irrigation water‐use efficiency.The indeterminate groups of cultivars had higher lint yields at all moisture levels than did the determinate groups. Irrigation water‐use efficiency of all cultivars was higher at the intermediate moisture level (preplant irrigation) than at the higher moisture level (full irrigation). At the intermediate moisture level, the indeterminate cu]tivars had a higher irrigation water‐use efficiency than did the determinate cultivars. The determinate cultivars had a higher irrigation water‐use efficiency than the indeterminate cultivars at the higher moisture level. Correlation analyses between individual cultivar indeterminacy values and lint yield and irrigation wateruse efficiency suggested that a cotton cultivar with a relatively inteterminate growth habit is better adapted in an environment with seasonally limited soil moisture than a cotton cultivar with a relatively determinate growth habit.
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