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Physiological responses of six sorghum (Sorghum bicolor (L.) Moench) hybrids and their respective parental lines were evaluated under high and low soil moisture conditions at Tucson, Arizona in 1980 and 1981. Apparent photosynthesis, transpiration, diffusive resistance, and temperature differential (ambient temperature minus leaf temperature) were measured under field conditions at weekly intervals. To measure apparent photosynthesis, a small plexiglas chamber was sealed over a section of leaf blade and gas was sampled with two syringes pulled at a 30 or 60 second interval. The gas samples were injected from the syringes into an infrared gas analyzer to measure CO(,2) concentrations. Transpiration, diffusive resistance, and temperature differential were measured with a steady state porometer. Regression analysis was used to compare the physiological performance of the germplasm sources over a wide range of environmental conditions. The physiological characteristics of the highest yielding sorghum hybrid in 1980 were the most stable across all environments. This hybrid was superior to both its male and female parent for all four physiological characteristics. In 1980, this hybrid was superior to the other hybrids in temperature differential and transpiration. The superior yielding hybrid had the highest mean apparent photosynthesis and the lowest mean diffusive resistance. All hybrids had higher yields than their respective male parents under both irrigation treatments. Thirty-five days after planting, the superior yielding hybrid had the greatest leaf, stem, and root dry weights. This hybrid also had the highest relative leaf area expansion rate. Heterosis for stomatal density was not observed either year. Regression analysis proved to be an effective tool for analyzing the sorghum germplasm over a diverse range of environmental conditions. By comparing the response of an individual germplasm against the mean response of the population under numerous environmental conditions, the slope, mean, and coefficient of correlation may be used to evaluate genotype-environment interactions.

The development, yield and water use of six sorghum (Sorghum bicolor (L.) Moench) hybrids and their respective male and female parents were evaluated under stressed and well irrigated conditions during 1980 and 1981 at Tucson, Arizona. Changes in soil moisture storage were measured by neutron modulation on a semiweekly schedule. Transpiration, diffusive resistance and leaf-ambient temperature differentials were monitored biweekly using a steady state porometer. Meteorological data was collected on a daily basis. The 1980 season had higher maximum temperatures and pan evaporation than the 1981 season. Differences in soil moisture extraction among sorghum entries were not apparent within water treatments. Mean cumulative evapotranspiration (ET) for the stressed treatment was 270 and 261 mm, for 1980 and 1981, respectively. Mean cumulative ET for irrigated treatment was about twice that at 520 and 648 mm during 1980 and 1981, respectively. There were no apparent differences in cumulative ET for entries in the stressed treatment while genotypic differences were manifested under well irrigated conditions. Temperature differential demonstrated a significant and negative correlation with diffusive resistance especially under stressed conditions (r = -.64 in 1981). Temperature differential was positively correlated with transpiration (r = .70 in 1980 stressed treatment). Plant height was significantly affected by water level both years while stem weight was affected by water level only in 1980. Soil moisture treatments did not affect leaf area either year and genotypic differences were demonstrated only in 1981. Hybrids produced greater grain yield than their male parents under both water treatments. This was due to greater seed number for hybrids. Seed number was also more stable for hybrids under both moisture levels. Hybrids four and seven had the greatest grain yield in 1980 and 1981, respectively. Harvest index was improved with increased water application due to increased seed number. Hybrid four in 1980 and hybrid seven in 1981 were extremely efficient in water use exhibiting ET ratios of 283 and 378, respectively under high water application. Reduced water application had little affect on the performance of these entries.

Recently, canopy temperature measurements and atmospheric vapor pressure deficits have been used to determine water stress in numerous plant species. A linear regression of the two parameters yields a crop water stress index (CWSI) baseline capable of determining a fraction of water stress between 0 (wet) and 100 (dry). Such a baseline was determined for one line of guayule (N396) in the spring of 1983 and used to determine time of irrigation for field plots. Three irrigation treatments were chosen based on CWSI measurements to aquire a relationship between rubber yield and water Stress. Treatments were irrigated when their respective CWSI measurements reached 0.30 (wet=1), 0.60 (medium=2), and 0.90 (dry=3). Duplicate tests were planted to determine if water delivery by drip irrigation differed from furrow irrigated plots. Very good correlations exist between rubber yield and seasonally averaged CWSI (r = 0.85). The interrelationship of rubber yield and total water applied was also high with r = 0.87. The highest rubber yield occurred in March in treatment 1 (wet) in the furrow irrigated field. Rubber yield was positively correlated with total water applied and inversely correlated with CWSI. Small differences were observed between the type of water delivery system used with similar treatments from both fields not being significantly different. The wet and medium treatments in both fields were about the same with the dry treatment being significantly different from the wet and medium treatments for total water applied. This indicates that guayule is not as sensitive to changes of 0.30 CWSI units as other species measured. Correlations between the CWSI and soil moisture deficits were very good with r=0.83 for 1983 and r=0.91 for 1984 indicating the CWSI can be used accurately to determine soil moisture deficits and vice-versa. A 0-stress moisture deficit range (0-SMDR) was determined for guayule where 0.0-2.26 and 0.0-4.58 cm (1983 and 1984, respectively) of water could be depleted from the soil profile before the plants showed stress as indicated by the CWSI. The 0-SMDR appears to be constant for a particular plant species in the same field for a particular year and may further define and standardize plant available soil moisture.

The grain amaranths, Amaranthus cruentus and Amaranthus hypochondriacus have been promoted as grain-bearing plants of possible high productivity in saline or hot arid habitats. To investigate these claims, seeds of both species were germinated at 10, 15, 20, 25, 30, 35 and 40°centigrade. Germination percentage for both species was above 90% after four days at 20, 25, 30, and 35°C. Germination was negligible at 10 and 15°C and very low at 40°C. Seeds were germinated in isotonic solutions of PEG and NaCl at 0.0, -0.2, -0.4, -0.5, -0.6, -0.8, and -1.0 MPa osmotic potential at 30°C. Germination percentage was high in the range 0.0 to -0.4 MPa and dropped rapidly to zero in the -0.6 to -1.0 MPa range. Differences due to chemical effects were significant. Species differences were not. Radicles and hypocotyls were measured after six days in the above media. PEG was more inhibitory of seedling growth than was NaCl and generally inhibited A. cruentus more than A. hypochondriacus. This was also true of NaCl. All growth functions were slightly inhibited at 0.0 to -0.4 MPa and very inhibited above -0.6 MPa. PEG radically increased root/shoot ratio in both species.

The performance of three maize (Zea mays L.) hybrids, grown under two irrigation levels, was used to investigate the effects of soil moisture competition between adjacent plots, the transmission of these effects into multi-row adjacent plots and types of multi-row plots and plot borders most effective in shielding from these interplot competition effects. On the basis of grain yield, competition effects intended to the second rows of five-row plots necessitating more than five-row plots to accurately evaluate the full transmission of interplot competition effects into adjacent plots. Evaluation of genotypes in one-row plots all with the same common border row genotype to make them three-row plots would be more suitable for evaluation of relative competitiveness for soil moisture under soil moisture stress conditions compared to no border rows or border rows of the same genotype being evaluated.

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Severe water stress reduced the number of flowers produced by Capsicum annuum var. annuum L. Longum plants, but the timing of flower production was less affected. The use of different plant establishment techniques modified flower production. Bare rooted transplants slowed the rate of flower production in comparison with direct seeded plants or those established from cell tray transplants. Bare rooted transplants delayed the onset of water stress. The capabilities of male and female gametophytes were reduced by water stress, with the female more affected, and the interaction of male and female gametophytes was affected by moderate water stress. Moderate water stress increased the time to fruit set, but affected neither the number nor percentage of fruit set, whereas severe water stress increased the time and reduced the number and percentage. Severe water stress reduced the number and percentage of mature fruit, fruit quality indices and total fruit yield. Moderate water stress reduced the number of seeds per fruit and fruit dry weight, but total fresh weight yield was not significantly affected. The time to fruit set was negatively correlated with the quality indices of mature fruit, whereas the number of seeds was positively correlated with the same. Fertilisation determined the success of seed set, and the rapidity of fruit set. Successful fertilisation can only occur when the pollen tube arrives at a viable ovule. The processes of pollen tube growth and longevity of the ovule are the factors most critically affected by water stress in determining the yield of C. annuum Longum. / Master of Science (Hons)

Graduation date: 1992

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