| A number of commercial and experimental lines of spring wheat (Triticum asetivum L.) grown as 'dryland' winter crops in two desert localities of Arizona were examined to determine if physiological or developmental traits could be correlated with yield. At Mesa, plants were grown on a clay loam soil in 1978-1979, and also in 1979-1980. In Tucson, plants were grown on a sandy loam soil in 1979-1980. All dryland treatments received 150 mm pre-plant irrigation. In Mesa, 150 mm of rainfall occurred during the first season, and 153 mm occurred in the second season. In Tucson, there was 134 mm rainfall during the growing season. In addition to the dryland studies, plants were also grown in Tucson on borders that received (a) 75 mm water 2 to 3 weeks before flowering; (b) 75 mm water 1 week before flowering and (c) recommended levels (525 mm) of water.; Yields in Mesa ranged from 2400 to 3400 kg/ha in 1979, and 2400 to 3700 kg/ha in 1980. Under dryland conditions in Tucson, the yields ranged from 1100 to 3000 kg/ha. When watered 2 to 3 weeks before flowering, yields ranged from 2300 to 3600 kg/ha; when irrigated 1 week prior to anthesis, yields were 1600 to 3400 kg/ha; and the well watered treatments yielded 2700 to 4500 kg/ha. The rankings of the different lines according to yield was maintained regardless of the site, growing season, or amount of irrigation.; When grown under dry land conditions, highly significant correlations were found between yield and grain weight/1000 seeds (correlation coefficients listed in order: Mesa 1978-1979; Mesa, 1979-1980; and Tucson, 1979-1980 were r = 0.93, 0.96, 0.99); grain weight/spike (r = 0.93, 0.96, 0.97); Head weight/plant (r = 0.93, 0.97, 0.96); LAI after anthesis (r = 0.91, 0.98, 0.95); total dry weight/plant (r = 0.98, 0.95, 0.93).; Similar correlations were also found in trials which received additional irrigation(s). No significant correlation was found between yield and tiller number/m('2) except for the well watered treatment (r = .85) indicating that regardless of the yield potential, all cultivars tended to produce the same number of tillers/m('2). Usually, no significant relationship was found between yield and grain number/spike or grains/m('2). Correlation coefficients between yield and LAI improved from nonsignificant at early vegetative stages to highly significant after anthesis and as the season progressed, suggesting the importance of photosynthesis during head development.; Wide differences in leaf water potential and leaf elongation rates were also found. Generally, high yielding cultivars had higher leaf water potential than lower yielding ones under well watered and dry land conditions in Tucson. Osmotic adjustment was observed in all cultivars but to a lesser extent in low yielding cultivars. Total length of leaves measured 1 to 2 weeks prior to anthesis were less under dryland conditions than that of well watered treatments. |
