Physiology and Rooting Characteristics of Drought Tolerance in Barley

Abstract

The development and release of low-irrigation barley cultivars mark a significant achievement in breeding efforts for drought tolerance; however, the specific physiological traits associated with their drought tolerance remain unclear. The goal of this dissertation was to examine the hypothesis that barley cultivars bred for low-input conditions have particular adaptive traits that improve crop performance under drought conditions. The general objectives of this study were: (1) to compare plant growth and yield of low and high-input barley varieties under high and low irrigation regimes; (2) to evaluate rooting characteristics of tested varieties under high and low irrigation regimes; and (3) to explore differences in root tip physiology of tested varieties at early stages of plant development. Two years of replicated field trials were conducted in Tucson, Arizona comparing low-input varieties Solar and Solum to high-input, semi-dwarf varieties Kopious and Cochise. Observed traits associated with improved performance of the low-input varieties under drought conditions included early vigor, early flowering, greater root density at lower depths (40-80 cm), and more effective water use exhibited by greater water use post-anthesis. Observations from the root profile wall revealed all varieties, especially the low-input cultivars, had thicker, web-like roots under low irrigation and that Solar roots were most able to penetrate through a hard subsoil caliche layer at 80 cm depth. Field trials were followed by an empirical survey comparing early root development between the field-tested varieties. The results of this study revealed the low-input varieties exhibited faster seed germination and a decreased root elongation zone. Border cell number of the low-input varieties was also higher than that of the high-input variety Kopious, but lower than that of Cochise. It was also found, compared to the other varieties, Solar root tips produced a significantly larger mucilage layer and developed more root hairs in the presence of water. These observed traits, if found to be linked to the drought adaptive physiology of Solar could be used for simple, rapid, and inexpensive screening of new drought-adapted varieties.