Morphological and physiological characteristics associated with heat tolerance in creeping bentgrass

Growth of creeping bentgrass (Agrostis palustris finds,) is limited by heat stress during summer. Understanding the morphological and physiological characteristics associated with heat tolerance of creeping bentgrass would facilitate breeding programs in improving those characteristics. The objectives of this experiment were to study responses of single-leaf photosynthetic capacity, tillering, and root growth to heat stress for two creeping bentgrass cultivars differing in performance under heat stress and to determine the relative importance of these factors in heat tolerance. The cultivars L-93 (heat tolerant) and Penncross (heat sensitive) were exposed to day/night temperatures of 20/15 degreesC (control) and 35/30 degreesC (heat stress) in growth chambers. Canopy net photosynthetic rate (Pn), single-leaf Pn, and RuBP carboxylase (Rubisco) activity were reduced by heat stress for both cultivars. Canopy Pn of L-93 was significantly higher (more than double at 64 d of treatment) than that of Penncross under heat stress, Cultivars were not different in single-leaf Pn and Rubisco activity under either control or heat stress conditions. High temperature reduced plant density, tiller density, root number, and root fresh weight for both cultivars, L-93 had higher plant and tiller densities, greater root to tiller ratio, and more and finer roots than Penncross under control and high temperature renditions, The better performance of L-93 under heat stress was due largely to its morphological characteristics, including tillering and root growth, but was not related to single-leaf photosynthetic capacity. Narrow leaves, small plants, dense tillers, big root system, and high root-to-shoot ratio could be used to select heat tolerant cultivars.