Effects of Long-Term Drought Stress and Variation in Traits Related to Post-Drought Recovery, Persistence, and Summer Dormancy in Two Species of Orchardgrass (Dactylis glomerata L.) and Smooth Bromegrass (Bromus inermis Leyss.)

This study was conducted to evaluate drought tolerance of recombined genotypes of orchardgrass (Dactylis glomerata L.) and smooth bromegrass (Bromus inermis Leyss.), and investigate the effect of long-term drought stress on persistence, summer dormancy, and post-drought recovery. For this purpose, 36 genotypes of each species randomly selected from polycross populations, were clonally propagated, and evaluated under normal and drought-stressed conditions during 2013-2015 at the research farm of the Isfahan University of Technology, Isfahan, Iran. In the fourth year (2016), irrigation was withheld in both moisture regimes for two months, and then plants were re-watered and investigated. For most of the measured traits, high genetic variation was observed among the genotypes of both species. In orchardgrass, the genetic coefficient of variation varied from 4.31 to 65.45% under normal conditions, and from 3.93 to 79.93% under drought stress conditions. In smooth bromegrass, the range of genetic coefficient of variation was variable from 3.56 to 67.18% under normal conditions and from 3.42 to 54.63% under drought stress conditions. This indicated a high potential for improving these traits through targeted selection in breeding programs of the two species. In both species, the higher increase in genetic coefficient of variation under drought stress was observed for recovery-related traits (i.e., degree of recovery and recovery ratio in orchardgrass; and recovery yield, degree of recovery, recovery ratio, and percentage of recovery in smooth bromegrass). Results showed that smooth bromegrass had a better performance regarding recovery-related traits. Furthermore, post-drought recovery-related traits in both species were reduced under drought stress, except for the recovery ratio in smooth bromegrass. However, reductions were higher in orchardgrass than in smooth bromegrass. In the current study, the persistence of orchardgrass genotypes increased under drought stress, and decreased in the smooth bromegrass. Less fodder production during summer by the genotypes of this germplasm showed that these genotypes had incomplete dormancy.