Abstract Drought is one of the most important abiotic stress reducing growth, survival, and crop productivity in some areas of the world such as Iran. Different plant species genetically pursue various methods to deal with drought. Stress memory is one of the mechanisms in plants evolved to adapt to environmental fluctuations. Plant in the previous encounter with different types of stress (or initiator) can change subsequent responses and prepares for a faster or more aggressive response to future stress, called stress memory. Unfortunately, limited studies have been conducted on genetics of drought tolerance in association with stress memory and development of tolerant cultivars in Bromus inermis. In this study, 33 half-sib families obtained from polycross were eva‎luated in a greenhouse experiment to find better understanding of drought stress memory and estimate genetic parameters of traits related to stress memory. Half-sib families were examined under three irrigation treatments including continuous normal irrigation (control) (C), treatment with one final drought (D2), and treatment with drought at two times (primary and secondary) (D1D2) by a factorial arrangement according to a randomized complete blocks design with two replications. Drought stress decreased forage yield, root dry weight, leaf relative water content while increased carotenoids, peroxidase, and proline content. The results indicated that drought stress memory affected some morphological and physiological traits. Reduction of dry forage yield was 45% and 36% in the D2 and D1D2 treatments compared to the control, respectively. The reduced amount of root dry weight in D2 was 32% and in D1 was 19%. In addition, the chlorophyll and carotenoid content in D1D2 treatment were significantly greater than D2 treatment. Our results indicate that the mechanisms associated with drought stress memory can help this plant to keep growth and have smaller changes when re-experiencing drought stress. Moderate to high estimates of narrow-sense heritability obtained for root and physiological traits indicating phenotypic selection can lead to genetic progression. Narrow-sense heritability of dry forage yield increased in normal tratment compared to the other drought stress conditions. However the heritability of root length, total chlorophyll, carotenoid content, peroxidase, and proline increased under D1 and D2 treatments. Besides, under D1D2 condition, higher narrow-sense heritability was observed for plant height, root dry weight, and ascorbate peroxidase compared to the normal and D2 conditions. The superior half-sib families were identified for future studies based on the results of principal components analysis. For example, genotype 8 can be suggested as the most drought-tolerant genotype in both drought treatments (D1D2 and D2). The results indicated that under D1D2 condition, genotypes 8, 20, and 35 can be selected if the aim is the improvment of drought tolerance index and root traits while genotype 29 can be selected if the goal is improvment of chlorophyll content. Overall, the results indicated that Bromus inermis has the ability to activate drought stress memory mechanisms associated with morphological, physiological, and root traits which mostly are under additive gene actions. Superior genotypes can be used in future genetic studies.

محمد مهدي مجيدي، پرويز احسان زاده

محمدرضا مصدقي

علي محمد ميرمحمدي ميبدي