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Orchardgrass (Dactylis glomerata L.) is a long‐lived perennial forage grass and one of the main perennial grasses that naturally grow in temperate pasture and rangelands in northern and western Iran. This study was conducted to increase knowledge about the genetic basis of agro‐morphological traits in orchardgrass, which may help further improvement of this species. Half‐sib families derived from a polycross of 25 parental genotypes were evaluated during 2 yr, and 11 agro‐morphological traits together with two quality traits were measured. Families were significantly different for all the traits measured. Significant differences were also observed between the 2 yr of evaluation for all the traits except for mean percent of dry matter and panicle length. Narrow‐sense heritability ranged from 0.12 (number of fertile shoot) to 0.79 (mean percent of dry matter). The estimate of narrow‐sense heritability for the most economically important trait (total dry matter yield) was relatively low (0.17 to 0.30), showing that both additive and non‐additive gene effects played a role in the genetic control of this trait. In addition to a weak phenotypic correlation, total dry matter yield had a high genetic correlation with plant height and number of fertile shoots. No significant phenotypic correlation was observed between forage yield and crude protein, though a negative genetic correlation was evident. According to the results of heritability estimations and correlation between the traits, indirect selection for dry matter yield would be possible through selection for plant height.

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An experiment was conducted to estimate drought tolerance of some cocksfoot genotypes based on seed and forage yield and related indices (including tolerance index, mean productivity, geometric mean productivity, reduction percentage index, stress tolerance index and stress susceptibility index) and to identify relationships between measured traits. Twenty-five genotypes were evaluated in the field under control and drought-stress environments over 2 years. The results revealed a high variation for seed yield and forage yield and the measured indices under both moisture conditions. No correlation was observed between seed yield and forage yield under the control treatment, but this correlation was positively significant under the water-stress treatment. Drought-tolerant and susceptible genotypes were identified based on seed and forage yield performance. Genotypes 2, 4 and 7 had high seed yield, while genotypes 7 and 10 had high forage yield under both stressed and non-stressed conditions and were identified as the most tolerant genotypes in each category. The results also revealed that genotypes 1, 2, 4, 6, 7, 8 and 24 had relatively high seed and forage yield in both control and droughtstressed conditions. These genotypes can be used for further studies to improve both seed and forage yields concurrently.

Improvement in drought tolerance is an important component of forage grass breeding. To assess the potential of selecting drought tolerant genotypes of orchardgrass, a polycross population was created in 2010 and evaluated in the field under normal and drought stress conditions during 2011-2013. Drought stress reduced performance in forage yield, growth characteristics, and most of the physiological traits measured, but increased carotenoid content, proline content, and the chlorophyll a/b ratio. High estimates of narrow-sense heritability for chlorophyll and carotenoid content, as well as forage yield components, indicated that phenotypic selection would be successful in achieving genetic progress. Indirect selection to improve forage yield under drought stress conditions was efficient through selecting for chlorophyll a, chlorophyll b, total chlorophyll and carotenoid content. These physiological traits were also significantly associated with drought tolerance index. Overall, families 5, 7, 8, 13, 14 and 24 with high stress tolerance index values and high forage yield under both water conditions were identified as suitable families for breeding drought adaptive varieties. K E Y W O R D Sdrought, orchardgrass, physiology, selection