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Water deficit is a most limiting factor for wheat in rain-fed agricultural systems worldwide. The effects of drought stress on some root features and yield and yield components in wheat (Trticum aestivum L.) were carried out in a factorial experiment based on completely randomized design, under greenhouse condition. The four experimental irrigation regimes, irrigation after 75% of the water was depleted (control), irrigation after 65% of the water was depleted (mild stress), irrigation after 55% of the water was depleted (moderate stress) and irrigation after 45% of the water was depleted (severe stress) were randomized for the main plots. The subplot treatments included eight wheat genotypes. Results showed that Interaction Drought stress with Variety had significantly affected on Total Root Volume and Dry Matter, Number of Tiller and also Shoot Dry Matter. Value of Total Root Volume and Dry Matter, Shoot Dry Matter and Number of Tiller in irrigated varieties were more than rainfed in whole of Drought stresses. N-87-20 variety had most amounts of Total Root Dry Matter, Total Root Volume (exception of control) in all of stresses and control. Root properties influence on yield and other morphological traits of wheat. Stress intensification increase root growth than plant organ so that wheat root can uptake water from soil to compensate damage caused by stress.

A randomized complete block design with three replicates using 20 genotypes of rain-fed wheat was applied. Cluster analysis of different wheat genotypes segregated the genotypes into 3 groups. Comparison between the groups in the first crop year revealed that the second and third groups exhibited the highest rate of radiation-use efficiency (RUE), and the first group had the lowest. Grain yield was highest in the third group and lowest in the first group, with an average of 219.87 g/m2 and 173.40 g/m2, respectively. In the second crop year, the highest rate of RUE was reported in the first group and lowest in the second and third groups. The highest grain yield was observed in the second group and the lowest in the third group (315.40 g/m2 and 253.75 g/m2, respectively). Based on the results of the biplot, high-yield genotypes in the first year of cultivation included G14 (263.00 g/m2), G20 (264.50 g/m2), G18 (214.00 g/m2) and G19 (222.50 g/m2). Based on the results obtained by cluster and PCA analysis under stress conditions, we concluded that several traits play a role in determining the grain yield of wheat.

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