Assessment of tolerance to drought stress of thirty-five bread wheat (Triticum aestivum L.) genotypes using boxplots and cluster analysis

Drought is an acute abiotic stress that limits wheat production worldwide, particularly in arid and semi-arid zones, due to the uneven distribution of rainfall, possibly as a consequence of climate change. In south Asia, including Bangladesh, India and Pakistan, wheat is generally grown under rainfall deficit in winter causing the reduction of wheat yield during this period. This study aimed to characterize the drought tolerance of 35 wheat genotypes of diverse morphologies grown in the field. Plants were grown under drought (irrigation was stopped after the crown root initiation (CRI) stage and the crop was protected from receiving rainfall) and well-watered (control) conditions. Phenological variation on days to first visible awn, days to heading, days to anthesis, days to full expansion of flag leaf, days to awn drying, and days to physiological maturity of all 35 wheat genotypes were significantly different (p≤0.01) under water deficit (drought stress). Similarly, plant height, tillers m^-2 , spike length, spikelets spike^-1 , grains spike^-1 , grain weight, grain yield (GY) and straw yield of all 35 genotypes were significantly reduced under water deficit. Among the tested genotypes, nine genotypes i.e., ‘BARI Gom 26', ‘Sourav’, ‘BAW 1169' and ‘BAW 1158' (GY reduction < 30%), and ‘BAW 1151', ‘BAW 1157', ‘BAW 1159', ‘BAW 1161', ‘BAW 1165' and ‘BAW 1170' (GY reduction < 40%) were classified as tolerant on the basis of minimum variation in phenology, growth and yield attributes, while also considering the lowest yield reduction (< 40%) under drought stress. Genotypes ‘Prodip’, ‘Shatabdi’, Gourav, ‘Sufi’, ‘Kanchan’, ‘Barkat’, ‘Balaka’, ‘Aghrani’, ‘Akbar’, ‘Protiva’, ‘Ananda’, ‘Bijoy’, ‘BARI Gom 25', ‘BAW 1160', ‘BAW 1162', ‘BAW 1163', ‘BAW 1164', ‘BAW 1168' and ‘BAW 1172' were categorized as moderately sensitive (< 50% GY reduction), while genotypes ‘Seri’, ‘Pavon’, ‘BAW 1166', ‘BAW 1167', ‘BAW 1171' and ‘BAW 1173' were considered to be highly susceptible to drought (>50% GY reduction). Therefore, among the 35 genotypes, nine may be recommended as drought-tolerant wheat genotypes for cultivation under water deficit (drought) conditions or may be used in a future breeding program to develop drought-tolerant varieties.