Assessment of genetic diversity of some Iran bread wheat (Triticum aestivum L.) landraces using multivariate statistical analysis

It is expected that world wheat production would be about 761.5 million tons in 2020 while world demand would be doubled by 2025. Drought stress is one of the most important factors of yield loss that can decrease wheat production significantly. In the Middle East, drought stress usually happens at the end of the growing season and after the spike appearance. Late-season drought stress can slow down the seed development stage and decrease grain yield. In order to have stable food security one of the ways is to use the genetic diversity of germplasms.

An association panel including 199 Iran bread wheat landraces was sown in Alborz and Zanjan provinces under late-season drought stress and normal irrigation conditions where climate zones are semi-arid. The experiments conducted using two alpha lattice designs with two replications for each of the conditions in each of the locations. The drip irrigation method was used for watering till spike appearance. Then, watering terminated for one of the designs whereas another design was normally irrigated for more three times in each location. Phenotypes measurements included days to heading, days to heading, duration of heading-to-maturity, plant height, grain yield/m2, thousand kernel weight, seed length, seed width, seed number per spike, spike length, spike weight, flag leaf length, flag leaf width, peduncle length, shoot diameter, and awn length.

Agronomic traits varied lower under late-season drought stress conditions compared to normal irrigation conditions (except days to heading). Significant genetic effects observed for all of the traits under both irrigation systems. The genetic by environment effect was only significant for days to heading, days to heading, duration of heading-to-maturity, plant height, and grain yield. Heritability values were increased under normal irrigation conditions. Days to maturity and days to heading had lowest (0.35 and 0.47) and highest (0.85 and 0.86) heritability under both late-season drought stress and normal irrigation conditions, respectively. The highest correlation coefficients were achieved for the traits of days to heading and plant height (0.65) and grain yield/m2 with seed number per spike (0.60) under late-season drought stress conditions and the traits of days to heading and plant height (0.76) and spike weight with seed number per spike (0.64) under normal irrigation conditions. The first two components in principle components analyses were explained 0.40 of phenotypic variations under late-season drought stress conditions and 0.39 of phenotypic variations under normal irrigation conditions. A significant negative correlation was observed between days to heading and duration of heading-to-maturity under both late-season drought stress and normal irrigation conditions (-0.42 and -0.54, respectively). Using path analysis, thousand kernel weight (0.60) and seed number (0.79) under late-season drought stress conditions and days to heading (-0.57), days to maturity (0.40), duration of heading-to-maturity (-0.53), thousand kernel weight (0.52), and seed number per spike (0.81) under normal irrigation conditions had the highest direct effects on grain yield. The indirect effect of seed number through spike weight (0.51) on grain yield was highest under late-season drought stress conditions, and the indirect effect of days to heading through the duration of heading-to-maturity (0.42), as well as seed number through spike weight (0.52) on grain yield, were highest under normal irrigation conditions. The dendrograms obtained for grouping landraces showed a very good match with principal component analyses, while more landraces were placed in higher-yielding groups under normal irrigation conditions. The results showed that additional waterings increase grain yield in Iran bread wheat landraces. The landraces such as 57785, 57733, and 54502 are suggested to be used in applied breeding programs due to high yield performance under both late-season drought stress and normal irrigation conditions.

The results of this study suggest that the available genetic diversity of Iran bread wheat landraces be used in applied breeding programs.