Variation caused mutation and identification of new drought tolerant genotypes by crossing landrace and mutant Tarom in Rice

One of the most important goals of researchers is to overcome environmental constraints and maintain food security by identifying and achieving cultivars that have optimal and sustainable yield under difficult conditions. Drought is one of the most important factors limiting crop production in arid and semiarid regions. The average rainfall of 240 millimeters has made Iran one of the world’s driest countries. Drought stress, especially in late season (late stages of growth) is one of the most important and the most common factors limiting plant growth in arid and semi-arid lands. After wheat, rice is the most important food crop in the world and the main source of food for over half of the world's population. Rice is the plant that has the most water needs in these crops. This plant needs about 8000 to 20000 m3 of physiological maturity and 1 kg of dry matter to produce 1 liter of water.

In order to investigate the response of rice families caused from landrace Tarom and mutant blends under flooding and deficit irrigation conditions, two separate experiments were evaluated in a lattice design under normal and Deficit irrigation conditions in three replications in Babol. Each of the 356 families was planted in two rows of 25 cm between and within the 25 cm row. Irrigation under stress conditions was flooded during the growth period of genotypes, but was stopped in field irrigation stress condition 40 days after transplanting (maximum tillage stage). Tehen, irrigation was done, after 15 days. The soil was sampled and its dry and wet weight was measured and its moisture content was measured. According to the soil moisture curve, it was estimated that in the first stage, the soil water potential was 12.5 bar and in the second stage the soil water potential was 19 bar. Days from planting to flowering and maturity, biomass, plant height, number of fertile tillers, total tiller number, flag leaf length and width, panicle exertion, stem diameter, main panicle length, total panicle weight, main panicle weight, total weight Stem, weight of filled grains, weight of unfilled grains, number of filled grains, number of unfilled grains, number of primary branches, number of secondary branches, leaf firing and leaf rolling were recorded.

The results showed that rice families had a good genetic diversity for the selection of families in flood watering and stress. The effect of drought stress on all traits was significant. The decrease in yield under low-irrigation stress conditions was related to the decrease in grain yield components, especially fertility. The results of forward regression showed that under flooding conditions, 100 grain weight, tiller number, fertility, and stem thickness and leaf firing and rolling rate were the most important traits affecting grain yield. Factor analysis summarized the yield variations under flooding and deficit irrigation conditions in 5 factors. In flooding conditions, the first, second, third, fourth and fifth factors were number, yield, and fertility, length, grain dimension and time, respectively, and in the first, second, third, fourth and fifth factors under Deficit irrigation conditions physiology, number, length, Grain dimension and time were named. Cluster analysis classified 352 families under flood and drought stress conditions into 4 and 3 groups, respectively.

This study showed that mutation can be used as a very suitable source for producing drought cultivars. Also, the study indicated that to achieve a higher grain yield, one had to rely on the number of filled grains. The results also showed that leaf firing and leaf rolling can be considered as a very important criterion in the selection of top families. This study identified families with low water deficit and maximum grain number, grain weight and panicle number with minimum leaf firing. This family can be used as a great resource for other breeding programs.