Response of Iranian Melon Populations to Deficit Irrigation Condition

In Iran, there are various melon populations due to properties of cross pollination, which are mostly cultivated in the desert, so it is important to identify populations and study their response to low irrigation conditions and their selection. Sistan is one of the most important melon production areas in the country. Every year, in the optimal water conditions of the region, cultivation area reaches nearly to 6,000 hectares, but the area under cultivation is affected by fluctuations in the Hirmand River. Its famous melons in the region include Sefidak, Firoozi and Helmendi, which are very popular among farmers in terms of taste. The amount of rainfall in this region is very small and the agriculture of the region is affected by the fluctuations of Hirmand River and these fluctuations cause damage to agricultural producers, but recognizing the best and most suitable genotypes can help a lot to melon production. Variation and selection are the important elements of the breeding program and the selection by the breeder requires a good variation in the population. In Iran, the largest producer of melons is province of Khorasan Razavi, with 48.7 percent of the production in country, and province of Sistan and Baluchistan with the 5.62 percent is in the fifth rank. Therefore, in this regard, it is necessary to consider the desirable populations and cultivars in terms of production and yield. The quality of soil and the limitation of water resources, especially in recent decades, have intensified the world's agriculture. In the most parts of Iran, especially in Sistan, due to recent drought, identification of resources and cultivars with the potential of optimal production is important. Therefore, the present study was conducted to evaluate the populations of melons and their response to different irrigation regimes.

In this study, the populations of the gene bank (34 population), mostly from the central and eastern regions of the Iran, along with two local sefidak and suski, which were relatively tolerant and sensitive, respectively to drought stress were cultivated in a simple square lattice design with 2 replications for comparison under normal and drought stress conditions. Under water deficit conditions, irrigation was carried out at water depletion of 75% and for normal irrigation with 50% water depletion from the field capacity. Soil moisture monitoring was carried out using a TDR device. Some morphological and physiological traits such as yield, number of fruits per plant, average fruit weight, fruit length and width, plant length, hole diameter, chlorophyll content, canopy temperature, relative water content were measured

Based on the results of combined analysis of variance, there was a significant difference between the populations for all traits except for the number of fruits per plant. The effect of the environment was significant only for the traits of soluble solids, single plant yield, canopy temperature and days to maturity also the interaction of the population with the environment was significant only for plant length, canopy temperature and root length, which indicated a different population reaction in relation to these traits under two conditions of normal and moisture stress. The results of the mean comparison of the traits showed that in normal conditions, the highest number of fruits belonged to numbers 1, 2, 6, 7 and 8, which had no significant difference with the check number 36. The results of analysis of factor in moisture stress condition showed that the first four factors justify nearly 70% of the variation among the traits. Therefore, the positive values of the first factor can be effective for selection of genotypes with a high yield and high fruit weight. However, the second factor with negative values of canopy temperature and positive values of leaf relative water content is effective in determining the high tolerance genotypes to moisture stress conditions.

Under normal and stress conditions, population number 23 had acceptable yields. The traits of fruit weight and size, flesh diameter and fruit length and width are among the traits that should be considered by the breeders according to their relationship with the yield. Genotypes with high root length had high tolerance to water deficit condition. In general, under stress conditions, more soluble solids were observed in the populations.