Relationships Between Yield and Related Traits Yield in Melon Under Drought Stress Using Principal Factor Analysis

Background and aim: the present study aimed to evaluate the iranian melon genotypes along with some other genotypes under drought stress. the experiment was conducted in a randomized complete block design with three replications at boroujerd research station. irrigation in both stress and non-stress environments up to 50 percent flowering was the same. environments with drought stress, irrigation, 50 percent of flowering to maturity and harvest the product were discontinued. the fy was decreased in drought stress conditions by 39% compared to the control. the results of pca demonstrated that the first two components explained more than 68 and 65% of the total variation among the genotypes under control and drought stress conditions, respectively. the development of genotypes with high yield under normal conditions and maintaining its yield under biotic and abiotic stresses is the main purpose of plant breeding programs in arid and semi-arid areas.methods: the experiment was conducted at the agricultural and natural resources research campus, borujerd, lorestan, iran (33° 55′ n, 48° 50′ e, 1620 m above sea level) during the growing season 2017-2018. three randomized complete block designs, each with three replications, were conducted. the seeds were cultivated in a greenhouse under 20-24 °c and 80% relative humidity conditions, where the average ratios of light/dark hours per day were 16 and 8 h, respectively. after one month, the seedlings were transferred at the filed condition. the irrigation regimes were different in the two experiments, which irrigation after 50 and 100 mm evaporation from a class a evaporation pan as the control (normal) and drought stress conditions, respectively. these irrigation regimes were applied after flowering. the mean values were compared via the lsd test (steel and torrie, 1980). principal component analysis (pca) was conducted to identify the interrelationships among the melon genotypes by the spss software (spss inc., chicago, il)results: however, all genotypes were harvested earlier in drought stress condition compared to the control condition. similar results were observed in other plants such as okra (gunawardhana & de silva, 2011), wheat (mehraban et al., 2019), and safflower (nazari et al., 2017; rahmani et al., 2019). ). this finding indicates the presence of considerable genotypic variation in the studied melon genotypes. (p < 0.01; table 1). under control condition all characters related to the fruits including weight, length, and width had higher values compared to the drought stress condition however, some genotypes had higher or equal values under the stress condition compared to the control, such as ginsen makuwa, samsoori –niagara, isabelle, honeydew, and galia-2” genotypes for fruit length and dastanbo and galia2 genotypes for fruit width. yildirim et al. (2009) and widaryanto et al. (2017) reported that the different levels of irrigation during the vegetative stage period of melon affect both size and weight of fruits. based on these fruit weight, length, and width, “galia2” was less affected by drought stress than the other genotypes. the largest and smallest fruit sizes were belonged to mamghani and mazandarani genotypes, respectively. according to the results the range of these characters under normal conditions were as following; fruit weight (0.02 to 5.32 kg), fruit length (4.16 to 33.11 cm), and fruit width (3.13 to 29.26 cm), which were larger than previous reports (rad et al., 2017; henane et al. 2003). these three characters were useful to separate melon genotypes (rad et al., 2017; henane et al. 2003). similar to the three characters, for two other characters of fruits including flesh thickness and skin and flesh weight the genotypes had fewer values under drought stress condition compared to the control. however, for cavity diameter character some genotypes had higher values under drought stress compared to the control, such as “dastanbo, rishbaba, galia1, and galia2”. ibrahim et al. (2012) reported that drought stress significantly decreased the four characters of melon fruits including weight, length, width, and flesh thickness. flesh diameter was the most effective variable to estimated fruit weight followed by fruit length, number of days to flowering, fruit width, and cavity diameter (rad et al., 2014). the present study revealed high levels of variation for these characters, as they were important for final yield, therefore the iranian melon genotypes could be a useful source for breeding varieties with high yield performance. similar to the fruit size characters, “galia2” genotype was less affected by drought stress than the other genotypes for flesh thickness and cavity diameter, however, the skin and flesh weight reduced by 40% under drought stress compared to the control. the largest and smallest leaf size was observed in “soskisabz and mazandarani” genotypes, respectively. in all the studied genotypes, both leaf characters including leaf length and leaf width were decreased under drought stress compared to the control. similar effects by nacl were observed, which salinity significantly reduced leaf area, leaf length and width (solmaz et al., 2011). the inhibition of leaf size development under drought condition was also reported on other plants such as date palm (al-khateeb et al.,2019), soybean (he et al., 2020) the result of correlation analysis revealed that under control condition, the fy had significant positive correlations with fruit length, cavity diameter, flesh thickness, skin and flesh weight, fruit weight, and fruit width (r = 0.48, 0.66, 0.77, 0.79, 0.80, and 0.81, respectively; p < 0.01). in agreement with our finding, rad et al. (2010) reported that fruit size and fruit weight had strong positive correlations with fy. however, based on the results under drought stress condition, the fruit size characters including fruit length and fruit width did not have significant correlations with fy. under both conditions, the highest correlation coefficient was observed between fruit weight with skin and flesh weight (r = 0.99, p < 0.01). rad et al. (2014) reported that fruit length and width had negative correlation with fruit weight, however the result of present study revealed that these two fruit characters had significant positive correlation with fruit weight under control condition (p < 0.01), but this relationship was not observed under drought stress condition. according to the results of pca, under control condition these two characters had positive significant correlations with pc1, but under drought stress they had positive significant correlations with pc2, it seems under drought stress the source of variation for these two characters have changed.conclusion: this variation can be used for selecting high potential fy and drought-tolerant genotypes. the fy was decreased in drought stress conditions by 39% compared to the control. the results showed that the highest and lowest fy were obtained in “mamghani” (9.6 kg per plant) and “mazandarani” (0.36 kg per plant) genotypes at control and drought stress conditions, respectively. the development of genotypes with high yield under normal conditions and maintaining its yield under biotic and abiotic stress conditions is the main purpose of breeding programs.