Investigation on Morphological and Physiological diversityof Iranian Watermelon (CitrulluslanatusThunb.) Accessions

Watermelon (CitrulluslanatusThunb)belongs to Cucurbita genus and Cucurbitaceaefamily. Some people know Watermelon native to India and othersthought of it as native to African countries. The greatest diversity can be seen in West Africa, China and parts of India. Near East and Mediterranean countries are also good places to find relatives and ancestors of watermelon. Like all Cucurbita genuscrops,, Watermelon has a variety of flowers including base, male and female separately located on one slip. In terms of production atglobal level, China is located in the first place followed by America, Iran and the Republic of Korea, respectively.
In order to evaluate genetic diversity among Iranian watermelon landraces by morphological traits, 16 landraces alongwith two commercial watermelon cultivars were planted in completely randomized block design with three replications inAgricultural Research Center of Urmia in 2013.
Morphological markers can be an effective means to determine genetic relationsamong cultivars and among selections used in watermelon breeding programs. 18 traits including cotyledon length, fruit length, fruit weight, fruit mass, fruit skin, rind thickness, flesh thickness, yield, seed length, seed width, weight of 100 seeds, vitamin C, pH, TSS, EC, chlorophyll content and plant length were assessed in the studied genotypes. During the fruit ripening,four fruits were selected randomly from each plot and according to the International Institute germplasms (IBPGR / IBGRI),solidscontent (TSS)was measured by using refractometer, pH by using pH meter, and fruit and seed weight by using digital scale. The amount of vitamin C (milligram per 100 grams) was measured using iodometry.
Results of variance analysis showed that there were significant differencesamong watermelon cultivars in terms of cotyledon length, fruit length, fruit weight, flesh weight, yield, seed length, seed width, seed weight, vitamin C, soluble solids and EC at the 1% level, while the level of significance with respect toskin weight, chlorophyll content and photosynthetic rate was5%.The results also showed that there were not significant differences among the cultivars in terms of pH, skin and flesh thickness, and plant length, suggesting that there is no diversity among the masses. Based on the means comparisontable,the highestfruit length (39 cm), fruit weight (8.03 kg), fleshweight(4.3 kg), skin weight (3.36 kg) and performance rate (24926 kg in hectare) were observed in Charleston Gray.Isfahan 808 mass showed the minimum fruit length (23.66 cm);Khorasan 806 mass had the least fruit weight (3.33 kg) andskin weight (1.8 kg); and East Azerbaijan 800 and Hamedan 817masses showed the lowest fruit flesh weight (1.5 kg) and performance (13444 kg per hectare), respectively.The highest positive phenotypic correlation (0.968) was observed between fruit mass and fruit weight,whilethe highest negative correlation (-0.815) existedbetween TSS and seed length. The highest positive (0.987) and negative (-0.990) genetic correlation was foundbetween fruit weight and fruit length, and between flesh thickness and photosynthesis, respectively. The greatestheritability was related to 100-seed weight, whereas minimum heritability was due to ph. The studied accessions were classified into three different groupsby using Cluster analysis based on Ward method. Based on the intervaltable,the highest space rate was observed between groups one and three (8.985).The resultsalso showed that the maximum expected heterosis obtained in crosses between genotypes one and three.
Based on the results of this research, improved varieties (Charleston Gray and Crimson Sweet) had the highest level of performance, TSS, fruit weight and flesh weight compared to the native masses.