Use of phenotypic selection and hypocotyl properties as predictive selection criteria in pumpkin (Cucurbita moschata Duch.) rootstock lines used for grafted cucumber (Cucumis sativus L.) seedling cultivation

Abstract

In recent years, grafted cucumber seedling use has been rapidly increasing worldwide, especially for providing tolerance to stress conditions and positively affecting yield potential. However, graft incompatibility is still an important issue in grafted seedling production. Hypocotyl properties of rootstocks and scions are of great importance for ensuring graft compatibility. This study aimed to select superior rootstock genotypes based on certain selection criteria, such as hypocotyl morphology, grafted seedling visual evaluation, and graft compatibility properties, of 42 pumpkin (Cucurbita moschata) genotypes that are included in the cucumber rootstock breeding program and are resistant to Fusarium oxysporum f. sp. cucumerinum. Three C. moschata and three C. maxima x C. moschata rootstocks were used as control cultivars. All genotypes were grafted with the Gordion F-1 cucumber cultivar using the splice grafting method. In the pumpkin rootstock genotypes, the cross-sectional area of the hypocotyls varied between 3.47 mm(2) and 10.42 in mm(2), pith cavity area varied between 0.59 mm(2) and 4.14 mm(2), and pith cavity rate varied between 10.3% and 65.2%. Vascular bundle numbers of the genotypes were between 6 and 12. In the rootstocks, success rates of the grafts ranged from 56% to 100%. Among the rootstock/scion combinations, 100% success rate was obtained in 19 inbred pumpkin rootstocks. Scion rooting never occurred in 11 of the pumpkin rootstocks. The correlation analysis of the investigated properties showed that there was a statistically nonsignificant relationship between the crosssectional area of the hypocotyl, vascular bundle number, and graft success rate (P > 0.05). The parameter with the greatest negative effect on graft success rate was scion rooting (r: -0.49, P < 0.05). The results showed that scion rooting depended on the pith cavity rate and decreased as the pith cavity rate decreased (r: 0.56, P < 0.05). he weighted-ranking method was employed to select the most promising pumpkin rootstock genotypes for grafted seedling production. According to the evaluations, 12 pumpkin rootstocks were selected as the most superior rootstock candidates. We aim to develop new hybrid rootstocks for cucumber in the near future by carrying out special combinations of tools from test-based hybridization studies among the selected pumpkin lines.