Evaluation of Morphological Traits Associated with Productivity in F1 Interspecific (Cucurbita maxima Duch. x C. moschata Duch.) Hybrid Processing Squash

Abstract

Interspecific hybrids can be produced from certain cross combinations of Cucurbita maxima x C. moschata. These hybrids have been used extensively as rootstocks for melon and watermelon grafting, but only occasionally for fresh market use. The objective of this study was to assess the potential of interspecific hybrids for use in pie processing in terms of morphological traits related to productivity. We used a bush-processing inbred line of C. maxima, NH65, as the female parent and two vining-processing cultivars of C. moschata, Long Island Cheese (LIC) and Dickinson Field (DF) as pollen parents to produce two interspecific hybrids with large orange fruit, potentially suitable for processing. A greenhouse study was conducted to compare internode lengths, main stem diameters, flowering patterns, and leaf area at first appearance of female flowers in NH65, LIC, DF, and two interspecific hybrids, NH65xLIC and NH65xDF. Plants were grown in 8.7 L nursery pots, watered and fertigated with drip tubing, and trellised to a single main stem. In LIC and DF, internode lengths increased rapidly beyond the fourth node before reaching a maximum by node 12. Internodes in NH65 did not exceed 3 cm until node 15, and average lengths never exceeded 4 cm. In interspecific hybrids, internode lengths mimicked bush plants for 6 or 7 internodes, remaining below 3 cm, but then increased rapidly to lengths approaching that of the vining cultivars after internode 10. Staminate flowers were more abundant than pistillate flowers in NH65, LIC and DF; whereas the interspecies hybrids produced primarily pistillate flowers. In NH65xLIC, the first pistillate flowers appeared on nodes 9–11, on average 38.3 days after transplanting (DAT), and in NH65xDF, on nodes 9–17, 42.3 DAT. First pistillate flowers in NH65 occurred on nodes 9–11, 34.3 DAT, compared with nodes 9–13, 39.3 DAT and nodes 17–21, 50.0 DAT, respectively, for LIC and DF. A field study was conducted for comparing flowering patterns and growth habits in NH65xLIC, NH65xDF, DF, LIC, NH65, and ‘Golden Delicious’ (GD), a popular C. maxima processing winter squash. Stem length was short and petioles highly elongated in the two interspecific hybrids until about 34 DAT, such that plants exhibited a uniform, compact phenotype similar to NH65. Subsequently, stems elongated rapidly, with lengths approaching and occasional exceeding those in vine cultivars. In the two vining C. moschata cultivars, LIC and DF, 4–6 laterals developed near the base of plants, usually consisting of 12–30 nodes. NH65xLIC produced mostly short laterals (4–15 nodes) interspersed along much of the main stem, whereas NH65xDF produced numerous lateral branches, mostly ranging from 11 to 30 nodes long, between the base and about the halfway point along the main stem. Mature leaves were about twice as large in the two interspecific hybrids as in DF and GD; this together with differences in early growth habit and branching patterns contributed to a much faster leaf canopy cover in the interspecific hybrids in comparison with the vining cultigens.