HORTSCIENCE 52(9):1156–1163. 2017. doi: 10.21273/HORTSCI12018-17 normal looking fruit with the aid of a pollen donor strain. Interspecific hybrid plants have been described as vigorous and highly gynoe- Evaluation of Morphological Traits cious, with leaf shape intermediate to parental lines, vines resembling the C. moschata parent, Associated with Productivity in F1 and fruit with the general appearance of the C. maxima parent (Castetter, 1930; Erwin and Interspecific (Cucurbita maxima Haber, 1929; Robinson et al., 1978; Whitaker and Bohn, 1950). Interspecific hybrids are C. moschata largely seedless and therefore may exhibit high Duch. x Duch.) Hybrid pericarp yields because assimilates do not have to be allocated to seed development. Because the Processing Squash root systems of interspecific hybrids are highly 1 2 resistant to abiotic and biotic stress, they have Jake Uretsky and J. Brent Loy been used widely as rootstocks for melon and Department of Biological Sciences, University of New Hampshire, Durham, watermelon production (Davis et al., 2008). NH 03824 They express insect tolerance of the C. moschata parents, showing resistance to squash vine Additional index words. winter squash, pumpkin, bush squash, growth habit, internode length, borers [Melittia cucurbitae (Harris)], and are flowering patterns, leaf area less attractive to squash bugs [Anasa tristis Abstract. Interspecific hybrids can be produced from certain cross combinations of Cucurbita (DeGeer)] than cultigens of C. maxima.In maxima x C. moschata. These hybrids have been used extensively as rootstocks for melon and addition, we have observed that the interspe- watermelon grafting, but only occasionally for fresh market use. The objective of this study cific hybrids exhibit intermediate resistance to was to assess the potential of interspecific hybrids for use in pie processing in terms of powdery mildew disease [Podosphaera xan- morphological traits related to productivity. We used a bush-processing inbred line of thii (Castagna) U. Braun and N. Shirshkoff]. C. maxima, NH65, as the female parent and two vining-processing cultivars of C. moschata, At the University of New Hampshire, Long Island Cheese (LIC) and Dickinson Field (DF) as pollen parents to produce two bush breeding lines of C. maxima squash interspecific hybrids with large orange fruit, potentially suitable for processing. A greenhouse with large, orange fruit, similar to GD, have study was conducted to compare internode lengths, main stem diameters, flowering patterns, been developed for use in hybrids for pie or and leaf area at first appearance of female flowers in NH65, LIC, DF, and two interspecific baby food processing. We considered these hybrids, NH65xLIC and NH65xDF. Plants were grown in 8.7 L nursery pots, watered and breeding lines to be good candidate parents fertigated with drip tubing, and trellised to a single main stem. In LIC and DF, internode for producing C. maxima x C. moschata lengths increased rapidly beyond the fourth node before reaching a maximum by node 12. interspecific hybrids exhibiting a favorable Internodes in NH65 did not exceed 3 cm until node 15, and average lengths never exceeded semibush growth habit for rapid leaf canopy 4 cm. In interspecific hybrids, internode lengths mimicked bush plants for 6 or 7 internodes, cover and high yield potential (Loy, 2004; remaining below 3 cm, but then increased rapidly to lengths approaching that of the vining Loy and Broderick, 1990). In terms of fruit cultivars after internode 10. Staminate flowers were more abundant than pistillate flowers in set, seed yield, seed fill and germinability, NH65, LIC and DF; whereas the interspecies hybrids produced primarily pistillate flowers. initial testing indicated that two of four In NH65xLIC, the first pistillate flowers appeared on nodes 9–11, on average 38.3 days after bush C. maxima lines, NH245 and NH65, transplanting (DAT), and in NH65xDF, on nodes 9–17, 42.3 DAT. First pistillate flowers in exhibited good compatibility when crossed NH65 occurred on nodes 9–11, 34.3 DAT, compared with nodes 9–13, 39.3 DAT and nodes to C. moschata cultigens (Uretsky, 2012). For 17–21, 50.0 DAT, respectively, for LIC and DF. A field study was conducted for comparing C. moschata parents we relied on two estab- flowering patterns and growth habits in NH65xLIC, NH65xDF, DF, LIC, NH65, and ‘Golden lished processing cultivars LIC and DF. We Delicious’ (GD), a popular C. maxima processing winter squash. Stem length was short and also evaluated the open-pollinated cultivar petioles highly elongated in the two interspecific hybrids until about 34 DAT, such that plants Waltham Butternut (WBN) as a male parent, exhibited a uniform, compact phenotype similar to NH65. Subsequently, stems elongated but in contrast to LIC and DF, interspecific rapidly, with lengths approaching and occasional exceeding those in vine cultivars. In the two hybrids from this parent exhibited precocious vining C. moschata cultivars, LIC and DF, 4–6 laterals developed near the base of plants, appearance of pistillate flowers (Loy and usually consisting of 12–30 nodes. NH65xLIC produced mostly short laterals (4–15 nodes) Uretsky, 2010), resulting in production of interspersed along much of the main stem, whereas NH65xDF produced numerous lateral numerous fruit near the base of plants. branches, mostly ranging from 11 to 30 nodes long, between the base and about the halfway To more thoroughly evaluate the yield point along the main stem. Mature leaves were about twice as large in the two interspecific potential of interspecific hybrids, we conduct- hybrids as in DF and GD; this together with differences in early growth habit and branching ed greenhouse and field research to compare patterns contributed to a much faster leaf canopy cover in the interspecific hybrids in flowering patterns and traits affecting leaf comparison with the vining cultigens. canopy development in two interspecific hy- brids, NH65xLIC and NH65xDF, and three open-pollinated processing cultivars DF and In recent decades, F1 hybrids in the genus summer squash, ornamental pumpkin and acorn LIC (C. moschata), and GD (C. maxima). Cucurbita have increasingly gained prominence cultivars of C. pepo L. and kabocha cultivars of over open-pollinated varieties, particularly in C. maxima (Loy, 2012; Robinson, 2000). By Materials and Methods contrast, open-pollinated cultivars such as GD (C. maxima)andstrainsofDF(C. moschata) Plant materials. A bush C. maxima breed- Received for publication 11 Apr. 2017. Accepted still dominate the production of squash or ing line, NH65, with fruit type and quality for publication 15 May 2017. pumpkin used for pie processing (Loy, 2004). approaching that of the open-pollinated Scientific contribution number 2567. This work Interspecific C. maxima x C. moschata F1 cultivar GD was used as the female parent was supported by the USDA National Institute of hybrids may offer unique combinations of traits in interspecific crosses. Open-pollinated, Food and Agriculture (Hatch Projects NH00548 and NH00609). attractive to growers and processors. Castetter vine cultivars of C. moschata,LICandDF, 1Current address: Department of Viticulture and (1930) and Erwin and Haber (1929) reported that were used as male parents. Interspecific Enology, University of California, Davis, CA certain parental combinations of C. maxima x C. maxima x C. moschata crosses were 95616. C. moschata set fruit and produced viable F1 performed in the field during the summer 2 Corresponding author. E-mail: [email protected]. seed, and moreover, F1 plants often produced of 2010 by controlled hand pollination 1156 HORTSCIENCE VOL. 52(9) SEPTEMBER 2017 | BREEDING,CULTIVARS,ROOTSTOCKS, AND GERMPLASM RESOURCES using standard squash pollination protocol before bed formation (61 cm width · 15 cm 42 DAT (Fig. 1). Both interspecific hybrids, (Whitaker, 1960). Staminate and pistillate high) and application of BioTelo biodegrad- NH65xLIC and NH65xDF, exhibited main flowers were tied off 1 d preanthesis to prevent able mulch (15.2 mm · 135 cm width; stem lengths similar to that of the bush parent pollen contamination, and pollinations were per- Dubois Agrinovation, Saint-Remi, Quebec, until 25 DAT, but by 42 DAT stem length formed between 0600 and 0800 HR on the Canada) and drip tape (203 mm T-tape, 30 cm of the interspecific hybrids was intermediate morning of anthesis. Additional open-pollinated emitter spacing; T-Systems International, San to that of the bush and vine cultigens (Fig. 1). fruit were removed from plants. Fruits resulting Diego, CA). Plants were fertigated weekly for Leaf numbers at 14, 27, and 42 DAT from crosses were harvested 55–60 d after 4 weeks beginning the first week of July with among the two interspecific hybrids and their pollination (DAP). Harvested fruits were stored soluble fertilizer at a rate of 2.8 kg N and parental strains were not significantly differ- in a greenhouse at 18–26 °C until 65 DAP to 2.3 kg K/ha. Disease and insect control ent with the exception of NH65xLIC at 14 d, ensure complete seed fill. Seeds were extracted, followed the general recommendations of a reflection of slow germination and smaller cleaned, and dried on screens in a forced air dryer the 2010–11 New England Vegetable Man- seedlings at transplant (Table 1). However, at 30 °C. agement Guide (Howell et al., 2010–2011). mean rates of leaf initiation for all cultigens Greenhouse, 2011. A comparative study Weed control was achieved with mechanical between 27 and 42 DAT (0.67 leaves/d) was of plant growth traits was performed at the cultivation between raised beds. 75% higher than between 14 and 27 DAT Macfarlane Greenhouses, Durham, NH in the Plants were seeded in 50-cell plug trays (0.38 leaves/d). The increased rate of leaf spring of 2011 with interspecific hybrids containing Pro-Mix BXÒ soilless potting initiation among cultigens coincided with NH65xLIC and NH65xDF and parental cul- medium on 27 May and transplanted 10 June plants entering the exponential phase of tigens.