Developing Cucurbita maxima x C. moschata Interspecific Hybrids for the Processing Industry

Previous reports indicate that F₁ interspecific hybrids produced by crossing selected cultigens of C. maxima Duchesne (female) x cultigens of C. moschata Duchesne (male) are vigorous and productive.  We crossed several bush maxima processing lines (‘Golden Delicious’ type) to ‘Waltham Butternut’ (WBN), and two C. moschata processing cultigens, ‘Long Island Cheese’ (LIC) and ‘Dickenson Field’ (DF), in the summer of 2009.  Several hybrids from these crosses were grown at the Kingman Research Farm, Madbury, NH during the summer of 2010 and evaluated in both replicated and non-replicated experiments.  Field data on growth, flowering, fruit set, and several fruit traits confirmed previous reports that interspecific hybrids display vigorous growth, are highly gynoecious, and set abundant fruit.  Hybrids having ‘WBN’ as the male parent flowered exceedingly early, resulting in fruit set by the fifth node, small fruit size (1.4 kg) and low fruit dry matter (9.5% DW) of early crown sets.  Pruning of crown-set fruit resulted in development of two fruit per plant, set between nodes 15 and 20 that were larger (2.5 kg FW) and had consistently higher DW (14.2%) than crown-set fruits.  A few interspecific hybrids having ‘LIC’ as the male parent initiated female flowers and set fruit much later than crosses to ‘WBN’ and produced several fruit per plant, indicating choice of male parent can a significantly affect flowering pattern.  A greenhouse study was conducted in spring of 2011 to compare internode lengths, main stem diameters, flowering patterns, and leaf area at first appearance of female flowers in interspecies hybrids using NH65 as the female parent in combination with ‘WBN,’ ‘LIC,’ or ‘DF’ cultigens.  Interspecific hybrid NH65 x WBN initiated female flowers 23 days after transplanting (DAT) below node 4, and canopy leaf area averaged 2,192 cm².  Female flower initiation in NH65 x LIC and NH65 x DF occurred at 38 and 42 DAT, respectively, between nodes 9-12.  Leaf areas were 11,437 cm² in NH65 x LIC and 16,279 cm² in NH65 x DF.  Plants of NH65 x LIC and NH65 x DF appeared more compact than those of NH65 x WBN, both because progressive increases in internode length from less than 3.0 cm to more than 16.0 cm occurred more rapidly in the latter hybrid, and because the former hybrids had thicker stems, 12.42 mm and 12.17 mm in NH65 x LIC and NH65 x DF, respectively, as compared to NH65 x WBN (8.85mm).