2018 ASHS Annual Conference

In addition to Fusarium wilt resistance, the interspecific hybrid squash rootstock (Cucurbita maxima × C. moschata) is also known for its tolerance to low temperatures. This field experiment was conducted at the Suwannee Valley Agricultural Extension Center in Live Oak, FL to explore the impacts of grafting with interspecific Cucurbita rootstocks on seedless watermelon yield and fruit quality at two planting dates during the spring 2017 season. Seedless watermelon ‘Melody’ was grafted onto two interspecific Cucurbita rootstocks ‘Carnivor’ and ‘Super Shintosa’, respectively, with non-grafted ‘Melody’ as the control. Two types of grafted plants were also included, i.e., plants with original rootstock roots and plants with rootstock root excision and regeneration, as both are currently provided by commercial nurseries. Plants were transplanted into the fumigated field on 20 Mar. (early) and 6 Apr. (late), respectively. Destructive plant sampling before the first harvest showed that all the grafted plants had more female flowers compared with the non-grafted plants, while similar numbers of female flowers were found between the two types of grafted plants. However, the full-season yield components including marketable and total fruit numbers and yields as well as the average fruit weight did not differ significantly between grafted and non-grafted plants. In contrast, early planting led to significantly higher marketable and total fruit yields primarily due to increased averaged fruit weight, in comparison with late planting. No significant interactions between planting date and grafting were observed. With respect to each harvest, early planting significantly improved marketable fruit yield compared with late planting at the first harvest. Although statistical significance was not observed (P = 0.068), grafted plants especially those with ‘Super Shintosa’ rootstock tended to have higher marketable fruit yield than non-grafted plants at the first harvest. At the second harvest, non-grafted plants showed the highest marketable fruit yield, while no significant effect of planting date was observed. Average fruit weight was significantly higher at early planting than late planting for both harvests, while it did not differ significantly between grafted and non-grafted plants. Planting date and grafting did not show any significant impacts on fruit yield from the third harvest. Fruit quality assessment showed similar levels of soluble solids content, pH, and titratable acidity between grafted and non-grafted plants regardless of root excision and regeneration. However, early planting resulted in a significant increase in fruit pH with lower titratable acidity compared to late planting.