| The watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai var. lanatus] is a major vegetable crop in the United States. The genetics of this crop have been widely studied and several genes reported. Nevertheless, further investigation was needed for genes determining the appearance of the fruit (rind and flesh colors), the weight of single fruit, and resistance to gummy stem blight, a severe disease of watermelon caused by Didymella bryoniae (Auersw.) Rehm. In this work the inheritance of novel rind phenotypes was measured and the genetics of flesh color verified. Three new genes were identified: Dr for the deep-red flesh color of 'Dixielee' and 'Red-N-Sweet', Yb for the yellow belly of 'Black Diamond Yellow Belly', and is for the intermittent stripes of 'Navajo Sweet'. The spotted phenotype from 'Moon and Stars' was transferred to light green and gray cultivar for the development of novel varieties with distinctive rind patterns. Yield of 80 diverse cultivars was evaluated in replicated experiments. Some of the new, elite hybrid cultivars were in the top yielding group, however old, inbred cultivars appeared in the top group as well. Consistent and significant differences among the 80 cultivars tested suggests genetic variation for yield. Since most watermelon consumers are interested in smaller fruit, six adapted cultivars bearing the largest and smallest fruit were crossed in a half-diallel, producing F1, F 2, and backcross generations. Genotypic variances, heritability, and gain from selection were estimated. High environmental variance and low narrow- and broad-sense heritability were recorded. Finally, the inheritance of resistance to gummy stem blight, previously attributed to the db gene, was verified. A genetic system more complex than a single gene seems to regulate the transmission of resistance from resistant to susceptible germplasm. Due to the complexity of phenotypic testing for this disease in watermelon, a new project for the development of molecular markers linked to resistance was initiated. Nevertheless, the use of F3 phenotypic data and F2 genotypic markers and the apparent complexity of the trait did not allow the identification of a tightly linked marker. |
