Utilization of exotic germplasm in a Cucurbita breeding program

Crops in the Cucurbitaceae plant family are an important part of agricultural systems worldwide. This family includes economically important crops such as watermelon, cucumber, pumpkins, melons, and squash. These crops are plagued by a wide variety of both insect and plant pathogen pests. Breeding for genetic resistance to these pests represents a key component of many cucurbit breeding programs in both public and private sectors. Sources for disease and pest resistance often include wild species and landraces found across the world. Often, such species show poor adaptability to temperate climates. This limits plant breeders’ abilities to utilize exotic germplasm and introgress valuable traits. Wild species may also show limited compatibility with domesticated species, thus hindering the generation of fertile interspecific breeding lines. Wild species and landraces from tropical regions often fail to flower or flower very late under the long days experienced during the growing season in northern regions. Despite recent advances in molecular genetics such as the sequencing of the Cucurbita spp. genome, little is known about the genetic basis for important traits such as regulation of flowering time. To address this, we first aimed to learn more about the genetic basis for early flowering by comparing flowering time in two different lines of acorn squash with very different flowering times. Flowering time is a complex phenomenon and involves a variety of genetic and environmental factors. We identified a new major locus for acorn squash that promotes early flowering. Next, we evaluated various protocols to determine an optimal method to induce flowering in very late flowering Cucurbita spp. cultigens by grafting them to early flowering rootstocks. We found that early flowering and fruit set of late flowering cultigens could be achieved by grafting them if lateral shoot development occurs on the rootstock and leaf removal is conducted on the scion. Finally, we explored a new source found of powdery mildew resistance discovered in a landrace of tropical pumpkin. We showed that its resistance is conferred by a single gene and this gene appears to be at a different locus than either of the named dominant resistant genes, Pm and Pm-0. These findings should be useful for plant breeders and germplasm curators along with scientists interested in discovering more about the genetic basis and mechanisms behind flowering and disease resistance