Intergeneric hybridization of Carica papaya with wild Vasconcellea relatives

Crop wild relatives are a valuable source of genetic variation for cultivated crops. In the case of papaya, the only wild relatives are in other genera. Species in the related genus Vasconcellea can hybridize with papaya, but the F-1 progeny display a high degree of sterility, which limits breeding efforts. In order to overcome reproductive barriers, induced tetraploidy is proposed as a method to recover fertility in hybrid plants. Intergeneric hybrids between papaya and five Vasconcellea species were produced by embryo rescue, as well as several Vasconcellea interspecific hybrids. Different hybrids displayed different degrees of vigor, but the most successful crosses were generally healthy. The mitotic inhibitor oryzalin was employed to induce polyploidy in vegetative meristems. An oryzalin-treated Vasconcellea quercifolia x Vasconcellea parviflora F-1 interspecific plant transiently produced pollen of a size consistent with tetraploidy, but it did not display increased pollen stainability.