2017 ASHS Annual Conference

Working with resources obtained from the USDA National Clonal Germplasm Repository in Hilo, we attempted intergeneric crosses of Carica papaya L. with 10 papaya wild relatives, mostly of the genus Vasconcellea. Embryo rescue enabled five of the hybrids to be established in the greenhouse, and three appear robust, including hybrids with V. goudotiana Triana & Planch. (Phytophthora tolerant), V. pubescens A.DC. (PRSV resistant), and V. x heilbornii V.M. Badillo (V.M. Badillo) (closely related to the edible ‘babaco’). Pollen staining of C. papaya x V. goudotiana and reciprocal F1’s indicated male sterility, and it is assumed from previously published research that the other hybrids will also be sterile, with the possible exception of C. papaya x V. x heilborni, which has not been described previously. Since large-scale backcrossing attempts by earlier researchers have failed to transfer wild parent genes to papaya, our approach to overcome sterility has been to create allotetraploids by chromosome doubling. Treatment of vegetative meristems with the mitotic inhibitor, oryzalin, has yielded only ploidy chimeras, so far, but flowers with altered morphology and enlarged pollen grains were observed arising from a transient tetraploid sector of an interspecific Vasconcellea F1 [V. quercifolia (Saint-Hilaire) Hieron. x V. parviflora (A.DC.) Solms-Laub.]. We are focusing on clonally propagating and maintaining the hybrids we have and on developing more effective chromosome doubling methods for allotetraploid creation, including in vitro treatments.