2019 ASHS Annual Conference

Production of ’Rainbow’ papaya in Hawaii relies on seed propagation, which necessitates culling female plants from commercially desirable hermaphrodites in seedling progenies segregating for sex. Although vegetative propagation techniques such as tissue culture have been developed for cloning hermaphrodites, morphological and physiological disorders caused by culture environment and persistent effects of phytohormones have hindered widespread adoption. Current protocols for in vitro culture of papaya use 6-Benzyladenine (BA), one of the most common cytokinins employed for shoot induction. However, BA has been linked to hyperhydricity, stunted growth, reduced rooting and poor root quality. This study aimed to explore the potential of an aromatic cytokinin, meta-Topolin (mT), to improve shoot and root proliferation and overall morphology during in vitro culture. ’Rainbow’ papaya seeds were germinated in vitro. Nodal segments and shoot tips from the germinated seedlings were excised and cultured in modified Murashige and Skoog (MS) medium containing mT or BA at 2.2 µM. After 4 weeks in culture, 85% of the nodal and 100% of the shoot tip explants in 2.2 µM mT produced shoots ≥ 1 cm compared to 5.8% of nodal and 100 % of the shoot tip explants grown in 2.2 µM BA that produced shoots ≥1 cm. A 100% reduction in incidence of hyperhydricity was observed in explants cultured in 2.2 µM mT. Additionally, subculture of mT induced shoots to MS medium devoid of plant growth regulators led to 50% more new shoots produced as compared to BA-induced shoots Moreover, rooting was observed in 30% of the shoots previously cultured in 2.2 µM mT. The substitution of mT for BA is a useful modification for in vitro culture of cytokinin-sensitive plants such as papaya.