Elucidating the effect of plant bioregulators on embryo maturation for shortening the breeding cycle in papaya

Abstract

Papaya (Carica papaya L.) is a tropical fruit crop with commercial importance due to its nutritional and
medicinal value. The long generation time required by papaya plants during the breeding process significantly slows crop improvement, and developing a variety takes 15-16 years (7-8 generations). As a solution in this direction, using plant bioregulators (PGR) to improve seed maturity in conjunction with the embryo culture technique may aid in reducing the time between fruit set and seedling establishment. We investigated the effect of ethrel, abscisic acid (ABA), and methyl jasmonate (MeJa) in different concentrations during early fruitdevelopment on hastening embryo maturity followed by embryo culture for shortening the breeding cycle of dioecious papaya var. Pusa Nanha. Fruits after 60 and 75-days old fruit (DOF) were treated with ethrel (100, 120 ppm), abscisic acid (10-6, 10-4 M), and MeJA (10-5, 10-3 M); the effect of treatments was observed after 15 days of PGR application. Among the treatments, ethrel 120 and 100 ppm at 75 DOF were found to be effective for hastening seed maturity, as measured by seed colour (light brown), embryo formation (85%), and embryo size (2.93 mm), maximum in vitro germination (85%), rapid shoot emergence (5.67 days), earliest radicle emergence
(2.67 days), resulting in maximum plantlet regeneration (86.67%). The embryos isolated from the fruits treated with MeJA (10-5 M) showed the maximum number of roots (5.13), with 75.50 % plantlet regeneration. As a result, using the above method, the breeding cycle of papaya could be reduced to as low as 3 months, compared to the standard period of 6-9 months (from pollination to seedling establishment).