Shortening the breeding cycle of papaya (Carica papaya L.) by culturing embryos treated with ethrel

Abstract

To shorten the breeding cycle of papaya by embryo culture, we attempted to improve the embryo quality (dimensions, germination ability, and/or seedling vigor) by treating fruits (attached to plants) with ethrel solution. Forty-five-, 60-, and 75-day-old fruits (DOF) were treated with 100 μl l−1 ethrel for 10 or 20 days. The fruits treated with ethrel tended to be lighter in weight compared to those treated with water (the control). Seed coat coloration in 85 DOF (75 DOF plus 10 days of ethrel treatment [DET]) and 95 DOF (75 DOF plus 20 DET) was clearly promoted by the ethrel treatment. Embryo development was enhanced by ethrel treatments in 55 DOF (10 DET), i.e., the ethrel-treated embryos progressed to the mature cotyledon stage earlier than those in the control. The embryo size (length and width) was significantly larger in 55 DOF treated with ethrel than those of the control. In 55 and 65 DOF (20 DET), the embryo germination rates were higher in the ethrel-treated group than those in the control. The seedlings in the ethrel group grew more vigorously than those in the control. Therefore, we found that the embryo quality was improved by the ethrel treatment in 65–95 DOF. The breeding cycle of papaya could be shortened by embryo culture using embryos qualitatively improved by ethrel treatment, i.e., the period (generally 6–9 months) from pollination to seedling establishment could be shortened by approximately 3 months using these breeding techniques.