Seed quality of physic nut (Jatropha curcas L.) at different stages of fruit maturity

The potential of physic nut (Jatropha curcas L.) as an alternative energy source even under marginal land and with minimal inputs would require an adequate understanding of the production and post-production practices for this crop. Post-production practices such as proper seed handling and storage are important to maintain seed quality. At present few studies were done on proper seed handling of J. curcas, particularly on the aspect of harvesting at the right stage of maturity to get high quality seeds. The study was conducted to evaluate the seed quality of J. curcas harvested at different stages of fruit maturity and to determine the right stage of harvesting to get high quality seeds. The effectiveness of air-drying in lowering seed moisture content and maintaining seed quality was also evaluated. Fruits of varying maturity determined based on color were sorted before seed extraction. Percent germination, moisture content, and seed vigor indices such as shoot and root lengths and seedling dry weight were determined after seed extraction and weekly thereafter for 12 weeks. Seeds from all stages of fruit maturity were able to germinate but only the seeds of yellow green fruits maintained a germination above 95% after the 12-week period. Seeds of black colored fruits were considered the most vigorous among the four stages of maturity having high mean shoot length and seedling dry weight. But with a low mean percent germination, this stage cannot be considered to be the right stage for harvesting fruits. The percent germination and vigor parameter values suggest that the right maturity for harvesting seeds is at yellow green stage. One week of air-drying reduced seed moisture content from 47% to 10%, a level that was detrimental to seed quality because this favored fungal attack. Therefore, air-drying alone is not sufficient to bring down seed moisture content and maintain high seed germination and vigor. Depending on the use of the seeds, air-drying should be followed by other appropriate methods of lowering moisture content, such as sun-drying if to be used for planting or short term storage or the use of desiccant like silica gel if seeds are intended for long term germplasm conservation.