Influence of duration of storage at room temperature, pre-sowing seed treatment and fruit colour harvest index on germination and seedling growth of Jatropha curcas L.

Abstract

Jatropha curcas L. is being promoted by governments for greening marginal areas for rural development and biodiesel production in sub-Saharan Africa, however large gaps in knowledge on its agronomy and yield potential exist. The effect of duration of storage at room temperature, pre-sowing seed treatment of Jatropha seed and fruit colour harvest index on germination and seedling growth parameters was investigated. There was a significant negative correlation between the duration of storage of Jatropha seed and seed oil content (P < 0.001, r = −0.99), viability (P < 0.01, r = −0.93), percent germination (P < 0.05, r = −0.90) and germination index (P < 0.05, r = −0.89). The relationship between duration of seed storage and seed oil content and seed germination parameters was best described by quadratic and exponential functions which showed rapid declines in seed oil content and germination parameters in the first 3 years of storage and a slower decline between 3 and 8 years of storage. There was a significant negative correlation between duration of storage and seedling height (P < 0.01, r = −0.97), stem diameter (P < 0.01, r = −0.93) and dry weight (P < 0.05, r = 0.91) that was best described by quadratic functions. Seed oil content was significantly and positively correlated to seed viability (P < 0.01, r = 0.96), germination per cent (P < 0.01, r = 0.94) and germination index (P < 0.01, r = 0.93). The relationship between seed oil content and seed germination parameters was best described by exponential functions which showed an exponential increase in seed germination parameters as oil content increased above 30% and smaller increases below 30% oil content. Progressive peroxidation of lipids as seed aged explains the loss of oil from the seed. Peroxidation of lipids produced highly reactive radicals that damaged membranes and proteins reducing seed germination and seedling growth parameters as seed aged. Pre-sowing seed treatments (seed soaking and scarification) produced marginal gains in germination and seedling growth parameters in Jatropha seed stored for 3 months to 8 years. Seeds harvested at the yellow fruit maturity index, 60 days after anthesis (DAA), showed the highest seed germination percent while seed harvested at the black fruit maturity index, 75 DAA, had the highest oil content. Harvesting of Jatropha seed for oil expression is therefore recommended at the black maturity index while harvesting for seed is recommended at the yellow maturity stage. The results of this study indicate that Jatropha seed should be stored for as short a period of time as possible to maximize seed germination, seedling growth and oil yield.