Effects of the cytokinins 6-benzyladenine and forchlorfenuron on fruit-, seed- and yield parameters according to developmental stages of flowers of the biofuel plant Jatropha curcas L. (Euphorbiaceae)

Jatropha curcas L. as a bio energy plant belonging to the Euphorbiaceae family is gaining progressive importance over the last years. In 2012 and 2014 field experiments were carried out to assess the effects of cytokinins 6-Benzyladenine (BA) and Forchlorfenuron (CPPU) acting as plant growth regulators (PGRs). Number of flowers per inflorescence, female-to-male ratio of flowers, fruits per infructescence, fruiting rate, number of seeds per fruit, seed size and weight as well as seed oil content were determined. It was suggested that concerning effectiveness of exogenous application of PGRs the developmental stage of flower is very important. Due to that, special interest was laid on the age of inflorescences at the time of application. Our experiments revealed a strong dependence of cytokinin effectiveness on the developmental stage of flowering. So treatment of plants with 6-Benzyladenine at the beginning of flower formation (stage 1) significantly increased the number of male and female flowers per inflorescence, whereas treatment at an advanced flowering stage (stage 2) or at the stage of fully developed flowers (stage 3) had only slight or no effects. In contrast, fruit retention was progressively increased by treatment in stage 2 and 3. Application of Forchlorfenuron significantly increased female-to-male ratio in stage 1 flowers but showed no effects on stage 2 and 3. 6-Benzyladenine as well as Forchlorfenuron showed equal effects on number of fruit inflorescences treated in stage 1. Our results show a significant decrease in seed weight due to BA- and CPPU-application while kernel weight remained stable. Concerning fruits, clusters and oil yield per tree, BA-application showed significant increasing effects. This study indicates that 6-Benzyladenine and Forchlorfenuron can improve yield affecting parameters in J. curcas when the phenological stage of flowering at time of application is precisely considered.