Promoting branching of a potential biofuel crop Jatropha curcas L. by foliar application of plant growth regulators

Jatropha curcas L. (Euphorbiaceae) has the potential to become a key biofuel crop. Manual pruning (MP) is one of the major management practices in commercial plantations of this crop, resulting in production of more branches and thus increased potential for more inflorescences leading to a higher seed yield. However, this method is time-consuming, labour-intensive and expensive. This study was conducted to determine the potential of different plant growth regulators (PGRs) to increase the number of lateral branches of J. curcas. A single foliar application of N6-benzyladenine (BA) at 12 mM significantly increased branches in both the pot (4.0) and field (13.2) trials compared to MP (1.8 and 5.7, respectively) and control (no new branches) plants. In the field, a single foliar application of 1.0 mM 2,3,5-triiodobenzoic acid (TIBA) resulted in a significant increment in the number of branches (15.9) after 7 months. Of all the PGRs examined, 2,3:4,6-di-O-isopropylidene-2-keto-l-gluconic acid (dikegulac; DK) at 2.0 mM produced the maximum number of branches (18.0) in the field 7 months after application. Concentrations of 2.0 and 3.0 mM of 1,2-dihydro-3,6-pyridazinedione (maleic hydrazide; MH) significantly increased the number of branches, 4 and 7 months after spraying in both the pot trial in the shade house and field, respectively. Under field conditions, J. curcas plants responded better to all the PGRs (DK < TIBA < BA < MH) when treated once, with insignificant variations in other growth parameters. This study indicates that a single foliar application of PGRs under field conditions can be an alternative method to MP for increasing the number of lateral branches of J. curcas.