Propagation of Pongamia pinnata (L.) Pierre: Effect of auxins, age, season and C/N ratio on rooting of stem cuttings

Pongamia pinnata (L.) Pierre, an important multipurpose tree prized source of biodiesel, is difficult to propagate commercially either by stem / root cuttings or layering. The present investigation is carried out to regenerate the species through stem cuttings with different doses of auxins in juvenile and mature stem cuttings during three seasons. Indole-3-butyric acid (IBA) was found to be effective auxin in inducing rooting. The 800 mg L−1 IBA was outstanding and yielded over 80% rooting in juvenile cuttings. Cuttings taken from juvenile plants gave significantly higher rooting than those from mature trees, irrespective of auxin treatment and season. Among three seasons, spring (March) was the best for rooting of mature stem cuttings that yielded almost 60% rooting with 800 mg L−1 IBA treatment. Orthogonal contrast analysis showed that the linear, quadratic and quartic effects together explained 99.98% variation for rooting, 99.04% for root number, 99.96% for root length and 97.4% for root biomass. The results also revealed that relatively high C and low N concentrations triggered rooting in cuttings set in spring, while low C and high N in cuttings limited rooting in cuttings set in winter. It is recommended to treat the cuttings with 800 mg L−1 IBA and set the cuttings derived from mature trees in spring, while juvenile stock in both spring and rainy seasons for successful rooting. It is possible to commercially propagate P. pinnata by cuttings with success ranging between 60%–80%, if these recommendations are followed, and thus help in establishment of clonal plantations of the species for bio-diesel production in India .