Factors affecting the nodulation of Pongamia pinnata (L.) Pierre inoculated with Rhizobium mesoamericanum (Lopez-Lopez et al., 2012)

Abstract

Pongamia pinnata or “bani” in the Philippines is a non-food crop that can grow on marginal land where food crops do not grow. Its seeds are used for biofuel production such as biodiesel and aviation fuel. It is resilient against abiotic stresses such as drought, salinity and acidity. It can also grow in nitrogen-limited soils. It is capable of nitrogenfixation activity through its root nodules developed by symbiosis with rhizobia. Rhizobium mesoamericanum (Lopez- Lopez et al., 2012) promotes the nodulation of Pongamia as confirmed by strain symbiotic effectiveness testing where shoot length, number of nodes, number of leaflet ts, nodule number, and plant dry weights were analysed. Variability test was carried out to determine any variability of nodulation in the seeds coming from one mother tree. A time course of nodulation revealed that there was an increasing pattern of nodule number, leghemoglobin concentration, area of zone of infection and dry weights. Nodulation increased when nitrate concentration was increased from 2 to 5 mM, but was inhibited in 10 mM nitrate. Nodulation decreased as salinity increased from 1% to 3%. R. mesomaericanum improved the growth and nodulation in Pongamia, whether as a group or as individual inoculants, provided that a sufficient concentration of the inoculant was achieved.