Abstract

A survey was conducted in Tamil Nadu to examine nodulation and Vesicular Arbuscular Mycorrhizal colonization of Casuarina equisetifolia using soil samples and root nodules (for use as a Frankia inoculum) collected from 23 provinces. Nodulation occurred more frequently on soils of higher available phosphorus status. This experiment supported the hypothesis that low phosphorus supply and the absence of infective Frankia were two of the factors responsible for the low frequency of nodulation in some soils. The VA-mycorrhizal fungi exhibited distinct distribution patterns when associated with Casuarina equisetifolia host in different habitats. The reduction in mycorrhizal activity was attributed to the high-P availability in the soil. The greater effectiveness of some inoculum for increasing P concentration in the host plant may indicate adaptation in these mycorrhizal fungi to low P soil conditions. Thus differences in nodulation and mycorrhizal infection may occur among native Frankia and VA-mycorrhizal fungi when the native soils are different yet contiguous.

Keywords: Casuarina equisetifolia, Frankia, Nodulation, Survey, Symbiosis, VAM