SIMPLE AND REPRODUCIBLE NODULATION TEST FOR CASUARINA-COMPATIBLE FRANKIA STRAINS - INHIBITION OF NODULATION AND PLANT PERFORMANCE BY SOME CATIONS

Reliable nodulation of Casuarina equisetifolia seedlings was obtained by inoculating them with syringe-homogenized Frankia hyphae under defi ned greenhouse conditions. Among the various morphological variants of Frankia, exponentially growing Frankia hyphae yielded the highest per centage of nodulation, followed by N-starved cultures containing diazo vesicles and spore-enriched cultures. Nodulation of 100% of the seedli ngs, as well as maximal nodule number, acetylene reduction, and plant growth, was already obtained by inoculating just 5 mu g of exponential Frankia protein pre plant. Among a variety of parameters determined, shoot dry weight appeared to be by itself a simple and reliable parame ter, which is statistically correlated with plant biomass acetylene re duction activity (ARA). Nodulation, ARA, and growth of Casuarina equis etifolia seedlings were weakly inhibited by CaCl2, MgCl2, and MnCl2 an d strongly by CdCl2. Sodium alginate did not significantly alter the n odulation or ARA but reversed the slight inhibition observed with CaCl 2, or kaolin. Our method should facilitate reliable testing of the nod ulation capacity and competition of introduced strains, as well as the effect of a number of substances, including pollutants, on nodulation under greenhouse conditions.