Effects of land irrigation with partially-treated wastewater on Frankia survival and infectivity

The effect of partially treated wastewater on Frankia growth and infectivity on Casuarina equisetifolia plants was studied. This water contained high amounts of cyanide, arsenic, mercury ions, and contaminating microorganisms. Three Frankia strains were grown on elevated concentrations of wastewater up to 100% as a preliminary test to determine the possibility of their growth on these concentrations. Their growth was reduced to about 50% with slight variations between strains. Twelve Frankia strains were then grown on 100% wastewater and their growth was not much affected but showed only variations in growth rates. Six of these strains, when grown on wastewater, lost their infectivity when inoculated on Casuarina seedlings irrigated with the same water. In contrast, nodulation occurred on plants that were irrigated with wastewater when inoculated with Frankia grown on liquid BuCT medium although nodule size and weight was reduced for all strains. Statistical analysis (twoway ANOVA) showed no significant differences (P = 0.05) in the number of nodules or shoot dry weight for different treatments. Significant differences were found between treatments in root length, shoot height and root and nodule dry weight. No significant differences were recorded also within the same treatments for all plant growth criteria. These results indicate the possibility of inhibitory effect on the infectivity of natural Frankia populations but not on the selected and introduced (i.e., tolerant) strains.