EFFECT OF TEMPERATURE AND SOIL-MOISTURE ON THE SURVIVAL AND SYMBIOTICEFFECTIVENESS OF FRANKIA SPP

Comparison of the effects of temperature on the growth in culture (inc rease in protein) of Frankia showed that three strains isolated from C asuarina were more tolerant of high temperature (45 degrees C) than a strain from Alnus rubra. Optimal temperatures for growth of the Casuar ina strains were in the range 25-30 degrees C. Growth of the Alnus str ain was good at 25 degrees C but poor at 37 degrees C. High temperatur es (35-40 degrees C) during storage for 7 months of these Frankia stra ins in sand, inoculated initially with liquid culture or with Frankia incorporated into alginate beads and permitted to dry, resulted in sub stantial loss of infectivity for the host plant species. Loss in infec tivity was greater with an Alnus Frankia strain than strains from Casu arina cunninghamiana, C. equisetifolia and C. junghuniana. Three Frank ia strains from C. equisetifolia were incorporated into a sand/perlite mixture with three different moisture regimes (field moisture capacit y - wet: watered and maintained at field capacity; watered to field ca pacity but then allowed to dry-moderately wet; or watered to half fiel d capacity and then permitted to dry - dry) and then stored for 12 wee ks at 25 degrees C and 35 degrees C. Assessment by the most probable n umber (MPN) technique of the infectivity of the sand mixture for nodul ation of C. equisetifolia showed significant interactions between Fran kia strain, temperature and soil moisture content. The infectivity of Frankia strains ORS020607 and UGL020602q was not affected by incubatio n in wet sand at 25 degrees C but fell by more than half after 12 week s in moderate and dry conditions. Changes in infectivity were similar when incubation was at 35 degrees C. By contrast, the infectivity of U GL020603q fell substantially under all moisture conditions and at both temperatures. The data show the importance of screening for tolerance of both temperature and moisture content when selecting strains for p reparation of inoculum for use in hot climates.