Effects of storage time and temperature on the infectivity and effectiveness ofFrankia entrapped in polyacrylamide gel

Abstract

Four Frankia-Casuarina endosymbiont strains were tested for their infectivity and effectiveness on C. equisetifolia plants after 1 d, 3 and 6 months of Frankia storage at 7, 28 and 40 degrees C as liquid-cultures and polyacrylamide gel (PAG)-immobilized inocula. At lower temperature the number of nodules was the same or higher than control for liquid inocula except after 6 months of storage. For the PAG-entrapped Frankia lower numbers of nodules were recorded due to the use of high Frankia titers. In general, the results showed comparable plant dry mass, total nitrogen, root to shoot and nodules to plant ratios at lower temperature treatments. Increasing time and temperature was accompanied with reduced infectivity and effectiveness on inoculated plants. No nodulation was scored on plants inoculated with liquid and PAG-entrapped inocula stored at 40 degrees C for 6 months; subsequently, plant growth was inhibited. The variations in results obtained for different strains and treatments lead to variations in plant nitrogen-fixing ability. The use of PAG as a carrier for different Frankia strains is suggested; the recommended storage temperature for PAG-immobilized Frankia in 7-28 degrees C for up to 3 months.

Tolerance to environmental stress by the nitrogen-fixing actinobacterium Frankia and its role in actinorhizal plants adaptation

“…These Casuarina strains retained their infectivity at all temperature regimes tested (25, 30, 35 and 40 °C), but an Alnus strain in alginate beads lost its infectivity at 35 °C and at 40 °C in liquid culture. For three other Casuarina isolates, C. equisetifolia growth was higher when the plants were inoculated with both liquid and gel-immobilized Frankia that had been stored at 28 °C (Sayed et al 2002). Total dry mass and total nitrogen content of plants were higher compared to plants that were inoculated with Frankia strains that had been stored at higher or lower temperatures.…”

“…As a result, it is crucial to screen isolates to select strains which will be used as an inoculum in temperate climates (Sayed et al 1997). Growth response of Frankia isolates to different temperature regimes is well documented (Burggraaf and Shipton 1982;Tisa et al 1983;Smolander et al 1988;Sayed et al 1997;Sayed et al 2002). In liquid culture, the optimum temperature for growth was about 30 °C for Frankia isolates LDAgp1 and AvcI1 and between 30 and 35 °C for CpI1 (Burggraaf and Shipton 1982).…”

“…The effect of storage temperatures on the symbiotic ability of Frankia isolates has been described (Sayed et al 1997;Sayed et al 2002;Mansour 2003). Casuarina strains CcI3, CeF and Cj1.82 showed a greater tolerance to high temperatures when stored for seven months in sand inoculated with a liquid culture or with a culture immobilized in alginate beads.…”