Infectivity variation of Discaria trinervis-nodulating Frankia in Patagonian soil according to season and storage conditions

CHAIA E; SOLANS M; VOBIS G; WALL LG

Umea, Suecia

Simposio; 14 th Meeting on Frankia and actinorhizal plants; 2006

The infectivity variation with season and storage conditions of Frankia, from rhizospheric soil of Discaria trinervis (Rhamnaceae) plants growing in northwest Patagonia (Argentina), was quantified using the most probable number method. Soil samples seasonally collected, stored either moist at 4ºC or air-dried at room temperature for few days; and air-dried soil samples stored for prolonged periods, effectively nodulated D. trinervis seedlings. Nodulation units (NU) varied according to season and storage conditions. NU ranged from 44 in spring to ca. 1 NU mL-1 soil in summer and autumn collected soils. Autumn collected soils moist-stored were significantly more infective than air-dried stored. Summer air-dried stored soils for 12 years, 6 months, or a week had a similar infective capacity. Frankia NU were positively correlated with soils humidity (r=0.66, P=0.02), suggesting the occurrence of saprophytic Frankia in moist soils. Therefore the observed variability in the infectious capacity of the soils is not necessarily related to the quantity of Frankia in the soils. Although Frankia have long retention times of the infectious capacity, seasonal variations and storage conditions should be considered cautiously when studying Frankia ecology in natural environments.