[Population of Fusarium spp. in soils from the arid regions and effect of water potential on their growth].

In trials of wheat establishment in irrigated areas in the Patagonian valleys (Picún Leufú), sectors with plants showing symptoms of typical foot-rot were detected. In order to investigate the phytopathogenic mycoflora of these soils (arid zone), the population of Fusarium spp was analysed quali- and quantitatively and its tolerance to water stress by measuring the mycelial growth in the presence of different water potentials. Fusarium spp detected in that type of soil did not coincide with those commonly present in traditional wheat zones. In 100% of the samples analysed the predominant fungus present vas Fusarium equiseti. This species was the one isolated from wheat plants with foot-rot. It was isolated in soil sown with wheat as well as in soils free of wheat. In none of the samples, was the number less than 10,000 propagules/g of soil. In sporadic cases F. moniliforme and F. oxysporum appeared. When comparing, in different water potentials, the growth capacity of isolated species in the arid zone with respect to the other phytopathogenic species common in wheat (F. graminearum an F. poae), it was noted that F. equiseti showed the greatest tolerance to water stress. This species had the capacity to grow in water potentials as low as -12 MPa. This physiological characteristic was manifest in the strains of F. equiseti found in the arid zone and also in those isolated in a wet zone.(ABSTRACT TRUNCATED AT 250 WORDS)