Biodiversity of the genus Fusarium in saline soil habitats

Abstract

Fusarium species assemblage and diversity were investigated in eight different contrasting extreme saline soil habitats of the hot arid desert environment of Bahrain. Saline habitats are located towards the central-southern part of Bahrain and featured by high electrical conductivity, slightly alkaline sandy soil, poor in nutrient sources and water holding capacity and mainly dominated by a salt-tolerant flora. Quantification of data for the recovery of Fusarium species was based on morphological characters and counts by a series of ten fold dilutions plate method and direct soil plating, using two selective media supplemented with different NaCl concentrations. A total of 68 isolates, fluctuated between 1 and 23 per soil sample, were recovered among all habitats mostly at 0 and 5% NaCl concentrations, while no recovery was achieved at 20 and 25%. Grouping of these isolates has resulted in only five species (F. solani, F. oxysporum, F. chlamydosporum, F. equiseti and F. compactum), all of which were previously reported from the arid terrestrial habitats of Bahrain. F. solani was the most predominant species, based on relative density, frequency of occurrence and dominance values, followed by F. oxysporum, a finding consistent with other similar arid Sahara ecosystems. Evaluation of data, supported by analysis of diversity indices and community coefficients, revealed that desert mountain habitat followed by burial mounds habitat were highly homogeneous coupled with maximum species richness, diversity indices and evenness, whereas soil habitats like cliffs, coastal and Al-Lowzy pit were the poorest. Moreover, in vitro tests showed that among other fusaria, F. solani exhibited the highest tolerance to increase NaCl concentrations (25%) and temperature (28.3 mm linear growth at 35 degrees C). At 10% NaCl concentrations, significant reduction in linear growth extensions suppressed all species accompanied by massive thick-walled, drought-resistant chlamydospores formation, indicating that species are mainly thermo-osmotolerant. Fusarium species recoveries were negatively significantly correlated (p < 0.05), with soil edaphic factors including salinity (r = -0.849) and soil moisture (r = -0.711). It is thus, proposed that inter and intra specific variation in the Fusarium species community, in particular soil niche, is an outcome of the influence of bioclimatic, multi-soil-edaphic and biotic factors.