Biological Mechanism

An enhanced presence of microorganisms antagonist of plant pathogens was generally observed in solarized soil, due to the increased availability of substrate and nutrients following the death of most mesophilic microorganisms (Stapleton 1981; Gamliel et al. 1989; Stapleton and DeVay 1995). Paul and Clark (1996) hypothesized that higher assimilation efficiency of antagonistic bacteria may favor them in the presence of the heat-induced increased availability of nutrients. Moreover, Gupta and Yeates (1997) suggested that further shifts in soil microflora may be due to the lower grazing pressure on soil microorganisms by solarization-targeted bacterial grazer and predators. These antagonist populations, including Bacillus spp., fluorescent pseudomonads, thermotolerant fungi, and some free-living nematodes, were found to survive solarization or rapidly colonize soil and prevent pest recolo-nization, providing also a better plant growth (Katan 1987; Gamliel and Stapleton 1993a; Stapleton and DeVay 1995). Moreover, fluorescent pseudomonads were also found to be positively affected by the increase of humic substances above reported as following solarization (Chen et al. 1994, 2000). Among microorganisms surviving solar heating, thermotolerant fungi Trichoderma spp. were shown to inhibit growth of many fungal pathogens and reduce related diseases (Ben-Yephet et al. 1987; Harman 2000; Suarez et al. 2004).

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