Survival and genotypic variation of Pseudomonas corrugate and P. mediterranea in response to soil solarization and biofumigation.

摘要

The objective of this study was to evaluate the effect of biofumigation alone and in combination with soil solarization, on the survival, and on the occurrence of genotypic variation of a spontaneous rifamycin-resistant derivate strain of P. corrugate (Rif A344-R) and a streptomycin-resistant derivate strain of P. mediterranea (Sm A54-R), pathogenic in tomato. A randomized block design experiment included solarized and non solarized soil, with three soil treatments: without and with biofumigation with soil application (50 t ha-1) of sheep manure and of organic cabbage (Brassica oleracea var. capitata) crop residues. Rif A344-R and Sm A54-R strains were inoculated (108 cfu g-1 soil) in the soil at 10 and 40 cm depth before incorporation of organic materials. Solarized plots were covered with transparent polyethylene film (200 micro m) and left undisturbed for 54 days. Detection and survival of bacteria were performed by a combined biologic and enzymatic amplification (Bio-PCR) method. Genetic diversity of Rif A344-R and Sm A54-R strains was compared by BOX-PCR genetic fingerprints. The soil treatments had a very significant influence in reducing populations of bacteria inoculated in the soil, where they survived in the absence of the host for a period of 54 days. Soil solarization had a significant effect on the size of P. corrugate and P. mediterranea populations, which were reduced from 108 cfu g-1 soil to 3.7x104 cfu g-1 soil and 7.4x104 cfu g-1 soil, respectively. A very different (p<0.01) behavior was noticed for bacteria populations under stressful conditions at 10 and 40 cm depth. No significant differences were found on the reduction of bacteria population with the different biofumigation treatments. However, when combined with solarization a very positive effect was observed. BOX-PCR genetic profiles indicated genetic stability of all Rif-Sm resistant strains isolated after the soil treatments.