Search

Watermelon Fusarium wilt is one of the most severe soil-borne diseases caused by Fusarium oxysporum f. sp. niveum. In this study, the population of F. oxysporum was quickly monitored by real-time PCR and DNA array in watermelon Fusarium wilt infected soils treated with Paenibacillus polymyxa SQR21 enhanced bio-organic fertilizer (BIO) at the beginning of nursery growth and/or at the beginning of transplanting. The fungal community composition was investigated by molecular cloning and DGGE techniques. The real-time PCR results showed the F. oxysporum population in the rhizosphere soil decreased from 8.56 × 10 colony-forming units (cfu) g rhizosphere soil to 9.41 × 10 cfu g rhizosphere soil after BIO application and the DNA array detection signals of F. oxysporum population weakened. The difference between F. oxysporum abundance of BIO amended and not amended bulk soils was lower than 10 cfu g soil. DGGE profile indicated that BIO application changed the fungal community structure in the rhizosphere soils; the molecular cloning data revealed that consecutive applications of BIO at nursery and transplanting stages not only decreased Ascomycota and increased Basidiomycota abundance in the rhizosphere soil but also caused the apperance of unique fungal group which were not found in the control. The beneficial fungi Chaetomium sp. Aspergillus penicillioides were found in the BIO amended treatment, while some harmful fungi such as F. oxysporum, Rhizoctonia solani, and Fusarium solani were only detected in the control. Data from this study indicated that BIO application can control watermelon Fusarium wilt by suppressing the population of F. oxysporum and changing the fungal community structure in the rhizosphere soils. [ABSTRACT FROM AUTHOR]

Fusarium wilt is one of the major constraints on cucumber production worldwide. Several strategies have been used to control the causative pathogen, Fusarium oxysporum f. sp. cucumerinum J. H. Owen, including soil solarization, fungicide seed treatment and biological control. In this study, F. oxysporum f. sp. cucumerinum was successfully controlled by a newly isolated strain, Bacillus subtilis SQR 9, in vitro and in vivo. Greenhouse experiments were carried out to evaluate the effect of inoculation and solid fermentation of organic fertilizer with B. subtilis SQR 9, hereby defined as bio-organic fertilizer (BIO), on the control of Fusarium wilt. In comparison with the control, the wilt incidence was significantly reduced (49-61% reduction) by application of BIO. The rhizosphere population of F. oxysporum f. sp. cucumerinum, as detected both by selective plating and realtime PCR, was significantly lower in BIO-treated plants than the control. The localization of bacterial cells, pattern of colonization and survival of B. subtilis SQR 9 in the rhizsosphere of cucumber, was examined by fluorescent microscopy and explored following recovery of the green fluorescent protein ( gfp)-labeled SQR 9 with the new gfp-marked shuttle vector pHAPII through selective plating. The preferential sites of the labeled strain were the differentiation and elongation zone, root hair and the lateral root junctions. The population of the strain was 10 cfu/g root in rhizoplane. These results indicate that the strain was able to survive well in the rhizosphere of cucumber, suppressed growth of F. oxysporum in the rhizosphere of cucumber and protected the host from the pathogen. [ABSTRACT FROM AUTHOR]