Plant Growth-Promoting Bacteria from Solarized Soil with the Ability to Protect Melon Against Root Rot and Vine Decline Caused by Monosporascus cannonballus

2013 
AbstractThis study was undertaken to isolate indigenous plant growth-promoting(PGP) bacteria from solarized soil effective in the biocontrol of Monosporas-cus cannonballus, the cause of root rot and vine decline of melon, which isone of the most destructive soilborne diseases of this crop worldwide. Thescreening strategy resulted in the selection of two interesting PGP bacteriaas biocontrol candidates against M. cannonballus belonging to the samemicrobial community. The two bacterial species, identified according tophenotypic, physiological tests and analysis of the 16S rDNA sequence asBacillus subtilis/amyloliquefaciens (BsCR) and Pseudomonas putida (PpF4),showed PGP traits and in vitro antagonistic activity towards M. cannonbal-lus. Antagonism by BsCR was characterized by a consistent inhibition ofthe pathogen in vitro growth; PpF4 strongly inhibited the development ofperithecia of the pathogen. Under greenhouse conditions, the selectedbacteria were tested for their biocontrol activity in the pathosystemmelon-M. cannonballus. BsCR alone and in combination with PpF4 deter-mined a consistent decrease in the disease symptoms. BsCR and the com-bination of the bacterial strains significantly increased root biomass inboth inoculated and un-inoculated plant. Upon seed treatment withBsCR, the accumulation and isoenzyme induction of peroxidase in rootsas biochemical marker for induction of resistance were found, thus indi-cating that BsCR may reduce the disease severity also by the activation ofthe plant defence responses. The study highlights the synergistic biocon-trol potential of B. subtilis BsCR and P. putida PpF4 in the integrated man-agement of root rot and vine decline of melon caused by M. cannonballus.IntroductionMonosporascus root rot and vine decline of meloncaused by the soilborne fungal pathogen Monosporas-cus cannonballus Pollak and Uecker is one of the mostdestructive soilborne diseases of this crop worldwide(Martyn and Miller 1996; Cohen et al. 2012) andprominent in several melon-producing areas in Italy(Chilosi et al. 2008). Symptoms of the disease arelocalized on the root system, represented by lesions,rots and loss of smaller feeder roots, resulting in wiltof plants prior to harvest, premature fruit ripeningand low sugar content of fruits. Although wilting anddeath are manifested in the late growing season, theonset of melon root infection can occur during theearly growth stages (Stanghellini et al. 2004). Mono-sporascus cannonballus produces distinctive ascosporesin fertile perithecia within the host roots. Ascosporesfunction as the only known survival structures andinoculum for root infection (Stanghellini et al. 2000).
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