Screening of bacteria for the suppression of Botrytis cinerea and Rhizoctonia solani on lettuce (Lactuca sativa) using leaf disc bioassays

Abstract

Two leaf disc bioassays were developed for screening bacteria as putative biological control agents of Botrytis cinerea and Rhizoctonia solani on lettuce. Aerobic spore and non-spore forming bacteria were isolated from the phylloplane, rhizoplane and rhizosphere of symptom-free lettuce plants grown in the presence and absence of chitin or composted bark soil amendments. Bacteria, previously isolated from other plants, were also included in the primary screen initially against B. cinerea. One hundred and twentyseven of 700 isolates reduced botrytis rotting of lettuce leaves by more than 50% in the primary screen. Following a secondary screen against B. cinerea, the lead 50 isolates were also tested for suppression of R. solani infection. Four isolates significantly reduced both botrytis and rhizoctonia leaf rotting. Eleven and five isolates gave control of botrytis and rhizoctonia, respectively, equal to that given by the standard fungicides Rovral WP (iprodione) and Basilex (tolclofos methyl). The two most effective isolates against B. cinerea and R. solani were both identified as Bacillus subtilis. Use of soil amendments did not increase the proportion of efficacious isolates recovered. Effective isolates were originally recovered from roots of oilseed rape and lettuce leaves. In general, it was found that bacteria which controlled one disease effectively did not control the second disease nearly as well. The bioassay protocols developed in this study were used successfully in screening a large number of bacterial isolates in a short time.

Characterization and origin of infection of Rhizoctonia solani associated with Brassica oleracea crops in the UK

“…Unlike many forms of resistance, this was stable in the absence of the fungicide over five generations. Severe attacks of bottom rot occurred in the UK lettuce crop in 1997, despite pre‐planting use of tolclofos‐methyl (Fiddaman et al ., 2000). This could suggest that the levels of fungicide resistance are rising in the pathogen population and has led to concern within the advisory industry body, the UK fungicide resistance action group (FRAG‐UK), over unnecessary use.…”

Conferred resistance to Botrytis cinerea in Lilium by overexpression of the RCH10 chitinase gene

“…Spore solutions were prepared by a method modified from Fiddaman et al (2000) by flooding the Petri dishes with 10 ml of spore nutrition solution [0.1 g/L of glucose, 0.1 g/L of KH 2 PO 4 and 0.5 % (v/v) Tween 20]. Plates were scraped to dislodge the conidia and the suspensions filtered through four layers of sterile muslin.…”

Effect of bacterial antagonists on lettuce: active biocontrol of Rhizoctonia solani and negligible, short-term effects on nontarget microorganisms

“…Our study aimed (1) to assess the biological control properties of three bacterial strains antagonistic to R. solani under conditions similar to those used in commercial lettuce production, and (2) to analyse their interaction with the indigenous microbial communities of field‐grown lettuce using cultivation‐independent PCR‐single‐strand conformation polymorphism (PCR‐SSCP) analysis combined with gaining new information about autochthonous lettuce‐associated microbial communities. So far, studies on lettuce‐associated microorganisms have been performed mainly on processed lettuce and using common microbiological cultivation practices (Maloney et al , 1997; Fiddaman et al , 2000). We report here for the first time on the indigenous endophytic and rhizosphere plant‐associated microbial community of unprocessed field‐grown lettuce.…”