Abstract
Pseudomonas fluorescens isolates Clinto 1R, Wayne 1R, and Wood 1R, which produce the antibiotic 2,4-diacetylphloroglucinol (DAPG), can suppress soilborne diseases and promote plant growth. Consequently, these beneficial bacterial isolates were tested on watermelon plants for suppression of Meloidogyne incognita (root-knot nematode: RKN) and Fusarium oxysporum f. sp. niveum (Fon). In a greenhouse trial, Wayne 1R root dip suppressed numbers of RKN eggs per gram root on 'Charleston Gray' watermelon by 28.9%. However, in studies focused on 'Sugar Baby' watermelon, which is commercially grown in Maryland, a Wayne 1R root dip did not inhibit RKN reproduction or plant death caused by Fon. When all three isolates were applied as seed coats, plant stand in the greenhouse was reduced up to 60% in treatments that included Fon ± P. fluorescens, and eggs per gram root did not differ among treatments. In a microplot trial with Clinto 1R and Wayne 1R root dips, inoculation with P. fluorescens and/or Fon resulted in shorter vine lengths than treatment with either P. fluorescens isolate plus RKN. Root weights, galling indices, eggs per gram root, and second-stage juvenile (J2) numbers in soil were similar among all RKN-inoculated treatments, and fruit production was not affected by treatment. Plant death was high in all treatments. These studies demonstrated that the tested P. fluorescens isolates resulted in some inhibition of vine growth in the field, and were not effective for enhancing plant vigor or suppressing RKN or Fon on watermelon.
Highlights
Pseudomonas fluorescens isolates Clinto 1R, Wayne 1R, and Wood 1R, which produce the antibiotic 2,4-diacetylphloroglucinol (DAPG), can suppress soilborne diseases and promote plant growth
Strain CHA0 and the complemented mutant CHA625/pME3128 were more effective than the DAPG-deficient strain CHA625 for inhibiting growth of F. oxysporum on agar, CHA625 could still produce hydrogen cyanide (HCN) and pyoluteorin (Keel et al, 1992)
Isolation of DAPGproducing P. fluorescens from roots of pea plants growing in soils suppressive to Fusarium wilt (F. oxysporum f. sp. pisi) indicated that these bacteria were involved in suppression of the pathogen, with the D genotype predominating in the rhizosphere (Landa et al, 2002)
Summary
Pseudomonas fluorescens isolates Clinto 1R, Wayne 1R, and Wood 1R, which produce the antibiotic 2,4-diacetylphloroglucinol (DAPG), can suppress soilborne diseases and promote plant growth. These beneficial bacterial isolates were tested on watermelon plants for suppression of Meloidogyne incognita (root-knot nematode: RKN) and Fusarium oxysporum f. Plant death was high in all treatments These studies demonstrated that the tested P. fluorescens isolates resulted in some inhibition of vine growth in the field, and were not effective for enhancing plant vigor or suppressing RKN or Fon on watermelon. Mazurier et al (2009) found that DAPG production was not a primary cause for suppression of Fusarium wilt on flax; the activity was attributed to production of phenazine by Pseudomonas spp. combined with carbon uptake by nonpathogenic F. oxysporum (Mazurier et al, 2009)
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