Possible Role of Xanthobaccins Produced by Stenotrophomonas sp. Strain SB-K88 in Suppression of Sugar Beet Damping-Off Disease

Abstract

Three antifungal compounds, designated xanthobaccins A, B, and C, were isolated from the culture fluid of Stenotrophomonassp. strain SB-K88, a rhizobacterium of sugar beet that suppresses damping-off disease. Production of xanthobaccin A in culture media was compared with the disease suppression activities of strain SB-K88 and less suppressive strains that were obtained by subculturing. Strain SB-K88 was applied to sugar beet seeds, and production of xanthobaccin A in the rhizosphere of seedlings was confirmed by using a test tube culture system under hydroponic culture conditions; 3 μg of xanthobaccin A was detected in the rhizosphere on a per-plant basis. Direct application of purified xanthobaccin A to seeds suppressed damping-off disease in soil naturally infested by Pythiumspp. We suggest that xanthobaccin A produced by strain SB-K88 plays a key role in suppression of sugar beet damping-off disease.

Lysobacter capsici AZ78 produces cyclo(l -Pro-l -Tyr), a 2,5-diketopiperazine with toxic activity against sporangia of Phytophthora infestans and Plasmopara viticola

“…Previous studies have shown that other Lysobacter strains control soilborne plant pathogenic oomycetes such as Aphanomyces cochlioides and Py. aphanidermatum (Nakayama et al 1999;Folman et al 2001Folman et al , 2003Folman et al , 2004Islam et al 2005;). Recently, Ko et al (2009) demonstrated that L. antibioticus HS124 effectively protects pepper plants against P. capsici attacks and linked this activity with the production of lytic enzymes (i.e.…”

“…The evidence that a Lysobacter member produces secondary metabolites with anti-oomycete activity is also corroborated by previous studies carried out on Lysobacter sp. SB-K88, L. antibioticus HS124 and L. capsici YC5194 (Homma et al 1993;Nakayama et al 1999;Islam et al 2005;Park et al 2008;Ko et al 2009). In particular, Lysobacter sp.…”

“…adzukicola and Py. ultimum (Nakayama et al 1999) and in suppressing damping-off of sugar beet caused by Pythium spp. in soil (Homma et al 1993;Nakayama et al 1999).…”

“…These three macrocyclic lactams were isolated and identified after the screening of chromatographic fractions for their ability to inhibit the mycelial growth of Py. ultimum and Rhizoctonia solani (Nakayama et al 1999). In our study, on the other hand, we focused our attention on low molecular weight compounds, and the chromatographic fraction groups were evaluated for their toxicity against sporangia of P. infestans and Pl.…”

“…SB-K88 effectively controls the damping-off of sugar beet caused by Pythium spp. in soil (Homma et al 1993;Nakayama et al 1999). Recently, we showed that the prophylactic application of Lysobacter capsici AZ78 to grapevine leaves results in the drastic reduction of grapevine downy mildew caused by the plant pathogenic oomycete Pl.…”