The Relation of Different Crop Roots Exudates to the Survival and Suppressive Effect of Stenotrophomonas maltophilia (PD4560), Biocontrol Agent of Bacterial Wilt of Potato

Abstract

Experiments were performed under greenhouse conditions to control bacterial wilt of potato (potato brown rot), caused by Ralstonia solanacearum race 3 biovar 2, Phylotype II, sequevar 1 using various biocontrol strategies. These strategies involved the use of the bacterial biocontrol agent Stenotrophomonas maltophilia (PD4560), in clay or sandy soils, planted with cowpea, maize or tomato which was grown separately in different pots in the inoculated soils. After harvest, the soil derived from each cultivated crop was inoculated with a mixture of three virulent R. solanacearum strains (K3, K10 and K16) to achieve a final concentration of 5 9 10 8 cfu/ g dry soil and used in pots under greenhouse conditions to cultivate potato seed tubers. The highest survival of S. maltophilia in soil (more than 160 days) coincided with a remarkable suppressing effect on disease incidence caused by R. solanacearum that expressed by wilt severity (up to 100% reduction), area under disease progress curve (AUDPC) (up to 99% reduction) and counts of the pathogen in soil (up to 75% reduction), rhizosphere (up to 80% reduction) and plant tissue (up to 97% reduction) of potato plants. The amino acid analysis of root exudates of crops under investigation revealed high percentages of asparagines (15.5-21%), glutamine (16-20%) and sulphur-containing methionine (7-9%) in both of the cowpea and maize, respectively. In tomato root exudates, high percentages of arginine (around 26%) and lysine (around 23%) were detected. Methionine is known to favour the growth of S. maltophilia suggesting that especially cowpea and maize are suitable for crop rotation with potato and will enhance the sustainability of the biocontrol agent S. maltophilia.

Evaluation of antibacterial activity of Stenotrophomonas maltophilia against Ralstonia solanacearum under different application conditions

“…Similar antagonistic characteristics for both the wild and the mutant strains were confirmed (Messiha et al 2007 andElhalag et al 2015). Both the wild type and mutant strains were confirmed to be nonhuman pathogenic (Elhalag 2014;Elhalag et al 2015). Since the reason of the antibacterial activity of Sten.…”

“…maltophilia strain used in this study is a mutant strain resistant to rifampicin and chloramphenicol (100 lg ml À1 each) (PD 4560) (Messiha et al 2007). Similar antagonistic characteristics for both the wild and the mutant strains were confirmed (Messiha et al 2007 andElhalag et al 2015). Both the wild type and mutant strains were confirmed to be nonhuman pathogenic (Elhalag 2014;Elhalag et al 2015).…”

“…Also, survival of the biocontrol agent when applied on peat‐moss carrier was longer than nonamended soil (Elhalag et al . ).…”

“… and Elhalag et al . ). Both the wild type and mutant strains were confirmed to be nonhuman pathogenic (Elhalag ; Elhalag et al .…”

“…Both the wild type and mutant strains were confirmed to be nonhuman pathogenic (Elhalag ; Elhalag et al . ). Since the reason of the antibacterial activity of Sten.…”