Experiments were performed under greenhouse conditions to control bac-
terial wilt of potato (potato brown rot), caused by Ralstonia solanacearum
race 3 biovar 2, Phylotype II, sequevar 1 using various biocontrol strate-
gies. 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 inci-
dence 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), rhi-
zosphere (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%), gluta-
mine (16–20%) and sulphur-containing methionine (7–9%) in both of
the cowpea and maize, respectively. In tomato root exudates, high per-
centages of arginine (around 26%) and lysine (around 23%) were
detected. Methionine is known to favour the growth of S. maltophilia sug-
gesting that especially cowpea and maize are suitable for crop rotation
with potato and will enhance the sustainability of the biocontrol agent
S. maltophilia. |
