Wgd. Fernando et Rg. Linderman, INHIBITION OF PHYTOPHTHORA-VIGNAE AND STEM AND ROOT-ROT OF COWPEA BY SOIL BACTERIA, Biological agriculture & horticulture, 12(1), 1995, pp. 1-14
Bacteria isolated from Sri Lankan cowpea fields significantly reduced
in vitro mycelial growth and sporangial production of Phytophthora vig
nae by producing agar-diffusable and volatile inhibitors. Bacterial vo
latile inhibitors were evolved when the bacteria were grown on tryptic
soy agar, nutrient agar, or King's B medium, although relatively less
on the latter two media. The pH of agar exposed to the volatiles rapi
dly increased, suggesting that ammonia was involved in the inhibition.
Volatile inhibitors were produced by the bacteria in soil amended wit
h tryptic Boy broth or cowpea seed extract, but not in unamended soil.
Oospore-induced disease by P. vignae was inhibited by Brevibacterium
strain DF-3101 in soil. Soil or seed treatment with three Sri Lankan b
acteria, Brevibacterium linens (DF-3101); Bacillus thuringiensis (DF-7
107), and Bacillus pumilus (DF-1481) in greenhouse studies suppressed
the disease on cowpea caused by P. vignae. None of the bacteria tested
functioned as plant growth-promoting rhizobacteria (PGPR) on cowpea.
Colonization of roots by strain DF-3101-R, a rifampicin-resistant muta
nt of Brevibacterium linens DF-3101 was initially lower on resistant '
Mississippi Purple' (6 log cfu/g root) than on susceptible 'California
Blackeye' (8 log cfu/g root) but, after two weeks, the population lev
el on both varieties was equal at 6 log cfu/g root.