In dual culture antagonism test, six of eight cyanogenic bacteria were able to reduce the growth of
Sclerotium cepivorum. The strains Glocoacetobacter diazotrophicus and Paenibacillus. polymyxa
GQ375783.1 were the most effective bacteria that recorded the highest inhibition of S. cepivorum mycelial
growth by 75% and 70% respectively. Based on HCN production, two strains recorded complete inhibition
of fungal growth. Moreover, the ground tissues of the nasturtium plant were able to inhibit the mycelium
growth of S. cepivorum by 100%. Results of the greenhouse experiment emphasized that white-rot
incidence percentage recorded the lowest values in onion cultivated in soil amended with nasturtium plant
and inoculated with G. diazotrophicus plus P. polymyxa GQ375783.1. This treatment recorded the highest
values of onion vegetative growth and their yield. Under field conditions, the soil treated with investigated
two methods of biofumigation led to suppress white rot disease by the rate of 100% while using each one
individually, it reduced disease by the rate of 94.4 and 94.9 % respectively. All onion treatments that
inoculated with cyanogenic bacteria showed higher records of DH and N2-ase activity than uninoculated
ones. The highest values DH and N2-ase were recorded with soil amended with nasturtium and inoculated
with cyanogenic bacterial strains. Additionally, the same treatment gave the highest values of peroxidase
and polyphenoloxidase activity, onion NPK content, and the plant's vegetative growth as well as their yield.
Therefore, the biofumigation using nasturtium and investigated bacterial strains can be recommended in
controlling White-rot disease in onions and increasing their productivity |
