This study found that the in vitro and in planta effect of the
methanol extract of X. nematophila TB culture on B. cinerea and
P. capsici showed difference. The inhibitory effect of the methanol
extract on both the mycelial growth and spore germination of P.
capsici was stronger than on B. cinerea in vitro, but there was no
obvious difference between its effect on tomato plants infected with
B. cinerea and pepper plants infected with P. capsici in planta,.
Traditionally, many studies on the antimicrobial activities of
Xenorhabdus spp. are determined by in vitro assays that can give
an indication of the inhibitory potency quickly, while there are few establishment and expansion of the pathogen on the fruit or leaf
surface. This suggests that the methanol extract can retain its antimicrobial
activity for at least 24 h after being applied to fruits or
leaves. Moreover, the methanol extract exhibited similar efficiency
on both plant diseases tested in this study. Thus, the methanol extract
of the cell-free filtrate of X. nematophila TB culture may be used to
control plant diseases in agricultural production system. The methanol
extract not only has strong activity on plant pathogens in vitro
but also has strong control effect on plant diseases in planta. These
justify the necessity of additional work to determine the effect of the
methanol extract on tomato grey mold caused by B. cinerea and
pepper leaf scorch caused by P. capsici in the field. Further work will
also be conducted on using nonpolar solvents to extract active compounds
and on identifying active compounds from X. nematophila
TB culture to find alternate ways to reduce the application of chemical
fungicides for sustainable agriculture production.