Mixtures of plant growth promoting fungi (PGPF) and arbuscular mycorrhizal fungus (AMF) Glomus mosseae induce resistance in cucumber plants

Abstract: Plant growth-promoting fungi (PGPF) are saprotrophic fungi isolated from
zoysia grass rhizosphere that are capable of enhancing plant growth and suppressing
plant diseases. The composite application of the PGPF with the arbuscular mycorrhizal
fungus (AMF) G. mosseae (Gm) to the soil during planting enhanced growth of
cucumber and suppressed cucumber mosaic, anthracnose, and damping-off diseases
caused by Cucumber Mosaic Virus (CMV-Y), Colletotrichum orbiculare, and
Rhizoctonia solani, respectively. The enhancement in plant growth was estimated to be at
the average of 1-4 folds increase over the control plants. Depending on the PGPF, Gm
showed a variable tendency to depress, enhance, or to have no effect to the root and/or
rhizosphere population of PGPF. Similarly, the PGPF reduced, enhanced or had no effect
on percent root colonization of Gm. We are currently elucidating the mechanisms by
which PGPF and Gm suppress symptom development of leaf pathogens like CMV-Y and
anthracnose in cucumber plants. Leaf and/or root samples were taken from cucumber
grown in soil medium amended with PGPF and/or Gm at sowing at different periods
after challenge inoculation with CMV-Y or C. orbiculare. Preliminary results of
molecular studies indicated that defense-related genes like PR1-1a, Pal, β-1-3 glucanase,
and basic chitinase exhibited elevated expression. We hypothesize the involvement of
multiple defense mechanisms leading to ISR in cucumber against CMV-Y or C.
orbiculare.