Mechanism of Soybean Root Infection by Macrophomina Phaseolina (MSPB Project Abbas 34-2015)

Objective 1: To examine the mechanism by which Macrophomina (M.) phaseolina locates soybean root tips in soil by screening substances reported to be secreted from roots for ability to: (1) induce chemotaxis in M. phaseolina isolates from Mississippi soybean fields, and (2) stimulate synthesis and release of botryodiplodin in culture. It is hypothesized that M. phaseolina finds and enters soybean root tips by chemotaxis to one or more substances released from roots and at the root tip secretes botryodiplodin to facilitate entry. Objective 2: To examine the mechanism of entry of M. phaseolina hyphae into soybean seedling root in hydroponic co-culture with M. phaseolina using transmission electron microscopy and ultrastructural analysis. The analysis will focus on meristematic tissue at root tips. It is hypothesized that: (1) botryodiplodin added to hydroponic medium will induce necrotic tissue in the absence of M. phaseolina; (2) electron micrographs can be obtained showing M. phaseolina hyphae that have propagated in through necrotic meristematic tissue in previously uninfected soybean seedlings; and (3) electron micrographs can be obtained showing M. phaseolina hyphae that have propagated out through necrotic meristematic tissue in previously infected soybean seedlings.