Phytotoxic Responses of Soybean (Glycine max L.) to Botryodiplodin, a Toxin Produced by the Charcoal Rot Disease Fungus, Macrophomina phaseolina

Abstract

Toxins have been proposed to facilitate fungal root infection by creating regions of readily-penetrated necrotic tissue when applied externally to intact roots. Isolates of the charcoal rot disease fungus, Macrophomina phaseolina, from soybean plants in Mississippi produced a phytotoxic toxin, (−)-botryodiplodin, but no detectable phaseolinone, a toxin previously proposed to play a role in the root infection mechanism. This study was undertaken to determine if (−)-botryodiplodin induces toxic responses of the types that could facilitate root infection. (±)-Botryodiplodin prepared by chemical synthesis caused phytotoxic effects identical to those observed with (−)-botryodiplodin preparations from M. phaseolina culture filtrates, consistent with fungus-induced phytotoxicity being due to (−)-botryodiplodin, not phaseolinone or other unknown impurities. Soybean leaf disc cultures of Saline cultivar were more susceptible to (±)-botryodiplodin phytotoxicity than were cultures of two charcoal rot-resistant genotypes, DS97-84-1 and DT97-4290. (±)-Botryodiplodin caused similar phytotoxicity in actively growing duckweed (Lemna pausicostata) plantlet cultures, but at much lower concentrations. In soybean seedlings growing in hydroponic culture, (±)-botryodiplodin added to culture medium inhibited lateral and tap root growth, and caused loss of root caps and normal root tip cellular structure. Thus, botryodiplodin applied externally to undisturbed soybean roots induced phytotoxic responses of types expected to facilitate fungal root infection.

Macrophomina phaseolina: General Characteristics of Pathogenicity and Methods of Control

“…Furthermore, phytotoxic metabolites produced by M. phaseolina have been described, including phaseolinon, botryodiplodin and patulin, which are believed to play a role in the initial stages of infection, causing wilting of seedlings and formation of necrotic lesions on leaves and roots (Bhattacharya et al, 1987;Ramezani et al, 2007;Abbas et al, 2020;Salvatore et al, 2020). This increases the virulence of M. phaseolina and may contribute to explain the highly efficient mechanism to infect different hosts and tissues.…”

Pigment Produced by Glycine-Stimulated Macrophomina Phaseolina Is a (−)-Botryodiplodin Reaction Product and the Basis for an In-Culture Assay for (−)-Botryodiplodin Production

“…Serial dilutions of glycine and a series of other amines in water were examined for pigment production with added (±)-botryodiplodin [ 40 ] in air. Red, orange, or yellow pigments were observed ( Figure 5 ) with the most intense pigmentation being observed for glycine and β-alanine supplementation.…”

“…Moniliformin was the gift of the late Dr. Ronald Vesonder, National Center for Agricultural Utilization Research, Peoria, IL, USA. (±)-Botryodiplodin was synthesized as described previously [ 40 ]. Unless otherwise indicated, all other chemicals and organic solvents were obtained from Fisher Scientific, Pittsburgh, PA, USA and used without purification.…”

Macrophomina phaseolina–host interface: Insights into an emerging dry root rot pathogen of mungbean and urdbean, and its mitigation strategies

“…Botryodiplodin production by M . phaseolina may lead to the contamination of soybean foodstuffs such as tofu and vegetable oil (Abbas et al, 2020).…”