Abstract Detail

Mycology

Solórzano, José [1], Kartika, Rendy [2], Richards, Jonathan K. [1], O. Ganiu, Moshood [3], Van Houten, Joshua P. [3], Doyle, Vinson P. [4].

Understanding the etiology of taproot decline of soybean caused by Xylaria necrophora.

Taproot decline (TRD) of soybean is an emerging disease caused by Xylaria necrophora, but the mechanisms by which it infects soybean and produces symptoms are unknown. Symptoms of TRD include foliar interveinal chlorosis and necrosis and root necrosis, yet X. necrophora has only been isolated from the roots. The symptoms of TRD resemble those of sudden death syndrome of soybean, which produces foliar symptoms through the translocation of a phytotoxic protein from the roots to the leaves. Xylaria species, while predominantly wood decomposers, are known to produce secondary metabolites (SMs) with multiple bioactivities, including phytotoxicity and antimicrobial activity. Preliminary experiments using soybean stem cuttings suggested X. necrophora was producing SMs that produce similar symptoms to those observed in the field, but these SMs had not yet been identified. We evaluated cell-free culture filtrates (CFs) for phytotoxicity on soybeans by infiltrating CFs into soybean leaves and testing for changes in chlorophyll content. Results showed that the CFs elicit chlorotic symptoms on soybean leaves similar to those observed under field conditions and in the stem cutting assay at five days after infiltration. CFs were then subjected to extraction using 4 solvents with a range of polarity (hexane, dichloromethane, diethylether, and ethylacetate). These extracts were then screened for phytotoxicity. The ability for X. necrophora CFs to cause phytotoxicity; however, may not be the only role for these compounds in the etiology of TRD. The rate of isolation of X. necrophora from soybean roots showing TRD symptoms are remarkably high (~80%), suggesting it has a competitive advantage over other soil-inhabiting fungi. In order to determine if the CFs may play a role in competition, we evaluated the CFs for antimicrobial activity against 15 fungal pathogens. We conducted both a dual direct interaction assay and an antimicrobial assay using 10% and 50% (v/v) CFs in PDA against 15 different fungal pathogens. Results showed high rates of antimicrobial activity of the CFs against all the 15 pathogens tested, ranging from 11%-94% and 37%-97% inhibition in the antimicrobial assay, respectively. After further evaluation of the extracts, the dichloromethane extract showed the greatest antimicrobial activity; therefore, it was evaluated with high-resolution mass spectrometry, where we were able to identify SMs with the same mass as cytochalasin compounds. The identification of SMs capable of causing phytotoxicity and inhibiting a diversity of fungal pathogens suggests an important role for these SMs in the etiology of TRD.

1 - Louisina State University, Department of Plant Pathology and Crop Physiology, 302 Life Science Building, Baton Rouge, Louisiana, 70803, United States
2 - Louisina State University, Department of Chemistry, 232 Choppin Hall, Baton Rouge, Louisiana, 70803, United States
3 - Louisina State University, Department of Chemistry, 232 Choppin Hall, Louisiana State University, Baton Rouge, Louisiana, 70803, United States
4 - Louisina State University, Department of Plant Pathology and Crop Physiology, 302 Life Science Building, Louisiana State University, Baton Rouge, Louisiana, 70803, United States

Keywords:
TRD
Xylaria necrophora
Soybeans
secondary metabolites
Phytotoxicity
antimicrobial
Taproot decline
fungi
Mycology.

Presentation Type: Poster
Session: MYP3, Mycology Posters III
Location: /
Date: Wednesday, July 21st, 2021
Time: 5:00 PM(EDT)
Number: MYP3010
Abstract ID:1140
Candidate for Awards:MSA Best Poster Presentation Award by a Graduate Student