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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Genetic Improvement for Fruits & Vegetables Laboratory » Research » Research Project #434973

Research Project: Control of Pythium Leak (Pythium Ultimum) and Silver Scurf (Helminthosporium Solani) Infection of Potato Using Antagonistic Streptomycetes

Location: Genetic Improvement for Fruits & Vegetables Laboratory

Project Number: 8042-21000-283-13-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Jul 1, 2018
End Date: Sep 30, 2019

Objective:
1. Identify non-pathogenic Streptomyces strains that are antagonistic to P. ultimum and H. solani. 2. Determine whether the most antagonistic Streptomyces strains prevent P. ultimum and H. solani infection of potato in soil-based, greenhouse pot assay and on stored tubers. 3. Identify Streptomyces-produced compounds and biosynthetic genes in the Streptomyces genome responsible for antagonism toward H. solani.

Approach:
1. Test 70 non-pathogenic Streptomycetes for the ability to inhibit growth of P. ultimum and H. solani in a plate assay. The Streptomyces strains will be co-cultured with P. ultimum and H. solani. Zones of inhibition will be measured at 7 and 14 days after inoculation onto a Petri dish. Additionally, H. solani and selected non-pathogenic Streptomyces strains will be co-cultured in a 96-well plate and growth and inhibition of H. solani will be measured. 2. Ten to twenty Streptomyces strains that exhibit pathogen antagonism in Approach 1 will be cultured and dry-coated onto Red Norland (susceptible to silver scurf) seed tubers known to have high levels of silver scurf, and onto Russet Norkotah (susceptible to Pythium leak) tubers. The seed tubers will be planted into 5-gallon pots of soil and allowed to grow to maturity. Progeny tubers will be assayed for silver scurf infections at harvest and again 2 months after storage. Russet Norkotah tubers will be bruised, treated with Streptomyces strains, and evaluated after three weeks of storage. 3. The Streptomyces strain that exhibits the most promising control of silver scurf disease (Approach 2), will be selected for in-depth characterization. Secretion extracts will be from that strain, apply the extract to H. solani, and quantify inhibition. If the extract is antagonistic to H. solani, we will characterize the properties of the antimicrobial activity (using size selection chromatography, protease treatment, and thermostability). In parallel, the most promising Streptomyces strain will be mutagenized using UV light and single colonies of individual transformants will be collected. Up to twenty mutant strains that no longer inhibit H. solani growth, will be selected and checked for general growth defects. Whole genome sequencing will be performed on up to ten strains that do not have any general growth defects to identify mutations in the genome that will be considered top candidates as the cause of the loss of the H. solani antagonism.