1a. Objectives (from AD-416):
The proposed research aims to: 1) Examine the efficacy of hypovirulent Rhizoctonia solani strains Rhs1A1 and Bs69 as biocontrol agents, alone or in combination with each other and/or bacterial biocontrol agent Bacillus subtilis, for control of potato pathogens R. solani AG-3, Streptomyces scabiei and Phytotphthora infestans, under greenhouse and field conditions; and 2) Further establish Rhs1A1 and Bs69 as robust biocontrol technologies by understanding the genetic basis of the M2 dsRNA-mediated hypovirulence through identification of genes involved in hypovirulence by comparison of RNA-seq libraries.
1b. Approach (from AD-416):
Improved management practices are needed to control soilborne potato diseases while also helping to enhance sustainability and crop yield. Biological control is a promising alternative to conventional practices, but more assessments are needed to determine how to optimize and best utilize and implement biological control for greatest efficacy. In particular, the use of hypovirulent isolates of Rhizoctonia solani, which may reduce disease through multiple mechanisms including induction of plant defense responses, contains promise, but little is known regarding the mechanism and genetics of hypovirulence-mediated disease control. In this research, we will conduct greenhouse and field assays evaluating two hypovirulent strains of Rhizoctonia solani (Rhs1A1 and Bs69) alone and in combination with a bacterial biocontrol agent (Bacillus subtilis strain GB03) for control of multiple different soilborne disease problems, including stem canker and black scurf (caused by R. solani AG-3), common scab (caused by Streptomyces scabiei), and late blight (caused by Phythphthora infestans). Tuber yield will also be compared among treatments. In addition, we will examine the underlying genetic basis of hypovirulence-mediated disease control in these biocontrol isolates in order to more fully understand the relationship between hypovirulence and biological control and to more firmly establish the biocontrol potential of this approach. To identify genes involved in hypovirulence and biological control, we will construct RNA-Seq libraries for the hypovirulent isolates Rhs1A1 and Bs69 and the virulent R. solani Rhs1AP, and apply the RNA-Seq technology to profile changes in transcriptomes. Each transciptome library will be sequenced in an Illumina HiSeq 2000 at a depth sufficient to monitor differential expression of virtually every single gene in the genomes of these fungi. The genes involved in hypovirulence will be identified through comparisons of the three libraries. Identification of these genes will provide us with a powerful tool to understanding the genetic basis of hypovirulence-mediated control.
3. Progress Report:
Soilborne diseases are persistent problems in potato production. Biological control strategies have potential to provide enhanced disease control, but must be developed beyond what is currently available. Hypovirulent (low-virulence) strains of Rhizoctonia solani, which are known to reduce disease and may enhance plant defense responses, are being investigated for their efficacy as biocontrol agents in potato production. In addition, to better understand how to best utilize this approach, the genetic basis of hypovirulence is being investigated. Field experiments evaluating two hypovirulent isolates alone and in combination with a bacterial biocontrol agent were conducted in 2012 and are continuing in 2013, and preliminary results indicate that both isolates reduced Rhizoctonia disease on potato, but did not significantly affect yield. In experiments to identify genes involved in hypovirulence and biological control, RNA-Seq libraries have been constructed and analyses are in process to profile differential expression of genes among isolates. Identification of these genes will provide a powerful tool for understanding the genetic basis of hypovirulence-mediated control. This study is providing new information for the effective use and further development of hypovirulence for the control of soilborne diseases and enhanced potato production.