Management of 'Seed' Transmitted and Postharvest Diseases of Sweetpotato

INVESTIGATOR: Clark, C. A.

PERFORMING INSTITUTION:
Plant Pathology & Crop Physiology
Louisiana State University
Baton Rouge, Louisiana 70803

NON-TECHNICAL SUMMARY: There are two pressing disease problems in sweetpotato production. Decline in yield and quality of cultivars occurs as planting material accumulates pathogens during multiple cycles of vegetative propagation. While seed programs have been established to address this problem, it is still not known which pathogens are most responsible for this decline or how to reduce the rate at which they reinfect healthy planting material. Secondly, even though Beauregard is more resistant to Rhizopus soft rot than older cultivars, the industry has continued to rely heavily on fungicides applied to the sweetpotatoes as they are packed for shipment to market to control postharvest diseases. The problem of cultivar decline will be addressed by trying to identify previously unrecognized viruses and by learning how the important virus and bacterial pathogens spread in the field. It is anticipated that this will lead to better methods for detecting the presence of the pathogens and identifying critical points to reduce their spread into healthy planting material. The purpose of the research on postharvest diseases is to develop an advisory program to enable farmers and packers to use cultural practices in the field and practices on packing lines that will enable them to take advantage of the resistance of Beauregard to Rhizopus soft rot to manage the disease effectively with reduced reliance on fungicides.

OBJECTIVES: 1. To screen sweetpotato breeding lines for disease resistance with the ultimate goal of generating multiple disease and pest-resistant cultivars for the Louisiana and US sweetpotato industries. 2. To isolate and identify pathogens transmitted in sweetpotato propagating material that are involved in cultivar decline and develop management strategies to reduce reinfection by these pathogens. 3. To determine preharvest and postharvest factors that affect postharvest disease development in sweetpotato and use this information to develop an advisory system that will allow growers and packers to reduce postharvest losses with less reliance on postharvest application of fungicides.

APPROACH: 1. Established methods will be used to screen advanced breeding lines from the LAES sweetpotato breeding program for resistance to Streptomyces soil rot, root-knot nematode, Fusarium wilt, Java black rot, bacterial root and stem rot, and Fusarium root rot. Research will be conducted to improve methods to screen for combined resistance of storage roots to Rhizopus soft rot and mechanical injury. Research will also be conducted to develop methods to screen for resistance to viruses, concentrating initially on using field screening for yield effects combined with real-time PCR analysis of virus titers to develop horticulturally acceptable lines with resistance to SPLCV. 2. A variety of approaches will be used to try and isolate and/or identify previously unrecognized viruses in sweetpotatoes exposed to natural infection in the field for many years. These will include subtraction hybridization using dsRNA from the common potyviruses and different insects as potential selective vectors. Field studies will be conducted to determine the roles of annual and perennial species of Convolvulaceous plants in movement and increase of both viruses and their insect vectors. 3. Survey plots will be conducted in 20 commercial sweetpotato fields in LA each year to determine the relationship between site factors and cultural practices and subsequent susceptibility to Rhizopus soft rot and bacterial soft rot of stored storage roots. Storage environments and packinghouse practices will be monitored to determine their effect on occurrence of these two postharvest diseases and promising new biological and chemical control agents will be evaluated for their efficacy in controlling Rhizopus soft rot.

KEYWORDS: disease resistance; ipomoea batatas; cultivar decline; sweet potato feathery mottle virus; sweet potato virus g; ipomoea vein mosaic virus; sweet potato leaf curl virus; postharvest disease; rhizopus stolonifer; erwinia chrysanthemi

PROJECT CONTACT:
Name: Clark, C. A.
Phone: 225-578-1381
Fax: 225-578-1415
Email: cclark@agctr.lsu.edu

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