Understanding blackleg in seed potato operations and the development of management strategies for the control of blackleg and tuber soft rot, caused by Pectobacterium spp.
Date
2018
Authors
Houser, Andrew Joseph, author
Davidson, Robert, advisor
Manter, Dan, committee member
Stromberger, Mary, committee member
Wallner, Steve, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Pathogenic bacteria in the genera Pectobacterium and Dickeya are of major concern in many potato growing regions around the world and are the causal organisms of blackleg and tuber soft rot. Bacteria in these genera are pectolytic, meaning they utilize pectin, of which potatoes are a good source. Crystal Violet Pectate (CVP) media was used in this project to detect the presence of pectolytic bacteria. If this bacteria is present, pits will form on the media. Pitting refers to the presence of a concave indentation in the media resulting from actively growing pectolytic bacteria. This project evaluated different stages of seed potato production to determine possible bacterial reservoirs during a seed cutting operation, optimal timeframe for bacterial screening of potato seed, and the use of different crop rotations to manage these bacteria. In addition, a summary of the findings from this project was used to develop a grower friendly blackleg/tuber soft rot management guide. The first objective was to evaluate two seed cutting operations and determine whether reservoirs of bacteria were present and could act as possible sources of contamination. Pectolytic bacteria are often spread through the seed cutting process. Cutter surfaces exposed to pectolytic bacteria include cutting knives, belts, rollers, etc. This study evaluated two seed cutting operations for their potential to limit the spread of pectolytic bacteria. Grower 1 used a Milestone seed cutter while grower 2 used a hot cutter with heat sterilized blades. There were no statistical differences between the Milestone and hot seed cutter at reducing the spread of pectolytic bacteria than the Milestone cutter. However, when individual cutter surfaces were compared, there was a higher percentage of pectolytic bacteria on the stationary knives of grower 1 (26.7 % pitting) compared with the hot cutter knives from grower 2 (1.0% pitting). Results from this study show that the use of heat to sterilize cutting blades reduces the amount of pectolytic bacteria better than stationary knives that were not sanitized. The second objective was to determine an optimal timing for estimating bacterial levels in a seed crop. Pectolytic bacteria that cause potato blackleg (Pectobacterium spp. and Dickeya spp.) can often be detected in field-grown, early generation certified seed potato lots, even though the origin seed stocks were tested as free of the bacteria. Because of this, growers have a need for a predictive tool to assist in making good, appropriate decisions about any given seed lot. This project used a crystal violet pectate (CVP) - tuber poke method to screen early generation potato seed to predict possible outbreaks of blackleg. Potato samples from several certified seed operations were tested using this method and compared with summer inspection blackleg readings. Results showed operations that differed in the number of blackleg outbreaks also differed in % pitting when a sample from the same seed crop was tested. At early generations, an increase in % pitting on CVP corresponded to an increase infield blackleg levels. However, in operations with little blackleg present, less pitting was found. The outcome of this project provides potato growers with a potential tool to help predict potential blackleg outbreaks in later generations used for seed production. The third objective was to evaluate potatoes for blackleg and tuber soft rot levels under different crop rotation systems. One potential management practice that a potato grower can use to reduce disease incidence in their crop is by utilizing different crop rotations. This study evaluated seven different crop rotations in 2013 and 2014, using the potato cultivar Colorado Rose, in the San Luis Valley, CO. Potato seed was inoculated with a slurry of Pectobacterium atrosepticum prior to field planting. The potato crop was evaluated to determine the effect each of these rotations had on disease incidence and severity. Blackleg, tuber soft rot and pectolytic bacteria levels were evaluated. Results indicated an increase in pectolytic bacteria population in tubers when Canola, in the plant family Brassicaceae were included in the rotation. When following canola, a decrease in yield and an increase in the number of culls and rotten tubers was also observed in the potato crop. When a potato crop followed the remaining rotational crops, there was no significant changes in yield, grade or disease incidence. Based on this study, the use of Canola in a crop rotation should not be used if there is a history of blackleg or tuber soft rot within the farming operation. The final objective of this project was to summarize the findings of this project by developing a grower friendly management guide. This management guide will include results from this project and other contemporary blackleg/tuber soft rot research available that is pertinent to the San Luis Valley potato industry.