Incorporation of naturally occurring late blight and Colorado potato beetle resistance genes into Canadian commercial potato cultivars

Project Code PRR08-010

Project Lead

Qin Chen - Agriculture and Agri-Food Canada

Objective

To advance potato varieties with improved late blight and Colorado Potato Beetle resistance to national or regional cultivar registration trials

Summary of Results

Background 

Potato late blight caused by Phytophthora infestans and Colorado potato beetle (CPB) are the most devastating disease and insect pests in potatoes worldwide, respectively. CBPs can reduce yields by 30-50% and late blight, under suitably wet or humid conditions, can spread rapidly in potato plants, resulting in defoliation, plant death and yield losses up to 100%. Chemical control is one of the major management solutions for both pests. Approximately 20 million kilograms of pesticides are used annually for the control of these two pests in Canada. Heavy application of pesticides causes public concerns about pest resistance to pesticides, food safety, and environmental contamination, which have fueled interest in developing alternative methods of control. Host plant resistance offers long-term, sustainable and cost-efficient pest control, and is an important part of an integrated pest management system. Therefore, the development of new potato cultivars with high or even moderate levels of resistance to both late blight and CPB would significantly benefit potato production while reducing pesticide-associated risks. The present project builds on the success of project PRR03-140, in which resistance to late blight and CPB was identified and characterized from the wild Mexican species Solanum pinnatisectum, and resistance genes were transferred into cultivated potato lines. In the current project, resistance to both late blight and CPB was further incorporated into elite commercial potato lines via laboratory and field trials. Promising resistant lines were further evaluated in breeding programs to develop resistant cultivars for commercial registration.

Approaches

To develop resistant lines of potato, new somatic hybrids with resistance genes derived from S. pinnatisectum were backcrossed to elite potato cultivars to produce hybrid seeds. Backcrosses were made under controlled environmental conditions using emasculated flowers on plants growing in pots. Potato seedlings developed from hybrid seeds were screened in greenhouse for late blight and CPB resistance. For resistance evaluation to late blight, detached seedling leaves were inserted into prepared moist vermiculite and inoculated with P. infestans zoospores. Resistance was evaluated based on the severity of detached leaves. The resistance of potato lines to CPB was determined by assessing plant reactions to CPB damage in an in vitro feeding preference assay performed in Petri dishes using adult CBPs. Superior phenotypes for late blight or CPB resistance were selected and field planted to evaluate appearance, agronomic performance and yield. Promising resistant lines were further screened in the field for their resistance and stability of agronomic traits in breeding programs. During the course of the project, specific PCR primers were developed from SSR, EST and STS markers linked to resistance genes, and used to identify and confirm resistant lines.   

Results

Healthy hybrid seeds were developed over the three years of the project. A total of approximately 3300 hybrid plants were produced from backcrossed hybrid seeds. Half of these plants have shown resistance to late blight, but only less than one third have shown resistance to CPB. Lines with the highest levels of resistance to late blight and CBP were selected to backcross with elite potato germplasm. Lines derived from this backcross were then evaluated for resistance in the greenhouse setting, and resistant lines were planted in the field for the evaluation of agronomic performance. Approximately 5% of the hybrid lines planted in single hills was selected based on overall appearance, tuber number, tuber shape, and agronomic traits. These selected lines were tested again in the greenhouse for late blight and CPB resistance. Approximately 20 lines with the highest level of resistance and good agronomic performance were selected for further breeding trials for cultivar development. In the course of the trial, several pairs of specific primers were developed from SSR, EST and STS markers linked to resistance genes and used to identify resistant clones. Several molecular markers closely linked with late blight resistance have been developed and will be used for marker assisted selection breeding.

The development of resistant potato lines during the past three years has provided new sources of late blight and CPB resistance. New resistant cultivars may be developed from those lines and potato industries will benefit from these new cultivars to manage late blight and CPB in potatoes.

During the trial, an annual potato industry field day was held in 2008 at which potato industry representatives and potato farmers from western Canada participated in a tour of the Lethbridge Research Centre. Dr. Chen gave a tour and a presentation on this project. In addition, four poster presentations on potato germplasm enhancement and breeding for disease and insect resistance were presented at an annual meeting of Potato Growers of Alberta.

Next steps

1.Continue to propagate new advanced resistant potato lines developed in this project in order to produce suitable numbers of tissue culture plantlets for further lab and field tests.

2.Conduct screening and characterization of progeny lines under laboratory and field conditions for pest resistance and agronomic traits (appearance, maturity, yield, dry matter content, and quality characteristics).

3.Continue to select high quality potato clones carrying resistance traits for entry into national and/or regional trials and for cultivar registration.

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