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United States Department of Agriculture

Agricultural Research Service


Location: Vegetable and Forage Crops Production Research

2013 Annual Report

1a.Objectives (from AD-416):
Select potato germplasm resistant to two pathogens, a leafhopper vectored phytoplasma which causes purple top and an oomycete that incites late blight.

1b.Approach (from AD-416):
Tuber families will be sent to PICTIPAPA from various sources in the the US. These will be planted out in field plots in Metepec, Mexico under the supervision of Hector Lozoya Saldana. Obvservations on foliar damage due to Phytophthora infestans and Purple Top Phytoplasma will be recorded. At harvest, selection will be based on field notes and tuber yield and type. Tubers will be retained during the off-season and re-planted the following growing season. Documents SCA with Universidad Autonoma Chapingo.

3.Progress Report:

This is the final report for this project. This project relates directly to the parent project sub-objective 2B: "Develop and improve diagnostic procedures for insect transmitted viruses (potato virus Y [PVY] and potato leafroll virus [PLRV]) and phytoplasmas (purple top phtoplasma and aster yellow) in potatoes. Evaluate advanced poatato lines for resistance to diverse viruses." The most serious disease of potato (Solanum tuberosumL.) is "late blight" caused by Phytophthora infestans (Mont) de Bary. It develops most quickly at low temperatures and high humidity, as in the central highlands of Mexico. The disease can be controlled with fungicides. Host resistance however is the best solution to the disease. In the summer of 2011, under rainfed conditions, 82 clones from segregating potato families (Solanum tuberosum) from the USDA-ARS potato breeding programs at Idaho and Washington St., were evaluated for resistance to Phytophthora infestans (Pi) and Bactericera cockerelli (Bc), in the Agricultural Experimental Station, Autonomous University of Chapingo in Chapingo, México. Seven of which were promising, while from Washington St 18 clones were resistant, although with limited tuberization. Simultaneously, and with the aim of selecting Pi fungicide resistance variants, the susceptible cv Snowden was established in an experimental plot, spraying half the dosage of five products. A control with no fungicide was included. The Pi incidence in the foliage was evaluated and weekly isolates of theoomycete were collected. Although fungicides are effective against Pi, the use of phosphites is a recent alternative to stimulate the defense mechanisms in plants. The purpose of the present study was to determine the effect of potassium, calcium, magnesium, zinc and copper phosphites in the control of P. infestans in potato crops in the valley of Toluca, Mexico, by weekly foliar sprays of different phosphites to the susceptible variety Alpha under rainfed conditions and natural infection in the summer of 2009, with seven treatments and four replications under an completely randomized experimentaldesign with the following objectives. Objective 1: To quantify the total phenol synthesis by the plant and relate to both the degree of infection by P. infestans as treatments. There was no direct relationship between synthesis of total phenols with the degree of late blight infection and yield. Objective 2: Identify the phosphite which has greater control of the disease. Treatment with Codaphos® Zn y Codaphos® Cu were the most efficient phosphites in the control of late blight, but not more than the commercial treatment. Objective 3: Evaluate the tuber yield obtained by treatment, correlating with the production and infection. Conclusion: The commercial treatment was much higher, with statistically significant difference, compared to the rest of the treatments on tuber yield. Among the phosphites, zinc, copper and magnesium were the best, no significant differences between them. Objective 4:Analyze the cost / benefit to determine whether or not the use of treatments. The phosphites of Zn and Cu were the best options in terms of cost / benefit.

Last Modified: 4/18/2014
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