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NMSU researchers find natural immune stimulator for chile plants

Farming is a high-risk business. Crops are planted and a variety of things can impact the harvest, yield and ultimately the profit made by the farmer.


Man holding two petri dishes over his head.
NMSU College of Agricultural, Consumer and Environmental Sciences graduate student Esteban Molina looks at cultured growths of Phytophthora riparia being studied as a natural immune stimulator for chile plants. (NMSU photo by Jane Moorman)

Within New Mexico?s chile pepper industry, growers have many potential economic impact issues to face ranging from adverse weather and labor availability to pressure from plant diseases.

During the last 10 years, these issues have caused the acreage planted and harvested to decrease by 9,000 acres, thus reducing the value of production as much as $9 million, depending on the yield per acre and price per 100 pounds, according to the U.S. Department of Agriculture National Statistics Service.

New Mexico State University?s researchers are working with chile pepper growers to find solutions to the controllable issues, such as mechanical harvesting and integrated pest management methods.

?Plant diseases that cause economic impacts to chile production in the Southwest include Phytophthora blight, caused by the plant pathogen Phytophthora capsici; Verticillium wilt, caused by the fungus Verticillium dahlia; and beet curly top, caused by the beet curly top virus that is transmitted by the beet leafhopper,? said NMSU College of Agricultural, Consumer and Environmental Sciences graduate student Esteban Molina of Los Lunas.

Growers stay vigilant for these diseases in hopes of preventing total loss. However, in general, plant diseases caused by these pathogens are difficult to control chemically.

In addition, consumer concerns regarding the use of chemicals on edible produce are increasing, causing NMSU researchers to seek alternative ways to combat the diseases.

NMSU?s Department of Entomology, Plant Pathology and Weed Science researchers are striving to find integrated pest management methods to help chile pepper growers in their battle with the diseases.

?We are looking at biocontrol agents for controlling chile diseases,? Molina said.

Under the direction of research faculty Jennifer Randall and Rio Stamler, Molina is evaluating the effectiveness of a non-pathogenic Phytophthora species, P. riparia, to prevent diseases.

?Dr. Stamler discovered that P. riparia does not kill chile plants,? Molina said. ?Since it thrives in riparian environments on decayed biomass, especially cottonwood leaves, we have a readily available source.?

P. riparia was tested on chile and other crops planted in the Southwest to be sure that it did not cause disease in these plants.

Molina?s assignment as an undergraduate lab assistant was to cultivate the organism found in the Rio Grande watershed.

?I isolated the P. riparia by a technique called leaf baiting,? Molina said. ?Once lesions form on the leaf they are surface sterilized and plated on a specific media where we cultured the organism to inoculate the chile plants with a liquid culture.?

The first stage of the test was to see what effect P. capsici infection would have on the inoculated chile plants.

?We determined that P. riparia induces resistance to blight,? Molina said. ?Next we did a field study comparing treated plants to non-treated ones.?

Preliminary results from the field study conducted during the last two years indicate that the P. riparia treated chile exhibited fewer disease symptoms than non-treated plants.

?Induced resistance using P. riparia increased the fitness of the plants in the field but did not completely alleviate disease pressure,? Molina said. ?The riparia treated plants produced almost 10 percent more weight and yield.?

Molina is conducting further research with P. riparia this year.

?Since it did not completely alleviate the disease pressure, we?ve decided to combine the treatment with naturally occurring beneficial soil microbes to see if it will increase the fitness of chile plants when exposed to disease pressures in a greenhouse study and in a field trial,? he said. ?We also need to see if P. riparia can induce resistance to insect-transmitted beet curly top virus in a greenhouse study.?

Molina has planted the inoculated plants in a field study at the NMSU research plots in Las Cruces and at NMSU?s Agricultural Science Center at Los Lunas this summer.

?There is a lot we don?t know about this treatment,? Molina said. ?During my graduate studies, I will study how the chile plant reacts to the P. riparia so we can understand its mechanisms of protection.?

Molina?s goal is to help solve problems that impact farmers? profits.

?Hopefully our research will give the chile pepper growers one more tool in an integrated pest management approach to produce healthier and better yielding plants to help increase their profits,? he said.