Phytophthora blight, caused by Phytophthora capsici, is a major plant disease that affects many crop species worldwide, including chile peppers in New Mexico.

Farmers' observations suggest that the organism causes less damage in hotter peppers than in low-heat varieties.

A research team from New Mexico State University's Chile Pepper Institute in Las Cruces set out to prove or disprove the anecdotal reports. They published their work in a recent edition of HortScience.

The most effective way to control Phytophthora blight is to plant resistant cultivars. Although breeders have identified some lines, there are no cultivars that can withstand the disease under all environments.

Chile pepper fruit becomes infected during prolonged periods of heavy rain and high humidity in flooded and poorly drained fields.

Based on documented field observations in New Mexico, Arizona and South Carolina, the researchers—led by plant pathologist Soumaila Sanogo—found no relationship between heat levels and Phytophthora blight resistance.

While the disease was slowest to develop on the roots of jalapeño variety, for example, it was quickest to develop on the fruit of the same plant.

Conversely, the disease was faster to develop on roots and slower on fruit of all other cultivars.

As the root of the plant contains no heat-inducing agents but the fruit does, the slow development on the root and rapid development on the fruit of the jalapeño indicates that heat level is not a factor.

The results of this study indicate that factors other than heat level may be involved in fruit response to Phytophthora capsici.

Genetic differences and cuticle thickness of the plants and fruits are among other issues that could be relevant, but further study is needed, the researchers say.

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