Multi-barrier Management Strategies of Phytophthora Blight in Peppers and Cucurbits

Vegetable phytophthora blight

Dr. Soum Sanogo visits a local vegetable farm affected by Phytophthora blight. His guest Vince Hernandez, a local company agronomist, addresses the economic effects the disease has on vegetable growers.

Soilborne disease research laboratory

Dr. Soum Sanogo discusses Phytophthora blight research conducted at the Soilborne Disease Research Laboratory at the Entomology, Plant Pathology, and Weed Science Department at NMSU.

Phytophthora: A life cycle

This simulation of the life cycle of the fungi-like organism Phytophthora explains the mechanism behind Phytophthora blight. Diseased crops due to Phytophthora can be devastating to chile producers in the Southwest US.

The USDA has identified vegetable crops as challenged specialty crops. Peppers and cucurbits are important cash crops with an annual farm gate value of over $2 billion in the United States. The profitable and sustainable production of peppers and cucurbits is severely impacted by a destructive soilborne disease, Phytophthora blight, caused by the pathogen Phytophthora capsici. Symptoms of Phytophthora blight include root rot, crown rot, leaf and stem lesions, fruit rot, and complete plant blight, resulting in significant yield loss. This disease inflicts up to 100% crop losses in favorable environmental conditions if left uncontrolled. In addition to damage in the field, fruits that do not show symptoms when harvested may rot in storage and transit. First reported on chile pepper (Capsicum spp.) in New Mexico in 1922, Phytophthora blight has become extremely damaging on peppers and cucurbits in most of the growing areas in the US, especially in the Southeast, Southwest, Mid-Atlantic, and Midwest regions. The disease has also been reported in several countries outside the US. For more information on this disease, see the publication: “Phytophthora capsici, 100 years later: research mile markers from 1922 to 2022.”

Image showing infected stem and branches from phytophtora

The success of Phytophthora capsici as a plant pathogen

Phytophthora capsici is a pathogen that causes severe damage to several vegetable crops. The success of the pathogen is due to the fact it possesses a powerful toolbox, which contains many structures that allow it to survive, grow, spread, and reproduce.

How does Phytophthora capsici use its toolbox to inflict damage to crops?

Phytophthora capsici has several structures for surviving in soil. These surviving structures allow the pathogen to grow.

As the pathogen grows, it produces many other structures such as sporangia, small balloons filled with swimming cells called zoospores.

The sporangia and zoospores can move through flowing water, and through splashing rain and irrigation water. Zoospores can actively move because of flagella that allow them to propel through water.

Once the zoospores reach the roots, stems, leaves, or fruit, they germinate, penetrate, and colonize these plant parts and cause tissue damage leading to rotting and ultimately plant wilting and death.

The infected plants become the source of new structures of the pathogen leading to the start of a new cycle of infection.

Management of Phytophthora capsici

Extensive research has been conducted over the last 100 years to determine the effects of i) environmental variables including soil factors, ii) irrigation, iii) host plant resistance, and iv) fungicide application on the biology and management of P. capsici.

This pathogen remains a serious risk in the production of many crops. Combinations of strategies are critical for effectively managing Phytophthora blight. For more information on this disease, see the publication: “Phytophthora capsici, 100 years later: research mile markers from 1922 to 2022.”

Perspectives on management research for Phytophthora blight

A new paradigm for managing Phytophthora capsici
- We are proposing a system-thinking approach focused on reducing the risk of Phytophthora in crops, with a new philosophy of disease management . This philosophy focuses on managing the production environment to increase crop performance. In any production environment, plants are exposed to signals from biotic and abiotic stimulants and to signals from biotic and abiotic stressors. Producers must manage these signals through inputs to lessen the impact of stressors and amplify the effect of stimulants.
Phytophthora Management Risk Index (PMRI)
- Within the context of the philosophy of disease management outlined above, we envision the development of a Phytophthora Management Risk Index (PMRI) based on integrating the risk across five risk components, which include Phytophthora Inoculum Level, Moisture, Host Resistance, Fungicide Resistance, and Soil Health. This practical concept provides an assessment of the risk of Phytophthora blight in any system and can be used to guide the incorporation of strategies to minimize disease risk in crops and increase crop performance and yield.
- We are proposing several innovative components to be used in the development of a multibarrier management approach to significantly reduce PMRI and increase yield and profits. The PMRI-guided system is built on four management toolbox components: moisture, host resistance, fungicide resistance, and soil health.
- For the moisture management toolbox, we are proposing the development of drought-tolerant and flood-tolerant genotypes to enable production of vegetables under conditions unfavorable (drought) and favorable (flooding) to the development of Phytophthora blight. For the host resistance management toolbox, we are proposing the development of genotypes resistant or tolerant to P. capsici. For the fungicide resistance management toolbox, we are proposing alternations of fungicides and biofungicides to remedy fungicide resistance problems. For the soil health toolbox, we are proposing strategies to increase beneficial soil microbiome.
Impact
- The Phytophthora Management Risk Index (PMRI) will provide an assessment of the risk of Phytophthora blight in any system and can be used to guide the incorporation of strategies to minimize disease risk in crops.

Overview flowchart of phytohthora toolbox which includes groth, dispersal, reproduction, and survival

New Mexico State University
Multi-barrier Management Strategies of Phytophthora Blight