Integrated Management of Phytophthora spp. in Tomato Crops: Etiology, Prevention, and Control

Etiopathogenesis and Early Diagnosis of Phytophthora in Solanum lycopersicum

Tomato production, a fundamental pillar in the gastronomy and agricultural economy of Argentina and the region, faces constant challenges. Among these, collar rot emerges as a significant threat, capable of seriously compromising yields and crop viability. This disease, primarily caused by species of the genus Phytophthora, affects the base of the plant stem, disrupting the transport of water and nutrients, leading to wilting and eventual death. Understanding its dynamics and applying advanced management strategies is essential to preserve the health of tomato plants and ensure abundant harvests.

The collar rot of tomato (Solanum lycopersicum) is a disease caused by oomycetes of the genus Phytophthora, with Phytophthora nicotianae (formerly known as Phytophthora parasitica) being one of the most prevalent species. This pathogen thrives in conditions of high soil moisture and warm temperatures, factors common in many producing regions. Initial symptoms include darkening and softening of the tissue at the base of the stem, just above or at soil level. As the disease progresses, the lesion expands, forming a necrotic ring that girdles the stem. Lower leaves may turn yellow and wilt, even before the plant completely collapses. Early identification of these signs is critical for implementing control measures before the infection spreads to other plants. The dissemination of Phytophthora zoospores occurs mainly through irrigation water, rainfall, and the movement of contaminated soil, underscoring the importance of cultural hygiene and water management.

Designing Drainage Systems and Substrates to Mitigate the Disease

Effective control of collar rot is based on preventive cultural practices that minimize conditions favorable to the pathogen. The selection of the planting site is crucial; cultivation in soils with a history of the disease or poor drainage should be avoided. Soil preparation involves incorporating organic matter to improve its structure and drainage capacity, a fundamental aspect in common clay soils in some areas. Crop rotation with non-host species (such as cereals or legumes) for at least three years interrupts the pathogen’s life cycle and reduces its presence in the soil. Adequate planting density ensures good air circulation between plants, reducing leaf humidity. An innovative aspect is the application of planting techniques on raised beds or mounds, a practice that improves drainage around the base of the stem, elevating it above the soil surface and reducing direct contact with stagnant water. Furthermore, the use of tomato varieties with some genetic resistance to Phytophthora represents a growing trend in sustainable agriculture, offering an intrinsic line of defense against the disease.

The management of collar rot benefits greatly from an integrated pest and disease management (IPM) approach. This involves combining cultural methods with biological options and, if necessary, chemical ones, always prioritizing solutions with the lowest environmental impact. Biological control has gained traction with the use of antagonistic microorganisms such as Trichoderma harzianum or Bacillus subtilis. These biological agents can be applied to the soil or seeds, colonizing the rhizosphere and competing with Phytophthora for nutrients and space, or even directly parasitizing the pathogen. Recent research has demonstrated the effectiveness of biofungicides based on plant extracts or compounds derived from microorganisms, offering alternatives to synthetic chemicals. In situations of high disease pressure or as part of a contingency plan, specific fungicides against oomycetes may be employed. However, their application must strictly follow technical and safety recommendations, integrating them into a rotation scheme to prevent the development of resistance in the pathogen. The implementation of drip irrigation systems is a key technological trend, as it minimizes water splashing onto the plant collar and optimizes the delivery of water and nutrients directly to the root zone, reducing surface moisture that favors the disease.

Integrated Management of Nutrition and Irrigation for Crop Resilience

The agricultural sector is undergoing a transformation driven by technology, and disease control is no exception. Precision agriculture, through the use of soil moisture sensors and weather stations, allows for the optimization of irrigation schedules and monitoring of environmental conditions that influence Phytophthora development. Remote monitoring platforms and drones equipped with multispectral cameras are being investigated for early detection of plant stress and identification of infection foci before they are visible to the naked eye. These advancements enable faster and more localized intervention, reducing input use. Genetic improvement techniques, including gene editing with CRISPR/Cas9, promise to develop tomato varieties with durable and multifactorial resistance to complex pathogens like Phytophthora, adapted to the challenges of climate change and the demands of more sustainable agriculture. The integration of this knowledge and these tools within a framework of permaculture and regenerative agriculture offers a holistic vision for tomato crop health, promoting biodiversity and the resilience of the agricultural ecosystem.

Effective management of tomato collar rot requires a proactive and multifaceted approach. From selecting resistant varieties and optimizing cultural practices to integrating biological controls and leveraging modern technology, each step contributes to crop resilience. Adopting these integrated strategies not only protects tomato production but also drives more sustainable, efficient, and environmentally friendly agriculture, ensuring the long-term viability of this valuable crop.