The importance of pathogens in plant propagation materials and in soil

By José Otávio Menten, agricultural engineer, senior professor at USP/ESALQ and president of CCAS

25.11.2022 | 10:50 (UTC -3)

Cultivated plants are subject to diseases caused by fungi, bacteria, viruses and nematodes. For diseases to occur and cause damage, causal agents (pathogens) must establish themselves in susceptible hosts (plants) and the environment (mainly relative humidity, free water on the surface of plants and temperature) must be favorable.

All parts of plants are subject to being colonized by pathogens (roots, stems, leaves and fruits). These diseases can occur at all phenological stages of crops (sowing, germination, emergence, vegetative and reproductive phases and harvest). For the disease to become established in the plant, the pathogen must survive between crops or seasons. Among the main means of survival for pathogens are propagation materials and their activities or “dormancy” in the soil.

The use of propagation materials (seeds, seedlings, tubers, setts, rhizomes, etc.) free of pathogens or adequately treated and planting in areas free of pathogens in the soil are important integrated disease management measures. One of the disease management measures is the treatment of propagation materials, with chemical or biological products, but also by heat treatment. Treatment can be carried out on an industrial scale or on rural properties (“on farm”). Chemical and biological treatments can control pathogens present in propagation materials or in the soil.

Recent work, “Quantification of losses” published in Revista Cultivar – Grandes Culturas (n. 282, November 2022), pages 08 to 14, authored by J.O. Menten, J. C. Machado and C. S. Siqueira, showed that every 1% incidence of Pathogens in soybean seeds cause a 1 to 2% reduction in productivity (yield).

One of the reasons for losses caused by seed-associated pathogens is stand reduction, which can be caused by both seed-associated pathogens and species of Colletotrichum, Phomopsis, Stenocarpella etc. as well as soil-infesting pathogens, such as Pythium, Phytophthora etc. There are pathogens, such as species of Rhizoctonia, Macrophomina, sclerotinia e Fusarium, which can be present both in propagation materials and in the soil.

As seeds and seedlings are agricultural inputs, subject to regulation, it is important that they are subjected to adequate health tests, which inform the species detected and incidence/severity. It is important that health standards are established, which define the maximum tolerance of each pathogen in each propagation material. To achieve this, there is a need for quality research and experimentation, in addition to teaching and training, which are essential for the adequate training of competent professionals.

By José Otávio Menten, agricultural engineer, senior professor at USP/ESALQ and president of CCAS

Mosaic Biosciences March 2024