Soils contain diverse communities of microscopic organisms that are capable of damaging plants. A detrimental interaction between a soil organism and plant is often highly specific. The soil organisms that have the potential to be plant pathogens include fungi, bacteria, viruses, nematodes and protozoa. Some pathogens of the above ground parts of plants (leaves, stems) survive in the soil at various stages in their life cycles.
Therefore, a soil phase of a plant pathogen may be important, even if the organism does not infect roots. Three important factors needed for affecting soil borne diseases. A.pathogen (the microorganism that causes the disease. B. A host (our plants). C.The right environmental conditions.
In the case of soilborne diseases, the pathogens can remain in the soil for long periods, waiting for the host - our plants - to come along. The environmental conditions can vary widely. Some pathogens favor damp conditions, some like certain soil pH levels and others target tender, succulent growth.
Types of Soilborne Pathogens:
Fungi: The pathogens infect the plant's roots and block the uptake and flow of water and nutrients through the plant. Symptoms may include wilting, yellowing, stunting, dieback and eventual death and can be confused with other problems such as drought and nutrient deficiencies Common pathogens to watch out for include: Phytophthora, Rhizoctonia, Fusarium, Pythium, Verticillium, Macrophomina, Sclerotinia and Sclerotium.
Bacteria - less common pathogens and most don't stick around long. Some examples: Erwinia (soft rot), Rhizomonas (corky root of lettuce) Streptomyces (potato scab, soft rot of sweet potatoes) and Agrobacterium (Crown gall).
Viruses - rare, thankfully, and most require living plant tissue to survive, but they can also hitch a ride on fungi or nematodes and flow in on water. When a virus enters a plant cell, it can cause the cell to produce more virus cells. Lettuce necrotic stunt virus affects Romaine lettuce plants, causing stunting and yellowing and sometimes spotting of lower leaves, while newer leaves remain green and thick.
Seed Selection and Storage: Planting pathogen-free and high-quality vegetable seed is a critical first step in managing diseases. This is a broad category of treatments that includes hot water, biological and plant extracts, bleach disinfection, and biological (microbes). These treatments can improve seed and seedling health by eradicating seed borne pathogens from the seed or protecting germinating seeds from attack by soil borne pathogens.
Seed treatment Seedling treatment
The resistant varieties should always be used in combination with other management practices for a complete management program. Scions onto compatible disease-resistant rootstocks have become a means to raise popular varieties susceptible to certain diseases in fields infested with those pathogens. Grafting can be used to manage soil borne diseases such as bacterial wilt and root knot nematode of solanaceous vegetables and fusarium wilt of cucurbits. The causal agents of crop problems are necessary to select appropriate resistant varieties.
The organic matter such as cover crop green manure (single and mixed species), seed meals, dried plant material, good quality compost, organic waste, and peats can aid in reducing diseases caused by soil borne pathogens. cropping during the transition periods can enhance soil suppressiveness to damping-off caused by Pythium and Phytophthora; in addition, although compost amendments applied during transition can improve crop vigor by significantly enhancing soil fertility, their effects on soilborne diseases are not predictable when transitioning to certified organic production. Soil drenching with Neem cake 150 kg/ha mixed with soil and apply on and around the roots of the plant. It has antifungal properties and highly suitable for application in Greenhouses.
Biological disease control is an attractive alternative strategy for the control of soil borne diseases. Interactions between antagonists and pathogens may allow us to select and construct the more effective biocontrol agents and to manipulate the soil environment to create a conducive condition for successful biocontrol.Soil application of biocontrol agent like fungal antagonist Trichoderma, bacterial antagonist Pseudomonas and Bacillus2.5 kg /ha mixed with 50 kg of FYM or sand for soil application at 30 DAS and 60 DAS interval for after sowing.
Karmelreetha, A1 and Jeevika, K2
1&2 Assistant professors, Dept. Plant Pathology and Soil science
Vanavarayar Institute of Agriculture, pollachi, Tamil Nadu