Soil Borne Disease Of Plant Crops
Fungi species live saprophytically on dead organic matter on or in soil (biosphere) where they are regarded as that most important decomposers of plant residues and other organic ‘matter. Many fungi species produce the enzyme needed to degrade the lignin and cellulose in plant residues and so initiate the decomposition of these complex compounds. The disease that are caused by fungi pathogens which persist (Survive) in he soil matrix and in residues on the soil surface are defined as soil borne disease. Thus the soil is a reservoir of innoculum of these pathogens” which are distributed in agricultural soils causing damages to the roots and crown tissue which may not be noticed because they occur in the soil ‘until foliar or plant are affected showing symptoms such as stunting. wilting, chlororsis and death. These disease are difficult to control because they are cause by pathogens which can survive for long periods in the absence of the normal crop host, e.g. chlamdospores (a thick wall spore), a resistant spore Other means, of survival are: resting bodies called sclerotia, which consist of aggregations of Hyphal cells into dense, rounded or irregular structures. Fruiting structures called perithecia which release spores when conditions become favorable for sore germination and growth.
When soil borne plant pathogens attack roots and stems, they disrupt the uptake and transiocation of water and nutrients from the soil; therefore, they cause similar symptoms to drought and symptom
deficiencies such as wilting, yellowing, stunting,
and plant death.
Diseases of Soil-Borne Plant Pathogen And
Root, stem, and head rot characterized by a decay of the true toot system and are caused by pythium and phytophthora, Rhizoctonia,
cylindrocladium and amillaria spp
showing symptoms such as wilting, leaf death
and fall, death of branches and limbs and in
severe cases causes death of the whole plant.
Wilt disease caused, by fusarium oxysporum
and verticillirtm spp. Symptoms includes
wilting of the foliage and internal necrosis of the vascular tissue in the stem of the plant.
Seeding blights and damping -off diseases caused by pythium spp. They infect the seedling during the germination pre-emergence or post-emergence phase of seedling establishment.
In seldom encountered in fresh bunched vegetables. Spores from dead and dying plants contaminate the root at harvest. Most of the infections occur at the crown where the tissues are injured by hopping or through wounds on the sides of the roots. The decay is light brown and water soaked at first. Later it is somewhat spongy and darker brown. Affected areas usually have a fine white surface mold, which becomes grayish brown as the spores are formed. Once infection has occurred, the decay will continue to progress in cold storage at 32, but the rate of decay will be retarded. Root crops suspected of having gray mold infection should be inspected periodically in storage.
Late blight disease: Late blight disease of tomatoes and potatoes is serious when moist. moderately cool weather prevails for some time during the growing season. It sometime destroys a large part of the potato and tomato crops through out the worid. The causal fungus, phytophthora infect ants seem always to be waiting for a favorable weather conditions to start an epidemic. Besides being, a serious field disease, it causes great loss in potatoes is a total; loss by the time they reach the market or their final destination.
The disease originates each season from infected tubers used for seed from seed from volunteer plants that develop from diseased tubers left in the field, or from plants growing on cull piles that have been alowed to remain in or near the leld. The amount of late blight infection can be reduced greatly by carefuly disposing of the cull potatoes or by killing the sprouts from cull potatoes by burning or weed killing chemicals.
Late blight may be satisfactorily controlled in most season by the use of thorough spray programs, but sometimes the weather is so favorable for development of the disease that satisfactory control cannot be obtained. When the potato plants are infected, a marked degree of Control of tuber rot can be had by killing the plants with chemicals or by other means a week or 2 before the potatoes is influenced greatly by the storage temperatures.