What are soil- borne diseases of crop plant
Answers
Answer:
Air borne diseases. These crop diseases are transmitted by the air, e.g., 'rust of wheat' , "blast of rice" , etc. Air-borne diseases attack all aerial parts of the plants, e.g., leaf, flower, and fruits. Water borne diseases.
Soilborne diseases can be a major limitation to crop production, particularly for vegetables. They are often difficult to control, even with conventional strategies. Fungal, plasmodiophorid, oomycete, and bacterial pathogens, as well as viruses and plant parasitic nematodes, may all cause soilborne diseases. Important soilborne fungal pathogens are species of Fusarium (Fig. 1), Rhizoctonia (Fig. 2), Verticillium, and Sclerotinia (Figs. 3–5). Important Phytomyxea (plasmodiophorids) pathogens are species of Plasmodiophora (Fig. 6) and Spongospora. Important oomycete pathogens include Phytophthora (Figs. 7 and 8) and Pythium (Fig. 9). Many soilborne fungi persist in soil for long periods because they produce resistant survival structures such as melanized hyphae, chlamydospores, oospores, and sclerotia. Important soilborne bacterial pathogens are Ralstonia (Fig. 10), Pectobacterium, Agrobacterium, and Streptomyces. Pathogens in the Pseudomonas and Xanthomonas groups usually persist in the soil for only a short time. Soilborne viruses that affect vegetables are few in number and generally survive only in the living tissues of the host plant or in the nematode or fungal vectors that transmit them. An exception is the Tombusvirus group, in which the viruses can survive in the soil without being inside a host plant or vector. Soilborne plant parasitic nematodes affect vegetables by reducing plant vigor and growth. Important plant parasitic nematodes are root knot and cyst nematodes.
Soilborne pathogens often survive for long periods on host plant debris, soil organic matter, or as free-living organisms. Each vegetable crop may be susceptible to several pathogens. Many soil factors including soil type, texture, pH, moisture, temperature, nutrient levels, and ecology affect the activity of soilborne pathogens.