Tomato; WILT

Tomato: Lycopersicon esculentum Mill. Family: Solanaceae     1. WILT The wilt is one of the serious diseases of tomato reported from several countries of the world including India. The disease has been reported from every state of India where crop is growing. The disease is very severe in the tomato crop where this is repeatedly grown year after year in the same fields. Symptoms: The first symptom of the disease is appearing as clearing of the veinlets and leaf chlorosis. As the disease advanced, the petiole and leaves are droop and wilt. The entire plant may wilt and die in few days. If the roots and stem cut transversely, a dark brown or black discolouration of the vascular tissues may be seen. Causal Organism: The wilt of tomato is causing by Fusarium oxysporum f. lycopersici (Sacc.) Snyder and Hansen. The fungal pathogen produce both inter and intra-cellular mycelium which produced macro- and micro-conidia. The mycelium is delicate, peach coloured, sparse or abundant then floccose becoming felted and sometimes winkled in older cultures. Microconidia: borne on simple phialides arising laterally on the hyphae or from the short sparsely branched conidiophores, abundant, variable, oval to ellipsoid and straight to curved, 5 – 11 x 2.4 - 3.5 µm. Macroconidia: borne on more elaborately branched conidiophores or on the surface of sporodochia, thin walled, 3 – 5 septate, fusoid- subulate and pointed at the both ends, hooked apex and a pedicillate base; 3 septate, 33 – 41  x  3 – 5 µm; 5 septate,  37 – 58 x 3 – 5 µm. 3 septate conidia were more abundant. Chlamydospores: smooth, abundant, terminal and intercalary, solitary or occasionally in pairs. Disease Cycle: The fungal pathogen is present in many soils as saprophyte. The pathogen infects host plants if grown in infested soils. The pathogen attacks root, rootlets and spread upwards in the host vascular tissues. The pathogen multiplies rapidly within the vascular tissues and clogs them which interferes the upward movement of solutes and nutrients, resulting in wilting of host plants. The pathogen also produced toxins (fusaric acid and lycomarasmin) inside the host tissues that may play a vital role in disease development. Disease Management: The pathogen is soil borne and persists saprophytically for many years. Thus, the disease control is very difficult. The cultivation of resistant varieties is the only effective method for disease control.