CategoryHealth & Medicine
WELCoME Presentation on Guava Wilt and Cotton Wilt Presented byBipin KarkBijendra pradhanBivek GyawaliDorna Giri
Wilt is a pernicious disease of guava in India.In India the disease was first recorded near Allahabad in 1935 . The infection was reported 15 -30 %. The disease is a serious threat to guava cultivation in U.P. In West Bengal it reduces the yield in affected orchard by 80% .The disease is also prevalent in Haryana Rajasthan , A.P , Punjab and M.P.It has forced uprooting of about 150 acre of guava orchard in Panjab and 300 acres in Haryana during 1971-81.
OCCURENCE AND IMPORTANCE
The exact cause of the disease is still not fully understood but the pathogens viz. Fusarium oxysporum f. sp. psidii (Prasad, Mehta & Lal), Rhizoctonia bataticola Marcrophomina phaseoli and various pathogens are reported by different workers may be the incitant of the disease.
Survival and spread: Through movement of plants containing sick soil in virgin areas. Short distance spread is by water. Root injury predisposes wilt disease.
Favourable conditions High rainfall during August/ September. Stagnation of water in guava field for long duration. Maximum and minimum temperature ranges 23-32 C with 76% RH are conducive. Lack of timely application of suitable control measures. There is severe incidence of wilt in alkaline soils at pH ranging from 7.5 to 9.0 or in lateritic soils at pH 6.5 . Guava seedlings are more susceptible to F. solani as well as F. oxysporum f.sp. psidii than older plants of 3 years age. On the other hand researchers reported that F. solani could infect guava plants from 1-month-old to more than 4 years old.
SYMPTOMSThe leaves shed of premature , fruit size remain smaller, bare twig fail to develop new leaves and flower dry up. Browning and wilting of leaves from tip.Discolouration of stem and death of branches and then the whole tree dry up. The inner part of stem and root upto cambium and vascular tissues show a distinct discolouration.
Proper sanitation.Soil solarization. Uprooted and burnt wilted plants. Severe pruning followed by a drench with .2 % Benlate or Bavistine 4 times in a year. Injection guava plant with 0.1 % water soluble 8- quinolinol sulphate may provide protection against wilt for at least 1 year. Use of resistant and tolerant varieties like , Allahabad Safeda , Dholka , Sindh etc.MANAGEMENT
Wilt of cotton(Fusarium wilt)Importance and occurenceFound in all cotton growing areas.Believed to be started from Mexico or central America.Disease more prevalent in black cotton soil which are heavy clay with an alkaline reaction.
ETIOLOGY AND SYMPTOMSFusarium oxysporum f.sp. VasinfectumThe earliest symptoms appear on the seedlings in the cotyledons which turn yellow and then brown.The earliest symptoms appear on the seedlings in the cotyledons which turn yellow and then brown.In young and grown up plants, the first symptom is yellowing of edges of leaves and area around the veins, i.e. Discolouration starts from the margin and spreads towards the midrib.
Owning or blackening of vascular tissues is the other important symptom, black streaks or stripes may be seen extending upwards to the branches and downwards to lateral roots.In severe cases, discolouration may extend throughout the plant. In transverse section, discoloured ring is seen in the woody tissues of stem.
Fig:- Marginal chlorosis and necrosis
Fig:- Browning of vascular bundles
DISEASE CYCLEThe fungus can survive in soil as saprophyte for many years and chlamydospores act as resting spores. The pathogen is both externally and internally seed-borne. The primary infection is mainly from dormant hyphae and chlamydospores in the soil. The secondary spread is through conidia and chlamydospores which are disseminated by irrigation water.
EPIDEMIOLOGY Soil temperature of 20-30 0C, hot and dry periods followed by rains.Heavy black soils with an alkaline reaction, increased doses of nitrogen and phosphatic fertilizers, soil amendment with manganese and wounds caused by nematode (Meloidogyne incognita) and grubs of Ashweevil (Myllocerus pustulatus).
MANAGEMENTTreat the acid-delinted seeds with Carboxin or Chlorothalonil at 4 g/kg or Carbendazim@2g/kg seed. Remove and burn the infected plant debris in the soil after deep summer ploughing. Apply increased doses of potash with a balanced dose of nitrogenous and phosphatic fertilizers. Apply heavy doses of farm yard manure or other organic manures at 10 t/ha. Follow mixed cropping with non-host plants. Grow disease resistant varieties of G. hirsutum and G. barbadense like Varalakshmi, Vijaya, Pratap,Jayadhar, Jarila, Jyothi, G 22 and Verum, HD 324, HD 432.