Studies on mango branch wilt disease caused by neofusicoccum mangiferae  [2009]

El-Trafi, M.A. Sudan Academy of Sciences, Khartoum (Sudan) [Corporate Author]

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Diagnostic surveys were carried out in Gezira on Mango orchards to determine incidence of branch wilt at two geographically different locations, (Elbagair and Wad Medani). The disease infected 70% of the mango trees in individual orchards in Elbagair area, while incidence of the disease ranged from 10 to as high as 100% in Wad Medani area. Samples were collected from different infected trees from both locations. A fungus with characteristics of Neofusicoccum mangiferae was isolated from diseased mango tissues on PDA, pure cultures of each According to cross infection experiment it was evident that there were different isolates of N mangiferae from the different tree species (Saraca indica, Albizia lebbek, Eucalyptus camaldulensis and Azadirachta indica). Failure to infect tree species with isolates from other hosts, suggests presence of more than one strain of N mangiferea. Isolates evaluated were able to produce symptoms on their original hosts, but not always in others, only mango isolate consistently produced symptoms when inoculated into all other hosts. The tree species under investigation responded differently to Neofusicocum infection. In mangiferae indica, Saraca indica and Albizia Lebbek, the symptoms appeared 12, 12, and 14 days after inoculation, respectively. However, in E. camldulensis and A. indica the infection was slower and appeared 51 and 78 days after inoculation respectively. Tricoderma harzianum was screened for antagonistic potential
against N mangiferae as the predominant species of Tricoderma regularly isolated from soil in Sudan. T harzianum significantly inhibited growth and colony diameter of N. mangiferea whereas the control plates were completely covered with N mangiferea 9 days after incubation, inhibition rate was 50.4, 83.2 and 71.1 % at 25, 30 and 35°C respectively. The optimum temperature for growth of T harzianum and N. mangifera was 30 and 35°C respectively. However, growth of both fungi ceased completely at 40°C. Tebuconazole (Raxil) and Metalaxyl (Apron) were used to evaluate their efficacy to inhibit in-vitro growth of N. mangiferae, Tebuconazole was highly effective and superior to the other systemic-fungicide. Tebuconzole at all concentrations tested (1000, 800, 500, 200, 100, and 50 ppm) inhibited the invitro growth of N. mangiferae isolated from mango, the inhibition was 34, 24, 22, 14, 6% and zero in 1000, 800, 500, 00, 100 and 50-ppm concentrations respectively. The fungicide Metalaxyl was less effective than Tebuconazole and inhibited growth of N. mangiferae by 14, 5, 6, zero, at 1000, 800, 500, and 200 ppm concentration respectively. The in vivo activity of the systemic fungicide Tebuconazole (Raxil) was compared with the biological fungus Trichoderma harzianum (Biocont) in a naturally infected Mango orchard in Wad Medani area. The treatments were applied twice in the season at an interval of 4 weeks between them; however they were either applied to the soil only or in combination with spraying. All mango trees received 1.5 kg urea and 1.5 kg of chicken manure 3 days before treatments application. Tebuconazole resulted in 96% disease control when applied only to the soil compared to 100% recovery when combined with Tebuconazole spray at 15 gram \\tree 10 months later. In this respect the fungicide application increased the branch number of treated mango trees by 166% at the end of the test period (10 months). T harzaium when either added to the soil at 20 g or combined with a foliar spray at 20 g per tree was less effective than Tebunconzole, but significantly reduced the % infection to 13-21 % compared to 95% in the control treatments. The increase in branch number due to T harzianum soil treatments accounted for 43% compared with 157% when it is combined with a single spray with the bioagent. Addition of urea to infected trees that received no chemical or bioagent treatment resulted in only 5% increase of branches number. In addition, disease severity was significantly reduced by all treatments

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