Studies on Branch Wilt Disease (Nattrassia mangiferae Nattrass) of Citrus Species and other Hosts in Dalanj Locality, Southern Kordofan State

Abstract

The survey of branch wilt disease or sooty canker was conducted in 2008, 2009 and 2010 in the three locations (Dalanj city area, Eltokmaa and Elfarshaia) of Dalanj locality, South Kordofan State . The surveying concentrated on different hosts species; citrus (lime, sweet orange, grapefruit, mandarin and sour orange), other fruit trees (mangoes, guava, sugar apple, pawpaw, mulberry, cassava and date palm. The surveying extended to the forest trees (Mahogany, Eucalyptus microtheca, Acacia spp.( A. Senegal, A. seyal and A. mellifera), tabaldi, tamarind (Tamarindus indica), christe's thorn (sidir) araad (Abizza amaara) and sahab (Anogessus shemperi). Moreover, the survey included shade and ornamental trees as neem, Ficus spp. (F. nitida, F. benjamina and F. benghalensis), Cassia siamea and Thevitia sp.and Dodonea sp. . The symptoms of dieback, bark cracking and sloughing off, gum exudates on pockets at the base of infected branches of mangoes, euclayptus and sour orange, calus tissues, complete wilt of neem, mahogany and Eucalyptus and discoloration of phloem and xylem on mango were seen. Bark and phloem cracking and sloughing off and sooty layer of arthropores beneath were found to be he most characteristic symptoms of the branch wilt disease on citrus species and other hosts . The infection frequency was high on Balady lime (40.0%, 43% and 50.0%) in the three surveyed areas; Eltokmaa, Elfarashaia and Dalanj respectively. In Eltokmaa, grapefruit (50.0%) was more susceptible than lime (17.45%) in season 2010. Sweet orange was more resistant than Balady lime and grapefruit in three seasons in Eltokmaa. Mandarin and sour orange were least susceptible in Eltokmaa and Dalanj city area during the three seasons. The variations in infection rate between citrus species were attributed to poor cultural practices, water shortage stress during the summer and species resistance. Mulberry and pomegranates recorded higher rate of infection (33,5% and 50.88) in Dalanj city area and Eltokmaa respectively whereas there was no infection recorded on date palm and cassava . In ornamental trees, Ficus bengalensis (54%) and Cassia siamea(38%) were higher in infection during seasons 2008,2009 and 2010 ,whreas lower infection rate xiii were found on Ficus benjamina (2%) . In forest trees, araad(56.16) was higher and tabaldi(6.44) was lower in infection rate in three surveyed locations during three seasons . Isolation of the the fungus from infected plant parts collected from Dalanj city area and Eltokmaa were determined the isolates as Acacia, Orange, Orange DG, Orange VDG, Grapefruit and Mandarin. Nattrassia mangiferae was dominant pathogen in the samples collected. Other opportunistic fungi were found such as Penicillium sp., Aspergillus niger and Fusarium oxysporum. No significant difference between the isolates depending on dimensions (mycelium diameter and length of spores) measurements by computer program of SensCell and pathogencity test on Citrus spp. by twigs cutting technique. In artificial inoculation of N. mangiferae on citrus and other hosts proved symptoms of chlorosis and yellowing, dieback, leaf defoliation, gum exudates and sooty canker were typically similar to those occurred in natural infections. Chemical control of N. mangiferae In vitro the causal agent of branch wilt disease explained significant differences between the Collis, Tilt and Stroby on the linear growth on 3rd day. Tilt (93.44%) recorded higher inhibition of the fungus growth followed by Collis(73.95) and Stroby(93.5) while no significant difference between the concentrations of the applied fungicides. Biological control of N. mangiferae the causal agent of branch wilt In vitro showed significant difference in effect of Trichoderma viride, Bacillus subitilis, B. sp (1) and B. sp.(2) on three days linear growth of the fungus . Bacillus sp(2) (32.59%) recorded higher rate of inhibition while T. viride at the minimum rate. This work opened the way for further studies In vitro and In vivo that the host range of the causal fungus N. mangiferae is so wide, and this work requires great efforts for control of this disease.