Screen house and field resistance of taro cultivars to taro leaf blight disease (Phytophtora colocasiae)

Introduction: Taro leaf blight disease cause by Phytophtora colocasiae has become an economic disease in Cocoyam growing regions of Cameroon. Aims: To screen for resistance 10 improved and 4 local cultivars of taro against taro leaf blight disease. Study Design: A randomized complete block design study. Place of Study: Studies were conducted at the International Institute of Tropical Agriculture (IITA) Yaounde Nkolbisson from July 2013 to January 2014. Methodology: Taro cultivars from tissue culture were planted in the screen house conditions and Original Research Article Charles et al.; BBJ, 15(1): 1-15, 2016; Article no.BBJ.14317 2 tested for virulence and pathogenicity with 4 isolates of Phythophthora colocasiae at spore density of 3×10 4 spores /ml of distilled water. Plants were planted in the field to assess disease incidence and severity. Results: The results obtained on the different taro cultivars, revealed that all the 4 isolates showed variable pathogenicity. They caused lesions on inoculated leaves. There was variability in pathogenicity based on the small lesion lengths produced on cultivars, these included BL/SM132 and Red petiole. Isolate 3 showed a stronger sensitivity to leaf collapse and defoliation irrespective of the cultivar tested. There was a significant difference (p = 0.05) in tissue collapse and leaf defoliation on exposure to the different fungal isolates. The result of field infection rates of P. colocasiae at 126 DAP-154 DAP on 10 improved and 4 local cultivars indicated that there was significant variability (p = 0.05) in incidence and disease severity, with high incidence and severity occurring at 154 DAP in all cultivars. Improved cultivar BL/SM132 showed no classic symptoms of P. colocasiae and therefore it was resistant to Phytophthora colocasiae. Conclusion: The results obtained on virulence and pathogenicity of Phythophthora colocasiae on the different taro cultivars revealed that all the 4 isolates showed variable pathogenicity. They caused lesions, on inoculated leaves. Isolate 3 showed a stronger sensitivity to leaf collapse and defoliation irrespective of the cultivar tested. The result of field infection rates of P. colocasiae at 126 DAP-154 DAP on 10 improved and 4 local cultivars indicated that there was a significant variability (p = 0.05) in disease incidence and severity, with high incidence and severity occurring at 154 DAP in all cultivars. Improved cultivar BL/SM132 showed no classic symptoms of P. colocasiae and therefore it was resistant to Phytophthora colocasiae as compared to all the other cultivars which showed high severity rates of infection of the disease and thus were susceptible to the disease.