Development of bunchy top virus-resistant bananas through mutation

Banana is one of the most important fruit crops in the Philippines both for domestic and export markets. At present, the industry is beset with low productivity due to banana bunchy top virus (BBTV). Yield reduction is a result of stunting, leaf malformation, and ultimately death of infected plants. Rapid propagation of disease-free planting materials is a viable disease management option but its effectivity is limited where residual inoculum sources are present. Banana cultivars are not appropriate for sexual breeding because both male and female are sterile. Thus, BBTV resistance cannot be incorporated into the banana by conventional breeding method. The use of mutation technique through gamma irradiation is a viable breeding option to improve disease resistance. Mutation in tissue-cultured banana plantlets was caried out with cobalt 60 gamma irradiation. The availability of tissue culture and regeneration procedures for banana facilitated induction, selection, and multiplication of mutants. Damasco et al (UPLBCA-IPB) developed BBTV-resistant banana cultivars using mutation. This study was done from June 1999 to May 2005. The shoot proliferation rate in banana cv 'Lakatan' was significantly affected by varying dosage of radiation. Irradiation at 5Gy exhibited higher shoot proliferation rate and the LD50 dose for bulk mutation induction in cv 'Lakatan' was established at 20-25 Gy. A total of 7,366 regenerated plants was screened for BBTV resistance using artificial inoculation by the aphid vector, Pentalonia negronervosa. Of the total, 29 lines were found highly resistant to the virus as there were no symptoms expressed. From the potentially resistant lines, significant variations in plant height were observed as well as production of bigger and heavier fruits. Suckers from the potentially resistant lines were micropropagated and will be evaluated in the field for three cycles to determine the stability of the resistant gene.