Control of lethal browning of tissue culture plantlets of Cavendish banana cv. Formosana with ascorbic acid

Cavendish banana cv. Formosana is a high yielding commercial cultivar resistant to race 4 of Fusarium oxysporum f. sp. cubense. Mass micropropagation of this cultivar has a serious problem of high mortality due to lethal browning of plantlets. The mineral contents in leaves and corms of diseased and healthy plantlets were similar. Amendment of culture medium with anion exchange resins, cation exchange resins, polyvinylpyrrolidone or activated charcoal did not reduce the disease incidence. However, addition of ascorbic acid to the surface of culture medium not only prevented the development of lethal browning but also greatly increased the number of plantlets produced. Even at 0.005% ascorbic acid was able to reduce the disease incidence by more than 60% and caused over 8-fold increase in number of plantlets produced. When cultures raised from 12 different Formosana corms were tested, ascorbic acid was able to reduce disease incidence by an average of 83%, and increase the number of plantlets in each test. When diseased plantlets were transferred to culture medium with ascorbic acid, all of them recovered, and resumed normal growth and multiplication, while all control plantlets on culture medium without ascorbic acid died after one month.