In vitro germination of cupuassu [Theobroma grandiflorum (Willdenow ex Sprengel) Schumann]

Abstract

Five stages of the cupuassu flower anthesis were characterized viewing the development of a technique to test the in vitro germination of the pollen grain as well as to determine its longevity and which the best stage to collect fresh pollen grain to be used in controlled pollination. It was verified that the sample size in order to count pollen grains does not need to be larger than 300 grains. Pollen grains originated from stamens in the same flower did not show uniform germination. The anthesis stage E (which took place around two hours after anthesis onset, when the flower was completely open) was that in which the largest number of viable pollen grains was found. The conservation of the pollen grain in the flower, under environmental conditions, allows the highest germination for 3 hours after the flower is separated from the plant. Under this condition, germination is maintained for 72 hours, although total germination after this period drops to very low values, around 5%. Several liquid and solid germination substrata containing glucose, sucrose, galactose, and lactose in different concentrations, with or without boric acid, were tested and the best one was found to be that containing 5% of lactose, boric acid at 0.0%, agar at % at a pH of 6., under temperatures between 29 and 30 °C, this combination being the one in which the pollen tube showed the best development. The counting of the erminated pollen grains must take place within two hours after ermination initiation. Under the temperatures of 29 – 30 ºC the pollen tube grows too rapidly making difficult the counting.Additional keywords: artificial pollination; pollen viability.