Standardization of different media for in vitro pollen germination of almond and evaluation of the germination capacity of stored pollen
Almond is an important nut crop which, mostly for fruit set, needs the pollination of flowers followed by fertilization. Therefore, pollen viability and its germination capability are essential. To optimize the pollen culture medium of almond and standardization of the best medium, the present study was carried out with 48 different culture media containing different compositions, including diverse levels of boric acid (0 and 100 mg/L), calcium nitrate (0, 150 and 300 mg/l), magnesium sulphate (0 and 200 mg/l), potassium nitrate (0 and 100 mg/l), sucrose (10 and 15%) and agar (1%). Following the optimization of the best medium, pollen grains of three almond cultivars were cultured in the same optimized medium and subjected to three temperature treatments (15, 24 and 30°C) in order to determine the best thermal condition for pollen germination. Furthermore, the viability of stored pollens of these almond cultivars, three months after maintenance at 4, -20 and -80°C, was assessed through evaluation of their germination percentage using optimized medium. Maximum pollen germination (99.80%) was recorded in B2K1M2C1S2 medium containing boric acid (100 mg/l), magnesium sulphate (100 mg/l), potassium nitrate (0.0 mg/l), calcium nitrate (0.0 mg/l), sucrose (15%) and agar (1%), while the lowest (30.57%) was found in B1K1M2C3S1 medium containing boric acid (0.0 mg/l), potassium nitrate (0.0 mg/l), magnesium sulphate (100 mg/l), calcium nitrate (150 mg/l), sucrose (10%) and agar (1%). Pollen culture at 15 and 24°C showed better germination percentage than at 30°C. The data recorded for the pollen germination of stored pollens shows that Rabie pollen stored at -80°C has the highest germination rate (90.66%), while Touno pollen stored at 4°C has the lowest germination rate (36.66%). However, the findings of the present study may be of help to fruit breeders and anyone involved in pollen analysis studies.
Keywords: In vitro, pollen viability, almond