Optimization and Development of Pollen Germination Medium for Cultivated and Wild Cajanus Pollen in vitro

The germination of pollen and the growth of pollen tubes are preconditions for fertilization and seed development. A complete knowledge of pollen viability will help in a proper understanding of pollination and fertilization in plants. Pollen from different cultivated and wild species of Cajanus were used to study the influence of different medium components on Cajanus pollen germination. This study established a reliable medium for pollen germination in Cajanus cajan by modifying the Brewbacker and Kwack (BK) medium to enhance understanding of pollination and fertilization dynamics.

The in vitro pollen germination studies were carried out in Pre-breeding department at the International Crops Research Institute for the Semi-Arid Tropics, Hyderabad, India. We developed 108 distinct media formulations by systematically varying concentrations of key constituents: sucrose (10%, 30%, 40%), boric acid (0, 100, 250 ppm), calcium nitrate (100, 300 ppm), magnesium sulfate (100, 200, 300 ppm), potassium nitrate (100 ppm) and polyethylene glycol 6000 (15%).

Optimal results were achieved with medium G, which contained 30% sucrose, 100 mg/l boric acid, 100 mg/l calcium nitrate, 100 mg/l potassium nitrate, 100 mg/l magnesium sulfate and 15% PEG, yielding 69.5% pollen germination. When tested on wild relatives (Rhynchosia bracteata, Cajanus platycarpus and Cajanus scarabaeoides), this optimized medium demonstrated over 70% germination efficiency with robust pollen tube development. The improved medium shows promise for facilitating inter-specific and inter-generic hybridization where biological barriers exist, potentially enabling in vitro pollination/fertilization approaches to introgress valuable traits for pigeonpea variety development.