188.8.131.52. Pollen germination and pollen tube growth in vitro
The evaluation of pollen germination in vitro takes into account not only pollen viability but also pollen vigour (Shivanna and Johri, 1985; Shivanna et al., 1991). One drawback of the method is that the germination medium and germination conditions (e.g. pollen pre-hydration, temperature conditions) must be optimized for each species to avoid false negatives. Different media for in vitro pollen germination have been recommended for several species (Taylor and Hepler, 1997), mainly using the basic medium developed by Brewbaker and Kwack (1963) in a sucrose solution with or without agar, depending on the species. The optimum method has to be tested for each species empirically. A pollen grain is considered as germinated when the length of the pollen tube is at least twice the diameter of the pollen grain.