[Investigations on variability of pollen tube growth in diploid and tetraploid plants of sugar beet : I. Conditions for germination of Beta pollen in vitro].

a) Attempts to germinate freshly harvested pollen of Beta vulgaris L. on semisolid media were carried out in 1966/67. The basic nutrient medium consisted of 5% gelatin, 30% sucrose and 0.03% boric acid (pH 6.4). Very poor germination occurred in aqueous solutions. During the flowering time from August to October the pollen was taken from field grown plants and during the rest of the year from greenhouse plants. b) One of the requirements for satisfactory in vitro germination rates is the optimal degree of ripeness of the pollen grains which is attained immediately after the dehiscence of the anthers. c) From January to March in vitro germination was very poor. Highest germination rates occurred during August and September. d) The germination of Beta pollen is strictly dependent upon the presence of boron in the medium. Optimal concentration of boric acid for pollen germination is 10(-1)% and for pollen tube growth 10(-2)% ; pollen tubes in this case reached a maximum length of 750 μm, in rare cases even of up to 1200 μm. Borax and butyl boric acid are less active in promoting germination. Phenyl boric acid has a very slight promoting effect and becomes toxic with concentrations higher than 10(-3)%. e) Highest germination rates (85%) were obtained on the basic medium at pH 5.4 to 5.7 after addition of n/10 HCl. Ca(++)-ions had no positive effect on germination. f) Germination of Beta pollen as compared to other pollen is relatively slow. g) A coating of callose was always observed on the inside of the walls of in vitro grown pollen tubes, less frequently callose plugs were found. Occasionally branching of the tubes occurred.