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Growth of Alsike Clover Pollen In Vitro¹

Pollen germination and pollen tube elongation in vitro and their relationship to self-incompatibility were investigated in diploid alsike clover (Trifolium hybridum L.). Of four culture media evaluated, the most suitable one contained 25% (w/v) sucrose, 100 ppm of CaCO₃ and 50 ppm of H₃BO₃ in deionized distilled water. Pollen germination was 82% and average pollen tube length was 0.43 mm after 24 hours at room temperature. Pollen tube elongation was approximately 10% of that necessary to effect fertilization. In a subsequent study, sucrose concentration of the selected medium was varied as follows: 10, 25, and 35% (w/v). Pollen germination was best (92%) in the solution containing 35% sucrose, but pollen elongation was best (0.41 nun) in the 25% sucrose solution. Pollen germination and pollen tube elongation were the poorest at the 10% sucrose concentration. Germination and tube elongation appeared to be two separate processes with different nutritional requirements.

Pollen from 25 plants representing 11 S-allele genotypes was evaluated in vitro for percentage germination and tube elongation. Although there were differences among genotypes and among plants within genotypes for these characters, no relationship was established between pollen grain nutrition and S-allele genotype. Tube elongation sufficient to effect fertilization was not obtained.

Key Words: Trifolium hybridum L. • Pollen grain nutrition • Self-incompatibility

² Graduate Research Assistant, Department of Agronomy, Colorado State University, and Research Geneticist, ARS, USDA, Crops Research Laboratory, Colorado State University, Fort Collins, Colorado 80521.

Received for publication April 14, 1973.