REPRODUCTIVE-BEHAVIOR OF TETRAPLOID ALFALFA PLANTS OBTAINED BY UNILATERAL AND BILATERAL SEXUAL POLYPLOIDIZATION

The objective of the present study was to evaluate the fertility of te traploid plants obtained from diploid mutants that produced 2n gametes via bilateral (BSP) and unilateral sexual polyploidization (USP) sche mes. Controlled matings between selected plants from BSP and USP were carried out according to a complete diallel. The level of male and fem ale fertility of each plant was estimated within full-sib, half-sib an d non-inbred crosses. Crosses with unrelated self-fertile and male-ste rile testers were also performed. Pollen size and stainability were de termined by acetocarmine staining. The number of ovules per ovary was counted and the callose deposition within ovules examined to evaluate embryo sac fecundity. Cross-fertility was generally much higher for US P than BSP plants (on average, 0.3 vs. 0.03 seeds per flower pollinate d). Both male and female fertility were inversely related to the inbre eding level of cross combinations. The in vitro pollen germinability w as positively correlated to male fertility of BSP plants. The level of in vivo embryo sac sterility was not correlated to female fertility i n either BSP or USP plants. Female fertility was restored in both BSP and USP groups when plants were crossed with unrelated tetraploid test ers. Male fertility also increased in USP plants but remained rather l ow in the BSP plants. Scaling up the ploidy level by means of 2n gamet e union resulted in tetraploid plants with low fertility. In particula r, the BSP process yielded virtually self-sterile and highly cross-ste rile plants. The well documented positive effect of sexual tetraploidi zation on forage yield was accompanied by worsening of fertility trait s.