GENETIC TRANSFER OF GYNOMONOECY FROM DIPLOID TO TRIPLOID EASTERN GAMAGRASS

Seed yields of eastern gamagrass, Tripsacum dactyloides (L.) L. (Andro pogoneae), are limited by a scarcity of fertile female florets and exc essive maleness in its monoecious inflorescence. Gynomonoecious varian ts, with sex reversal in formerly male spikelets and reactivation of s uppressed female florets, are known that have a greater seed productio n potential than monoecious forms. Sexual reproduction is exclusively observed in diploid eastern gamagrass, whereas facultative apomictic r eproduction is the rule in polyploid forms. This study was designed to combine recessive genes for gynomonoecy from diploids with genes for apomixis from polyploids to develop true breeding (apomictic), prolifi c seed producing (gynomonoecious) lines. Diploid parents with allele(s ) for gynomonoecy were used in each of three generations of interploid y matings to transfer gynomonoecy from diploid to triploid eastern gam agrass. A first generation fertile triploid hybrid and a second genera tion B-m derived tetraploid hybrid were used as intermediates for gene tic transfer. Ninety triploid progeny from the third generation of cyt otype intermatings yielded three gynomonoecious individuals, one with relatively good female fertility and two that failed to set seed. The low percentage (3.3%) of triploid progeny that inherited the gynomonoe cious trait indicates a strong selection force against gynomonoecy at the triploid level. The breeding strategy employed is considered a pra ctical method to move genes from diploid to higher ploidy levels for s ubsequent stabilization by apomixis.