Reproductive behavior of Acroceras macrum Stapf

USANDIZAGA FERRARI, SILVANA C.; SCHEDLER, MARA; LEDESMA, DIEGO; MARTÍNEZ, ERIC J.; ACUÑA, CARLOS A.

Buenos Aires

Simposio; 5th International Symposium of Forage Breeding; 2015

Acroceras macrum is a warm-season grass used as forage and it is characterized for its high nutritive value. The low seed yield obtained from the more commonly adopted genotype obligates the farmers to spread it in a vegetative way, limiting its adoption as forage. There is a serious need of information about the reproductive behavior of this species to initiate a breeding program. A plant collection accomplished in northeastern Argentina resulted in 22 tetraploid and 5 hexaploid genotypes. The objective of this research was to determine the mode of reproduction in that collection. Clarified ovaries at different stages of development were observed using differential interference contrast microscopy to study the characteristics of the embryo sacs. Seed yield was studied in open and self-pollination. Cross-pollination between different genotypes with variables ranges of genetic distances also was performed and the hybrid origin of the seed obtained was tested with ISSR molecular markers. Development of sexual embryo sacs was observed for both cytotypes, and all the resulting sacs did have the Polygonum structure typical of Paniceae, with an egg cell, two synergids, a binucleated central cell and 3 to 7 antipodals. Tetraploid genotypes showed 8% of abortions, 9% of embryo sacs with no observable ontogenetic structures, 23% of mature meiotically derived sacs and 1% of structures arrested in an immature state at anthesis. Hexaploid genotypes showed 22% of abortions, 11% of embryo sacs with no observable ontogenetic structures, 28% of mature meiotically derived sacs and 19% of structures arrested in an immature state at anthesis. The remaining sacs, in both cytotypes, were not yet at anthesis and they showed a developmental state according with the normal meiotical pattern. The percentage of seed obtained from open-pollinated tetraploid inflorescences varied from 3.7 to 69%, with an average of 34.5%. The percentage of seed obtained from open-pollinated hexaploid inflorescences varied from 0.2 to 3.7%, with an average of 1.5%. The percentage of seed obtained from self-pollinated tetraploid inflorescences varied from 0.3 to 18%, with an average of 5.1%. No seed was obtained from self-pollinated inflorescences for the hexaploid. The crosses between tetraploids A. macrum genotypes produced several plants and 87.5% to 100% (an average of 94%) of them were verified as hybrids in each family. Inter-cytotype crosses did not result in fertile seeds. Our results indicate that both cytotypes are sexual, and allogamous due to self-incompatibility.