Meiotic behavior of Brachiaria decumbens hybrids

Abstract

ABSTRACT. Brachiaria decumbens is a forage grass of inestimable value for livestock in Brazil due to its production of good quality forage even when planted on acid and poor soils, although it is susceptible to pasture spittlebugs. Only one cultivar, cv. Basilisk, has been used as the pollen donor in crosses with Brachiaria ruziziensis since 1988 at Embrapa Gado de Corte Research Center. Breeding within the species only became possible from 2009 when sexual accessions were successfully tetraploidized using colchicine. Three sexual genotypes were obtained and hybridization within B. decumbens was finally achieved. Here, we evaluated microspore tetrads using conventional cytology and found meiotic indexes above 78% for all three female genitors (cD24-2, cD24-27, cD24-45), but a low meiotic index (<22%) in the natural apomictic genitor D62 (cv. Basilisk) and in 49 hybrids. Analysis of the relationship between abnormal tetrad frequency and non-viable pollen grains yielded a highly significant Pearson correlation coefficient. The t-test proved significant for the progeny of cD24-45 x D62, with lower abnormalities and pollen sterility when compared to the other two progenies resulting from cD24-2 and cD24-27 crossed to D62, but these two did not differ. Apomictic hybrids such as S036 and X030 with low pollen sterility have the potential for use in cultivar development, whereas the sexual hybrids T012, X072, and X078 might be of use as female genitors in polycross blocks if they display good agronomic traits.

A Parthenogenesis Gene Candidate and Evidence for Segmental Allopolyploidy in Apomictic Brachiaria decumbens

“…Seed yield potential is an important trait that determines whether a new variety can be profitably produced and distributed to farmers, and failed seed set is a persistent limitation in Brachiaria , where caryopsis formation rarely exceeds 30% ( Hopkinson et al 1996 ). Abnormal tetrad frequency appears to be significantly correlated with nonviability of pollen grains ( Souza et al 2015 ). The implications of the relationship between the incidence of meiotic abnormalities and reduced pollen viability are particularly troubling for bred hybrid genotypes.…”

“…The implications of the relationship between the incidence of meiotic abnormalities and reduced pollen viability are particularly troubling for bred hybrid genotypes. Because there are no known natural allotetraploid sexuals in the B. ruziziensis / B. brizantha / B. decumbens agamic complex, synthetic autotetraploid genotypes (AAAA) have been used as the source of sexuality in inter- and intraspecific crosses with segmental allopolyploid (BBB′B′) pollen donors ( Swenne et al 1981 ; Simioni and Valle 2011 ; Souza et al 2015 ). Therefore, pairing affinity is likely reduced in progeny (AABB′), which receive male gametes with low homology (BB′).…”

“…Therefore, pairing affinity is likely reduced in progeny (AABB′), which receive male gametes with low homology (BB′). Indeed, meiotic abnormalities appear to be more common in progeny of both inter- and intraspecific crosses than natural apomictic accessions ( Risso-Pascotto et al 2005 ; Fuzinatto et al 2007 , 2012 ; Mendes-Bonato et al 2007 ; Felismino et al 2010 ; Souza et al 2015 ). Many natural apomictic accessions, including CIAT 606 (cv.…”

“…Basilisk), produce adequate seed and are successful as cultivars despite low pollen fertility ( Mendes-Bonato et al 2001 ). Thus, the production of viable pollen may not be as critical in apomictic species as in sexual species, where seed development is dependent on successful pollination of both the embryo and the endosperm ( Souza et al 2015 ). Still, at least one hybrid Brachiaria cultivar with excellent forage traits, good stress resistance, and ample flowering failed in the marketplace due to poor seed yield caused by low seed set ( Hare et al 2007 ), indicating that further research on the relationship between meiotic abnormalities and seed yield in tropical forages is warranted.…”

Mutagenic influences of colchicine on phenological and molecular diversity of Calendula officinalis L.

“…In a similar study, Wu et al (2015) studied the induction and identification of Stylosanthes guianensis tetraploids. Souza et al (2015) observed the genetic alteration and meiotic behavior of Brachiaria decumbens hybrids.…”