Effect of Pollination Time on the Frequency of 2 n + n Fertilization in Apomictic Buffelgrass

Abstract

Fertilization of an unreduced egg (2n + n) increases ploidy level and creates a new hybrid. It occasionally occurs in apomictic species but at a frequency too low to be a reliable method for genetic improvement. This investigation was undertaken to determine if 2n + n fertilization could be increased by early pollination. Six buffelgrass, Pennisetum ciliare (L.) Link [syn. Cenchrus ciliaris L.], accessions, five apomicts and one sexual, were self‐pollinated and cross‐pollinated with birdwoodgrass, P. ciliare (L.) Link var. setigerum (Vahl.) Leek, at 3, 2, 1, and 0 d before anthesis. The 2n + n progeny were identified by flow cytometry. DNA content (pg 2C−1) was determined for 1962 self‐pollinated and 3072 cross‐pollinated plants. Twenty‐eight self‐ and 80 cross‐pollinated plants had a higher DNA content and were products of 2n + n fertilization. The overall frequency of 2n + n fertilization when self‐ and cross‐pollinated was 1.4 and 2.6%, respectively. For all protogynous intervals, the frequency ranged from 0 to 5.2% for self‐pollinated plants and 0 to 8.2% for cross‐pollinated plants. When self‐pollinated, there was no correlation between time of pollination and recovery of 2n + n hybrids. When cross‐pollinated, there was a linear relationship between time of pollination and number of 2n + n hybrids recovered. More 2n + n hybrids were recovered from crosses made 2 or 3 d before anthesis. Thus in apomictic buffelgrass, the frequency of 2n + n fertilization can be increased by pollinating early, and in apomictic species where sexual germplasm is not available, this approach has potential to produce new apomictic hybrids.

Genetic Diversity among Pentaploid Buffelgrass Accessions

“…Facultative apomicts in buffelgrass are known to occur in nature (Bashaw and Johns, 1983;Bray, 1978;Sherwood et al, 1980;Visser et al, 2000) and natural hybridization between sexual and apomict types undoubtedly occurs. In grasses, including buffelgrass, the probability of 2n + n fertilization increases the earlier pollination occurs following stigma exertion (Martinez et al, 1994;Burson et al, 2002). Thus the noncold-tolerant pentaploid buffelgrasses may have originated from natural crosses between sexual tetraploids and apomictic hexaploids.…”

“…Because buffelgrass is a protogynous, allogamous species (Bogdan, 1977;Shafer et al, 2000), this flowering behavior is conducive for natural hybridization. Therefore, this protogynous flowering behavior in buffelgrass increases the chance of 2n + n fertilization (Burson et al, 2002). Kharrat-Souissi et al (2013) proposed that pentaploid cytotypes in Tunisia originated from natural crosses between the tetraploid and hexaploid ecotypes.…”

Reproductive pathways of seed development in apomictic guinea grass (Panicum maximum Jacq.) reveal uncoupling of apomixis components

“…Uncoupled apomixis components may well be utilized in gene transfer in otherwise apomictic crops (Burson et al 2002), creation of novel variations (de Wet 1968;Mecchia et al 2007), and for formation (natural or targeted) of new cytotypes (Barcaccia et al 2006;Martelotto et al 2007). As an illustration, ssFCSS identiWed B III (i.e.…”

Genome Differentiation in Lycoris Species (Amaryllidaceae) Identified by Genomic in situ Hybridization

“…However, in the reverse combination of the cross using L. incarnata as the pollen parent, no seeds or plantlets were produced even in improved ovule culture due to the pollen sterility of the triploid species, L. incarnata (Ma et al 2001). Unreduced gametes generally result from either the failure of chromosome reduction at the first meiotic division or from the failure of cytokinesis at the second meiotic division during megasporogenesis and/or micromegasporogenesis (Burson et al 2002). In the present case, it was assumed that the unreduced gametes of L. incarnata were induced by the failure of chromosome reduction because of the presence of allotriploidy with a complex karyotype.…”