Abstract
Details of apomixis at levels of the gene, chromosome, and genome can be obtained with a comprehensive restriction fragment length polymorphism (RFLP) linkage map. The objective of this research was construction of a genetic linkage map of buffelgrass to investigate the molecular basis of apospory and serve as a framework map for marker-facilitated breeding of perennial forage grasses. Buffelgrass (Pennisetum ciliare (L.) Link syn. Cenchrus ciliaris L.) (2n=4x=36), a highly polymorphic, atomistic, perennial forage grass with rare sexual genotypes and typical meiotic behavior, is well-suited for linkage analyses. Four hundred forty-three homologous probes from an apomictic pistil-specific cDNA library were evaluated and combined with 862 previously analyzed heterologous probes from across the Poaceae. The homologous and heterologous sources yielded 360 and 100 polymorphic probes, respectively, which were mapped in 86 F₁ hybrid progeny. The female parent's map included 409 single-dose restriction fragments (SDRFs), 47 linkage groups, and 3464 centi-Morgans (cM), while the male parent's map contained 300 SDRFs, 42 linkage groups, and 2757 cM. Approximately 70-80% of the buffelgrass genome was covered, and average marker spacings on the respective maps were 10.8 and 11.1 cM. Repulsion-phase linkages were found in 47% of the linkage groups, implying significant preferential chromosome pairing in buffelgrass. Comparison of interval lengths in the maps bounded by markers heterozygous in both parents revealed less meiotic recombination in the gametes of the male parent. No marker associations to inflorescence type or rhizomes were detected in this small population, but two homologous probes were tightly linked to apospory. The apomixis linkage group was in repulsion with a single linkage group, suggesting disomic inheritance of apospory in buffelgrass.
Jessup, Russell William (1999). A genetic linkage map of buffelgrass. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1999 -THESIS -J47.