Principles of Plant Genetics and Breeding

324 CHAPTER 17
Experimental results
Confirmation of hybrids with molecular markers
Following the generation of any wide cross hybrid, especially in polyploid species that have relatively unknown or poorly studied
reproductive processes, it is worthwhile confirming the generation of true hybrids. Unique, but naturally occurring, events such
as patrogenesis or androgenesis could give rise to unanticipated products. To identify hybrids, random amplified polymorphic
DNA (RAPD) markers (Williams et al. 1990) or some other polymerase chain reaction (PCR)-based approach can be efficiently
utilized (Weising et al. 1995). For this purpose, a series of P. arachnifera and P. secunda PCR-RAPD-based primers were utilized
for evaluating genotypes. Standard DNA extraction and PCR-RAPD methods were utilized to evaluate the progeny of the hybrids.
Hybrid phenotypes
Of the 54 hybrids generated, 50 were true hybrids and four were androgenic haploids. Thirty-five flowered the first growing season
and all flowered in their second season. A preliminary assessment of their phenotypic variability indicated that F 1 individuals
could possess glossy to waxy leaves, wide to narrow leaves, an erect or prostrate plant profile, variation in flowering time, differences
in the shape and size of inflorescence, and variation in pollen viability. Twenty-four of the true F 1 hybrids expressed a
monoecious phenotype while 26 exhibited a dioecious phenotype. Of those exhibiting a dioecious phenotype, 12 were female
and 14 were male. All androgenic haploids were monoecious in their phenotype. Chromosome counts of randomly selected
hybrid individuals indicated that chromosome numbers ranged from 2n = 54 through to 2n = 72. Chromosome counts of the
androgenic haploids were: two with 16 chromosomes, one with 18 chromosomes, and one with 20. PCR analysis confirmed that
the androgenic haploids did not possess any of the P. arachnifera genome and only a subset of the P. secunda genome and each
possessed a fibrous, bunchgrass-type root system characteristic of the P. secunda parent. Each of the androgenic haploids was a
smaller version of the monoecious P. secunda parent. The generation of haploids in these and additional interspecific hybrids of
Poa spp. is not without precedent and has been reported elsewhere (Kiellander 1942; Kindiger 2004).
In the monoecious hybrid individuals, seed heads more closely resembled the P. secunda parent (Figure 2). In the dioecious
individuals, most exhibited a phenotype resembling the P. arachnifera parent; however glume size varied considerably among
the dioecious population. Stereoscopic examination of the florets of monoecious individuals indicated that the hybrids possessed
fewer cobwebby hairs than the P. arachnifera parent or the female individuals of the dioecious group.
Many of the taxonomic characters commonly utilized to differentiate between the parents were clearly expressed in the
hybrids. The segregation of monoecy and male or female dioecy was relatively equivalent among the F 1 hybrids. All the F 1
(a) (b) (c)
Figure 2 Inflorescences from (a) Poa arachnifera, (b) P. secunda, and (c) a monoecious F 1 interspecific hybrid.