Apomixis is asexual reproduction through seed. Apomixis in the genus Pennisetum is of the gametophytic (aposporous) type. Genes for apomixis have been transferred from a wild apomictic species (P. squamulatum) to pearl millet (P. glaucum) by conventional breeding to produce an obligately apomictic backcross 3 (BC3) plant (Dujardin and Hanna, 1989, J. Genet. Breed. 43:145). Molecular markers based on restriction fragment length polymorphisms and random amplified polymorphic DNAs were identified in BC3 that were shared only with the apomictic parent. Segregation of these informative markers in a BC4 population indicated that three linkage groups from P. squamulatum were present in BC3 and that minimal recombination between these alien chromosomes and those of the recurrent parent occurred. Transmission of only one of the linkage groups was required for transfer of apomixis. Recombination is essential for genetic mapping, thus we are beginning to map the informative molecular markers in an F, interspecific cross between pearl millet and P. squamulatum, a population that segregates for apomictic and sexual reproduction.
Facultative apomixis is characteristic of a number of Malus spp., but generally has been restricted to triploid and tetraploid forms (3, 4). However, apospory has been described in cultivated apples (2), but this phenomenon has not been thought to commonly occur. We believe that a seedling of ‘Anna’ in an experimental planting at Gainesville is evidence of such an occurrence.
self-compatibility and presence of apomixis in Callicarpa . Dirr (2009) reported that C. dichotoma (Lour.) K. Koch produces fruit consistently every year even when isolated from other seedlings or species, suggesting self-compatibility, but C
majority being tetraploid ( Kuruvadi et al., 1997a ). Diploid guayule plants reproduce sexually, but tetraploid guayule reproduces predominantly by facultative apomixis, which is embryo development without fertilization. However, even in apomictic plants
. More compact forms of this species may be preferred for modern landscapes or container gardens. However, reports of apomixis in Sarcococca present challenges to breeding. Dirr (2009) reported that seedlings of sweetbox grew true to type, such that
( Dirr, 2009 ; McKay, 2001 ). Aronia flowers are thought to be protogynous and self-compatible ( Connolly, 2014 ). Polyploid Aronia species have been reported to reproduce apomictically, via gametophytic apomixis, resulting in embryos that are
, there is little information available on ploidy levels of specific cultivars. Pseudogamy, a form of apomixis, has also been implicated as the sole means of reproduction in triploid R. triloba ( McCrea, 1981 ). A greater understanding of reproductive
The U.S. National Plant Germplasm System (NPGS) currently holds 36 separate accessions of the `Yichang' clone of Malus hupehensis (Pamp.) Rehd. The `Yichang' clone originally entered the United States in 1908 as seed collected for the Arnold Arboretum by E.H. Wilson near Yichang, Hubei Province, China. The original description of M. hupehensis omits fruit characters, and botanists frequently augment these omissions with descriptions of the `Yichang' clone. Apomixis occurs in Malus, including M. hupehensis, and is strongly associated with elevated ploidy levels. Simple sequence repeats (SSRs) were used to characterize 65 accessions of M. hupehensis. To check for polyploidy, a set of M. hupehensis accessions was evaluated with flow cytometry. The simple sequence repeat phenotypes and ploidy information revealed the `Yichang' clone under various accession names in arboreta. It was neither known nor suspected that the U.S. National Plant Germplasm System held many duplicate accessions of the `Yichang' clone prior to their molecular characterization. Germplasm conservation decisions for Malus species can benefit from an increased knowledge of the genetic variation or lack thereof in naturalized populations and ex situ collections.
Leaf extracts of diploid guayule were analyzed for phosphoglucomutase (PGM, EC 220.127.116.11) and menadione reductase (MNR, EC 18.104.22.168) isozymes by starch gel electrophoresis. Banding patterns of hybrids indicated that PGM is monomeric and MNR tetrameric in structure. Two codominant alleles were identified at each of two Pgm loci, designated as Pgm-2 and Pgm-3. Two codominant alleles were observed at Mnr-2; MNR-1 was monomorphic in the Parthenium argentatum genotypes analyzed.
New potential citrus germplasm accessions may be received as seed rather than budwood, thereby reducing phytosanitary risks. However, trueness-to-type may be an issue with seed materials because many varieties produce both apomictic (nucellar) and sexual (zygotic) embryos and most citrus is fairly heterozygous. To identify nucellar seedlings of polyembryonic types and to retain these as representing the type, we screened 1340 seedlings from 88 seed sources for markers amplified with two inter-simple sequence repeat (ISSR) primers. Sixteen seed sources produced no seedlings classified as being of nucellar origin. Among the remaining seed sources, seedlings classed as nucellar were identified for potential addition to the collection. In 37 accessions, both nucellar and zygotic seedlings were detected, and in some cases both types were retained. Inclusion of established accessions of the same cultivar group in the analysis allowed an initial assessment of similarity to existing accessions. This technique improved the efficiency of acquiring new germplasm of polyembryonic types by seed. The method identifies those seed sources that produce few or no nucellar seedlings, but it is not useful for determining which seedlings of monoembryonic types should be retained in collections.