, 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
2, Table 3 ), a form of apomixis/pseudogamy. Table 3. Probable reproductive pathways from open-pollinated seeds and seedlings of diploid and triploid maternal Pyrus hybrids. Seeds from open-pollinated triploid maternal parents also demonstrated
fruit development. Whether the seeds of artificial pollination and natural pollination are the products of apomixis by pseudogamy still needs to be determined by genetic and molecular biological studies. Occurrence and development of sexual and
Information on ploidy levels is extremely valuable for use in plant breeding programs. Fertility, crossability, and heritability of traits are all influenced by ploidy levels. Knowledge of reproductive pathways, including occurrence of apomixes, pseudogamy, and formation of unreduced gametes can also be important information for developing breeding strategies. Although ploidy level can be determined by counting chromosomes, flow cytometry provides a reliable and much faster means for determination of nuclear DNA content and associated ploidy level. Measurement of ploidy levels of seeds (embryo and endosperm) can also provide useful insights into reproductive pathways. The objective of this study was to determine the approximate genome size, estimated ploidy level, and range of reproductive pathways of a diverse collection of flowering crapbapples (Malus spp.). Genome sizes were calculated as nuclear DNA content for unreduced tissue (2C). Results from the taxa included in our survey showed DNA contents ranging from 1.52 to 1.82 for diploids, 2.40 to 2.62 for triploids, and 3.36 to 3.74 pg/2C for tetraploids. Based on these ranges, we identified 43 diploid, 10 triploid, and 4 tetraploid crabapple taxa in this collection. Results from open pollinated seeds and seedlings demonstrated a variety of reproductive pathways including apomixes and unreduced gametes. This research provides information on ploidy levels and reproductive pathways of flowering crabapples and will allow for more systematic and efficient progress in the development of improved cultivars.
self-incompatible but can sometimes produce apomictic seeds through pseudogamy ( Palmer et al., 2009 ). Autotetraploid accession H2008-239-002 had nine seeds germinate and accession H2008-239-004 had four seeds germinate (a significant reduction
of which, on the fruit set, needs to be investigated further. Fertilization with unreduced gametes, apomixis, and pseudogamy were documented in triploid-derived embryos/offspring but were relatively uncommon. The considerable reduction in female
pseudogamy, fusion of the polar nuclei with one of the sperm nuclei may produce endosperm that contains some paternal inheritance. The sexually reproducing accessions in this study produced a wide range of Jaccard’s similarity coefficients from 0.64 to 0
:flower ratio of 6.2% ± 1.7%. This is contrary to a previous study where only autonomous apomixis was observed in a population consisting of only pistillate flower types ( Desai, 1962 ). Nonautonomous apomixis (pseudogamy) might also be present in Z. americanum