Interploidy Crosses Research Articles

Effects of Inbreeding and Genetic Variation on Forage Quality Traits and Dry Matter Yield in Dactylis glomerata L. Subspecies

AbstractCultivated 4× clones, 2× germplasm and their respective S; progeny were utilized in this study. Dry matter yield and forage quality data (in vitro dry matter disappearance, cell wall constituents, total nitrogen) were obtained on composited vegetative plant material harvested during four successive 4‐week growth periods in the greenhouse. There was no detectable average inbreeding effect for any of the traits. The group mean of the diploids was significantly lower for in vitro dry matter disappearance than the tetraploid group mean. However, two out of six diploid 51 families exceeded the highest tetraploid family for this trait. The diploids had significantly higher cell wall constituents than tetraploids except for acid detergent lignin. There was more variation for any trait at the diploid level than at the tetraploid level among S1 families as well as within families. Dry matter yield and total nitrogen were significantly correlated in diploids and in tetraploids. However, little variation was detected lot total nitrogen at either ploidy level. The results suggest that selection for improved quality in progeny from interploidy crosses may be more efficient by first selecting at the diploid level followed by scaling to the tetraploid level, rather than selection at the tetraploid level after hybridization.

Evaluation of Indirect Ploidy Indicators in Dactylis L. subspecies1

The importance of maximizing heterozygosity in tetrasomic tetraploids, such as orchardgrass (Dactylis glomerata L. ssp. glomerata Hayek), has been demonstrated. Germplasm transfer from 2x Dactylis ssp. utilizing diploid clones that produce 2n gametes (meiotic mutants), enhances heterozygosity. Because most meiotic mutants produce n as well as 2n gametes, depending on environmental conditions, the ploidy level of progeny from interploidy crosses will not be uniform. Ploidy determinations are therefore necessary. Several indirect ploidy indicators (yield, vigor, leaf blade dimensions, leaf blade area, and stomatal guard cell length) were evaluated for their usefulness in identifying tetraploid hybrid progeny reliably and with minimal effort. Cultivated 4r clones, 2x germplasm, and their selfed and hybrid progeny were utilized in this study. Dry matter and vigor data were obtained during four successive growth periods in the greenhouse. The remaining traits were evaluated once at the beginning of the first growth period (10 Jan. 1984) and a second time immediately before the last harvest (1 May 1984). Dry matter yield was shown to be unsuitable as an indirect ploidy indicator because of a large overlap in clonal mean ranges from different ploidy levels. Stomatal guard cell length can be a reliable ploidy indicator only if tetraploid inbred clones and triploid hybrid clones are not expected among the progeny, as may be the case in 2x–4x crosses. Visual vigor rating was effective but required extensive experimental replication to achieve the necessary precision. Among the leaf blade dimensions, area gave the most dependable separation of tetraploid hybrids. Nongenetic causes were found to contribute less than 20% to the total observed variance for leaf blade area. Because aneuploidy influences fertility in Dactylis, final ploidy determination should always be made cytologically.

Genetic Progress through Hybridization of Induced and Natural Tetraploids in Crested Wheatgrass

Genetic Progress through Hybridization of Induced and Natural Tetraploids in Crested Wheatgrass

The significance of genic balance to endosperm development in interspecific crosses

The endosperm has played a significant role in the evolution of angiosperms because of its physiological and genetic relationships to the embryo. One manifestation of this evolutionary role is its abnormal development in interploidy crosses. It is now established that the endosperm develops abnormally in interploidy-intraspecific crosses when the maternal: paternal genome ratio deviates from 2∶1 in the endosperm itself. We propose an Endosperm Balance Number (EBN) hypothesis to explain endosperm development in both interploidy-intraspecific and interspecific crosses. Each species is assigned an EBN on the basis of its crossing behavior to a standard species. It is the EBN which determines the effective ploidy in the endosperm of each species, and it is the EBNs which must be in a 2∶1, maternal:paternal ratio. The EBN of a species may be determined by a few genes rather than the whole genome. This hypothesis brings most intraspecific-interploidy and interspecific crossing data under a single concept with respect to endosperm function. The implications of this hypothesis to isolating mechanisms, 2n gametes, the evolution of disomic polyploids, and reciprocal differences in seed development are discussed.

Hybridization Among Diploid and Tetraploid Forms of New Guinea, Java, and Celebes Impatiens spp.1

Abstract Interspecific hybrids were synthesized by intercrossing diploid and tetraploid of Impatiens spp. from New Guinea (2x=32), Java (2x=16), and Celebes (2x=8). Breeding analysis of the intra- and interploidy crosses showed that the species functioned as diploids in relation to each other. Diploid by tetraploid crosses produced little or no seed, and with few exceptions the triploid seedlings were sterile. All but 2 out of 43 seifs and reciprocal crosses among tetraploids produced viable seed. Amphidiploid and autotetraploid seedlings were pollen and seed fertile. Allotetraploids composed of 2 or 3 genomes in various unequal combinations and those with 4 genomes were pollen and seed sterile or nearly so. Most of the 3 and 4 allopolyploids were ornamentally inferior to the diploid and amphidiploid hybrids. New Guinea flower colors were recessive to those of Java and Celebes. The hybrid phenotypes were midparental for most traits and in some cases exhibited dosage effects. Some hybrids were superior to both parents in certain ornamentally important attributes.

Hybrids Between Tetraploid and Hexaploid Crested Wheatgrasses1

SummaryDoubled‐diploid Agropyron cristatum (L.) Gaertn., 2n=28, and tetraploid A. desertorum (Fisch. ex Link) Schult., 2n=28, hybridized with hexaploid A. cristatum, 2n=42. Meiosis in the parent plants was typical of that in autoploids. Pentavalent associations, up to five per cell, in the 35‐chromosome hybrids indicated close homologies between parental genomes. Occasional higher multivalent associations and bridge‐fragment formations at anaphase I indicated some structural heterozygosity.All crested wheatgrasses—whether diploid, tetraploid, or hexaploid—apparently contain one basic genome that has undergone some structural rearrangements. It is recommended that crested wheatgrasses be regarded as one species with taxonomic differentiation at the subspecies and varietal levels.The pentaploid hybrids were surprisingly fertile and ranged from 0.54 to 4.32 seeds per spikelet under open pollination. Some hybrids were considerably more vigorous than either parent and may have value in a breeding program. Interploidy hybridization is recommended to crested wheatgrass breeders.

Meiotic Bahavior and Sterility in an Avena Pentaploid Hybrid: C.I.7232 (2n=28) ✕ Mesdag (2n=42)1

A 1959 report3 that the interploidy cross [Avena saliva L. var. ‘Black Mesdag’ (2n=42)] ✕ [derived‐tetraploid C.I.7232 (2n=28)] resulted in highly fertile F1 hybrids and derivatives generated considerable interest and skepticism because such behavior was contrary to that expected. This led the current authors to make the reputed cross and to determine the meiotic and agronomic behavior of F1 plants. All F1's possessed 35 chromosomes and were sell‐sterile, indicating that tetraploid C.I.7232 was not a parent of the earlier hybrids.