Effects of Wheat Chromosome 1D Telosomes on Hybrid Seed Development in Wheat × Rye Crosses

Pollination of ‘Chinese Spring,’ monosome 1D plants with rye results in failure of hybrid seed development in a proportion of the F₁ seeds corresponding to the transmission rate of the nullisomic 1D egg cells. Development and viability of these hybrid seeds closely resemble that normally observed in T. aurum× rye crosses. Using ‘Chinese Spring’ chromosome ID telosomic plants in crosses with rye, it was possible to illustrate that the observed effect was associated with the long arm of this chromosome.     

Assignment of Endosperm Balance Numbers to the tuber-bearing Solanums and their close non-tuber-bearing relatives

The Endosperm Balance Number (EBN) of over 80 species and subspecies of the tuber-bearing Solanums and their close non-tuber-bearing relatives representing 13 taxonomic series has been determined, with no species assigned to more than one EBN level. Among North American species, most diploids are 1EBN, most tetraploids are 2EBN and all hexaploids are 4EBN; however, among South American species most diploids are 2EBN, most tetraploids are 4EBN and again all hexaploids are 4EBN. Thus species may be isolated from others of the same ploidy level by EBN differences, e.g., 4×(2EBN) from 4×(4EBN), while other species differing in ploidy but having the same EBN may be intercrossed, e.g., 4×(2EBN) and 2×(2EBN). Chromosome doubling or 2n gametes can be used to make a lower EBN species compatible with a higher EBN species. These findings also explain the major crossing difficulties previously inherent in the use of North American species in potato improvement. They also have direct implications for potato improvement, barring the occurrence of other incompatibility barriers. Any 4×(4EBN) cultivar is endosperm compatible and thus will cross with 4×(4EBN) and 6×(4EBN) species. The 2×(2EBN) haploids of 4×(4EBN) cultivars likewise will hybridize with 2×(2EBN) and 4×(4EBN) species. All 2×(1EBN) species are crossable with 2×(2EBN) haploids through 2n gametes or chromosome doubling.Cooperative investigation of the U.S. Department of Agriculture, Agriculture Research Service, and the Wisconsin Experiment Station.     

Hybridization barriers among the species of Arachis L., namely of the sections Arachis (including the groundnut) and Erectoides

Some members of section Erectoides have been found resistant to early leaf spot disease, a serious constraint to groundnut productivity. These accessions do not cross with cultivated species. Crossing between one such diploid species, A. paraguariensis (ICGs 8130 and 8973) of section Erectoides, and the diploids, A. batizocoi and A. duranensis, and the tetraploid A. hypogaea (groundnut) of section Arachis has helped understand barriers to hybridization between sections. These crosses result in the development of normal pegs and pods, but with of ovule and embryo development restricted or non-existent. Such restricted growth and embryo abortion is found to be due to cessation of early endosperm development in A. duranensis (2x) times A. paraguariensis (2x), the non-development of endosperm beyond the coenocytic stage in A. batizocoi (2x) times A. paraguariensis (2x), and the overgrowth of nucellar tissue into the embryo sac in case of A. hypogaea (4x) times A. paraguariensis (2x).The weak cross-compatibility between the species of two sections suggest relatively closer phylogenetic relationship between them, than with the other incompatible sections of the genus Arachis.     

Crossability relationships among wild potato species with different ploidies and Endosperm Balance Numbers (EBN)

Three wild potato species with different ploidies and Endosperm Balance Numbers (EBN) were crossed in a complete diallel design and the development of the embryo and endosperm as well as the type of seeds produced were analyzed. The compatible crosses – intraspecific intra-EBN and interspecific intra-EBN – produced more than 89% plump seeds, whereas in the incompatible crosses – intraspecific inter-EBN and interspecific inter-EBN – more than 85% of the seeds were not as well developed or were shrunken. The histological analysis revealed that inviable seeds had less developed or collapsed endosperms and thicker endotheliums than viable ones. A gradation of crossabilities was observed among species. The self-compatible species Solanum acaule had good performance as a female but not as a male parent. Among the self-incompatible species, Solanum gourlayi was the best male parent but had a poor performance as a female, whereas Solanum commersonii had an intermediate behavior. Differences in crossabilities among genotypes within species were also observed. These results can not be solely explained by the EBN hypothesis. It is, therefore, suggested that the EBN may be part of a more complex system of interspecific barriers acting at the pre- and post-zygotic levels. This revised version was published online in July 2006 with corrections to the Cover Date.     

Transgene introgression from Brassica napus to different varieties of Brassica juncea

Transgene introgression from transgenic rapeseed (Brassica napus) to different varieties of B. juncea was assessed in this study. Crossability between a transgenic rapeseed line Z7B10 (pollen donor) and 80 cultivars of 16 B. juncea varieties (including two wild accessions) was estimated by artificial pollination in a greenhouse. As a result, interspecific crossability between the transgenic Z7B10 line and the 80 B. juncea cultivars varied considerably, with seeds per flower from 0.00–10.67. Seed germination rates of the interspecific F₁ hybrids ranged from 49.0%–89.3%. The estimated frequencies of natural gene flow from the transgenic Z7B10 line to 10 B. juncea cultivars with different uses in the experiment field varied from 0.08% to 0.93%. The natural F₁ hybrids were highly sterile, with seeds per silique ranging from 0.27 to 1.03. In addition, seeds per flower of hybrid descendants varied from 0.02 to 0.22 when F₁ hybrids were self‐pollinated, and those ranged from 0.03 to 0.30 when F₁ hybrids were backcrossed with their corresponding B. juncea parents. Results of this study suggest a low level of transgene introgression from transgenic rapeseed to different B. juncea varieties, which provides a sound scientific basis for the safety management of coexisting transgenic B. napus and B. juncea varieties in China.     

The chromosomal locations of high crossability genes in tetraploid wheat Triticum turgidum L. cv. Ailanmai native to Sichuan, China

Chromosomal locations of crossability genes in tetraploid wheat Ailanmai with high crossability native to Jianyang of Sichuan province, China, was determined by aneuploid analysis employing the D-genome chromosome substitution lines of Langdon durum wheat and monosomic lines of common wheat, Abbondanza. High crossability of Ailanmai was attributed to recessive crossability alleles on chromosomes 1A, 6A and 7A. The effects of chromosomes 7A and 1A were stronger than chromosome 6A. These results indicated that high crossability in Chinese tetraploid wheat cv. Ailanmai and Chinese hexaploid wheat is controlled by different genetic systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

Polygon of crossability between eleven species of Ipomoea: section Batatas (Convolvulaceae)

Summary Crossability within Ipomoea section Batatas is complex because of genetic, cytogenetic and physiological interactions. This complexity is responsible for the fact that knowledge about phylogenetic relationships within this section remains preliminary. Between 1988 and 1991, studies of planting, pollination and evaluation of progenies were carried out at the facilities of CIP in La Molina and San Ramon, Peru. Self-compatibility was found in nine diploid species. Self-incompatibility was found in diploid I. trifida, tetraploid I. tiliacea and both tetraploid and hexaploid I. batatas. Sexual compatibility is though to be related to a multiallelic sporophytic incompatibility system which is expressed in the stigmatic papillae. Altogether, 4,162 cross pollinations were made between 11 species and 76 interspecific combinations of 110 possible combinations in a diallel 11×11 design. From these 76 interspecific combinations only 38 survived, and in these crossability (= proportion between number of fruits harvested/pollinations made) ranged from 0.01 to 1.00 at La Molina. At San Ramon, 11 out of 17 cross combinations were successful, and in these crossability ranged from 0.01 to 0.71. Crossability appeared to be influenced by latitude which is related to flowering synchrony. The early death of seedlings is hypothesized to be related to a genomic imbalance between embryo and endosperm. Maternal effects were found in crosses between diploids and tetraploids which produced triploid and diploid offspring, and in crosses between hexaploids and diploids which gave rise to hexaploid offspring. This study shows that I. trifida and I. x leucantha may act as bridge species for gene flow from wild Ipomoea species to the genepool of the sweetpotato.     

The characterization of autoallotetraploid hybrids between Iris ensata Thunb. and I. laevigata Fisch.

The characteristics of autoallotetraploid hybrids obtained from the cross between Iris ensata cv. Raspberry Rimmed (4X) and amphidiploids of I. laevigata × I. ensata were examined and compared with those of their parents. The color of inner and outer perianths in the autoallotetraploids were bluish purple and similar to those of the amphidiploid parent. However, the autoallotetraploids exhibited low pollen fertility. In addition, the autoallotetraploids were characterized by 17 or 19 anthocyanins and had high resemblance to their parents in the anthocyanin expression. Among these anthocyanins, malvidin 3RGac5G and petunidin 3RGac5G were regarded as major anthocyanins in the autoallotetraploids and their parents, but the differences in the ratios of malvidin 3RGac5G:petunidin 3RGac5G between the autoallotetraploids and their parents were ca. 2:1 for the former and ca. 1:1 for the latter. No viable hybrid seeds were obtained from the reciprocal crosses between I. ensata (2X and 4X) and the autoallotetraploids. Finally, the interspecific cross-breeding of I. ensata using the autoallotetraploids is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Production of interspecific F1 hybrids, BC1, BC2 and BC3 populations between Lycopersicon esculentum and two accessions of Lycopersicon peruvianum carrying new root-knot nematode resistance genes

Two accessions of Lycopersicon peruvianum Mill. (PI270435, PI126443) carrying Mi-2 and Mi-3, respectively, new root-knot nematode resistance genes, were selected as the male parents for crosses with L. esculentum Mill. in order to produce interspecific hybrids. Crossability barriers between these two distantly related species were circumvented by ovule culture. A total of ten interspecific F₁ hybrid plants were produced. The hybrid nature of the putative F₁ plants was confirmed by a comparison of several morphological characteristics and a PCR-based assay. Eight of ten hybrid plants were backcrossed with L. esculentum to generate a total of 98 BC₁ progeny. Two lines were advanced to the BC₂ and BC₃ levels. Based on these results, ovule culture was found to be an effective method for the production of novel interspecific F₁ and BC₁ plants. This revised version was published online in July 2006 with corrections to the Cover Date.