Uniqueness of the Gossypium mustelinum genome revealed by GISH and 45S rDNA FISH.

Gossypium mustelinum ((AD)4 ) is one of five disomic species in Gossypium. Three 45S ribosomal DNA (rDNA) loci were detected in (AD)4 with 45S rDNA as probe, and three pairs of brighter signals were detected with genomic DNA (gDNA) of Gossypium D genome species as probes. The size and the location of these brighter signals were the same as those detected with 45S rDNA as probe, and were named GISH-NOR. One of them was super-major, which accounted for the fact that about one-half of its chromosome at metaphase was located at chromosome 3, and other two were minor and located at chromosomes 5 and 9, respectively. All GISH-NORs were located in A sub-genome chromosomes, separate from the other four allopolyploid cotton species. GISH-NOR were detected with D genome species as probe, but not A. The greatly abnormal sizes and sites of (AD)4 NORs or GISH-NORs indicate a possible mechanism for 45S rDNA diversification following (AD)4 speciation. Comparisons of GISH intensities and GISH-NOR production with gDNA probes between A and D genomes show that the better relationship of (AD)4 is with A genome. The shortest two chromosomes of A sub-genome of G. mustelinum were shorter than the longest chromosome of D sub-genome chromosomes. Therefore, the longest 13 chromosomes of tetraploid cotton being classified as A sub-genome, while the shorter 13 chromosomes being classified as D sub-genome in traditional cytogenetic and karyotype analyses may not be entirely correct.

Ploidy manipulation of the gametophyte, endosperm and sporophyte in nature and for crop improvement: a tribute to Professor Stanley J. Peloquin (1921-2008).

BACKGROUND: Emeritus Campbell-Bascom Professor Stanley J. Peloquin was an internationally renowned plant geneticist and breeder who made exceptional contributions to the quantity, quality and sustainable supply of food for the world from his innovative and extensive scientific contributions. For five decades, Dr Peloquin merged basic research in plant reproduction, cytology, cytogenetics, genetics, potato (Solanum tuberosum) improvement and education at the University of Wisconsin-Madison. Successive advances across these five decades redefined scientific comprehension of reproductive variation, its genetic control, genetic effects, evolutionary impact and utility for breeding. In concert with the International Potato Center (CIP), he and others translated the advances into application, resulting in large benefits on food production worldwide, exemplifying the importance of integrated innovative university research and graduate education to meet domestic and international needs. SCOPE: Dr Peloquin is known to plant breeders, geneticists, international agricultural economists and potato researchers for his enthusiastic and incisive contributions to genetic enhancement of potato using haploids, 2n gametes and wild Solanum species; for his pioneering work on potato cultivation through true seed; and as mentor of a new generation of plant breeders worldwide. The genetic enhancement of potato, the fourth most important food crop worldwide, benefited significantly from expanded germplasm utilization and advanced reproductive genetic knowledge, which he and co-workers, including many former students, systematically transformed into applied breeding methods. His research on plant sexual reproduction included subjects such as haploidization and polyploidization, self- and cross-incompatibility, cytoplasmic male sterility and restorer genes, gametophytic/sporophytic heterozygosity and male fertility, as well as endosperm dosages and seed development. By defining methods of half-tetrad analysis and new cytological techniques, he elucidated modes, mechanisms and genetic controls and effects of 2n gametes in Solanum. Ramifications extend to many other crops and plants, in both basic and applied sciences. ACHIEVEMENTS: Based upon a foundation of genetics, cytogenetics and plant reproductive biology, Dr Peloquin and co-workers developed methods to use 2n gametes and haploids for breeding, and used them to move genes for important horticultural traits from wild tuber-bearing Solanum species to cultivated potato for the betterment of agriculture. The resulting potato germplasm included combinations of yield, adaptation, quality and disease resistance traits that were previously unavailable. This elite plant germplasm was utilized and distributed to 85 countries by the CIP, because it not only increased potato yields and quality, it also broadened the adaptation of potato to lowland tropical regions, where humanity has benefited from this addition to their food supply.

Wide-cross whole-genome radiation hybrid mapping of cotton (Gossypium hirsutum L.).

We report the development and characterization of a "wide-cross whole-genome radiation hybrid" (WWRH) panel from cotton (Gossypium hirsutum L.). Chromosomes were segmented by gamma-irradiation of G. hirsutum (n = 26) pollen, and segmented chromosomes were rescued after in vivo fertilization of G. barbadense egg cells (n = 26). A 5-krad gamma-ray WWRH mapping panel (N = 93) was constructed and genotyped at 102 SSR loci. SSR marker retention frequencies were higher than those for animal systems and marker retention patterns were informative. Using the program RHMAP, 52 of 102 SSR markers were mapped into 16 syntenic groups. Linkage group 9 (LG 9) SSR markers BNL0625 and BNL2805 had been colocalized by linkage analysis, but their order was resolved by differential retention among WWRH plants. Two linkage groups, LG 13 and LG 9, were combined into one syntenic group, and the chromosome 1 linkage group marker BNL4053 was reassigned to chromosome 9. Analyses of cytogenetic stocks supported synteny of LG 9 and LG 13 and localized them to the short arm of chromosome 17. They also supported reassignment of marker BNL4053 to the long arm of chromosome 9. A WWRH map of the syntenic group composed of linkage groups 9 and 13 was constructed by maximum-likelihood analysis under the general retention model. The results demonstrate not only the feasibility of WWRH panel construction and mapping, but also complementarity to traditional linkage mapping and cytogenetic methods.