Albinism in F1 Hybrids Hinders Geneflow Between Cultivated Chickpea (Cicer arietinum L.) and the Tertiary Gene Pool Species, Cicer Pinnatifidum

Wild Cicer species, especially those in the tertiary gene pool, carry useful alleles for chickpea improvement. The aim of this study was to evaluate the crossability and geneflow between three chickpea cultivars (as female parents) and four cross-incompatible Cicer pinnatifidum accessions (as pollen parents) from the tertiary gene pool. Ten crosses were conducted. One fully developed healthy F1 seed was harvested in vivo from the ICC 4958 × ICC 17269 cross, but the seedling developed an albino phenotype at 4–5 days after germination. Unlike other crosses, those involving the cultivar ICCV 96030 generated a large number of pods with comparatively large ovules. One albino plantlet was obtained from the ICCV 96030 × ICC 17269 cross by embryo rescue. Crosses involving ICCV 10 resulted in flower drop and poor pod set. These variable genotype-specific responses of pod, ovule, and seed development indicate that genetic factors affect the formation of interspecific hybrids. Although pod and seed formation in these interspecific crosses can be improved, geneflow between these materials is hindered by a strong genetic factor conferring albinism in the F1 hybrids.

Evolution and diversity of the wild rice Oryza officinalis complex, across continents genome types, and ploidy levels

The Oryza officinalis complex is the largest species group in Oryza, with more than nine species from four continents, and is a tertiary gene pool that can be exploited in breeding programs for the improvement of cultivated rice. Most diploid and tetraploid members of this group have a C genome. Using a new reference C genome for the diploid species Oryza officinalis, and draft genomes for two other C genome diploid species O. eichingeri and O. rhizomatis, we examine the influence of transposable elements on genome structure and provide a detailed phylogeny and evolutionary history of the Oryza C genomes. The O. officinalis genome is 1.6 times larger than the A genome of cultivated O. sativa, mostly due to proliferation of Gypsy type long-terminal repeat (LTR) transposable elements, but overall syntenic relationships are maintained with other Oryza genomes (A, B and F). Draft genome assemblies of the two other C genome diploid species, O. eichingeri and O. rhizomatis, and short-read resequencing of a series of other C genome species and accessions reveal that after the divergence of the C genome progenitor, there was still a substantial degree of variation within the C genome species through proliferation and loss of both DNA and LTR transposable elements. We provide a detailed phylogeny and evolutionary history of the Oryza C genomes, and a genomic resource for the exploitation of the Oryza tertiary gene pool.

Chromosome Rearrangements Caused by Double Monosomy in Wheat-Barley Group-7 Substitution Lines

Interspecific or introgressive hybridization is one of the driving forces in plant speciation, producing allopolyploids or diploids with rearranged genomes. The process of karyotype reshaping following homoploid interspecific hybridization has not been studied experimentally. Interspecific hybridization is widely used in plant breeding to increase genetic diversity and introgress new traits. Numerous introgression stocks were developed for hexaploid wheat Triticum aestivum L. (2n = 6x = 42, genome AABBDD). Double monosomic lines, containing one alien chromosome from the tertiary gene pool of wheat and one homoeologous wheat chromosome, represent a simplified model for studying chromosome rearrangements caused by interspecific hybridization. The pairing of a chromosome from the tertiary gene pool with a wheat homoeologue is restricted by the activity of the wheat Ph1 gene, thus, rearrangements caused by chromosome breakage followed by the fusion of the broken arms can be expected. We analyzed chromosome aberrations in 4 sets of lines that originated from double monosomics of barley (Hordeum vulgare L.) chromosome 7H and wheat group-7 chromosomes with dicentric or ring chromosomes. The dynamics of wheat-barley dicentric chromosomes during plant development was followed and an increased diversity of rearrangements was observed. Besides the targeted group-7 chromosomes, other wheat chromosomes were involved in rearrangements, as chromosomes broken in the centromeric region fused with other broken chromosomes. In some cells, multi-centric chromosomes were observed. The structure and dosage of the introgressed barley chromatin was changed. The transmission of the rearrangements to the progenies was analyzed. The observed aberrations emphasize the importance of cytogenetic screening in gene introgression projects.

Highly Fertile Intersectional Blueberry Hybrids of Vaccinium padifolium Section Hemimyrtillus and V. corymbosum Section Cyanococcus

The primary gene pool of Vaccinium species used by blueberry breeders has traditionally been the North American Vaccinium species of section Cyanococcus. Blueberries in commercial production represent three primary Vaccinium species and two ploidy levels. Significant use has been made of the secondary gene pool of Vaccinium, especially in the development of southern highbush blueberry (Vaccinium ×corymbosum) cultivars. Section Hemimyrtillus species are distantly related and are best considered part of the tertiary gene pool of Vaccinium. Vaccinium padifolium, a member of section Hemimyrtillus and native to the Madeira Islands, Portugal, has features of notable value to conventional blueberry development, among these: upright structure, strong growth, abundant flowering and fruiting, good self-fertility, inflorescence structure suited to mechanical harvesting, and indeterminate/repeat flowering. Our objective was to incorporate germplasm from this section into cultivated materials and transfer the desirable traits these species possess for commercial production. We used V. padifolium as a female in crosses with V. corymbosum and generated two highly fertile hybrids. These hybrids are intermediate in morphology, phonological, and their hybridity has been confirmed through DNA testing. These hybrids were used in further crosses to a variety of section Cyanococcus selections and have generated numerous second-generation hybrids. We have also determined by flow cytometry the ploidy levels of the hybrids and several previously unevaluated section Hemimyrtillus species.

Vaccinium species of section Hemimyrtillus: their value to cultivated blueberry and approaches to utilization1This article is part of a Special Issue entitled “A tribute to Sam Vander Kloet FLS: Pure and applied research from blueberries to heathland ecology”.

The primary gene pool of Vaccinium species used by breeders has traditionally been the North American Vaccinium species in section Cyanococcus. Blueberries in commercial production represent several Vaccinium species and ploidies. Moreover, significant use has been made of the secondary gene pool of Vaccinium, especially in the development of southern highbush cultivars. Section Hemimyrtillus represents species that are part of the tertiary gene pool of Vaccinium. Two species of section Hemimyrtillus, native to the Portuguese islands of Madeira (Vaccinium padifolium Smith) and the Azores (Vaccinium cylindraceum Smith), have features of notable value to conventional blueberry development such as upright structure, strong growth, abundant flowering and fruiting, good self-fertility, acceptable fruit quality, inflorescence structure suited to mechanical harvesting, and repeat flowering. Vaccinium cylindraceum is deciduous, whereas V. padifolium is evergreen. Vaccinium arctostaphylos L., a native of the Caucasus region, is closely allied to V. padifolium, hybridizes freely with it, and has many similar characters, but with the valuable addition of greater cold hardiness. Initial progress has been made at incorporating these species into forms compatible with Vaccinium corymbosum L. based blueberry cultivars, and further evaluations are being made of both parental material and the derived hybrids.

Distribution of downy mildew (Bremia lactucaeRegel) resistances in a genebank collection of lettuce and its wild relatives

Genebanks serve as a rich source of diversity that can be exploited for crop improvement. However, large numbers of accessions usually have to be evaluated to find material with the characters of interest, and therefore, enhanced trait information can facilitate the more efficient selection of accessions by users. In this study, we report on the distribution of resistances to 28 races of downy mildew among 1223 genebank accessions of cultivated lettuce (Lactuca sativaL.) and 14 related wild species. Due to modern plant breeding, the overall level of resistance of cultivars released after 1950 appears to have increased two- to three-fold compared with varieties from earlier periods. Although fully resistant reactions could be observed among the accessions of cultivated lettuce for each of the 28 investigated races, the resistance probability was more than two-fold higher on average for accessions from the wild gene pool. In general, species of the primary gene pool appeared less resistant than those of the secondary or tertiary gene pool. Probabilities for examinedLactucaspecies ranged from 0.29 forL. serriolato 1.00 forL. perenniscompared with 0.19 for cultivated lettuce, with lower overall resistance probabilities observed only forL. altaica,L. dregeanaandL. tenerrima. ForL. serriola, the closest relative of cultivated lettuce and the wild species with the highest number of examined accessions, resistance probabilities to each of the investigated downy mildew races were relatively high for populations originating from Eastern Europe and Northern Asia.