Genetic resources and breeding of Capsicum spp.

Five species of Capsicum have been domesticated in the American tropics, but breeding programs have concentrated on the non-pungent cultivars of C. annuum. Studies of the consequences of human selection during and after domestication support theoretical calculations that there will be significant amounts of genetic diversity within as well as between species. Breeders have only recently begun to exploit this diversity. Multiple resistances are available to several pests and diseases, but have to be transferred from one agronomic or market type of pepper to another. Problems in selecting simultaneously for multigenic resistances and polygenic quality characters may be eased by the development of molecular markers and a molecular linkage map for Capsicum. Ploidy changes (both tetraploidy and haploidy) are relatively easy to induce in Capsicum species. Doubled haploids have proved particularly valuable in the analysis of the genetically complex basis of some resistances to pests and diseases. Barriers to interspecific gene transfer are similar to those found in other genera of Solanaceae: unilateral incompatibility, post-fertilisation abortion, and nucleo-cytoplasmic interactions leading to male sterility or other abnormalities. Information on the occurrence and effects of these barriers should be available if or when breeders need to turn to interspecific hybridisation. This revised version was published online in July 2006 with corrections to the Cover Date.     

The importance of wild potato species resistant to the potato cyst nematode,Globodera pallida,pathotypes P4A and P5A,in potato breeding. II. The crossability of resistant species

Summary Over 2400 pollinations were made to investigate the crossability relationships between cultivated potatoes, and wild diploid species from Series Tuberosa and Circaeifolia, as well as wild polyploid species in Series Tuberosa and Longipedicellata resistant to potato cyst nematode, Globodera pallida pathotypes P₄A and P₅A. Wild diploids in Series Tuberosa crossed easily with cultivated diploid species, except with Solanum lignicaule where most pollinations failed, and seed set was extremely low (0.2 seeds per pollination or less). It is suggested that this species is 1EBN. S. capsicibaccatum is clearly isolated from Series Tuberosa, but can form hybrids with S. lignicaule, which can act as a bridging species to S. tuberosum haploids. S. gourlayi and S. oplocense can be crossed with both subspecies of S. tuberosum, but S. papita, Series Longipedicellata is reproductively isolated from the tetraploid cultigens. The crossability data are discussed in the light of germplasm utilisation for breeding potato varieties resistant to potato cyst nematode.     

Patterns of co-existence and hybridisation between narrowly endemic (Fundulus euryzonus) and broadly distributed (F. olivaceus) topminnows in a riverine contact zone

Abstract –  Two ecologically similar topminnow species ( Fundulus olivaceus and F. euryzonus ) were studied in a contact zone in the West Fork of the Amite River of the Lake Pontchartrain drainage. We assessed whether relative abundance and measures of fitness of each species, and their hybrids, were correlated with predictable abiotic or biotic factors. We sampled the full fish assemblage and measured a suite of local and landscape level environmental characteristics at ten sites. Topminnows were genotyped to identify individuals of hybrid ancestry. We compared the abundance and distribution of parental species in the context of overall fish assemblage structure and environmental variables. Hybridisation was generally rare with only nine of 244 genotyped topminnows exhibiting evidence of hybrid ancestry. The relative abundance of the two topminnows was related to site assemblage structure, species diversity and a number of local but not landscape level environmental variables. Both species were in better condition and females were more fecund at sites with greater abundance of F. olivaceus . Hybrid individuals were not morphological or ecological intermediates.     

Pollen selection for chilling tolerance at hybridisation leads to improved chickpea cultivars

The potential of pollen selection as part of the breeding efforts to increase chilling tolerance in chickpea was investigated. This alternative approach to apply selection pressure at the gametophytic stage in the life cycle has been proposed widely, but there are no reports of the technique being implemented in a crop improvement program. In this paper, we describe how we developed a practical pollen selection technique useful for chickpea improvement.Pollen selection improved chilling tolerance in crossbreds compared with the parental chickpea genotypes and compared with progeny derived without pollen selection. This is backed up by controlled environment assessments in growth rooms and by field studies. We also clearly demonstrate that chilling tolerant pollen wins the race to fertilise the ovule at low temperature, using flower color as a morphological marker. Overall, pollen selection results in a lower threshold temperature for podding, which leads to pod setting two to four weeks earlier in the short season Mediterranean-type environments of Western Australia. Field testing at multiple sites across Australia, as part of the national crop variety testing program, shows that these breeding lines have a significant advantage in cool dryland environments.The major factors which affected the success of pollen selection are discussed in the paper, from generation of variability in the pollen to a means to recover hybrids and integration of our basic research with an applied breeding program. We conclude that chilling tolerance observed in the field over successive generations are the result of pollen selection during early generations.     

Interspecific hybridisation of soybeans and perennial Glycine species indigenous to Australia via embryo culture

Summary Five sterile hybrids (2n=59) between a synthetic amphiploid of Glycine tomentella (2n=38) and G. caneseens (2n=40) as female and soybean cultivars Lincoln and Hark as males have been produced by embryo or ovule culture using transplanted endosperm. The hybrid plants are twining perennials like the female parent but possess a number of morphological characters which reflect the presence of the soybean genome. Indophenol oxidase isozymes from leaf extracts also provide good evidence of the hybrid nature of the cultured plants. These hybrids open the way for the exploitation of the diverse germplasm resources of the perennial Glycine species in soybean breeding.     

Fertilisation assessment and postzygotic development in several intra- and interspecific Prunus hybrids

Summary the clearing technique was applied to assess fertilisation and to follow the postzygotic development in ten intra- and interspecific crosses among Prunus species used as rootstocks. The technique allowed to distinguish fertilised ovules from unfertilised ones, as well as to calculate the fertilisation percentage in intra-and interspecific compatible crosses. All the stages from unfertilised to fertilised ovules were analysed in order to determine the best time for embryo rescue. Differences in postzygotic development among the crosses are discussed in terms of the genotype of the seed parent in the pollen-pistil interactions.Abbreviations DAP Days After Pollination     

Hybridisation between wheat and Aegilops geniculata and hybrid fertility for potential herbicide resistance transfer

Hybridisation between wheat and Aegilops geniculata was quantified in a 4‐year crossing experiment in the glasshouse, using three wheat cultivars as pollen donors and herbicide resistance as a phenotypic marker. Hybridisation rates ranged from 5% to 74%. Most of the hybrids were self‐sterile. However, seven F₂ seeds were obtained from 165 A. geniculata–wheat hybrids. Hybrid seeds were found in all backcross (BC₁) combinations at average rates of 4.2% (0–26.3%) and 5.88% (0–34%) under glasshouse and field experiments, respectively, with significant differences among years and cultivars. Wheat cultivars, F₁ and BC₁ plants, were resistant to herbicides while A. geniculata plants were susceptible. In the subsequent generations, although few plants were available, the BC₁F₁ had a certain degree of fertility and the fertility increased in the F₂ plants, with one plant that reached 66.7%. The commercial growing of genetically modified herbicide‐tolerant wheat is expected to have the potential for the inserted gene to escape from the crop and become incorporated in a closely related wild species, conferring a competitive advantage to these conferring weeds. Determining the frequency of crop‐wild transgene flow and the fertility of the formed hybrids is a necessity for risk assessment. Data presented here provide new knowledge on the potential A. geniculata–wheat herbicide resistance transfer.     

Isolation of Y Chromosome-specific Sequences and their Use in Embryo Sexing*

Y chromosome-specific sequences derived to date from cattle, sheep and pigs are described. The methods used to isolate these sequences and possible future approaches are discussed. Three different techniques of sex determination are described: in situ hybridisation, Southern/Dot blotting and PCR based assays. All three methods utilise Y chromosome-specific sequences. Necessary controls and precautions for PCR mediated assays are discussed.     

The use of wheat-alien and Aegilops-rye amphiploids for introgression of genetic material to wheat

An introduction of genetic material from rye, Aegilops and Elymus into durum and common wheat by crossing the wheat species with different amphiploids, has been attempted. Meiotic studies of the hybrids demonstrated that the wheat Elymus sibiricus amphiploid contained several (two or three) genes suppressing the activity of the wheat homoeologous pairing control system. Somatic chromosome studies of the hybrids revealed that the distributions of the alien chromosomes transferred to the second hybrid generation did not correspond to random (0.5 + 0.5)^2k and binomial (p + q)^2k distributions. An essential amendment for gamete and zygote viability, allowing the approximation of distributions by binomial equation, is discussed. The preferential E. sibiricus chromosome transmission was observed. The first backcross was found to be a critical stage while using the Aegilops-rye amphiploids for production of wheat introgressive forms. Stabilisation of the somatic karyotype and improvement of the meiotic regularity was observed in a number of generations. The isolation of stable cytological lines in BC₃ was found to be possible. This revised version was published online in August 2006 with corrections to the Cover Date.