Attempts to overcome partial incompatibility between Hordeum vulgare L. and H. bulbosum L.

Summary Partial incompatibility has already been reported between Hordeum vulgare and H. bulbosum during the course of doubled haploid production, and in this paper attempts to overcome the breeding barrier are described. The methods which seem to offer most success are those of environmental adjustments and the adoption of new genotypes of H. bulbosum. Further cultivars of H. vulgare exhibiting this phenomenon are also noted.     

Characterization of resistance genes against scald (Rhynchosporium secalis (Oudem.) J.J. Davis) in barley (Hordeum vulgare L.) lines from central Norway, by means of genetic markers and pathotype tests

Rhynchosporium secalis is a serious pathogen of barley (Hordeum vulgare L.) in central Norway. A breeding effort was initiated in 1977 to introduce resistance from different sources into adapted genotypes, and the first cultivar from the program was recently released. However, little is known about the resistance genes introgressed in this cultivar or in advanced breeding lines. An effort was made to address this issue through a set of isolates and available molecular markers. Fourteen breeding lines and their resistance donors were investigated by evaluating their reactions to 11 R. secalis isolates. Bulked segregant analysis was used to identify molecular markers linked to resistance genes in 12 of the breeding lines. The isolates were found to be of less discriminating value than the markers. Useful information has been obtained as to the nature of several of the resistance genes introgressed. Eight of the 12 breeding lines contained introgressed genes that were located at the `complex Rh' locus on chromosome 3H and hence may not easily be pyramided into the same genotype. Previous information about the nature of the resistance in `Jet' is questioned. Neither of the resistance genes Rh or Rh2 seems to have been incorporated into Norwegian breeding material.     

The need for characterisation and evaluation of germplasm: kiwifruit as an example

Genetic diversity provides the raw material for breeding and plant improvement. Breeders of plant species that have little or no history of improvement tend to make the greatest use of collections of raw or unimproved germplasm. Kiwifruit (Actinidia) are one such crop in that they have been subjected to little selection pressure and are still very similar to plants in the wild. To take advantage of the diversity in the genus Actinidia, breeders need to know the extent of the diversity and also need to be able to identify the plants with which they are working. Voucher specimens should be prepared for all plants used in experimental studies. A good understanding of the reproductive biology of Actinidia should facilitate incorporation of wild germplasm into kiwifruit breeding programmes. The HortResearch Actinidia collection has already proved its worth with the development of valuable new kiwifruit cultivars.     

Breeding system of Solanum integrifolium Poir. with an emphasis on sex potential and intercrossability

Summary The breeding system of Solanum integrifolium has been studied with the view of setting up a breeding programme. Three flower types are distinguished on the basis of style length. The results of crosses among these types have elucidated that only long-style flowers are female-fertile. The medium and short-style flowers are unable to set fruits. Some of the flowers, irrespective of their stylar morphism, also exhibit male sterility which is uncommon in Solanum. The biological significance of the stylar heteromorphism has been discussed in relation to evolutionary trends in the genus and the probable cause of this phenomenon speculated upon.     

Screening techniques and sources of resistance to parasitic angiosperms

Parasitic angiosperms cause great losses in many important crops under different climatic conditions and soil types. The most widespread and important parasitic angiosperms belong to the genera Orobanche, Striga, and Cuscuta. The most important economical hosts belong to the Poaceae, Asteraceae, Solanaceae, Cucurbitaceae, and Fabaceae. Although some resistant cultivars have been identified in several crops, great gaps exist in our knowledge of the parasites and the genetic basis of the resistance, as well as the availability of in vitro screening techniques. Screening techniques are based on reactions of the host root or foliage. In vitro or greenhouse screening methods based on the reaction of root and/or foliar tissues are usually superior to field screenings and can be used with many species. To utilize them in plant breeding, it is necessary to demonstrate a strong correlation between in vitro and field data. The correlation should be calculated for every environment in which selection is practiced. Using biochemical analysis as a screening technique has had limited success. The reason seems to be the complex host-parasite interactions which lead to germination, rhizotropism, infection, and growth of the parasite. Germination results from chemicals produced by the host. Resistance is only available in a small group of crops. Resistance has been found in cultivated, primitive and wild forms, depending on the specific host-parasite system. An additional problem is the existence of pathotypes in the parasites. Inheritance of host resistance is usually polygenic and its transfer is slow and tedious. Molecular techniques have yet to be used to locate resistance to parasitic angiosperms. While intensifying the search for genes that control resistance to specific parasitic angiosperms, the best strategy to screen for resistance is to improve the already existing in vitro or greenhouse screening techniques.     

The Occurrence of Rust Resistance Gene Ur-13 in Common Bean Cultivars and Lines

Summary For the past 10 years, the Andean-type Phaseolus vulgaris cultivar Kranskop has played an important role in South African bean production and breeding. Kranskop shares an ancestor with the internationally important Andean-type rust differential cultivar Redlands Pioneer. The Ur-13 gene in Kranskop and Redlands Pioneer gives protection to numerous internationally reported races of Uromyces appendiculatus and it is imperative to retain this gene in local breeding programmes.In this study, three co-dominant SCAR markers (SE_AACM_ACC430/405, SE_ACAM_CTT310/288 and SE_AAGM_CGT436 Hha I_186/250) were used to trace the origin of Ur-13, and its presence in 71 germplasm accessions, including the international rust differential lines and additional sources of already characterized genes, as well as 78 breeding lines.Each marker was present in approximately 30% of the accessions tested. Only accessions belonging to the Kranskop or Redlands groups contained all three markers. Contrary to expectations, the first two markers, as well as Ur-13, appeared to have originated from a Middle-American-type parent of the Redlands group, California Small White 643, whereas the third marker probably came from the Andean-type cultivar Brown Beauty. This has important implications for the new set of differential lines, as Redlands Pioneer can no longer be regarded as a representative of the Andean gene pool. The markers, in particular SE_AACM_ACC430/405, will be useful in tracing Ur-13 in large seeded breeding material, except where lines such as Mexico 309, PI 181996 and A 286 are used as donors of additional rust resistance genes, as these have the positive alleles of both SE_AACM_ACC430/405 and SE_ACAM_CTT310/288.Part of a Ph.D thesis submitted by the first author to the Department of Plant Sciences, University of the Free State.     

Screening techniques and sources of resistance against parasitic weeds in grain legumes

Summary A number of parasitic plants have become weeds, posing severe constraints to major crops including grain legumes. Breeding for resistance is acknowledged as the major component of an integrated control strategy. However, resistance against most parasitic weeds is difficult to access, scarce, of complex nature and of low heritability, making breeding for resistance a difficult task. As an exception, resistance against Striga gesnerioides based on a single gene has been identified in cowpea and widely exploited in breeding. In other crops, only moderate to low levels of incomplete resistance of complex inheritance against Orobanche species has been identified. This has made selection more difficult and has slowed down the breeding process, but the quantitative resistance resulting from tedious selection procedures has resulted in the release of cultivars with useful levels of incomplete resistance. Resistance is a multicomponent event, being the result of a battery of escape factors or resistance mechanisms acting at different levels of the infection process. Understanding these will help to detect existing genetic diversity for mechanisms that hamper infection. The combination of different resistance mechanisms into a single cultivar will provide durable resistance in the field. This can be facilitated by the use of in vitro screening methods that allow highly heritable resistance components to be identified, together with adoption of marker-assisted selection techniques.     

Diversity of penicillarian millets (Pennisetum glaucum and P. purpureum) as for the compatibility between their gynoecia and pollens from some other Poaceae

Summary The compatibility between gynoecia of different penicillarian millets (Pennisetum glaucum and P. purpureum) and pollens from some other Poaceae was evaluated in order to determine whether different penicillarian pistils showed the same pistil-pollen interactions with a same non-penicillarian pollen and to determine whether compatibility was dependent on the genetic divergence or the degree of sympatric evolution of the mating partners. Ten pearl millet lines (P. glaucum subsp. glaucum), six wild pearl millet accessions (P. glaucum subsp. monodii) and one P. purpureum accession were pollinated with five other Pennisetum species: P. pedicellatum, P. polystachyon, P. schweinfurthii, P. squamulatum, P. ramosum, and with three species from other genera: Cenchrus ciliaris, Panicum maximum and Zea mays. Each male species was represented by a unique accession. Pollen grain germination on the stigmata and pollen tube growth in the gynoecia were monitored by means of fluorescence microscopy after aniline blue staining. Significant compatibility differences were observed between a given pollen and gynoecia from different P. glaucum accessions. But there was no evidence of compatibility differences between the three female taxonomic groups. The eight pollen parents can be classified into three groups according to their mean degree of compatibility with the different penicillarian gynoecia. P. ramosum, P. schweinfurthii and P. squamulatum showed a high compatibility: more than 50% of penicillarian gynoecia had pollen tubes at the micropyle, six hours after pollination. Zea mays, Cenchrus ciliaris and Panicum maximum showed a low compatibility: pollen tubes were arrested in the style. P. pedicellatum and P. polystachyon showed nil compatibility: few pollen grains germinated on the stigmata and very rare tubes reached the entry of the style, where they stopped. It must be noted that such a strong gametic barrier has been observed only with pollinator species sympatric to pearl millet.     

In vitro techniques for genomic alteration in rice plants

Because of the explosive increase in world population, a sufficient food supply must be achieved by varietal improvement in the major cereal crops including rice. It is expected that new in vitro techniques incombination with conventional breeding methods may effectively raise the yield potential. On the other hand, there are many environmental problems to be solved world-wide such as, global warming, environmental pollution, ecological destruction, reduction in water supplies and so on. Therefore, it is necessary to rapidly develop new varieties for the future combining of higher yield potential with excellent grain quality, and resistance to both biotic and abiotic stresses for the promotion of sustainable agriculture. Although many efforts have been made to introduce useful traits from wild species to cultivated rice via hybridization, it is still difficult to overcome breeding barriers such as cross incompatibility and hybrid sterility and inviability in practical breeding. Now in vitro techniques are going to make it possible to use genetic manipulation and cell culture and fusion techniques to speed up the breeding process. For sustainable agriculture, it is important to utilize the useful genes from alien species. For this purpose, asymmetric protoplast fusions have already been used successfully to transfer disease resistance in Brassica napus. In this experiment, a high level of resistance to the rice blast disease was transferred from wild species through asymmetric fusions. It is also noted that manipulation of cytoplasmic genomes is possible through asymmetric fusions as shown in the induction of new cytoplasmic male sterility (CMS). This revised version was published online in August 2006 with corrections to the Cover Date.     

Natural variation within the genus Beta and its possible use for breeding sugar beet: A review

Summary Sugar beet is a relatively young crop, which supposedly has a narrow genetic base. Natural variation occurring in primitive beet varieties and in wild Beta species has been used for breeding sugar beet. This paper reviews information on desirable characteristics in Beta germplasm and the attempts made for the introgression of such characters into commercial breeding material. After an introduction on the availability of germplasm and the possibilities of hybridisation, attention is focussed on the mating system (especially male sterility), on morphological and physiological characteristics, including yield and sugar content, and on resistances to diseases and pests.     

Inheritance and genetic diversity of some enzymes in the sexual and diploid pool of the agamic complex of Maximae (Panicum maximum Jacq., P. infestum Anders. and P. trichocladum K.Schum.)

Summary The tribe Maximae (Panicum maximum Jacp., P. infestum Anders., P. trichocladum K.Schum.) includes two sympatric pools with different modes of reproduction and ploidy levels: an apomictic and tetraploid pool on the one hand, and a smaller, sexual and diploid pool on the other.In the latter, the sexuality allowed crosses and hence it was possible to gather evidence of the structure (monomeric or dimeric) of nine enzymatic systems and of their inheritance (16 loci). Some segregation distortion was observed in the malatedehydrogenase and esterase systems.The genetic diversity of the diploid pool is large, in agreement with its mode of reproduction (allogamy and anemophily). The diversity is divided into three groups corresponding to the geographical origin of populations. This organisation is very similar to that observed from morphological traits.     

The structure and breeding behaviour of a translocation involving the transfer of mildew resistance from Avena barbata Pott. into the cultivated oat

Summary The gene for mildew resistance has been succesfully transferred into the cultivated oat from the wild oat species Avena barbata by means of an irradiation-induced translocation. The translocation has been shown to involve the long arm of chromosome ST21 of A. sativa, the short arm, the centromere and a segment of the long arm of the barbata chromosome.The transmission of the translocation is normal in the cultivar Manod in which it was originally isolated. When the translocation was transferred into other cultivars of oats, transmission through the male gametes was found to be impaired in some genotypic backgrounds. However, there was no evidence that the translocation had any deleterious effect on development and fertility in a range of cultivars.The translocation was shown to involve an exchange between nonhomoeologous chromosomes.The behaviour of the translocation in diverse genotypes indicated that the translocation was a new source of mildew resistance that could be easily used in a breeding programme.     

Interspecific crosses as a tool in breeding Poapratensis L. 1. Poalongifolia Trin × P. pratensis L.

Summary By crossing amphimictic P. longifolia and apomictic P. pratensis fertile hybrids were obtained. In F₂ populations a vast range of types was observed. New combinations were found, which is shown by data on plant length and hairiness of the lemma. Crossing F₁ hybrids with P. pratensis gave more P. pratensis-like plants. Data on seed yield, uniformity and turf performance in later generations are given. The implications for breeding are discussed and it is concluded that interspecific crosses can be used for introducing a sexual phase in P. pratensis breeding. Non-hairiness of the lemma can be incorporated.     

A reproductive calendar of Lilium longiflorum Thunb. cv. Gelria

Summary The development and timing of different processes in the floral biology and sexual reproduction of Lilium longiflorum were studied and brought together into a chronological reproductive calendar. Care must be taken when emasculating flowers later than 4 days before anthesis (DBA), because the stomium of the anther was open from 8 DBA and the pollen grains appear to be mature from 3–2 DBA. The receptivity period of the pistil lasts for a rather long period, but before wilting of an unpollinated flower as determined by a change of the colour of the perianth from white into brown, the flower had already lost its receptivity. Because L. longiflorum pollen grains can easily be stored, the pistil receptivity should thus determine the pollination schedule. The relationships between pollen tubes and pistil are discussed with respect to plant breeding.Abbreviations DAA Days After Anthesis - DAP Days After Pollination - DBA Days Before Anthesis     

Successful hybridization of non-tuberous Solanum etuberosum Lind. and tuberbearing S. pinnatisectum Dun.

The results of extensive crosses between the non-tuberous species Solanum brevidens and S. etuberosum on the one hand and ten tuber-bearing Solanum species on the other are presented. Three crosses gave rise to viable progeny. Two progenies consisted of diploid plants only of the strictly self-incompatible species of the mother parent. One cross, viz. S. etuberosum × S. pinnatisectum, produced highly vigorous but fully male sterile F₁ hybrids.It is suggested that this hybrid together with those between the tomato, Lycopersicon esculentum, and S, pennellii and S. lycopersicoides constitute piers of a bridge between tomato and potato species which in the future might enable gene transfer between these two crops via their wild relatives. However, such idea has to be treated with all proper reserve.The production of this new hybrid is the first step in making accessible to potato breeding the valuable genes which have been detected in S. brevidens and S. etuberosum, viz. the genes for high resistance to frost, leafroll and Y-virus.     

Breeding for resistance to coffee berry disease in Coffea arabica L. II. Inheritance of the resistance

Summary The inheritance of resistance to coffee berry disease (CBD) has been studied by applying a preselection test to F₂ progenies of a half diallel cross between 11 coffee varieties with different degrees of resistance and to sets of parental, F₁, F₂, B₁₁ and B₁₂ generations of crosses between resistant and susceptible varieties. True resistance to CBD appears to be controlled by major genes on three different loci. The highly resistant variety Rume Sudan carries the dominant R- and the recessive K-genes. The non-allelic interaction between these two genes is of a duplicate nature. The R-locus has multiple alleles with R ₁R₁alleles present in Rume Sudan and the somewhat less effective R ₂R₂alleles in a variety like Pretoria, which also has the K-gene. The moderately resistant variety K7 carries only the recessive K-gene. The arabica-like variety Hibrido de Timor (a natural interspecific arabica x robusta hybrid) carries one gene for CBD resistance on the T-locus with intermediate gene action. It probably inherited this gene from its robusta parent. There is circumstantial evidence that the resistance to CBD is of a stable nature, but it is advisable to accumulate in one genotype as many resistance genes as possible by combining in the breeding programme the resistance of Rume Sudan with that of Hibrido de Timor.     

The origin and chromosome numbers of cultivars of Kalanchoe blossfeldiana Von Poelln.: Their history and evolution

Summary Kalanchoe blossfeldiana was described by Von Poellnitz in 1935. It is an endemic species of Madagascar where it was discovered in 1924 by Perrier de la Bâthie, who described it as the variety coccinea of K. globulifera. By 1930 living plants had been spread throughout Europe and the United States. At the same time commercial growing was initiated by Blossfeld at Potsdam, Germany. Selection within the species and, from 1939, hybridisation with several other Kalanchoe species yielded cultivars from which many have disappeared. K. blossfeldiana, like two selections, has 2n=34 chromosomes. The remaining cultivars, which are likely of hybrid origin, are polyploids. They are usually tetraploids (2n=ca 68), but in some cases numbers of 2n=72, 75, 84, 85 and 96 have been counted. Polyploidy already occurred in 1939, when the first interspecific cross, in this case with K. flammea (2n=34), was recoreed. Other species which have been crossed with K. blossfeldiana are K. pumila (2n=40), K. grandiflora (2n=34), K. schumacheri (2n=?), K. kirkii (2n=?) and K. manginii (2n=34).     

Ploidy analysis in water yam, Dioscorea alata L. germplasm

Poor reproductive development in yams (Dioscorea spp.) has often been attributed to the polyploid nature of the crop. In this study, flow cytometry was used to determine the ploidy level of 53 accessions of Dioscorea alata, mostly from West African countries, Chad and Puerto Rico. Nuclei were isolated from young leaf material and stained with DAPI(4,6-diamidino-2-phenylindole). The nuclear genome size (2C) was measured as an indicator of the ploidy level. Dioscorea rotundata genotypes with known ploidy levels were used as standards. The results showed that the majority of plants were hexaploid (84.9%) with a smaller percentage of tetraploids (15.1%). A higher number of male plants were hexaploid than tetraploids. This is at variance with earlier findings, which reported that hexaploid male plants are rare. Higher ploidy levels were not directly related to sparse or erratic flowering as previously reported as profuse flowering occurred in some male hexaploid accessions. These findings have important implications for yam breeding in relation to yam genetic resources. This revised version was published online in August 2006 with corrections to the Cover Date.     

Screening fruit tree genetic resources in Belgium for disease resistance and other desirable characters

Summary The wide diversity of old fruit-tree cultivars originating or introduced into Belgium during the 18 ^th and 19 ^th centuries was collected as far as feasible over the last fifteen years at the State Plant Pathology Station in Gembloux. Out of the 2400 accessions now collected, one quarter was recovered from old public collections, and three quarters came from farms or gardens. The initial intention was to screen the material for disease resistance and other characters of agronomic interest with a view to using the best cultivars as breeding parents. However, as the collection developed, genetic resources conservation also became an objectiveper se. The collection presently contains 1150 apple, 850 pear and 300 plum accessions, and smaller numbers of other fruit species. Each accession is evaluated in an experimental orchard for at least ten years. In view of the growing public interest in old fruit-tree cultivars, the Plant Pathology Station has for several years been releasing to the nursery trade the better cultivars emerging from the evaluation, namely nine apple and four plum cultivars, and one peach cultivar. The principal features of the apple cultivars are presented in this paper. Since 1988, old apple and plum cultivars have been being used at the Station as parents in a breeding programme, with both controlled and open pollination. In some instances, old apple cultivars have also been crossed with a modern parent carrying the Vf gene for scab resistance. The preliminary observations on some of these seedlings are presented.     

Current status and future strategy in breeding pea to improve resistance to biotic and abiotic stresses

The economic importance and current progress made in studies of the host-parasite relationship and identification of sources of resistance and breeding strategies of some important biotic diseases of pea are reviewed in this paper. The root rot complex caused by Rhizoctonia solani, Fusarium solani, Aphanomyces euteiches, Pythium ultimum and Fusarium oxysporum f. sp. pisi, race 1 and 2 has been reported from all commercial pea growing areas of the world. Adequate sources of resistance have been identified and there has been impressive success in the control of the Fusarium wilt pathogen following the introduction of wilt-resistant cultivars. Leaf and stem diseases of pea caused by the Ascochyta complex, Peronospora viciae and Erysiphe pisi are prevalent in most temperate pea growing regions of the world. Several sources of resistance are available, some of which are surprisingly durable. The biochemical genetic parameters of phenolic content used for assaying resistance to Erysiphe pisi offers an alternative method of evaluating breeding material. Wild relatives of pea (Pisum fulvum and P. humile) are valuable additional sources of genetic variation and provide good sources of resistance to pests and diseases. In temperate rainfed pea growing areas of southern Australia, pea seed yield is more closely related to dry matter production than harvest index. Tall and leafy cultivars proved more productive than afila types.