Showing papers in "Euphytica in 2000"

The development and use of microsatellite markers for genetic analysis and plant breeding with emphasis on bread wheat

Abstract: In recent years, a variety of molecular markers, based on microsatellites or simple sequence repeats (SSRs) have become the markers of choice, thus necessitating their development and use in a variety of plant systems. In this review, the basic principles underlying different hybridization-based (oligonucleotide fingerprinting) and PCR based approaches (STMS, MP-PCR, AMP-PCR/ ISSR/ ASSR, RAMPs/ dRAMPs, SAMPL), making use of microsatellites, have been outlined. Different methods for enrichment of genomic libraries for microsatellites have also been outlined. Relevant literature on the subject, giving a summary of results obtained using each approach, has been reviewed and critically discussed. The review also includes a discussion on literature, which deals with the use of microsatellites in genome mapping, gene tagging, DNA fingerprinting, characterization of germplasm and cytogenetics research. Special emphasis has been laid on the genome of bread wheat, where the work done in the authors' own laboratory has also been briefly reviewed.

A comparative assessment of DNA fingerprinting techniques (RAPD, ISSR, AFLP and SSR) in tetraploid potato ( Solanum tuberosum L.) germplasm.

Abstract: Several DNA marker systems and associated techniques are available today for fingerprinting plant germplasm but information on their relative usefulness in particular crops is limited. The study investigated PCR based DNA fingerprinting in a set of 39 potato cultivars using RAPDs (20 primers), ISSRs (6 primers), AFLPs (2 primers) and SSRs (5 primer pairs). Results show that each of the four techniques can on their own, individually identify each cultivar, but that techniques differ in the mean number of profiles generated per primer (or primer pair) per cultivar, referred to as Genotype Index (GI). The order of merit based on this criterium and in this material was AFLPs (GI = 1.0), a multi-locus SSR (GI = 0.77),RAPDs (GI = 0.53), ISSRs (GI = 0.47) and single locus SSRs (GI = 0.36). Problems in relating banding patterns to individual loci and alleles for polyploid genomes, using these techniques as they are currently employed, are also discussed.

Evaluation of grain yield and its components in wheat cultivars and landraces under near optimal and drought conditions.

Abstract: In a 2-years experiment, 30 wheat cultivars and 21 landraces from different countries were tested under near optimum and drought stress conditions. Plant height, number of sterile spikelets per spike, spikelets per spike, number of kernels per spike, kernel weight per spike, 1000 kernel weight and grain yield were evaluated. The number of kernels per spike, 1000 kernel weight and especially yield were more sensitive to drought stress in the cultivars than plant height and number of spikelets per spike, while in the landraces these traits did not differ under drought stress compared to near optimum conditions. The average yield of cultivars was significantly better than the average yield of landraces under near optimum as well as drought stress conditions. Path coefficient analysis showed that for cultivars under near optimum conditions there was no significant direct association of any of the analysed characters with yield, while under drought stress conditions, number of kernels per spike had a significant positive direct effect. Under drought stress conditions, the number of sterile spikelets displayed a negative direct effect, while kernel weight per spike had a positive direct effect on yield. Hierarchical cluster analysis was used as a tool to classify cultivars and landraces according to their yield ability under near optimum and drought stress conditions. Among the cultivars, two groups out of five and among one of three in the landraces were characterised by high yields in both near optimum as well as under drought stress conditions. These genotypes may serve as sources of germplasm for breeding for drought tolerance.

Leaf K/Na ratio predicts salinity induced yield loss in irrigated rice

Abstract: Summary Salinity is a major constraint to irrigated rice production, particularly in semi-arid and arid climates. Irrigated rice is a well suited crop to controlling and even decreasing soil salinity, but rice is a salt-susceptible crop and yield losses due to salinity can be substantial. The objective of this study was to develop a highly predictive screening tool for the vegetative growth stage of rice to estimate salinity-induced yield losses. Twenty-one rice genotypes were grown over seven seasons in a field trials in Ndiaye, Senegal, between 1991 and 1995 and were subjected to irrigation with moderately saline water (3.5 mS cm 1 , electrical conductivity) or irrigation with fresh water. Potassium/sodium ratios of the youngest three leaves (K/NaLeaves) were determined by flame photometry at the late vegetative stage. Grain yield was determined at maturity. All cultivars showed strong log-linear correlations between K/NaLeaves and grain yield, but intercept and slope of those correlations differed between seasons for a given genotype and between genotypes. The K/NaLeaves under salinity was related to grain yield under salinity relative to freshwater controls. There was a highly significant correlation ( p< 0.001) between K/NaLeaves and salinity-induced grain yield reduction: the most susceptible cultivars had lowest K/NaLeaves and the strongest yield reductions. Although there were major differences in the effects of salinity on crops in both the hot dry season (HDS) and the wet season, the correlation was equally significant across cropping seasons. The earliest possible time to establish the relationship between K/NaLeaves under salinity and grain yield reduction due to salinity was investigated in an additional trial in the HDS 1998. About 60 days after sowing, salinity-induced yield loss could be predicted through K/NaLeaves with a high degree of confidence ( p< 0.01). A screening system for salinity resistance of rice, particularly in arid and semi-arid climates, is proposed based on the correlation between K/NaLeaves under salinity and salinity-induced yield losses.

A methodological study on participatory barley breeding I. Selection phase

Abstract: Decentralized selection, defined as selection in the target environment, has been used to emphasize favorable interactions when significant genotype by environment interactions exist. However, crop breeding based on decentralized selection can still miss its objectives if it does not utilize the farmers' knowledge of the crops and the environment, and it may fail to fit crops to the specific needs and uses of farmers' communities unless it becomes participatory.One cycle of decentralized participatory selection was conducted in eleven locations in Syria. 208 barley entries (fixed lines and segregating populations) were planted unreplicated in two research stations and in the fields of nine Syrian (host) farmers, where they were managed (except planting) by the farmers themselves. Visual selection was conducted by a breeder at all locations and by the host farmers on their own fields and on both stations. In five farm locations, there was also a one-time group selection by neighboring farmers.Host farmers were able to handle the large number of entries making observations during the cropping season using different scoring methods. They did not use the performance of entries on station for their final selection and used a higher selection pressure than the breeder. In their own fields, they selected about one tenth the number of entries selected by the breeder, while on station the farmers selected, on average, about half the number of lines selected by the breeder. For some broad attributes, such as modern germplasm versus landraces, selection was mostly driven by environmental effects. Selection for other attributes was partly environmentally driven and partly based on individual farmers preferences.Selection preferences were similar for fixed or segregating populations. There was wider diversity among farmers' selections in their own fields than among farmers' selections on research stations and among breeder's selections, irrespective of where the selection was conducted. Larger kernels, higher grain yield and biomass, and taller plants (particularly in environmentally stressed locations) were the characteristics most frequently used as selection criteria by both breeder and farmers.Entries selected by the farmers yielded as much, and in one case significantly more, than those selected by the breeder.Decentralized-participatory selection was significantly more efficient in identifying the highest yielding entries in farmers' fields than any other type of selection. There was also evidence suggesting that the breeder was more efficient in selecting higheryielding entries in the research station in a high rainfall area, while the farmers were more efficient in selecting under stress conditions. The results suggest that farmers can handle selection choices among a large number of lines, and because farmers' selections are at least as high yielding as breeder's selections, it is possible to transfer the responsibility of selection to farmers in their fields.

Inter simple sequence repeat analysis of genetic relationships in the genus Vigna

Abstract: The utility of inter simple sequence repeat (ISSR) DNA polymorphisms to distinguish taxa within the genus Vignawas investigated. Nineteen primers, most containing either aGA or CA repeat, generated amplification products that differed among the taxa examined. The ISSR polymorphisms produced by 15 of these primers were very effective for distinguishing taxa at the species level or below. The Vigna unguiculataaccessions analyzed formed a cohesive group and appeared to be most closely related to V. triphylla and V. reticulata.In contrast, ISSR analysis was not able to clearly differentiate subgeneric divisions within Vigna. We attribute this loss of resolution at the subgeneric level to the high rate of evolution of the sequences we examined. Several probable instances of misclassification or hybrid origin of an accession were identified.

Farmers' seed selection practices and traditional maize varieties in Cuzalapa, Mexico

Abstract: Experimental results and farmer surveys from a Mexican community located in the buffer zone of a biosphere reserve indicate that farmers' seed selection practices protect the phenological integrity of their traditional maize varieties as they define them, despite numerous factors contributing to genetic instability. Analysis of morphological and genetic data suggests that when subjected to significant gene flow through cross-pollination, ear characteristics are maintained through farmers' selection even though other characteristics may continue to evolve. Because the effects of farmers' selection practices are confined largely to ear characteristics, their practices appear to offer only limited scope for variety improvement. Farmers' expectations of what they can achieve through seed selection are similarly limited. These findings suggest complementary roles for professional breeders and Mexican farmers in enhancing mass selection methods to improve maize landraces on farms – if farmers themselves perceive benefits from the collaboration.

Evaluation of genotype, environment, and genotype-by-environment interaction for capsaicinoids in Capsicum annuum L.

Abstract: The response, in terms of capsaicinoid content, of chile (Capsicum annuum L.) genotypes to different environments was studied. Double haploidlines, an F1 hybrid, and an open-pollinated cultivar estimated the genotype, environment, and genotype-by-environment interaction effect on the total capsaicinoids and on individual capsaicinoids. Significant differences were observed among the genotypes and among genotype-by-environment interactions over the environments. Among the genotypes in an environment, the within-genotype variances were also significantly different. The double haploid line, HDA 207, had low within-genotype variance for individual and total capsaicinoids, with the exception of the isomer of dihydrocapsaicin. Also for HDA 270, the genotype-by-environment interaction was negligible for individual and total capsaicinoids, Indicating stability across environments.

Molecular marker assisted tagging of morphological and physiological traits under two contrasting moisture regimes at peak vegetative stage in rice (Oryza sativa L.).

Abstract: Root morphology under well-watered conditions sampled on two occasions and under low-moisture stress was studied in a randomly chosen subset of 56 doubled haploid lines derived from a cross between IR64 and Azucena at two growth stages during the vegetative stage. A molecular map of the same population served as the basis for locating QTLs controlling root morphology and associated traits. The region flanking the RFLP markers RZ730 and RZ801 on chromosome 1 were associated with plant height in all three sampling environments. This position corresponds to sd-1 a semi-dwarfing gene. A total of 15 QTL were detected at the two developmental stages, of which only three QTL were common. Region flanked by RG157 and RZ318 (chromosome 2) contained QTL for root thickness under two different developmental stages. In total, 21 QTL for different traits were detected under low-moisture stress condition. While two QTL for plant height on chromosomes 1 and 3 were common, none of the loci for root morphological traits was common between the two different moisture regimes. The chromosomal segment between RG171 and RG157 contained QTL controlling tiller number per plant, total root length, root volume and total root number per plant. Absence of common QTL for root traits between two developmental stages and two moisture regimes suggests the existence of parallel genetic pathways operating at different growth stages and moisture regimes. Root volume and total root number per plant decreased significantly under stress, whereas maximum root length and plant height exhibited non-significant increases under stress.

A new powdery mildew resistance gene: Introgression from wild emmer into common wheat and RFLP-based mapping

Abstract: An Israeli accession (TTD140) of wild emmer, Triticum turgidum var. dicoccoides, was found resistant to several races of powdery mildew. Inoculation of the chromosome-arm substitution lines (CASLs) of TTD140, in the background of the Israeli common wheat cultivar ‘Bethlehem’ (BL), with five isolates of powdery mildew revealed that only the line carrying the short arm of chromosome 2B of wild emmer (CASL 2BS) exhibited complete resistance to four of the five isolates. To map and tag the powdery mildew resistance gene, 41 recombinant substitution lines, derived from a cross between BL and CASL 2BS, were used to construct a linkage map at the gene region. The map, which encompasses 69.5 cM of the distal region of chromosome arm 2BS, contains six RFLP markers, a morphological marker (glaucousness inhibitor, W1 I), and the powdery mildew resistance gene. Segregation ratios for resistance in F2 of BL × CASL 2BS and in the recombinant lines, combined with the susceptability of F1 progeny to all tested isolates, indicate that resistance is controlled by a single recessive allele. This alleleco-segregated with a polymorphic locus detected by the DNA marker Xwg516, 49.4 cM from the terminal marker Xcdo456. The new powdery mildew resistance gene was designated Pm26.

Breeding and genetics of Fusarium basal rot resistance in onion.

Abstract: Fusarium basal plate rot (FBR), caused by Fusarium oxysporum f. sp. cepae, is an important soil-borne disease of onions worldwide. The causal organism infects the basal stem plate of the bulb and eventually kills the entire plant through degradation of the basal plate. F. o. f. sp.cepae infections in dormant bulbs during storage allow secondary infections to occur. The primary method of infection by F. o. f. sp. cepaeis through direct penetration of the basal stem plate. Infection can also occur through wounded tissue particularly roots and basal portions of bulb scales. The most cost-effective methods of control are crop rotation and host plant resistance. Current research suggests that a single gene, two genes, or multiple genes govern resistance to FBR. Breeding programs have successfully used screening procedures to develop intermediate- and long-day, FBR-resistant cultivars.

Polyploidization and early screening of Rhododendron hybrids

Abstract: Polyploid induction represents a useful tool for breeders of floral crops as larger flowers, longer flowering period and deeper colors can be achieved through chromosome doubling. This study aimed at testing the efficiency of colchicine and oryzalin in inducing polyploidy in three Rhododendroncultivars grown in vitro. The chemicals were used in two concentrations with 24 h and 48 h treatment durations. The survival of the plants was better in colchicine than in oryzalin solutions. The higher concentration of both chemical skilled more plantlets. The treatment duration in oryzalin did not affect the survival, but 48 h in colchicine was more destructive than 24 h. The low survival rate may not be a disadvantage, if the treatment induces desired ploidy. The ploidy levels were screened with flow cytometry. Oryzalin was more efficient than cochicine in inducing polyploidy, the treatment duration and the concentration did not have significant effects as main factors. The biggest proportion of solid tetraploids (18.2% of the survived plants) was obtained from the 24 h treatment in 0.005% oryzalin. Immediately after the treatment the polyploids grew very slowly, whereas most of the unaffected diploids were vigorous from the very beginning. More mixoploids than solid tetraploids were obtained in all treatments. Most of the mixoploids retained their chimerism, one third shifted todiploidy and one single plant to tetraploidy.

Effectiveness of different classes of molecular marker for classifying and revealing variation in rice (Oryza sativa) germplasm

Abstract: We have examined the effectiveness of similar numbers of markers from four molecular marker systems (AFLP, isozymes, ISSR and RAPD) for revealing genetic diversity and discriminating between infraspecific groups of Oryza sativa germplasm. Each marker system classifies the germplasm into three major groups (most effectively with isozymes and AFLPs), but with differences (primarily with ISSR) between the precise classifications generated. However, at the highest levels of genetic similarity there was only partial agreement as to relationships between individual accessions when different markers were used. When variance was partitioned among and within the three subspecific groups, although the differences were not significant, greater variation was found among than within groups using AFLP and isozymes, with the reverse for RAPD and ISSR. Measurement of polymorphism using average heterozygosity and effective number of alleles gave similar results for each marker system. These results are discussed in relation to various genetic resources conservation activities, and the advisability of extrapolating to other sets of germplasm particularly of other crop species.

Sensory evaluation as a selection tool in apple breeding

Abstract: Several conventional sensory methods were adapted to provide aprocedure that is suitable for screening apple (Malus × domestica) breeding selections for dessert quality. Trained judges were presented with randomized coded samples (apple slices) and asked to rate them on 0 to 9 bipolar hedonic (liking) scales for texture and flavour, and 0 to 9 unipolar intensity scales for skin toughness, crispness, hardness, juiciness, aroma, sweetness and sourness. Appearance liking was rated on coded samples of five whole apples, using the 0 to 9 hedonic scale. A minimum panel size of eleven judges was generally sufficient to obtain statistical discrimination of one point on the 0 to 9 scales. Panel mean scores for breeding selections relative to standards have been consistent from panel to panel and year to year. A subset of selections and cultivars was rated for appearance and taste by consumers in blind taste tests. In-house panel findings were comparable to consumer ratings for taste and appearance liking, with a few exceptions in appearance. Panel mean scores for texture and flavour liking were regressed on texture and flavour components. Crispness accounted for about 90% of the variation in texture liking. Juiciness, aroma, sweetness and sourness were all important to flavour liking, but their relative importance changed from year to year and in total accounted for only about 60% of variation in flavour liking. Perceived sweetness and sourness were better predictors of liking than analytical measurements of soluble solids and titratable acidity. Formal sensory evaluation can be used successfully for screening breeding selections, and may provide more reliable data than the opinions of only one or two people.

Comparative analysis of cultivated melon groups (Cucumis melo L.) using random amplified polymorphic DNA and simple sequence repeat markers.

Abstract: Random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) markers were used to characterize genetic relationships among 46 accessions in two C. melo L. subsp. melo (Cantalupensis, Inodorus) and subsp.agrestis (Conomon, and Flexuosus) groups. Genetic distance (GD) estimates were made among and between accessions in four melon market classes [Galia, Ogen, Charentais, and Shipper (European and U.S. types)] of Cantalupensis, one market class of Inodorus (Cassaba and Honey Dew), one accession of Conomon, and one accession of Flexuosus by employing three GD estimators; simple matching coefficient, Jaccard's coefficient, and Nei's distance-D. Differences detected among 135 RAPD bands and 54 SSR bands (products of 17 SSR primers) were used to calculate GD. Band polymorphisms observed with 21 RAPD primers and 7 SSR primers were important (p =0.01) in the detection of genetic differences. Estimators of GD were highly correlated (p 0.0001; rs = 0.64 to0.99) when comparisons were made between estimation methods within a particular marker system. Lower correlations (rs = 0.17 to 0.40) were detected (P > 0.001) between marker systems using any one estimator. The GD of the Conomon and Flexuosus accessions was significantly different (p> 0.001)from the mean GD of all the market classes examined. The mean GD (Jaccard's coefficient) among accessions of Ogen, Galia, Cassaba, Charentais, European shipper, and U.S. shipper groups was 0.11 ± 0.04, 0.33± 0.09, 0.21 ± 0.04, 0.26 ± 0.10, 0.17± 0.05 and 0.22 ± 0.08, respectively. Market classes were distinct (p > 0.001), such that GDs between Galia and other accessions were the largest(mean GD 0.34 to 0.35), and GDs between Ogen and other accessions were the smallest (mean GD 0.29 to 0.30). Contrasts between the U.S. shipper cultivar Top Mark and accessions within any market class was relatively large (mean GD = 0.42 ± 0.06). Empirical estimations of variances associated with each marker type in the accessions examined indicated that, per band, lower coefficients of variation can be attained in the estimation of GD when using RAPDs compared to SSRs. Nevertheless, the genetic relationships identified using these markers were generally similar. The disparity between the analyses of the two markers made may be related to the amount of genome coverage which is characteristic of a particular marker system and/or its efficiency in sampling variation in a population. Results of RAPD marker analysis suggest that 80 marker bands were adequate for assessing the genetic variation present in the accessions examined.

Analysis of genetic variation in Cucurbita moschata by random amplified polymorphic DNA (RAPD) markers.

Abstract: Knowledge of genetic relationships among genotypes is essential for the effective utilisation of germplasm, especially for poorly characterised species. Random amplified polymorphic DNA (RAPD) analysis provides a quick and reliable method for resolving genetic relationships. Although Cucurbita moschata Duch, also known as tropical pumpkin, is one of the most important vegetable crops in Africa, being adapted to a wide range of climatic and soil conditions, it is a scientifically neglected species. The objectives of this study were to (1) analyse the amount of genetic diversity inC. moschata landraces grown in south-central Africa and (2) classify the landraces to assist in selection of parent genotypes for improvement of fruit characteristics. Cluster analysis, based on 39 polymorphic and 105 monomorphic DNA fragments amplified by 16 primers, was used to show relationships among 31 genotypes obtained from Zambia and Malawi. The analysis revealed four clusters, with genotypes from Malawi mainly clustering in three clusters while all genotypes from Zambia and three from Malawi clustered in one cluster. The pair-wise mean genetic distance was 0.32 ± 0.04 for samples from Malawi and 0.26 ± 0.04 for samples from Zambia. The possible application of the resulting classification in breeding of C. moschata is discussed.

A quick methodology to identify sexual seedlings in citrus breeding programs using SSR markers.

Abstract: In citrus breeding and genetics, it is very important to distinguish between zygotic and nucellar seedlings in order to eliminate unwanted genotypes. Usually, isozyme marker shave been employed to determine the genetic origin of young plants. In this work we propose the use of SSR markers as an alternative methodology and compare them with isozymes in this kind of screenings. Two different populations were analysed: one derives from an interspecific cross and the other from selfing. We conclude that, in most cases, microsatellites are more efficient than isozymic markers to identify the sexual origin of citrus seedlings, given their higher level of polymorphism and the scarce number of polymorphic isozymes in some populations. We describe a quick and efficient methodology for SSR analysis, including a fast DNA extraction in microcentrifuge tubes, and visualization through silver staining, which eliminates the need for a labelling step.

Genetic analysis of resistance to Fusarium head blight caused by Fusarium graminearum in Chinese wheat cultivar Sumai 3 and the Japanese cultivar Saikai 165

Abstract: The genetic constitution of resistance to Fusarium head blight (FHB, scab) caused by Fusarium graminearum in the Chinese wheat cultivar Sumai 3 and the Japanese cultivar Saikai 165 was investigated using doubled haploid lines (DHLs) and recombinant inbred lines (RILs). Frequency distributions of DHLs derived from two F1 crosses, Sumai 3 (very resistant to resistant; VR-R) / Gamenya (very susceptible; VS) and Sumai 3 / Emblem (VS), fitted well to 1: 2: 1 (resistant: moderately resistant: susceptible) ratios for reaction to FHB in the field. It is suggested that the resistance of Sumai 3 is controlled by two major genes with additive effects. One of the resistance genes may be linked in repulsion to the dominant suppressor B1 for awnedness with recombination values 15.1 ± 3.3% in Sumai 3 /Gamenya and 21.4 ± 4.3% in Sumai 3 / Emblem. Saikai 165 is a Japanese resistant line derived from an F1 Sumai 3 / Asakaze-komugi (moderately resistant; MR). The data for RILs derived from the cross Emblem / Saikai 165, indicates that three resistance genes control the resistance of Saikai 165.

Assessment of genetic relationships in Mentha species

Abstract: A set of 60 random primers was used to analyse 11accessions from six taxa of Mentha developed byCIMAP. These accessions were maintained in the nationalgene bank for medicinal and aromatic plants at CIMAP.A total of 630 bands could be detected as amplifiedproducts upon PCR amplification, out of which 589 werepolymorphic (93.5%). Further analysis of these RAPDprofiles for band similarity indices clearlydifferentiated five of the Mentha arvensis L.accessions from the rest. Among two accessions of Mentha spicata L. CIMAP/C33 could bedistinguished from CIMAP/C32. Mentha × gracilis Sole cv. cardiaca showed a muchhigher similarity with Mentha spicata L. as wellas Mentha arvensis L. which amongst themselvesshowed rather a greater distance indicating that Mentha × gracilis Sole cv. cardiaca might have evolved as a natural hybridbetween M arvensis L. and M. spicataL. In terms of uniqueness of amplified bands fordeveloping RAPD markers, it was observed that at taxalevel 298 bands were unique to one of the six taxa,singly amounting to 47.3% of total amplifiedfragments. Primers MAP 10 and 17 produced polymorphismonly in case of M. spicata L. and Menthaspicata L. cv. viridis while MAP 08 producedpolymorphic bands in all 4 other species than thesetwo. Similarly unique patterns were observeddifferentiating all six species and could be used asRAPD markers for differentiating Mentha species.

The effectiveness of evaluating wild species: searching for sources of resistance to bruchid beetles in the genus Vigna subgenus Ceratotropis

Abstract: A species level germplasm collection representing 76% of known taxa in the genus Vigna subgenus Ceratotropis was evaluated for resistance to two species of bruchid beetles, Callosobruchus chinensis and C. maculatus. Seven taxa consisting of 29 accessions were found to be resistant to C. chinensis and 4 taxa consisting of 24 accessions were found to be resistant to C. maculatus. This compared with no resistant accessions being found in several hundred landrace accessions of mungbean, V. radiata var. radiata, in the same subgenus. Sometimes resistance was found in all accessions of a particular taxon, such as complete resistance to both C. chinensis and C. macualtus in V. umbellata. Other taxa showed intra taxon variation for resistance such as V. reflexo-pilosa andV. minima. The levels and patterns of resistance among taxa were diverse. The results suggest that various factors cause resistance to bruchid in the subgenus Ceratotropis. While the number of eggs laid on seeds generally reflected seed size, one small seeded cultivar of V. mungo var. mungo, black gram, had an unusually high number of eggs laid per seed. No correlation was found between seed size and levels of resistance. The species level germplasm collection, which reflects the core collection concept in trying to maximize genetic diversity in a limited number of accessions, has enabled a large number of potentially useful sources of resistance to bruchid beetles to be found efficiently.

Quantitative evaluation of apple (Malus × domestica Borkh.) fruit shape by principal component analysis of Fourier descriptors

Abstract: Apples from 1253 genotypes representing 82 open pollinated families planted at three sites were cut along the stem-calyx axis at the widest point to analyse fruit shape. An image analysis program was used to extract calliper measurements of the fruit outline and calculated Fourier descriptors for each fruit outline. Five independent shape traits were identified from a principal component analysis of the Fourier descriptors. The shape traits and the proportion of the total phenotypic variation they accounted for were: fruit aspect (76.8%), asymmetric-crown (7.8%), fruit conicity (6.0%), asymmetric-sides (4.3%), and fruit squareness (2.0%). Genetic and residual variance components were estimated with data from two sites using restricted maximum-likelihood techniques to select genetically-inherited apple shape traits. Combined sites heritability was estimated to be 0.79 for aspect, 0.38 for conicity and 0.35 for squareness. Multiple regression between calliper measurements and aspect, conicity, and squareness traits showed firstly that aspect was best predicted by fruit length/width ratio (R2 = 0.97), secondly conicity could be described by both the distance of the maximum width from the base of the fruit/fruit length ratio and the calyx basin width/fruit width ratio (R2 =0.44), and finally squareness was best described by ratio of the product of calyx basin width and distance of the maximum width from the calyx end of the fruit by the product of fruit length and fruit width(R2 = 0.19). A chart based on the aspect, conicity and squareness principal component values was drawn to allow visual assessment of shape.

An allelic series at the Co-1 locus conditioning resistance to anthracnose in common bean of Andean origin

Abstract: In this study, we characterized the genetic resistance of the Andean bean cultivars Kaboon and Perry Marrow and their relation to other sources of anthracnose resistance in common bean. Based on the segregation ratio (3R:1S) observed in two F2 populations we demonstrated that Kaboon carries one major dominant gene conferring resistance to races 7 and 73 of Colletotrichum lindemuthianum. This gene in Kaboon is independent from the Co-2 gene and is an allele of the Co-1 gene present in Michigan Dark Red Kidney (MDRK) cultivar. Therefore, we propose the symbol CO-1 2 for the major dominant gene in Kaboon. The Co-1 is the only gene of Andean origin among the Co anthracnose resistance genes characterized in common bean. When inoculated with the less virulent Andean race 5, the segregation ratio in the F2 progeny of Cardinal and Kaboon was 57R:7S (p = 0.38). These data indicate that Kaboon must possess other weaker dominant resistance genes with a complementary mode of action, since Cardinal is not known to possess genes for anthracnose resistance. Perry Marrow, a second Andean cultivar with resistance to a different group of races, was shown to possess another resistant allele at the Co-1 locus and the gene symbol Co-1 3 was assigned. In R × R crosses between Perry Marrow and MDRK or Kaboon, no susceptible F2 plants were found when inoculated with race 73. These findings support the presence of a multiple allelic series at the Andean Co-1 locus, and have major implications in breeding for durable anthracnose resistance in common bean.

Geographical patterns of morphological variation in sorghum (Sorghum bicolor (L.) Moench) germplasm from Ethiopia and Eritrea : Quantitative characters

Abstract: A total of 415 sorghum (Sorghum bicolor (L.) Moench) accessions representing different regions of Ethiopia, Eritrea and a group of introduced lines were evaluated for 15 quantitative characters to determine the extent and geographical pattern of morphological variation. The extent of variation was highly pronounced for agronomically important characters for sorghum. These characters included plant height, days for 50% flowering, peduncle exsertion, panicle length and width, number and length of primary branches per panicle and thousand seed weight. Significant regional variation was also observed for most of the characters. The results implied that environmental factors such as altitude, rainfall, temperature and growing period are important in regional variation. Mean for plant height and for days for 50% flowering showed clinal variation along the gradients of rainfall pattern and growing period in Ethiopia. Moreover, there were significant positive correlation coefficients between most of the characters. This included the correlation between agronomic characters of primary interest in sorghum breeding such as plant height and days for 50% flowering and also between various characters and the altitude of the collection sites. The implications of the results in plant breeding, germplasm collection and conservation as well as the probable sources of the wide range of variation are discussed.

Molecular markers for cytoplasm in potato: male sterility and contribution of different plastid-mitochondrial configurations to starch production

Abstract: Distinct parental cytoplasms were combined in symmetric tetraploid hybrids of potato by somatic cell fusion. This allowed, in the presence of nearly isogenic nuclear genomes, to estimate the contribution of mitochondrial (mt) and chloroplast (cp) genomes to starch content. Analysis of mt-cp configurations in the complete gene pool of german potato cultivars [2n=4x], in a reciprocal dihaploid population [2n=2x],in di-haploid fusion parents [2n=2x] and in their respective hybrids [2n=4x] made visible the effects of different cytoplasmic backgrounds and mitochondrial subgenomic rearrangements. Genotypes identified by markers as cytoplasm Wγ were associated with cytoplasmic male sterility. Evaluation of cytoplasmic types leads to the conclusion, that in starch content the ‘wild type’ cytoplasms Wα and Wγ have a significant advantage to other cytoplasmic types(Tβ, Wδ, Se).This results from the experiments with a reciprocal population, 180 di-haploids, and from cultivar comparisons. In hybrids an interaction between starch content and different mt-cp combinations could be found. In general the highest field performance, measured in starch content and yield was associated with such cytoplasmic configurations which appeared to a high frequency within a population, when the segregation process was completed. This fact is explained by a selection advantage of clones with optimized organellar segregation already during in vitro phase. PCR markers for cytoplasm differentiation are actualized on a website, http://www.flg.tum.de/pbpz/mm/mt/hybrid.html

Breeding for resistance to rhizomania in sugar beet: a review.

Abstract: Currently rhizomania is the most important disease insugar beet worldwide, and attack can lead to seriousyield losses. The disease is caused by beet necroticyellow vein virus (BNYVV) that is transmitted by thesoil-borne fungus Polymyxa betae. Breeding sugarbeet cultivars with resistance to rhizomania isregarded as the most appropriate way to enablecontinued production of this crop in BNYVV-infestedfields and also to slow the spread of the disease.Breeding for resistance started with selection byscoring disease symptoms in field experiments. Thedevelopment of non-destructive greenhouse tests, withdetermination of the virus concentration in rootletsusing ELISA, has greatly improved the efficiency ofselection. In this paper the impact of scientificresearch on the progress in breeding cultivars withresistance to rhizomania is reviewed. This includesthe distribution, composition, and pathogenicity ofthe virus, the sources of resistance to virus andvector, the genetics of virus resistance, progresswith breeding methods, and the use of molecularmarkers and pathogen-derived resistance. The yieldsand quality characteristics of recently introducedresistant cultivars now equal those of the commercialsusceptible cultivars.

Potential marker-assisted selection for bc-1 2 resistance to bean common mosaic potyvirus in common bean

Abstract: Pyramiding epistatic resistance genes to improve long term disease resistance has challenged plant breeders. Indirect selection using tightly linked markers will often facilitate the breeding of desired epistatic resistance gene combinations. In common bean, the most effective strategy for broad spectrum control of the bean common mosaic virus disease is to combine I, bc-u, bc-1 2, bc-2 2, and bc-3 genes. We describe the use of near-isogenic lines and bulked segregant analysis to identify a marker tightly linked with the bc-1 2 gene. The recessive bc-1 2 gene conditions resistance to specific strains of bean common mosaic virus and bean common mosaic necrosis virus and is masked by the bc-2 2 and bc-3 genes. We identified a RAPD marker completely linked (0 recombinants) with bc-1 2, based on 72 F3 progeny generated from a cross between the contrasting near isogenic lines (I + bc-1/I + bc-1 2). Segregation in this I gene background revealed that bc-1 2 was dominant to bc-1 in conferring resistance to top necrosis in the allelic series Bc-1 > bc-1 2 > bc-1. To facilitate marker-assisted selection of bc-1 2 across breeding programs, the RAPD was converted to a SCAR marker, designated SBD51300. Tight linkage (0 recombinants) was confirmed in a second population of 58 F2 progeny co-segregating for SBD51300 and bc-1 2 gene from a different source. Based on a survey of 130 genotypes, the SCAR will be useful for MAS of bc-1 2 in most beans of Middle American origin and snap beans, but will have very limited utility in the case of kidney and cranberry beans. The SBD51300 marker mapped on linkage group B3, revealing independence of bc-1 2 from the I gene on B2 and bc-3 gene on B6, which supports the opportunity to readily combine genes for broad spectrum and pyramided resistance to bean common mosaic potyviruses in a single bean cultivar.

Evaluation of the genetic diversity among elite tea (Camellia sinensis var. sinensis) accessions using RAPD markers.

Abstract: The diversity of 27 superior tea (Camellia sinensis var. sinensis) accessions from Korea, Japan and Taiwan was examined with RAPD-PCR (Random Amplified Polymorphic DNA Polymerase Chain Reaction) markers. Out of the 50 primers screened, 17 primers generated 58 polymorphic and reproducible bands. A minimum of 3 primers was sufficient to distinguish all the 27 accessions studied. The Shannon's index used to partition diversity into inter- and intra-group, revealed that 71 percent of variability resided within groups and 29 percent between groups. Diversity was greatest within the Korean group followed by Taiwan and Japan. The relatively high diversity observed in Korea might reflect the larger genetic base of its plantations while the low diversity in Japan could be explained by the long and intensive tea selection programme in this country. A dendrogram based on the UPGMA-link method using Jaccard's distances and multivariate Factorial correspondence analysis clustered the tea accessions into two main groups, regrouping the Taiwan cultivars on the one side and the Korean and Japanese accessions on the other side. This suggests that the Taiwan tea studied here may have a different origin from that of Korea and Japan.

Analysis of a germplasm collection of loquat (Eriobotrya japonica Lindl.)

Abstract: A cultivar description of a loquat collection based on morphological traits, phenology and fruit quality is presented. Vegetative characteristics such as leaf blade length and width, leaf blade shape in cross section, thickness and distribution of lateral and central shoots, and size and shape of flower clusters were useful to distinguish cultivars. In this collection we found all categories described by UPOV for fruit characteristics such as size, skin and flesh color, shape in cross and longitudinal section, shape of stalk end of the fruit, shape of apex and calyx cavity, all of them allowed to distinguish cultivars. Flowering time was highly correlated to ripening time and percentage of fruiting spurs. Fruit set was correlated with flower cluster size. Vigor was highly correlated with fruit size and weight, which may be due in part to the method of cultivar selection by growers. Many fruit characteristics that are important to breeders are present in this collection with the exception of very late ripening genotypes. The PCA resulted in three main components that represented fruit size, phenology and quality of fruits respectively.

DNA fingerprinting and classification of geographically related genotypes of olive-tree (Olea europaea L.)

Abstract: Malaga is a province of Spain where olive-trees are cultivated in a large range of environments, climates and soils. We have developed a reliable and reproducible method to detect RAPD and AP-PCR polymorphisms, using DNA from olive-tree (Olea europaea L.) leaves. Starting from their natural orchards, fifty-six olive-tree cultivars throughout Malaga province, including oil and table olive cultivars, were screened and grouped into 22 varieties. A total of 62 informative polymorphic loci that provide 601 conspicuous bands were enough to differentiate the varieties. Clustering analyses managing 3 different pairwise distances, as well as phylogenetic analyses, led to the same result: olive-trees in Malaga can be divided into three main groups. Group I (90% of certainty) contains wild type and two introduced varieties, group II (83% of certainty) covers some native olive-trees, and group III (58% of certainty) is an heterogeneous cluster that includes varieties originating and cultivated in a number of Andalusian locations. Geographic location seems to be the first responsible of this classification, and morphological traits are needed to justify the group III subclustering. These results are consistent with the hypothesis of autochthonic origin of most olive-tree cultivars, and have been used to support a Label of Origin for the olive oil produced by the varieties included in group II.

Two RAPD markers linked to a major fertility restorer gene in pepper

Abstract: Both major and minor genes control the restoring of fertility in the cytoplasmic male-sterility system in pepper (Capsicum annuum L.). Bulked segregant analysis (BSA) was applied to identify molecular markers linked to a major restorer gene (Rf) using the F2 population of NiujiaojiaoNo.21 (rfrf)/Xiangtanwan (RfRf). Two random amplified polymorphic DNA (RAPD) markers linked to this allele were detected with 520 decamer primers with arbitrary sequences. OP131400 is a tightly linked marker with a genetic distance of0.37 cm. OW19800 is on the opposite side with a distance of 8.12 cm. Both markers were repeatable and easy to score. A panel of genotypes, including 13elite inbred lines with different fertility restoring ability, were assayed for the presence ofOP131400 and OW19800. The markers are absent in all sweet pepper lines, indicating that they will be most helpful for transferring Rf into sweet pepper lines. With the aid of these markers, the size of the backcross population for testcrosses can be minimized. Furthermore, these markers will be useful in genetic analysis of the minor genes.