Studies on the reproductive biology of white yam (Dioscorea rotundata Poir.)

Summary Investigations were conducted on the identification and distribution of yam natural pollinators, flowering pattern and hybridization of white yam (Dioscorea rotundata Poir.) at the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria, in order to provide informations for producing hybrid seeds needed for vam genetic improvement.Insects belonging to the Coleoptera (48.0%), Diptera (20.4%), Hymenoptera (20.0%), Hemiptera (5.8%), and Thysanoptera (5.8%) were caught around yam plants and presumed to be pollinators: they entered open-receptive-flowers and their presence on yam plants coincided with the duration of the flowering period.Studies on the flowering pattern revealed that: (i) Male and female clones differed in their periods of flower initiation as well as the flowering duration; (ii) Seed production and conventional breeding methods are feasible if staggered planting, water and soil fertility could be managed to ensure that flowering periods of males and females nick and also extend flowering.Artificial pollinations within white yam and between white yam and yellow yam (D. cayenensis Lam) using the camel hair brush method were successful, but resulted in a relatively low fruit set (31.8% maximum). This method was more effective than natural pollination (19.2%) and can thus supplement it for the production of hybrid seeds for introducing genetic variation in yam breeding populations.     

Ploidy variation in the cultivated yams (Dioscorea cayenensis-Dioscorea rotundata complex) from Cameroon as determined by flow cytometry

The ploidy levels of the twenty-two yam (Dioscorea cayenensis-D. rotundata complex) cultivars within germplasm Cameroon Guinea yam were determined by flow cytometry. Three different ploidy levels (4x,6x, 8x) were detected within the samples analysed. Fifteen cultivars were tetraploids, five were hexaploids, and two were octoploids. The cultivar group EKOTO showed a high level of ploidy variation with tetraploid, hexaploid and octoploid cultivars. The hexaploid nature of cultivars Dobnawo and Bilougnou supported the hypothesis that they are hybrids between cultivars of the EKOTO group and either the KPE or BAKOKAE groups. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Seed set and seedling variation in greater yam (Dioscorea alata L.)

Summary A high degree of fruit and seed set was obtained in Dioscorea alata L. by hand pollination. The sexual progeny was studied in comparison with the clonal plants. In general, the seedlings were poor in growth vigour, flowering and tuber production but the variations observed in the different characters were unprecedented, indicating scope for efficacious genetic improvement in this vegetatively propagated crop.     

Variation for dry matter yield,seed yield and other agronomic traits in Ladino white clover landraces and natural populations

Summary A set of Ladino white clover ecotypes including the last available landraces and some natural populations collected from old permanent meadows, together with some white clover varieties of various origins, were evaluated as monocultures for dry matter (DM) and seed yield assessed in separate field experiments. Other agronomic traits were also recorded. The best performing variety, Espanso, was significantly outyielded by some ecotypes for DM and seed production. Compared to landraces, natural populations yielded on average far less seed but as much DM and tended towards higher persistence indicating that domestication of the native Ladino at the farm level only improved seed yield of the crop. Natural populations showed, besides lower values of most seed yield components, a distinct canopy architecture characterized by smaller leaves, longer internodes and denser stolons. Seed weight proved the best character discriminating between the two ecotype groups. Significant variation for most traits was found both among landraces, in which it was mostly relatable to differences among provenances, and among natural populations. The relations between the main multivariate patterns of phenotypic variation and a set of environment collecting variables suggested that evolutive adaptation to different agronomic practices was a major determinant of the overall variation found in landraces. Evidence is provided that a relevant part of the variation observed among ecotypes for some important traits could be genetic.Abbreviations DM dry matter - DMY dry matter yield - NRH number of ripe heads - NFH number of florets per head - PL petiole length - LS leaf size - IL internode length - NS number of stolons - PRO protein content - SY seed yield - TSW thousand seed weight - NSF number of seeds per floret - PCA principal components analysis - PC principal component     

Variance component analysis of plant architectural traits and fruit yield in melon

Summary  A cross was made between a unique highly branched, early flowering line, U. S. Department of Agriculture (USDA) 846-1 (P_1; 7 to 11 lateral branches), and ‘Topmark’ (P₂; 2 to 4 lateral branches), a U.S. Western Shipping melon, to produce an array of 119 F₃ families. Subsequently, a genetic analysis was conducted at Arlington and Hancock, Wisconsin in 2001 to evaluate the segregating progeny for factors likely involved in yield-formation, including days to anthesis, percentage of plants with early pistillate flowering, primary branch number, fruit number and weight per plant, average weight per fruit, percentage of plants with predominantly crown fruit set, and percentage of plants with early maturing fruit. Although, genotype × environment (G × E) interactions were important for some traits (e.g., fruit number and fruit weight), considerable additive and/or dominance variance was detected for all traits. This research provides critical data associated with highly branched melon germplasm including trait correlations and heritabilies (broad- and narrow-sense ranged between 0.28 and 0.91) that used judiciously will allow the development high yielding melon cultivars with early, basally concentrated fruit suitable for once-over or machine harvesting operations.     

Factors affecting seed yield in white clover

Summary Eighteen clones of white clover chosen at random were examined for their seed setting possibilities. Large differences in the size of the inflorescence and the rate of fertilization were found among the clones, so that breeding strains of white clover with better seed-setting seems possible. The number of ovules per floret seemed not very variable.     

Investigation of yield and persistence of white clover using cluster analyses

Summary A visual growth score method was used to monitor the growth performance of 24 populations of white clover (Trifolium repens) over a three year period. The mean growth scores for each year were used as population x year data for cluster analyses. Cluster analysis methods based on a regression model where genotypes were grouped for similarity of both intercepts and slopes (Method 1) or slopes only (Method 2), were able to differentiate the persistent populations from those that showed a yield decline over time. The deviations from regression mean square was used as an indication of stability. Method 1 was able to cluster the high yielding persistent populations into a separate cluster, thus facilitating the selection of desirable populations. Deviations from regression identified the stable populations from the cluster. In combination with the simple growth score system, this analytical method is a powerful tool for evaluating a large number of breeding families of perennial pasture clovers and grasses for yield and persistence.     

Variation within and among Ladino white clover ecotypes for agronomic traits

Summary One set of 285 genotypes from three landraces and one natural population and a second set of 165 genotypes from two landraces and one natural population were evaluated in separate trials. Variation among populations was mostly accounted for by the difference between landrace and natural population genotype groups, the former showing features related to higher seed yield and short-term aerial dry matter (DM) yield and to lower persistence, cold tolerance and protein content. Compared to variance among ecotypes, that within ecotypes was never lower and it was at least four-fold higher for important traits such as aerial and total (aerial plus stolon) DM yield, stolon density, production of seed heads and cold tolerance. Landraces and natural populations showed similar levels of intra-population variation for all traits except cold tolerance, for which landraces tended to somewhat greater variation. Trait associations were less definite at the genotype level than what previously found in terms of mean values of the ecotypes. This finding and the relatively high broad sense heritability which was observed for all components of DM and seed yield can support the breeding activity on this clover. The level of variation and of heritability found for protein content do not suggest the routine evaluation of this trait in breeding programmes.     

Wheat quality traits and quality parameters of cooked dry white Chinese noodles

Dry white Chinese noodle (DWCN) is widely consumed in China, and genetic improvement of DWCN quality has become a major objective for Chinese wheat breeding programs. One hundred and four bread wheat cultivars and advanced lines, including 88from major Chinese wheat-producing areas, were sown in two locations for two years. Their DWCN quality, as evaluated by trained panelists, was studied to determine the relationship between wheat quality parameters and DWCN quality attributes. In general, the cultivars and advanced lines used in this study are characterized with acceptable protein content, but accompanied with weak-medium gluten strength and poor extensibility, and substantial variation is observed for all grain and DWCN quality characters. On average, Australia and USA wheat performed better DWCN quality than Chinese wheats. Simple correlation analysis indicated that both grain hardness and Farinograph water absorption were negatively associated with cooked DWCN color, appearance, smoothness, and taste. Flour whiteness and RVA peak viscosity was positively associated with all DWCN parameters, and their correlation coefficients (r) with DWCN score are 0.34 and 0.41, respectively. Their positive contributions to DWCN quality were mostly through improved color, appearance, smoothness, and taste. Farinograph mixing tolerance index (MTI) and softening were negatively associated with all DWCN quality parameters, and their correlation coefficients with DWCN score are –0.50 and–0.54, respectively. Further analysis indicated that association between protein content, Zeleny sedimentation value, Farinograph stability, and Extensograph extensibility, and DWCN score fit quadratic regression model significantly, with R² 0.12, 0.32, 0.22, and 0.20, respectively. The associations between Zeleny sedimentation value and DWCN's appearance and taste also fit quadratic regression model significantly. This suggests that to certain extent, increased protein content and gluten quality contribute positively to DWCN quality, mostly by improving palatability, elasticity, and stickiness. High flour whiteness, medium protein content, medium to strong gluten strength and good extensibility, and high starch peak viscosity are desirable for DWCN quality. Genetic improvement for flour whiteness, protein quality and starch paste viscosity would increase the DWCN quality of Chinese bread wheat cultivars. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heritability estimates of spot blotch resistance and its association with other traits in spring wheat crosses

Summary Spot blotch caused by Cochliobolus sativusis considered a major disease problem of wheat(Triticum aestivumL.) in the warm areas of South Asia. This study estimated heritability (h ²) of resistance to spot blotch and its correlation with days to heading DH) and maturity (DM), one-hundred-kernel weight (HKW), and plant height (PHT) in 14 crosses involving four resistant (‘Attila’, ‘Chirya 7’, ‘G 162’, and ‘SW89.5422’) and two susceptible (‘Sonalika’ and ‘HD2329’) wheat genotypes. Data were recorded on F₅and F₆lines in fields under natural epidemics of spot blotch in 2003 and 2004, respectively. Heritability was estimated for area under disease progress curve (AUDPC), AUDPC/day, and the highest disease score (HDS) using offspring-parent regression (h _op ²) and realized heritability (h ² _R) procedures. Heritability estimates were low to high in terms of AUDPC (0.21 < h _op ²< 0.64; 0.32 < h _R ²< 0.70), AUDPC/day (0.40 < h _op ²< 0.96; 0.42 < h _R ²< 0.99), and HDS (0.29 < h _op ²< 0.92; 0.32 < h _R ²< 0.95). The h ²estimates for AUDPC/day were higher than for AUDPC and HDS. Estimates of h _R ²were by and large higher than h _op ²in the same cross. A weak negative or nonsignificant correlation of spot blotch score with HKW, DH, DM, and PHT indicated that independent selection for resistance and these agronomic traits is possible.     

Effects of recurrent selection for grain yield on plant and ear traits of five maize populations

Summary Maize (Zea mays L.) breeders are interested in the effects of recurrent selection for grain yield on other traits. Changes in plant traits could alter agronomic acceptability of the populations under selection, and observed improvements in grain yield could be explained by changes in ear traits. We evaluated changes in combining ability for plant and ear traits of BS10(FR), BS11(FR), BSSS(R), BSCB1(R), and Lancaster Surecrop associated with recurrent selection for grain yield.Recurrent selection procedures generally did not change plant and ear heights or date of silking of testcrosses of populations or of the population crosses, BS10(FR)×BSS11(FR) and BSSS(R)×BSCB1(R). Grain yield improvements, however, were associated with increases in ear-sink size.Journal Paper No. J 9517 of the Iowa Agriculture and Home Economics Exp. Stn., Ames, Iowa. Project 2152.     

Genetic variation and cultivar identification of Jamaican yam germplasm by random amplified polymorphic DNA analysis

Summary We have used random amplified polymorphic DNA (RAPD) analysis to characterize eleven cultivars of the five economically most important yam species grown in Jamaica (Dioscorea alata, D. cayenensis, D. rotundata, D. trifida and D. esculenta). Amplification of genomic DNA samples with nine different arbitrary 10mer primers revealed a total of 338 different band positions, ranging in size from 0.3 to 2.5 kb. RAPD patterns proved to be highly reproducible and somatically stable. While no variation was observed among plants belonging to the same cultivar, a large number of intervarietal and interspecific polymorphisms enabled us to reliably discriminate between all Jamaican cultivars investigated.     

Genetic and environmental variation in architecture and yield components in determinate white lupin (Lupinus albus L.)

Summary Determinate architecture is of great interest for lupin production in Europe but the extent of genetic and environmental variation in the structure and yield of determinate lupins must be evaluated. Forty-three genotypes of determinate autumn-sown white lupin were studied in four environments in France in 1991/92 and 1992/93. Wide variation was observed for phenological (dates of mainstem and branch flowering, date of end of flowering and date of maturity), morphological (numbers of branch orders, branches and leaves) and seed characters (seed yield, mean seed weight, number of seeds/m²). Both genetic and environmental effects contributed to the observed variation. Heritabilities were high for all characters, and the interaction between genotype and location effects was low. There were significant positive correlations of flowering dates with vegetative plant development including the number of branches, number of leaves and number of branch orders. Seed yield and phenological and archtectural characters were significantly correlated. Distribution of yield on the vegetative orders showed important variations according the genotype, and the variations were related to variation for the architecture. There are possibilities for yield improvement using morphological characters in determinate autumn-sown lupin.     

Grain yield and other traits of tall and dwarf isolines of modern bread and durum wheats

Near-isogenic Rht lines of ten modern bread wheat (Triticumaestivum L.) and six durum wheat (T. turgidum L.) cultivars weredeveloped and evaluated in replicated trials under three soil moisturetreatments for two years in northwestern Mexico. The three soil moisturetreatments were created by providing one, two or six irrigations during eachcrop season. Grain yield and other traits were measured for each line ineach trial. Mean grain yields of short and tall T. aestivum or T.turgidum isolines were similar in the lowest yielding environment whenmean grain yields (0% grain moisture) of T. aestivum and T.turgidum were 2,232 and 1,870 kg ha^-1, respectively. Mean grainyield of dwarf T. aestivum was significantly higher than that of tallgenotypes in another five trials with moderate to high yields. Theperformance of dwarf and tall T. turgidum isolines was unpredictablein moderate yielding trials, and the dwarf isolines yielded significantly morein trials that received six irrigations. Given that the tall isolines producedsignificantly more straw than their shorter counterparts, cultivation of tallwheats may be beneficial in semiarid environments where farmers' yields areclose to 2.5 t ha^-1 or lower, and straw has value.     

Variation in quality traits in common wheat as related to Chinese fresh white noodle quality

The variation in grain compositional traits related to Chinese fresh white noodle (CFWN) quality was examined in 25 leading Chinese common wheat cultivars and advanced lines. Large variations were observed in flour yield, flour particle size, protein and ash contents, farinograph and rapid visco-analyzer (RVA) parameters, flour colour components, and polyphenol oxydase (PPO) activity. An improved sensory method was proposed for adequately evaluating CFWN quality of common wheat flour based on methodology used in the Japanese quality scoring system for white salted noodles, but with major modifications in the score weight given to each noodle quality parameter. Large differences in CFWN quality were observed among Chinese wheat cultivars. The correlation coefficients (r) between starch paste breakdown (RVA) and noodle viscoelasticity and smoothness were 0.63 and 0.59, respectively, suggesting that in breeding wheat for high CFWN quality, the starch pasting properties are of major importance. Low ash content was significantly correlated (r = – 0.66) with bright white noodle colour.     

Some yield components and ideotype traits in meadowfoam,a new industrial oil crop

Summary Three populations of Limnanthes alba and five of L. douglasii were investigated for relative growth rates, leaf area index, flowering time, seed and oil yield, seed size and shattering. Within each species the early flowering populations had the highest seed yield. Most accessions developed adequate leaf canopy by the time of onset of flowering.An ideotype for breeding goals could be defined in terms of the characters of L. douglasii var. nivea such as early flowering and high seed yield, provided taller plant stature and reduced seed shattering are incorporated.Domestication and breeding might involve a combination of induced mutation, interspecific hybridization and conventional breeding procedures.     

The inheritance of fruit yield and stolon production in everbearing strawberries

Summary The everbearing progeny from crosses between three short-day and four everbearing genotypes were assessed for early fruit yield and stolon production. General combining ability (GCA) was found to be important for fruit yield but specific combining ability (SCA) was more important for stolon production. The results suggested that it should be possible to combine early fruiting and adequate stolon production in an everbearing genotype. The breeding strategy necessary to achieve this aim is discussed.