Variation between and within Trifolium repens L. populations collected from sown swards in Uruguay

Nineteen Trifolium repens L. (white clover) populations were collected in different parts of Uruguay (where conditions are marginal for the species) from swards sown 2–15 years earlier. Twenty five genotypes of each population were grown as spaced plants on a single site. Leaflet length and width, petiole length, plant height, plant diameter and internode length were recorded. In a second experiment, ten of the populations were studied in a similar way. Large genetic correlations were obtained among leaflet length, leaflet width, petiole length and plant height as one group, and among major plant diameter, minor plant diameter and internode length as another group, in both experiments. Collection site characteristics that tended to result in relatively short, small-leaved plants were: the sowing of cv. Bayucuá or Santa Fé (rather than Zapicán orYi); a relatively old sward; relatively high available soil P; overgrazing; and dry conditions. There was an indication that, in some respects, there was less variation within a population in older than in younger swards. Overall and within populations heritabilities were relatively high for leaflet length, leaflet width and petiole length and relatively low for plant diameter, with plant height intermediate. Genotypes from populations (such as that from Romero) that survived for 15 years in unfavourable conditions could be useful in a plant breeding programme. Selection for rather smaller-leaved types might enhance persistence. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic variation in a Norwegian germplasm collection of white clover (Trifolium repens L.)

Genetic variation and genotype × environment interactions for important agronomic characters were estimated for eleven Norwegian populations of white clover (Trifolium repens L.), originating from between 58^°52′N and 69^°30′N latitude, and from altitudes of 10 to 450 m a.s.l. The populations were evaluated in monoculture clonal field plots for two years at two locations in Norway. The medium-leaved Danish cultivar Milkanova was also included in the experiment as a standard market cultivar. Considerable variation between populations was observed for winter survival, spring growth, morphological characteristics, dry matter yield, general performance, earliness and seed yield. Winter survival, measured as plant cover after two years, was significantly different at the two locations. All the populations had sufficient winter survival at the southern, continental highland site (61^°07′N).At the northern coastal location (69^°30′N),where the winter climate is unstable with physical stresses such as frost, ice-encasement and water-logging frequently occurring, only the northernmost, coastal populations showed sufficient winter survival. Highly significant interactions were found between populations and locations, and between populations and years for all characters measured at both locations and in both years, respectively. Interaction effects between populations, locations and years were significant only for leaflet length. The largest leaf lamina's were observed in the most southern populations. However, genotypes possessing relatively long leaflets were also found in the northernmost populations, although at low frequencies. In general, the populations originating from the northernmost locations had lower biomass production, and were smaller-leaved, more prostrate and exhibited shorter internodes and stolons compared to the populations from South and Middle Norway. These populations also initiated inflorescences earliest, and were among the lowest seed yielding populations. Otherwise, no clear clinal variation in growth characteristics was observed which could be related to the latitude or altitude of origin of the populations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nondestructive and Rapid Leaf Measurements for Use as Selection Criteria in Vicia faba L.*

Four Vicia faba F₂ populations were studied to identify leaf characters that can be scored precisely at low cost and cause minimal disturbance to the plant during the leaf scoring in a selection program to change leaf canopy architecture. From correlation and biometrical analyses, involving eight measurements of leaflet and rachis characters, it was ascertained that the area index (length × width) of the first basal leaflet and the total rachis length of the leaf on the 5th flowering node, were the most informative, rapidly, and nondestructively determined leaf characters serving- the above-men tinned requirements.     

Why SR52 is such a great maize hybrid? II. Heritability,correlation and path-coefficient analyses

Although exceptional heterosis for yield in the world’s first commercial single cross maize (Zea mays L.) hybrid SR52 has been confirmed, the role of secondary traits hasn’t been established. Objectives of this study were to establish relationship between grain yield and secondary traits, while assessing heritability and genotypic variation in SR52’s segregating populations. Knowledge on associations between yield and secondary traits would be crucial in extracting productive inbred lines from the population. Traits were subjected to correlation and path-coefficient analyses. Path analysis model accounted for over 70% of variation (R²) in all populations. Consistently high positive correlations with grain yield were observed for ear length and number of kernel rows on ear. Ear girth (0.19), and number of kernels per row (0.48) showed high direct effects on yield in the F₂ population and the trend was consistent in the backcrosses. Positive indirect effects of most traits on grain yield were negligible with the exception of kernel per row via total number of kernels on ear, which was above 0.40 in the F₂ and BCP1. Ear length can be exploited for indirect selection for yield in SR52’s segregating generations. 100-kernel weight and number of kernel rows on ear can, to a lesser extent, be targeted in selecting for grain yield. High to medium phenotypic variability in segregating generations of SR52 for traits such as ear length, number kernel rows on ear and grain yield should give impetus to selection of productive inbred lines from SR52 hybrid because of presence of diversity in the gene pool.     

Harvest index in lentil (Lens culinaris Medik.)

Summary Correlation and path coefficient analyses were conducted to find out the characters associated with grain yield and dry matter production and the ways to improve harvest index in lentil.Correlation studies revealed positive association of harvest index with grain yield but no association with plant dry matter. Grain yield and plant dry matter showed positive correlation with pod number, plant height, and number of primary and secondary branches but negative correlation with 100-seed weight. Generally, the genotypic correlations were in agreement with phenotypic correlations, though the magnitude of the values was higher in the former case. In path analysis, plant height and pod number showed the highest direct effect and, therefore, seem to be the main characters influencing grain yield and plant dry matter. Number of primary and secondary branches, on the other hand, showed negative direct effect on grain yield and plant dry matter. Use of phenotypic or genotypic correlations in path analysis resulted in similar conclusions. It is, therefore, suggested that either phenotypic or genotypic correlations may be used in path analysis with equal efficiency. Based on this study it is suggested to develop tall varieties with good pod bearing but with low number of branches.     

Inter-relationships among total crude protein and digestible dry matter production and their component traits in Guinea grass

Summary Phenotypic and genotypic correlation coefficients of total crude protein per plant (TCP) and digestible dry matter per plant (DDM) with dry matter yield per plant (DMY), tiller number, plant height, stem thickness and leaf-stem ratio, pooled over two years, revealed that TCP and DDM were correlated at both the phenotypic and genotypic levels with DMY, tiller number and plant height. But only DMY had high direct effects on TCP and DDM. Tiller number and plant height had only indirect effects on TCP and DDM via DMY. Thus, selection based on tiller number and plant height may not only improve dry matter yield per plant but also total crude protein per plant and digestible dry matter per plant. Further, screening of high TCP and high DDM clones among the high yielding clones would be a more remunerative approach to improve TCP and DDM in Guinea grass.     

Plant character correlations and path analysis of pod yield in okra (Abelmoschus esculentus)

Summary Genotypic, phenotypic and environmental correlation coefficients were calculated for fifteen characters during two growing seasons. Correlation coefficients varie between seasons. Edible pod weight, edible pod length, edible pod width, number of seeds per plant, weight of 100 seeds, length of mature pods and number of branches per plant showed significant genotypic correlation with pod yield per plant; only number of branches per plant, edible pod length and weight of 100 seeds were phenotypically correlated with pod yield. Environmental correlation coefficients were generally low but edible pod length, final plant height and edible pod weight showed significant environmental correlation with pod yield during the two seasons.The genotypic correlation coefficients of selected eight characters with pod yield were partitioned into direct and indirect causes. In the early seasons, edible pod weight had the largest positive direct effect on pod yield with its largest indirect effect through reduction in edible pod width. Edible pod width which was highly correlated with pod yield had a negative direct effect on pod yield. In the late season, edible pod weight had the largest direct effect on pod yield, with large indirect effects through reduction in number of days to flowering and number of pods per plant. Number of days to flowering had a large direct effect on pod yield with its largest indirect effect through reduction in edible pod weight. The residual factors during the two seasons were negative. The study indicated that only number of branches per plant, edible pod length and weight of 100 seeds would be useful for indirect selection for pod yield. The path analysis indicated that edible pod weight was the most reliable and effective character to select for when high yield is the objective.     

Culture selected somaclonal variation in five Triticum aestivum L. genotypes

Somaclones (R₃ and R₄ generations) regenerated from five winter wheat (Triticum aestivum L.) genotypes were evaluated for variation in agronomic and morphological characters. Immature embryos were used as initial explant material. Comparisons for plant height, top internode length, spike length, number of seeds per spike and 100 seed weight were made between the somaclones and their parents. Some morphological variations of stem and spike characteristics were registered which demonstrate that plant height and spike length can be changed by using immature embryo culture. The results obtained may be considered a biotechnological contribution to wheat plant improvement. This revised version was published online in August 2006 with corrections to the Cover Date.     

Plant Types and Gibberellin Responses of Chinese Dwarf-barley Genetic Resources

Plant types and gibberellin responses were investigated in 20 Chinese dwarf and two tall check-barley varieties Wide genetic variation was observed in plant height, ranging from 23.1 to 69.2 cm. Compared with the controls, no relationship was found between plant height and internode number, but a relationship was established between plant height and internode length. The ratio of the length to the diameter of each internode decreased greatly in most of the dwarfs. Three dwarf groups, three internode patterns and four leaf forms were differentiated in Chinese dwarf barleys based on the main culm height, successive internode lengths, and top three leaf widths and lengths. Most showed sensitivity to GA₃.     

Genetic analysis of mesocotyl length and its relationship with other agronomic characters in rice (Oryza sativa L.)

Summary Mesocotyl length is an important character in promoting seedling emergence of direct-seeded rice. Genetic analysis of rice mesocotyl length was conducted using a six parent diallel cross. Generation mean analysis was carried out on parents (P), F1, F2 and backcrosses (B) of three crosses to complement the genetic information from the diallel analysis. Both analyses demonstrated the presence of significant additive and dominance effects. Duplicate type of non-allelic interaction was detected by the generation mean analysis and two crosses showed significant negative dominance gene effect. Dominance was partial and the narrow sense heritability estimate for mesocotyl length was high, indicating the preponderance of the additive effects.Mesocotyl length was negatively but weakly correlated with the coleoptile length and length of the second internode L2. There was no correlation between mesocotyl length and other mature plant characters such as plant height and internode lengths L₁, (L₁ being the peduncle with subsequent internodes to the base of the plant). Selection for mesocotyl length can therefore be carried out independent of these plant characters and semidwarf rice varieties with long mesocotyl can be developed.     

Response of a new IR50/Moroberekan recombinant inbred population of rice (Oryza sativa L.) from an indica × japonica cross for growth and yield traits under aerobic conditions

Genetic variability, correlation, path coefficient analysis and test of normality was conducted in an F₈ recombinant inbred aerobic rice population developed by single seed descent method to evaluate its potential as a mapping population. Estimates of genotypic variance, phenotypic variance, genotypic coefficient of variance (GCV), phenotypic coefficient of variance (PCV), heritability in the broad sense (H) and expected genetic advance at 5% selection index (GA) for grain yield and other attributing characters were computed. In all the cases, PCV was higher than GCV indicating the influence of environment on the characters. High heritability coupled with high GA was observed for several plant traits; number of tillers, plant height, total number of spikelets panicle⁻¹, biomass plant⁻¹, straw weight, harvest index and grain yield plant⁻¹ and hence offered good scope for selection. Grain yield plant⁻¹ was found to be positively correlated with plant height, number of tillers, panicle length, panicle exsertion, number of panicles plant⁻¹, single panicle weight, test weight, number of fertile spikelets panicle⁻¹, straw weight, biomass plant⁻¹, harvest index and grain breadth both at genotypic and phenotypic levels. Harvest index exerted maximum positive direct effect, followed by biomass plant⁻¹ and straw weight on grain yield plant⁻¹ at phenotypic level. Shapiro-Wilks “W test of normality” indicated that the population was skewed towards female parent IR50 for some traits and for some others towards Moroberekan, the male parent. Most of the characters that showed skewness were platykurtic with a kurtosis value of less than 3.     

Variation in cold tolerance and spring growth among Italian white clover populations

Seven populations collected at different altitudes in northern Italy, two Ladino breeding populations and two control cultivars (AberHerald and Grasslands Huia) of white clover (Trifolium repens L.) were included in a series of experiments analysing: (i) levels of cold tolerance using artificial and field-based methods; (ii) relationships between these measures of cold tolerance; (iii) components of spring yield, various physiological traits, and their relationships with cold tolerance. Rates of seedling and growing point mortality in the populations over winter, assessed in separate field experiments, were closely related (r = 0.85). Grasslands Huia showed the highest death rates, and material originating from high altitudes the lowest. The LT₅₀ value, i.e., the temperature at which 50% of the growing points would die, estimated by an artificial freezing test, was significantly correlated with field-based measures of seedling (r = 0.64) and growing point (r = 0.84) mortality. The existence of these correlations is of potential interest for the development of indirect selection criteria for complex and expensive-to-evaluate traits such as winter survival in field plots. Besides being reliable, in this study the artificial assessment was also sensitive, providing a greater degree of separation of the populations means than field-based measures. Of the several physiological traits (water content,concentrations of water soluble and total non-structural carbohydrate, and water soluble protein content of stolons) measured at a mid-winter sampling date under field conditions, the only character showing significant variation between populations was soluble protein content. There was a slight trend for material with a higher protein content to exhibit greater field-based values of cold tolerance. High altitude populations tended to have low spring yields. The highest spring yield was found in one of the Ladino populations. The study identified two populations which combined, to differing extents, cold tolerance and spring yield characteristics that would be of potential use in breeding for specified agronomic/climatic zones. This revised version was published online in August 2006 with corrections to the Cover Date.     

Analysis of an incomplete diallel cross among three ssp. tuberosum varieties and seven long-day adapted ssp. andigena clones of the potato (Solanum tuberosum L.)

Summary The main aim of the experiment was to study the behaviour of seven long-day adapted clones of Solanum tuberosum ssp. andigena (A) and three varieties of S. tuberosum ssp. tuberosum (T) in an incomplete diallel cross. The four groups of crosses, TxT, TxA, AxT and AxA, held 2, 12, 20 and 21 populations, respectively. Eleven of the intersubspecific crosses were exact reciprocals. Thirty random clones per population were grown as second clonal generation in an incomplete block design with four replications in plots of two plants per clone in 1980, the parents included in many plots. Data were recorded on ten characters.The results showed that group TxA gave the highest tuber yield and AxT the second highest. The F-values indicated highly significant genotypic effects for all characters in all populations. The mean genotypic coefficients of variation (GCV), were the highest for group AxA for all characters. The ANOVA, based on population means showed significant mean squares for general combining abilities (GCA) and for differences of reciprocalls for all characters; the specific combining ability (SCA) mean squares were significant only for date of emergence, plant height and haulm type. Almost all GCA effects of the parents were significant positive or negative. Several populations showed also significant SCA effects. The correlations between the GCA effects and the parental values were of about the same magnitude as the heritabilities; those between the population means and the midparental values were slightly lower.Compared to the midparental values, most populations showed significant positive heterosis for date of emergence, haulm type, number of tubers and under water weight; all populations had significant negative heterosis for mean tuber weight and nearly all for plant height and general impression. All populations from groups TxT and AxA had significant negative heterosis for tuber yield and so had 13 out of the 20 populations from group AxT, while seven of the 12 from group TxA showed significant positive and four significant negative heterosis. The average heterosis for tuber yield of group TxT was –11%, of TxA 3.4%, of AxT–9% and of AxA–18%. The highest mean tuber yields were obtained from crosses with a very high yielding A-parent as female, while the heterosis was negative. Though significant differences between the 11 reciprocals occurred for all characters, consistent differences occurred only for tuber yield. Averaged over the 11 crosses the TxA populations outyielded their exact reciprocals by 10.7%. For the highest tuber yields in A-T crosses, therefore, the tuberosum cytoplasm seems to be preferable. By contrast for a high male fertility the andigena cytoplasm is preferable.     

Diallel study of open-pollinated maize varieties in Trinidad

Summary In Trinidad, maize (Zea mays L.) is primarily harvested in the immature stage as green ears for human consumption. The purchase of popular imported hybrid seed has become a substantial component of the economic inputs of maize production. The objectives of this study were to investigate combining abilities and heterotic patterns among available open-pollinated varieties and to assess correlations among five important traits: time to silking, plant height, grain yield, ear size, and marketable ears per hectare. General combining ability was significant for all traits. Specific combining ability was significant for all traits except ear size. Three intervarietal crosses showed moderate levels of heterosis (10–27%), and several yielded similarly to the control hybrids, Pioneer X304 and Pioneer 3078. The cross Acid Soil Tolerant 1991 SA-3 X ICTA Farm Corn was selected as the most suitable base population for mass selection. Phenotypic and genotypic correlations among the five traits studied were all positive and significant. Populations which flowered early were shorter and yielded less than the late flowering and taller populations and population crosses included in this study.     

Genetic variation for shoot elongation before winter and its correlation with vernalization requirement in winter oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis> L.)

Changing climatic conditions in north-western Europe are accompanied by occasional extreme weather conditions. This requires breeding of winter oilseed rape cultivars which are resilient to diverse abiotic stress factors, e.g. frost, drought and heat. The degree of vernalization requirement of winter oilseed rape has been found to be related to frost tolerance and winter hardiness. Shoot elongation before winter in particular has been identified as one decisive factor for frost tolerance in winter oilseed rape. However, the relationship between vernalization requirement and shoot elongation before winter is not known. In the present study the genetic variation for shoot elongation before winter and vernalization requirement of 19 genetic diverse breeding lines and cultivars were analyzed. Autumn and spring sown field experiments in multiple environments were performed to determine shoot elongation before winter and vernalization requirement, respectively. In spring sown field experiments, genotypes with a low vernalization requirement were characterized by the occurrence of long bolting plants with flower buds. Large and significant genotypic variation was found for shoot length in the autumn sown and spring sown environment. Broad sense heritability was quite high for shoot length in the spring sown environment (h²?=?97%), whereas it was only of medium size for shoot length before winter (h²?=?62%). Although the correlation between shoot length before winter and shoot length in the spring sown environment was positive (Spearman’s rank r_S?=?0.48*), a number of genotypes with reduced shoot elongation before winter and low vernalization requirement were identified. Results indicate that genotypes with a reduced shoot elongation before winter independent of their vernalization requirement can be selected in breeding programs.     

Sunflower seed yield as influenced by some agronomic and seed characters

Summary An investigation was made to the interrelationships of agronomic and seed characters and their effect upon seed yield. Twenty genotypes of sunflower (Helianthus annuus L.) from diverse origin were studied in spring and autumn season, 1989.Most of the studied characters exhibited different relationships in spring and autumn seasons. The correlations between plant height and oil content, 100-achene weight and number of achenes per head and plant height and head diameter were, however, consistent in both seasons and across the seasons. Stepwise multiple regression analysis identified six relevant characters on which path analysis was done.Path analysis indicated that yield components like head diameter, number of achenes per head and 100-achene weight had comparatively smaller direct effects on seed yield (0.22, 0.15 and 0.23, respectively). Days to physiological maturity, plant height and oil content had relatively stronger direct effects on seed yield (0.33, 0.38 and 0.29, respectively). Days to physiological maturity, plant height and head diameter had considerable indirect effects. Head diameter, 100-achene weight and number of achenes per head were indentified as selection criteria for yield improvement.     

Combining ability analysis for harvest index in winter wheat

Summary Cereal breeders have used harvest index (HI) as a selection criterion in segregating generations to identify physiologically superior lines with improved partitioning of total assimilate into grain. Information on combining ability for HI of the hard red winter wheat (Triticum aestivum L.) cultivars of the Southern Great Plains is not available. A study was undertaken to examine HI of seven genetically diverse winter wheat parents, evaluate their general combining ability (GCA) and specific combining ability (SCA) effects, and study correlations of HI with several agronomic traits. The seven parents were crossed in a half-diallel mating design to produce 21 crosses. The F₁'s, their F₂ progenies, and the parents were evaluated in replicated field tests at Stillwater and at Lahoma, OK. The combining ability analysis was performed using Griffing's Method 4, Model 1. The results showed significant variation among parents for HI. The GCA and the SCA effects were mostly inconsistent between generations and between environments. However, parents with consistently high HI and positive GCA estimates were identified. The progeny with high HI mostly resulted from parents with high GCA estimates. The correlations between HI and agronomic traits indicated that improvement in HI should also result in high grain yield, early maturity, and short plant height.     

The association of culm anatomy with lodging susceptibility in modern spring wheat genotypes

Selection for lodging resistant cultivars in cereal breeding programs is difficult due to the challenge of screening for this trait under natural field conditions. The identification of easily measurable culm traits related to lodging resistance would simplify the selection process. The present study was conducted to determine if differences in culm anatomy exist among modern wheat genotypes differing in lodging susceptibility, and to determine the association between culm characters and lodging. From a 2-year field study conducted in Edmonton, Alberta, 13 spring wheat cultivars were chosen based on predetermined susceptibility to artificially induced lodging. Morphological and anatomical culm measurements were made visually and with an environmental scanning electron microscope. Genotypes differed (P < 0.05) for plant height, number of internodes per culm, basal internode length and diameter, culm wall thickness and the number of vascular bundles, but not for adventitious root frequency, lumen diameter or sclerenchyma ring thickness. Mean genotype field scores for artificially induced lodging were correlated (P < 0.05) with plant height (r= 0.51) and the length of the fourth basal internode (r= 0.51). Short, wide basal internodes and thick culm walls were characteristic of three lodging tolerant genotypes: Kohika, Sapphire and Olso. Nevertheless, despite such apparent genotype specific association between culm anatomy and field lodging, general applicable associations were not observed for most traits. The most practical and easily selectable trait for lodging resistance within a wheat breeding program remains plant height. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic gain and correlations among traits for stink bug resistance in soybeans

An experiment was carried out at the State University of Londrina School Farm in a randomized complete blocks design with three replications; the plots underwent natural stink bug attacks to check correlations existing among agronomic traits and stink bug damage in 33 F₈ pure lines soybean. The seed size trait was measured by the weight of a hundred seeds (WHS) and the percentage of stink bug damage seeds (PDS) was measured by staining the seeds with tetrazolium at 0.01%. Seeds were considered damaged with at least one puncture and or with marks characteristic of stink bug. The phenotypic and genotypic correlations between the WHS and the PDS seeds were positive, being 0.51 and 0.67 ± 0.19, respectively. The relationship between the visual pod width (VPW) and PDS was also significant, being 0.41 and 0.54 ± 0.19 for phenotypic and genotypic correlations, respectively. Thus the breeder can select lines for stink bug resistance indirectly either by WHS or VPW. These two traits are very easy to assess when compared with the assessment of PDS damage, allowing the use of larger populations. However, in this case, the genetic gains by selection were smaller than those obtained by direct selection, but even so they were considered noteworthy. The VPW may be an efficient way of selection in large populations for stink bug resistance. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic variability and interrelationships of seed yield and yield components in switchgrass

Information on the genetic variability of seed yield and yield components is limited and no information is available on correlations among seed yield and yield components and direct and indirect effects of the yield components on seed yield in switchgrass, Panicum virgatum L. Accordingly, we conducted replicated experiments at Chickasha and Perkins, OK, in 1998 involving 11 lowland type switchgrass populations to assess genetic variation for seed yield and yield components, quantify interrelationships among them, and determine direct and indirect effects of yield components on seed yield through path coefficient analysis to identify traits for indirect selection of seed yield. Significant (P ≤ 0.01) variation existed among the 11 populations over locations for percent seed set and 100-seed weight. Seed yield/plant and the seed yield components panicle number/plant, spikelet number/panicle, and seed number/panicle had significant (P ≤ 0.05) population × location interactions, indicating substantial environmental influence on these traits for these populations. Accordingly, data for these traits were analyzed separately for each location revealing significant (P ≤ 0.01) differences among populations at both locations for each of these traits. Phenotypic correlation between seed yield/plant and seed number/panicle was positive (r = 0.76** at Chickasha and r = 0.72** at Perkins). Path coefficient analyses revealed that seed number/panicle had the highest positive direct effect on seed yield at both locations. Ample genetic variability was present among the switchgrass populations studied to allow breeding improvement of seed yield. Selection for increased seed number/panicle would be the most effective means of indirectly selecting for higher seed yield within this germplasm. Correlation and path coefficient analyses among biomass yield, seed yield, and harvest index indicated that, at least within the switchgrass germplasm studied, it would be possible to breed switchgrass cultivars with enhanced biomass yielding ability and sufficient seed production capability for their commercial propagation.