Implications of selecting improved strains of soybeans for dry-matter accumulation and grain yield

Summary Three maturity groups of soybeans (Glycine max L.) were used to investigate the relationship between dry-matter accumulation (DMA) and grain yield (GY), and the prospects for selection of high seed yielding strains among the existing soybean cultivars in a tropical environment. The positive and significant association between DMA and GY (r=0.888^***) indicated that selection for high DMA could give gains in GY. However, the higher harvest index (HI=37.5%) for the low seed yielding early maturing genotypes than the more vegetatively endowed and higher seed producing late maturity group, is an indication that excessive DMA could be disadvantageous. Total seed yield per land area for the three maturity groups of soybeans showed that the genotypes with high harvest index and low seed yield could be as good as those ones with high seed and dry-matter yields with low harvest index. The high coefficient of variation which ranged between 18.1 and 59.8% and the heritability estimations which also ranged from 34.4 to 82.2% are indicative of the presence of substantial genetic diversity and there are good prospects for the improvement of the crop through selection.     

Weed tolerance in soybean: a direct selection system

Weed competition can severely reduce soybean (Glycine max (L.) Merr.) yields, particularly in organic systems. An efficient screening and breeding approach is needed to increase breeding progress for weed tolerance. This study sought to (i) establish a system for direct selection of competitive genotypes, (ii) evaluate genotypic differences in weed tolerance among six early‐maturing genotypes and (iii) assess the contribution of selected morphological traits to weed tolerance. A direct selection system providing two different levels of weed competition through all development stages of a soybean crop was developed, using mixtures of selected crop species as sown competitors. Two resulting mixtures induced intermediate (<30%) and strong (>50%) yield reduction, respectively. This selection system can be applied in screening and breeding programmes to facilitate breeding for weed tolerance. No significant difference in weed tolerance was detected between six soybean genotypes of maturity groups 000 to 00. Morphological traits that might influence competitive ability, for example light absorption, leaf area and lateral shoots, were assessed, and their potential for indirect selection for weed tolerance is discussed.     

The interaction of genotype and environment in durum wheat

Summary Genotype-environment interactions for yield, final height and days to maturity were analysed by means of statistical and genetic techniques in five cultivars of durum wheat (Triticum durum Desf.) grown for 4–5 years in 5 locations in Western Canada. Differences in the response to environment were found among genotypes for the characters studied. A significant proportion of the genotype-environmental interaction component of variation proved linearly related to the additive environmental component in two and in three cultivars and as well as in one for yield, height and days to maturity, respectively. Sensitivity to environment, as measured by the linear regression, was correlated with mean performance only in the case of height. There was a significant positive correlation between height and yield.Contribution No. 217 from the Department of Plant Science, The University of Manitoba, Winnipeg 19, Manitoba.     

Zur Eignung nicht eingesäter Teilflächen in Getreideschlägen für die störungsfreie, bildanalytische Ermittlung von Unkrautschadschwellen

Suitability of not seeded test squares in crop fields for reliable ascertainment of weed threshold levels by quantitative image analysis
The possibility to measure weed ground cover using a computerized image analysis system has been reported in former investigations. In the present studies suitability of not seeded test squares in crop fields for reliable detection of weed ground cover for precise determination of weed threshold levels (beyond that crop yield losses are economically greater than costs for weed control) has been tested.
Test squares in which weed grew without competing crop as well as corresponding squares including both, growing crop and weeds, were examined for weed ground cover by computer assisted quantitative image analysis of color slides taken from the respective squares. In the squares, that includes crop and weeds, the former was removed immediately before taking the slides.
In both seasons from the beginning of weed growth in October to the latest feasible application time of herbicides in April weed growth as measured by ground cover in the not seeded test squares did not differ significantly from that grown under competition of winter barley.
Results indicate, that up to the growth stage of weed where herbicides if ever should be applied at the latest, crop-free test areas in the same field could serve for correct determination of weed growth by image analysis.     

Legume cover crops as living mulches for winter wheat: Components of biomass and the control of weeds

To gain information about the possible use of legume cover crops as an alternative and sustainable weed-control strategy for winter wheat (Triticum aestivum L.), an experiment was conducted at two sites in the Swiss Midlands in 2001/2002. Under organic farming conditions winter wheat was direct-drilled into living mulches established with four different legume genotypes or into control plots without cover crops. Compared to NAT (control plots without cover crops but with a naturally establishing weed community), white clover (Trifolium repens L.), subclover (Trifolium subterraneum L.), and birdsfoot trefoil (Lotus corniculatus L.) reduced the density of monocotyledonous, dicotyledonous, spring-germinating, and annual weeds by the time of wheat anthesis. Strong-spined medick (Medicago truncatula Gaertner) was less efficient in this regard. While the grain yield was reduced by 60% or more for all legumes when compared to NOWEED (control plots kept weed-free), a significant negative correlation between the dry matter of the cover crop and weeds as well as between the cover crop and the winter wheat was observed by the time of wheat anthesis. The effect of manuring (60 m³ ha⁻¹ liquid farmyard manure) was marginal for weeds and cover crops but the additional nutrients significantly increased total winter wheat dry matter and grain yields. The suppression achieved by some legumes clearly demonstrates their potential for the control of weeds in such cropping systems. However, before living legume cover crops can be considered a viable alternative for integrated weed management under organic farming conditions, management strategies need to be identified which maximise the positive effect in terms of weed control at the same time as they minimise the negative impact on growth and yield of winter wheat.     

不同熟期及产量类型的大豆生殖生长期生理特性的比较研究

通过分析不同熟期、不同产量类型的大豆，特别是高产品种（系）的群体生理特性，为栽培措施的合理运用及生态育种指标的有效选择提供理论参考。连续2年的试验结果表明，高产大豆应具有株高适宜，节数相对较多，产量形成的空间较大，生殖生长期LAI和LAD较高，R5期后叶片衰减慢，叶片在各个方向上的分布均匀，干物质积累量大，     

Genetic variation,heritability and path-analysis in landraces of bread wheat from southwestern Iran

Summary Nine pure lines of bread wheat collected from landraces of southwestern Iran and one local Iranian cultivar from the same area were used to estimate genetic variation and heritability for 12 developmental and yield component characters. Path-analysis was used to partition the genetic correlations between some of the characters into direct and indirect effects. Mean values for these lines were also compared with those of five improved cultivars from Iran and California. The goal of the experiment is to breed improved landraces and/or modern cultivars for areas of low input agriculture in southern California, southwestern Iran, and regions with similar environmental and agronomic conditions.Moderate genetic variation was displayed by the number of effective heads per plant, number of grains per head, and grain weight in the landrace genotypes. The heritability estimates ranged from 43 to 97%. Expected genetic advance with selection of the highest 5%, expressed as percent of the mean, was around 20% for number of heads per plant, number of grains per head, and 1000-grain weight.Days to booting, to heading, and to anthesis were positively correlated but none of them were significantly associated with days to maturity. Plant height had a negative genetic correlation with number of grains per head, 1000-grain weight, grain yield, and harvest index. The genetic correlation between number of heads per plant and number of grains per head, 1000-grain weight, and harvest index was also significantly negative. Harvest index had a negative genetic correlation with days to booting, to maturity, plant height, number of heads per plant, and straw yield and a positive correlation with number of grains per head, 1000-grain weight, and grain yield.Days to maturity, plant height, number of heads per plant, number of grains per head, 1000-grain weight, and harvest index each had a positive direct effect on grain yield. The first two characters exhibited the highest and lowest direct effects, respectively. The positive direct effects of days to maturity, plant height, and number of heads per plant, however, were partially or completely counter-balanced by their strong negative indirect effects through number of grains per head, 1000-grain weight, and harvest index. Pathanalysis indicated that late and tall landrace genotypes tend to produce more heads per plant, but with fewer number of grains per head, smaller grains, and lower harvest index.Comparisons between the local lines and the improved cultivars revealed that, in general, the former were much taller and produced a larger number of non-effective tillers. Mean number of grains per head, grain weight, harvest index, and grain yield of local lines were smaller than those of improved cultivars.Our observations indicate that the landraces could be improved by selecting for shorter genotypes with smaller numbers of tillers per plant, but with larger numbers of grains per head and heavier grains.     

Growth and Development of Six Barley (Hordeum vulgare ssp. vulgare L.) Cultivars in Response to a Model Weed (Sinapis alba L.)

The aim was to study the growth and development of six spring barley (Hordeum vulgare ssp. vulgare L.) cultivars as a response to a model weed population of Sinapis alba L. The development of light interception profiles over time was characterized for each cultivar in weed‐free stands. The cultivars were chosen such that they represent a range of weed‐suppressive abilities based on previously performed trials. One field experiment each was conducted in 1996 and 1997 at a site SE of Uppsala, Sweden. The two cultivars with low competitive ability against weeds, Etna and Blenheim, allowed the highest weed biomass and the lowest crop biomass in competition with the weeds. These two cultivars transmitted more photosynthetic active radiation through the canopy down to 20 and 40 cm height than did the other cultivars. Although the biomass of cv. Etna was low, the grain yield was higher than that of the other cultivars when grown in competition with weeds. In 1997, cv. Svani with good competitive ability against weeds transmitted least light and had greater grain yield than most other cultivars. The absence of a relationship between high grain yield and low weed suppressive ability in the present study indicates that it should be possible for plant breeders to combine high grain yielding capacity with approved weed‐competitive ability.     

Genotypic variation for competitive ability in spring wheat

Herbicides are the primary method of weed control for crop production in developed countries. For economic and environmental reasons alternative control strategies are being devised. One of these strategies is the development of competitive crop cultivars. The objectives of this research were to establish whether spring wheat (Triticum aestivum L.) genotypes differed in competitive ability and if those differences were related to specific growth characteristics. Sixteen genotypes of spring wheat were grown under simulated weed competition conditions at Saskatoon, Canada over a 3–year period. Four high and four low tillering genotypes from each of two crosses (Neepawa/M1417 and Ingal/M1417) were studied. Weeds consisted of cultivated oat (Avena saliva cv. ‘Waldern’) and oriental mustard (Brassicajuncea cv. ‘Cutlass’) sown at two densities (48 and 96 seeds/m² per weed species). Seedling establishment, ground cover, and seed yield for the three species were determined, as was wheat tiller number, spike number, maximum height, leaf area index, leaf orientation, and flag leaf length and size. Significant (P = 0.001) weed rate by genotype interactions involving changes in genotype rank were detected for wheat grain yield, indicating that the 16 wheat genotypes differed in competitive ability. Wheat grain yield reductions averaged over the two weed densities ranged from 45% to 59%. The highest-yielding genotypes under weed-free conditions were not necessarily the highest yielding under weedy conditions. Genotypes which suffered smaller yield reductions were more effective in suppressing weed growth. Although competitive genotypes were generally taller than non-competitive genotypes, other traits such as large seedling ground cover and flag leaf length were associated with wheat yield under competitive conditions.     

Variation in the photoperiodic response on several characters in soybean,Glycine max (L.) Merrill

Summary The photoperiodic response on 12 characters in 40 soybean, Glycine max (L.) Merrill, cultivars were investigated using 10-hour (short day) and 16-hour (long day) photoperiods. Seventeen cultivars showed no significant difference between photoperiods for all 12 characters. Seven cultivars showed significant difference for only one trait. Phenotypic changes in 17 cultivars may be due to factors other than photoperiod. Number of pods per plant, days to maturity, and number of nodes per plant were highly correlated with yield per plant in both photoperiods. Invariably, the cultivars which had significant differences in the numbers of flowers produced per plant between the two photoperiods also had significant differences in the numbers of pods per plant and yield. First node to flower, plant height at flowering, days to flowering, nodes at flowering, and the 100-seed weight were least influenced by the photoperiods in most of the cultivars, while the height at maturity, number of nodes at maturity, number of days to maturity, and yield were most influenced.AVRDC Journal paper 46 (78–88).     

Genetic variation and interrelationships of agronomic characters in landraces of bread wheat from southeastern Iran

There is renewed interest in wheat landraces as important sources of genetic variation for agronomic characters. Fifty-three pure lines of bread wheat (Triticum aestivum L.) derived from seven landraces collected from southeastern Iran were used to estimate genetic variation and heritability for 13 developmental and quantitative characters. Path-analysis was used to partition the genetic correlations between grain yield and six grain yield-related traits. Mean values of landraces were also compared with three improved cultivars from California and Iran. Genotypic differences among the landraces and among the pure lines collected from the landraces were highly significant for all characters considered. Compared with the modern cultivars, the landrace genotypes were, on average, later in days to heading and taller than the cultivars but had lower values for number of grains per spike, 1000-grain weight, grain yield and harvest index. Some landrace genotypes were similar to the modern cultivars for grain yield. Moderate to high genetic variation was displayed by number of grains per spike, number of spikes per plant, 1000-grain weight, and harvest index. The heritability estimates ranged from 59% for grain yield to 99% for days to anthesis. Expected genetic advance (as % of the mean) was ≈34% for number of spikes per plant, number of grains per spike, and 1000-grain weight. Days to heading and to anthesis correlated positively with number of spikes per plant, shoot biomass, and straw biomass but negatively with number of grains per spike and harvest index. The strong direct effect of number of spikes per plant on grain yield was completely counterbalanced by its indirect negative effects via number of grains per spike and 1000-grain weight. Number of grains per spike and 1000-grain weight were positively correlated with grain yield, and they had large direct effects. These two characters, however, were negatively correlated and exhibited a substantial counterbalance effect via one another and via number of spikes per plant. The landraces could be improved by intercrossing the promising genotypes identified in this study, with simultaneous selection for earliness, fewer number of spikes per plant, greater number of grains per spike and heavier grains. For further improvement, crossing programs between the landraces and introduced germplasm may be necessary. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reduced inter-row distance improves yield and competition against weeds in a semi-dwarf durum wheat variety

Weed and nutrient management in cropping systems of semi-arid areas is a major constraint to cereal yield. Where the use of herbicides is banned or discouraged, the competitive ability of a crop is crucial to reduce weed growth and diffusion. Genotypic differences in the competitive abilities of crops are an important trait to reduce weeds, especially for plant height. However, there is contrasting information about the interactions of other management practices and genotypic traits on wheat yield and competitive ability against weeds and weed growth. The present study investigated yield and quality of durum wheat (Triticum durum Desf.) and weed growth and composition for two wheat cultivars with contrasting competitive abilities against weeds. Wheat was grown under three spatial arrangements (5-cm, 15-cm, 25-cm inter-row distance) and three sowing densities, and broadleaf weeds were either removed or not. The sowing rate did not affect the yield of these wheat cultivars or the weed growth. Reduced inter-row distance dramatically reduced weed biomass for both wheat cultivars, and increased wheat yield and nitrogen uptake in the low-competitive, high-yielding, semi-dwarf cv. ‘PR22D89’, when both weed free and with weeds. These results have direct implications for weed and nutrient management in low-input and organic cropping systems.     

Photocontrol of Weeds

The reduction of weed emergence resulting from night‐time tillage in worldwide conducted field trials was very variable. The efficacy of night‐time tillage ranged from a reduction of weed ground cover of 97.5 % to an increase in weed seedling emergence of 80 % compared with daytime tillage. In most of the field trials, the reduction in the weed density as a result of night‐time tillage was <30 %. Important factors affecting this variation were: (1) the different light sensitivity of weed species, (2) the different light sensitivity of populations within the same species, (3) the dormancy status of the seeds, (4) the seasonal and short‐term variation of light sensitivity of seeds, (5) the variation of soil water content and (6) the type of soil tillage implement used. Less important were the small light intensity during night‐time tillage which cannot be excluded, and the penetration of light into the soil the days following night‐time tillage. The influence of different environmental factors on the effect of photocontrol of weeds is rather unclear because there are presumably complex interactions between environmental factors and the light‐dependent germination of weed seeds under field conditions. However, some field trials indicate that dry soil conditions reduce the efficacy of photocontrol of weeds. Several trials in the literature suggest that photocontrol of weeds during daytime using implements with a light‐proof cover was as effective as night‐time tillage. This review summarizes the results in research of photocontrol of weeds (soil cultivation in darkness), particularly those derived from field trials. Moreover, important factors are discussed, which might influence the effect of photocontrol of weeds.     

Predicting spring barley yield from variety-specific yield potential, disease resistance and straw length, and from environment-specific disease loads and weed pressure

For low-input crop production, well-characterised varieties increase the possibilities of managing diseases and weeds. This analysis aims at developing a framework for analyzing grain yield using external varietal information about disease resistance, weed competitiveness and yield potential and quantifying the impact of susceptibility grouping and straw length scores (as a measure for weed competitiveness) for predicting spring barley grain yield under variable biotic stress levels. The study comprised 52 spring barley varieties and 17 environments, i.e., combinations of location, growing system and year. Individual varieties and their interactions with environments were analysed by factorial regression of grain yield on external variety information combined with observed environmental disease loads and weed pressure. The external information was based on the official Danish VCU testing. The most parsimonious models explained about 50% of the yield variation among varieties including genotype-environment interactions. Disease resistance characteristics of varieties, weighted with disease loads of powdery mildew, leaf rust and net blotch, respectively, had a highly significant influence on grain yield. The extend to which increased susceptibility resulted in increased yield losses in environments with high disease loads of the respective diseases was predicted. The effect of externally determined straw length scores, weighted with weed pressure, was weaker although significant for weeds with creeping growth habit. Higher grain yield was thus predicted for taller plants under weed pressure. The results are discussed in relation to the model framework, impact of the considered traits and use of information from conventional variety testing in organic cropping systems.     

Variation Between Barley Cultivars in Early Response to Weed Competition

An experiment was conducted with three spring barley ( Hordeum vulgare ssp. vulgare L.) cultivars of contrasting competitiveness to identify variations in their early competitive response to weed competition and to study canopy architecture and growth development at the early stages of cultivar growth. The aim was also to investigate whether differences in shoot morphology, growth development and competitive response could explain the differences in competitive ability against weeds. The barley cultivars were grown outdoors in boxes either in monoculture or in a mixture with white mustard ( Sinapis alba L.) as a model weed. The experiment was run until the barley cultivars were in the stem elongation stage. The varieties with strong to medium competitive ability against weeds shortened the time of emergence in the presence of S. alba in contrast to the least competitive cultivar. The results also indicated that spring barley cultivars with strong competitive ability against weeds have an early stem extension as a response to weed competition and a low competitive response. Morphological traits, namely large length of the two first internodes, long main shoot in the tillering stage and a small leaf angle, may be important traits in competition for light.     

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.     

Incremental crop tolerance to weeds: A measure for selecting competitive ability in Australian wheats

Total reliance on herbicides for weed control is unsustainable with the spread of herbicide resistance and the environmental need to reduce pesticide use. Strongly competitive wheat crops that have high tolerance to weed pressure and therefore maintain high yields in the presence of weeds are a low-cost option for reducing dependence on herbicides. We examined the feasibility of selecting for wheat tolerance to weeds by crossing varieties differing for traits associated with competitiveness. Competitive ability and yield potential must be treated as separate traits for selection. Current measures of crop tolerance to weed competition do not separate the two traits so that selection based on these measures is often synonymous with selection for yield potential rather than pure tolerance. We propose a new measure, termed Incremental Crop Tolerance (ICT) that reflects the incremental yield difference between genotypes associated with tolerance, over and above differences in underlying yield potential.     

基于图像处理的冬小麦植被覆盖率测定及其遗传解析

植被覆盖率是反映植株生长势的重要生理性状,在旱作地区尤为重要。图像处理技术能够快速有效地对苗期和孕穗期植被覆盖率进行量化分析。以28份山东小麦主栽品种和品系为材料,在240株 m^-2和360株 m^-2密度下,连续2年测定了孕穗前不同发育阶段的植被覆盖率,并利用921个DArT标记和83个SSR标记分析了与植被覆盖率相关的遗传区段。结果表明。不同密度下,冬小麦植被覆盖率在越冬期、返青期和孕穗期存在显著差异,而起身期基本一致。起身期植被覆盖率与春季最高分蘖数、抽穗后群体叶面积指数、单位面积穗数和籽粒产量均呈显著正相关,r = 0.73~0.76 (P<0.01),表明起身期植被覆盖率可用于预测上述性状。共检测出12个遗传区段与植被覆盖率相关联,大部分区段直接参与调控苗期和孕穗期的生长势。10个遗传区段与已报道的苗期性状、产量性状及抗病位点一致,其中5BL、6AS和6BL染色体上携带的植被覆盖率相关遗传区段与已报道的苗期比叶面积和生物量等位点完全相同。建议将植被覆盖率作为生长势量化指标,用于育种选择和遗传研究。     

中国春大豆品种聚类分析及主成分分析

本文对８９个中国春大豆品种的１８个数量性状进行了聚类,逐步判别和主成分分析,聚类分析用“遗传距离”定量测定品种间的遗传差异,并根据“遗传距离”将春大豆品种分为六类：东北早熟春大豆,东北中熟春大豆,黄淮春（夏）大豆,长江春大豆,西北春大豆,黄淮晚熟春（夏）大豆及南方春大豆。在聚类分析基础上用逐步判别分析选出分枝数,节数,荚数,百粒重,单株粒重,粒形指数,生育后期,全生育期,蛋白质含量等１１个对品种分     

Genetic structure of landrace populations of the New World grain amaranths

Summary Grain amaranth populations from their centers of origin in the New World had shown a pattern of allozyme variation that suggested most landraces to be highly homozygous mixtures of genotypes. To compare this pattern of variation with the variation for morphological traits, 15 selfed families from each of six populations were grown in a replicated field experiment. Four pigmentation traits known to be smiply inherited were scored along 18 other morphological traits. Populations varied for the amount of polymorphism for marker loci, and exhibited little heterozygosity. Analysis of variance for the quantitative traits showed significant interpopulation differences for each of the observed characters. Populations differed for the number of metric traits showing significant between-family differences for just one of the metric traits whereas another had between-family differences for all ten. These results suggested high levels of homozygosity within these landraces; thus, variation for quantitative traits conformed well with the allozyme variation patterns.Stepwise multiple regression of all characters on yield as the dependent variable was used to compare the relative contributions of specific characters to yield within individual populations. Plant height, days to flowering, and leaf length were included in the regression equations for 6, 5, and 5, of the populations, respectively. Days to floweing was negatively correlated with yield, while plant height and leaf length were positively correlated. These correlations suggest the potential for developing early flowering, high yielding cultivars having short stature, selected by breaking its correlation with yield. Several breeding strategies based on these findings on genetic resources are discussed briefly.