Intergenotypic Competition Research Articles

Competitive behaviour of clones of picea abies in monoclonal mosaics vs. intimate clonal mixtures. A pilot study

The effect of competition on five Norway spruce (Picea abies (L.) Karst.) clones of different provenances growing monoclonally (intragenotypic competition) and in intimate mixtures (intergenotypic competition) at close spacing were studied until the age of five years. In height, root collar diameter, dry weight, and mortality rate, clones reacted differently to the treatments, showing significant inherent competitive differences. A positive competitive reaction between certain clones can raise total increment by overcom‐pensation and can reduce risks by maintaining genetic diversity until harvest.

The predictive value of quantitative genetic parameters in autogamous crops: Bias caused by intergenotypic competition. 1. F∞-mean

Quantitative genetic theory for autogamous crops enables the estimation of the parameters m (F∞-mean) and D (F∞-variance) in the F3-generation. With these estimated m and D a prediction can be made of the probability of finding superior inbred lines in the F∞-offspring of the cross. The accuracy of this procedure is influenced by the correctness of the genetic model, by the magnitude of the error variance, and by the bias caused by intergenotypic competition, which is present in the environment in which the F3 is grown and absent in the monoculture environment at which the selection is aimed, especially in a cereal crop like wheat. The influence of the intergenotypic competition was investigated by a special method of simulating segregating populations. In this method genotypes in the offspring of a cross are represented by varieties and segregating populations are composed by mixing the appropriate varieties according to the proper segregation frequencies. Growing the simulated population enables the estimation of m and D in the normal selection environment, while simultaneously growing the varieties in a large monoculture trial enables the calculation of ‘true’ values of m and D in the monoculture environment. Hence, a comparison is possible.

The predictive value of quantitative genetic parameters in autogamous crops: Bias caused by intergenotypic competition. 2. F∞-variance

The predictive value of quantitative genetic parameters in autogamous crops: Bias caused by intergenotypic competition. 2. F∞-variance

Intergenotypic Competition between Late‐Planted Determinate and Indeterminate Soybean

Studies of several crop plants including soybean, Glycine max (L.) Merr., have indicated a seed‐yield advantage for certain genotype mixtures over the weighted mean of the component genotypes grown in pure stand. This 2‐yr field study was designed to evaluate the performance of late‐planted soybean mixtures consisting of determinate (‘Braxton’, ‘Foster’, and ‘Gordon’)/indeterminate (G84‐ 9010, G84‐9043, and G82‐8611) genotype combinations, and to examine the nature of competition between the two growth‐habit types. Soybean genotypes differing in plant height and relative maturity were chosen to comprise the determinate/indeterminate genotype combinations. The two‐component mixtures were planted at Tallas‐see, AL in alternating 0.61‐m rows and in seed ratios of 0:1, 1:3, 1:1, 3:1, and 1:0. No significant differences in mean seed yield were observed among mixtures and pure stands. A significant quadratic regression component was observed in yield of all genotypic combinations that included G84‐9010 and G84‐9043, each indicating undercompensation (yield less than the weighted mean of the components grown in pure stand). Combinations involving G82‐8611 had no significant regression components, and were the most diverse in both height and maturity. Lack of overcompensation effects may have been related to a small range in diversity of days to maturity between the genotypes comprising each mixture (2‐7 d) as well as the general competitive ability of each genotype. Soybean planted in alternating rows tended to yield higher than 1:1 mixtures. We concluded that the nature of competition between determinate/indeterminate genotype pairs when planted late is dependent on the competitive ability of the genotypes in the pair, and is likely to be undercompensatory.

Genetic analysis of larval competition in Drosophila melanogaster.

A chromosome assay was employed to determine the genetic basis of the competitive ability of the larvae of Drosophila melanogaster when competing for a controlled amount of food. The effects of increasing stress due to intra- and inter-genotypic competition were analysed using a yield-density regression analysis producing estimates of the absolute performance at a standard reference density (e-values), the magnitude of intra-genotypic competition and the inter-genotypic competitive effect of one genotype on another. A distinction was made between the Sensitivity and the Pressure components of inter-genotypic competition. The probability of survival and mean adult weight were used as measures of competitive success. The genetic analysis revealed high levels of heterosis for the e-values and inter-genotypic pressure, with correspondingly high inter-chromosomal interactions. Inter-genotypic sensitivity was less consistently heterotic and less epistatic. All dominance was directed towards a competitively superior genotype and both major autosomes were involved in the determination of competitive ability with the greater effect residing on the third chromosome. There was evidence of early non-competitive larval mortality in one of the two sets of substitution lines investigated and the effect of this on the estimation of the genetic parameters is discussed.

Studies on Intergenotypic Competition in a Wheat Multiline Using Alternative Row Design

AbstractDifferences between the isolines in a multiline may result in differences in competitive ability and lead to changes in the frequency of the components after a few cycles of multiplication. Alternative‐row design of Hanson et al. (1961) was used to detect and characterize the presence of intergenotypic interactions among eight isolines of a multiline of bread‐wheat‘Kalyansona’. The material was grown in 1.5 meter row plots using a unique sequence of arrangement. The observations were recorded with respect to plant height and grain yield per plan:. The results of the analysis showed the components of variance for average competitive ability and specific combination to be highly significant, indicating the existence of intergenotypic interactions. Significant genotypic differences between isolines revealed that the genotype of the recurrent parent had not been fully reconstituted. On the basis of the effect of the border genotype averaged over all the genotypes (Ck.), the genotypes were classified into four groups, viz. a) highly depressive, b) mildly depressive, c) mildly cooperative and d) highly cooperative. Categories c and d were indicated as useful for the synthesis of multilines.

Design of Experiments for Studying Intergenotypic Competition

SUMMARY A method of construction and randomization of designs for experiments for studying intergenotypic competition is given. These designs are like row complete latin squares, but they include border plots, which are necessary under field conditions. These border plots permit intra-block randomization without destroying the neighbour-balance property. In several cases it is proved that the design is connected even under a general competition model.

A comparison of substitution and addition designs for the analysis of competitive interactions in Drosophila melanogaster

Two distinct experimental designs are commonly employed for the analysis of competitive interactions in genetically heterogeneous mixtures. These are referred to as substitution and addition designs respectively, and either may be used quantitatively to separate the effects of intra- and inter-genotypic competition. The results presented in this paper relate to two characters which measure competitive success in mixed cultures of Drosophila melanogaster, namely the proportion of developing individuals which survive to emerge as adults and the mean weight of those adults. For each of these characters the estimates of intra- and inter-genotypic competitive values obtained from substitution and addition design experiments were equivalent. The implications of this result with respect to the choice of a suitable experimental design and its application to competition in various plant and animal systems are discussed.

Analysis of competitive ability among genotypes of perennial ryegrass. II. Effect upon dry matter production

An analysis of the effects of competition upon the dry matter production per plant (after square root transformation) revealed no significant differences between the two genotypes of perennial ryegrass (Lolium perenne) used as regards the pressures which they exerted upon each other. Their response to these pressures differed significantly however. Using these estimates of the pressure and response parameters it was shown that the impact of intra-genotypic competition upon these two genotypes was considerably greater than that of inter-genotypic competition. In general this will be true whenever the pressure and response parameters take the same sign. Intensity of competition increased linearly with vigour of growth in both cutting regimes, though changes in vigour had a significantly greater effect upon the intensity of competition under frequent cutting.

INTERGENOTYPIC COMPETITION IN BIBLENDS OF SPRING WHEAT

Wheat (Triticum aestivum L.) breeding programs evaluate germplasm sources and/or segregating progenies comprising a mixture of genotypes. If intergenotypic competition is operating, then performance of mixtures of genotypes may not be indicative of the performance of its pure line components. Our objective was to measure and quantify intergenotypic competition in 1:1 mixtures of eight spring wheat cultivars representing both tall and semidwarf classes. The 28 possible 1:1 biblends plus the eight uniblends were evaluated in a replicated trial in 2 yr at Bozeman, Montana. Grain yield, test weight, and grain protein concentration were measured. Analysis of variance showed the eight cultivars differed as uniblends and for average performance in biblends for all three measured traits. Interactions, deviations of biblends from average performance of the two uniblend components, were detected for test weight and grain protein concentration in the first year and for grain yield in the second year and for grain protein concentration when combined over years. Intergenotypic competition reduced grain yield of biblends compared to uniblends in the second year but not in the first year. Grain protein concentration and test weight did not show a proportionate change in response to the reduced grain yield. General mixing effects isolated for each cultivar showed competitive ability could not be delineated on the basis of height class.Key words: Wheat, Triticum aestivum L., mixtures, competing ability

Intra- and intergenotypic competition in Drosophila melanogaster: effects of density on larval survival and rate of development

We have examined the effects of density and frequency in the larval competition of Drosophila melanogaster by measuring three fitness components: viability (V), mean development time (MDT) and a combination of these two (E). We have detected (contrary to most published results) non-linear effects of density in single-genotype cultures; in addition, different functions are required to describe the density effects below and above the optimal density. Frequency has also non-linear effects in the two-genotype cultures. Only one polymorphic equilibrium frequency, which is stable, occurs with respect to V; but two polymorphic equilibria, one stable and one unstable, exist with respect to E. The responses in single-genotype cultures do not allow one to predict the outcome of the competition in two-genotype cultures.

Competitive effects in monocultures and mixtures of spring barley (Hordeum vulgare)

The presence of significant levels of intergenotypic competition amongst barley (Hordeum vulgare) genotypes has profound consequences for barley breeding programmes. Breeding programmes based on the pedigree system attempt to identify genotypes in genetically heterogeneous populations but the elite genotypes are grown in monoculture. Thus, to attain varietal status genotypes produced by this breeding strategy must perform well in mixtures as well as in pure stands. The effectiveness of early generation selection may be hampered by intergenotypic competition. To examine this problem in spring barley, a modified substitution experiment (Mather and Caligari 1981, 1983) was used and included genotypes sampled from a random set of inbred lines generated without conscious selection. This approach to the investigation of competitive effects in barley indicated the presence of significant levels of intergenotypic competition for a range of agronomic characters. The analyses allowed a distinction to be made between aggression (a) and response (r) with the component r displaying greater variation than a. The lack of correlation in the distribution of a and r suggested that they were under separate genetic control and hence adjustable by selection. The implications of these results for barley improvement, the use of varietal mixtures and mixed cropping are discussed.

Dry Matter Partitioning as Influenced by Competition Between Soybean Isolines1

AbstractIntergenotypic competition has been shown to bias estimates of seed yield among soybean [Glycine max(L.) Merr.] genotypes. It is unknown how early in plant development intergenotypic competitive effects occur and what plant parts are affected. The objectives of this research were to determine what plant characteristics were affected by intergenotypic competition and how early in plant development these effects could be detected. Two soybean isolines ‘Clark’ and ‘Clark‐e2’, which matures 14 days earlier than Clark, were grown in hill plots at two spacings, 0.38 and 0.76 m between hills in 1981 and 1982. Plots were grown at Lafayette, IN on a Chalmers soil (finesilty, mixed, mesic Typic Haplaquoll). Three areas of hills were planted, (i) all hills of Clark, (ii) all hills of Clark‐e2, and (iii) alternate hills of Clark and Clark‐e2. At the fourth trifoliolate stage and at 2‐week intervals thereafter, three adjacent hills of Clark, of Clark‐e2, and three hills of each isoline in the area planted to alternate hills were harvested. Dry weight of stems, leaves, and pods plus seeds were recorded. Results were similar for the two spacings. Stem weight of Clark was significantly greater when bordered by Clark‐e2than when self‐bordered from the time of initial seed development through maturity. Stem weight of Clark‐e2was unaffected by the phenotype of surrounding plants. Leaf weight of Clark was significantly greater when bordered by Clark‐e2than when self‐bordered from the time of initial seed development until leaves began to yellow and drop. Like stem weight, leaf weight of Clark‐e2was unaffected by the phenotype of the surrounding hills. Competitive effects for pod weight (including seeds) were apparent throughout pod and seed development to maturity. Pod weight of Clark was enhanced and of Clark‐e2was depressed when the two genotypes were grown in alternate hills.

Effects of intergenotypic competition on selection within chrysanthemum progenies

Intergenotypic competition affected the growth and onset of flowering of target plants of four chrysanthemum cultivars planted within plots of the same four cultivars at commercial spacing. The relative competitive abilities of two of these cultivars, Pollyanne and Hurricane, strong and weak respectively, were confirmed when they were further grown in balanced, equal-proportion mixtures. Notwithstanding their different competitive abilities, these two cultivars had similar flower yields in pure stands and, for this character at least, would be judged to have equal commercial worth.

Frequency-dependent competitive abilities and differential resource use in competition between Drosophila hydei and D. melanogaster

Several experiments, each involving competition between Drosophila melanogaster and D. hydei in population cages, were set up and allowed to run for up to 50 weeks. The population sizes of both species, and hence the species frequencies, were monitored once a fortnight, i.e. approximately once per generation. Coexistence of the two species was observed in cages containing resource bottles with 5 g of food medium; cages whose resource bottles contained only 1.5 g resulted in competitive exclusion of D. hydei. Competitive abilities were frequency-dependent in the former case but not in the latter. Tests of larval depth distributions revealed that D. hydei larvae feed at a deeper level in the food medium than larvae of D. melanogaster. The explanation of the contrasting results of competition when bottles contained 5 g and 1.5 g of resources lies in the production of frequency-dependent competitive abilities by larval resource partitioning in the bottles with 5 g, and the preclusion of such partitioning in the 1.5 g bottles because of the very limited depth of food medium then available. The relevance of these results to a model of competition is discussed, and the potential generality of differential resource use as a stabilizing mechanism in both interspecific and intergenotypic competition is noted.

Inter- and Intra-row Inter-genotypic Competition Influences Selection for Avoidance of White Mold Disease in Dry Edible Beans

Abstract Two field experiments were conducted to explore possible causes of inefficient selection for architectural avoidance of white mold disease reported in dry beans (Phaseolus vulgaris L.). Near-isogenic breeding lines for maturity and plant growth habit were blended in 4 paired combinations (with 5 mixture levels/blend) to investigate their intrarow competitive influence on disease severity. Results from regressing the disease severity for each blend component on the mixture level showed the disease severity of an individual plant to be dependent upon its own maturity, as well as on the maturity of its neighbors. An increase in the proportion of late plants in the blend led to a significant and linear increase in their disease severity. A comparable decrease in disease severity was observed as the proportion of early plants in the blend was increased. Disease severity was not influenced by the proportion of indeterminate or determinate plants in the blend, regardless of maturity. The determinate growth habit, however, as well as early maturity, resulted in greater disease avoidance than the indeterminate growth habit or late maturity when grown in pure stands. In a 2nd experiment, 4 dry bean cultivars possessing different architectures were used to study the interrow influence of plant architecture on disease severity, incidence, and seed yield. Significant differences in disease severity and incidence observed between plots bordered by an upright genotype or a dense, prostrate genotype indicated that the level of disease in the test row was determined to a large extent by the architecture of adjacent rows. The failure to obtain an accurate assessment of a genotype's performance may account partially for the difficulty in selecting for architectural avoidance.

Intergenotypic competition in mixed stands of spring wheat genotypes

Grain yield and yield components were studied in the three spring wheat genotypes HD 2160 (dwarf), Kalyansona (semi-dwarf) and C 306 (tall) in pure stands as well as in their binary mixed stands during two years. The grain yields of the three genotypes in pure stands ranked as follows: HD 2160 > Kalyansona > C 306. Four mixed stands, 3:1 HD:K, 1:1 HD:C in the first year and 1:1 K:C, 1:3 K:C in the second year out-yielded the pure stand of the better component genotype by 4.4, 2.7, 3.3 and 0.8 percent, respectively. Out of the nine mixed stands four in the first year and seven in the second year out-yielded the midmonoculture yields and the increases ranged from 1 to 7.6 percent. Mixed stands were more stable than pure stands.

Comparison of Grain Yield of Uniblends and Biblends of 10 Spring Barley Cultivars1

Pure strands (uniblends) of 10 cultivars of spring barley (Hordeum vulgare L.) and the 45 possible 50:50 mixtures (biblends) were evaluated for 3 years in four‐replicate randomized blocks. In addition to plot grain yield, data were collected on grain weight, shoot weight, and harvest index from 20 plants (10 in 1977) sampled from each uniblend and from 10 plants of each of the components of each of the biblends. Single plant sampling was carried out in only two replicates in each year. Cultivar identification in the biblend samples was facilitated by evaluation of spike and seed characteristics of each plant. Analyses of whole plot yield and of single plant data indicated that there were no significant differences between average performances in uniblends and biblends. Absence of significant interaction implied that relative cultivar performance in uniblends and biblends was the same. These results suggest that intergenotypic competition among relatively well adapted genotypes should not be of serious consequence in barley breeding programs.

Some remarks on honeycomb selection

Up to now the only experiences in favour of the method of honeycomb selection were reported by the spiritual father of the method, i.e., Fasoulas. Three other reports presented very moderate results. Possible causes for these contrasting results are discussed. Fasoulas' preference for growing the plants in the selection field in absence of competition is in conflict with the conditions in commercial crops where intragenotypic competition occurs. This preference is considered in comparison with the more popular preference for growing the plants in the selection field in presence of intergenotypic competition, which in turn also deviates from the conditions in a commercial field. It is suggested that at some degree of interplant competition the highest response to honeycomb selection will be obtained. Further, it is explained why the average of the phenotypic values of the six neighbours of a central plant may be an unreliable measure for the growing conditions for the central plant.

Four generations of selection for high 56-day weight in the mosquitofish ( Gambusia affinis)

Two lines of mosquitofish were subjected to within-family selection for high 56-day weight for four generations. Comparison with the control line indicated a selection response in both sexes but only the male response was statistically significant. Relative to expected gains, males responded more strongly than females. A strong response was also observed in the proportion of males mature at 56 days of age. The performance of all lines in maturity and weight declined substantially during the study. What caused the decline is uncertain. The pattern of decline over time was not entirely consistent with an environmental cause, but there was also no direct evidence for a genetic cause. Unintentional selection, possibly involving intergenotype competition, is the most likely genetic cause of the decline.