Competition between cultivars of fodder kale (Brassica oleracea L.) in yield trials with single-row plots

Summary Two experiments were done to evaluate the use of single-row plots for assessing digestible organic-matter (DOM) yield.In the first experiment 29 cultivars were grown in both single-row plots (unguarded) and five-row plots from which only the centre row was harvested (guarded single-row plot). The correlation between yields in the unguarded and guarded plots was very low (r=0.20). Yield was correlated (r=0.89) with cultivar height in the unguarded plots, but not in the guarded plots (r=0.19). Therefore selection for yield in unguarded single-row plots is undesirable and would favour tall kales which are prone to lodging.In the second experiment 16 cultivars were grown in single row-plots guarded by the short cultivar Maris Kestrel, the tall cultivar Vulcan and by the cultivars themselves as control. The correlations between yield in the control plots and yields in the plots guarded with Maris Kestrel and Vulcan were only moderate (r=0.56 and r=0.64 respectively). Therefore the use of a single distinct cultivar to guard single row-plots is undesirable.Selection for DOM yield should therefore be made in multiple-row plots, from which the outer rows are discarded, in order to avoid the undesirable effects of competition.     

Selection for yield in small plots of spring wheat

Summary Four selection experiments were sown: single-row plots with single row-spacing (20 cm), single-row plots with double row spacing (40 cm), three-row plots and six-row plots both with single row-spacing (20 cm). Selection entries were mimiced by 16 different varieties or advanced breeding lines, which were also sown in a yield trial. Each experiment was laid out as a 4-times replicated randomized block design. Row length was 2 m. Alley borders and border-rows of multiple-row plots were harvested separately to evaluate the effects of different harvesting procedures on the selection efficiency. Removal of alley borders was found to be disadvantageous, since the gain in precision was more than offset by the loss in sampled area. Wide spacing of single-row plots improved the selection efficiency in comparison with normal spaced single-row plots. In multiple-row plots the selection efficiency was not improved by harvesting only the central rows.For gross plot yield (= yield of net plot + yield of alley borders) the differences in selection efficiency between the various selection plot-types were explained on the basis of the genetic variance, the environmental variance and the coefficient of genetic correlation with farm yield as determined in the yield trial.     

The effect of interplot competition on yield assessment in triticale trials

Summary A series of experiments was carried out to investigate the effects of interplot competition on grain yield among hexaploid triticale cultivars of widely differing heights grown in 1.5 m wide plots. Three experiments in 1982 tested four triticale cultivars, ranging in final height from 63 to 104 cm, with four wheat standards, 62 to 82 cm in height, using a design balanced for nearest neighbours. Two further experiments in 1983 with the same design included eight triticale cultivars ranging in final height from 92 to 183 cm. In four of the five experiments, plot yields of both wheat and triticale were decreased by between one and two grammes per square metre for every centimetre by which the plot was exceeded by the mean height of its two neighbours. Plots which were taller than their neighbours showed a similar increase in yield. Such systematic biases in cultivar means are not reduced by randomisation and increased replication. Hence, in breeding trials, every effort should be made to group genotypes according to their final height so that competition effects between plots are reduced. For the final evaluation of varieties differing widely in height, where an estimate of error is required for variety comparisons and varietal differences are likely to be small, guard plots should be grown on either side of each experimental plot or harvesting should be restricted to the centre of larger plots.     

Effect of moving mean covariance adjustments on error and genetic variance estimates and selection of superior lines in peanuts (Arachis hypogaeal L.)

Summary Effects of moving mean covariance adjustments on error control, genetic variance component estimates and selection were examined in nine trails in peanut breeding nurseries. Neighbourhood sizes of two to fourteen adjacent plots were used in two types of moving mean covariates: one based on adjacent plot yields and a second based on adjacent plot residuals after removal of replicate and treatment effects. Both covariate types reduced error variance, in one trial by up to 57%, although the covariate type giving the most error reduction varied among trials. Generally most error variance reduction occurred when six to eight adjacent plots were used.In some trials genetic variance component estimates following covariance adjustment were higher than those from unadjusted analyses and in other trials they were lower. As the neighbourhood size included in the moving mean increased from two to fourteen plots the genetic variance component estimate changed considerably in some trials. However, large rank changes did not appear to be associated with these genetic variance component changes as neighbourhood size had little influence on the selection of progenies. Also, genetic effects included in the yield covariate had little influence on selection of elite lines as essentially the same lines were chosen or rejected when residual covariates lacking these genetic effects wre used.     

Intergenotypic competition and border effect in bread wheat and barley

Summary A coordinated series of experiments aimed to estimate border effect and intergenotypic competition was carried out on bread wheat and barley in Italy and Germany. The performance of the varieties grown in alternate rows 14–17 cm apart proved to be strictly dependent on the bordering variety. The varieties grown in adjacent plots consisting of eight rows showed significant border effects: the two external rows yielded up to 40% more than the two innermost, and the two 30 cm end hills facing the alleys yielded 29% more than the central part of the plot. Is has been suggested that in variety trials the first 30–40 cm at both ends of each plot should be removed mechanically. In spite of the border effect detected in the outer rows of the plots, the varieties similarly exploited the extra space available at the borders, and the space of 30 cm left between adjacent plots seems to be sufficient to dilute the intergenotypic competition at plot level to an extent only marginally affecting variety performance.In conclusion, grain yield based on whole plot (8 rows, 6–10 m²) appears to provide a good estimate of true yield, providing that it is based on the actual area of the plot, including the uncropped strip between adjacent plots. By contrast, the reduction of plot size to 1–3 rows is not feasible without introducing considerable bias into the estimation of the yield potential of the varieties.Abbreviations WW winter wheat - WB winter barley - SB spring barley     

Interplot interference and the assessment of barley cultivars for partial resistance to leaf rust,Puccinia hordei

Summary The barley cultivars Akka, highly susceptible, and Vada, partially resistant to barley leaf rust, Puccinia hordei, were evaluated for the amount of leaf rust in five experimental field plot situations over three successive years. The field plot situations were: A) plots well isolated from each other by distance and non-leaf rust contributing host plants; B) adjacent plots of 4×41/2 m (18 rows); C) adjacent plots of 4×11/2 m (6 rows); D) adjacent plots of 4×1/4 m (1 row); E) adjacent plots of only one plant (cultivar mixtures).The sporulating leaf area of each plot was measured from samples of 20 tillers taken at random from each plot. In each year the difference in sporulating area between Akka and Vada was large to very large in the absence of interplot interference in the isolated plots, ranging from 150 to 2100 times. In the adjacent plots the partial resistance of Vada was greatly underestimated, 5 to 16 times in the situation B, 14 to 30 times in C, and 75 to 130 times in D and E.Testing lines or cultivars in adjacent plots is the standard procedure in use in breeding programs and in tests of cultivars for their agricultural value. To avoid such under estimation the following procedure is suggested. A few cultivars representing the known range of partial resistance and whose level of partial resistance is well known are evaluated together with the lines and cultivars whose partial resistance has to be assessed. This is demonstrated with a number of cultivars of which resistance values are know from the recommended variety lists for England and Wales. Cultivars have been assessed in Wageningen over four years together with the check cultivars Akka, Sultan, Julia and Vada representing the range of partial resistance with values (on a 1 to 10 scale) of 1, 3–4, 7 and 8 respectively, based on isolated plots experiments.     

Interaction of border and center rows of multiple row plots in watermelon yield trials

Researchers interested in evaluating watermelon (Citrullus lanatus(Thunb.) Matsum. & Nakai) cultivars for yield often use multiple-row plots to simulate the monoculture system growers use or ingle-row plots to save on land, labor, and seeds. An important question is whether there is significant interaction of border rows with center rows when diverse cultivars are planted in adjacent rows. Based on recommendations from watermelon researchers in the U.S., ‘Charleston Gray’, ‘Crimson Sweet’, and ‘Sugar Baby’ were chosen to represent long, medium, and short-vined cultivars, respectively. Cultivars were planted in three-row plots with all nine combinations of the three represented in border and center rows. The experiment was a randomized complete block with the nine border by center plot combinations, two locations (Kinston, Clinton), and three replications at each location. Vine length was measured during the season, and fruit from four harvests were graded (marketable and cull), counted and weighed. Results showed that ‘Charleston Gray’ had the longest vines, followed by ‘Crimson Sweet’ and ‘SugarBaby’. In the analysis of variance, the largest effects (F ratio) on yield were from cultivar, location, and the interaction of the two. The smallest effects were border row and the interaction of center with border row. Center by border interactions were significant (5%level) in some cases, but were usually small and did not involve change in rank. Therefore, researchers interested in running trials with many cultivars and small seed quantities can obtain good data using single-row plots. However, there is a small (but significant) interaction of center with border rows in some cases, so testing at the final stage should be with trials having multiple-row plots or with cultivars grouped by vine length. Additional research is needed to determine the effect of cultivars having extreme plant types, for example dwarf cultivars in bordering rows with long-vined cultivars. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of intergenotypic competition on selection within chrysanthemum progenies

Summary 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.In a further series of experiments, target plants of the female parent were grown in pre-determined positions within clonally replicated progeny plots and in equivalent positions in pure stands of the female parent. These two types of plot gave similar proportions of total target plant variance due to position, suggesting that individual plants within a segregating progeny are subjected to similar levels of competition. It is inferred that the level of competition approximates to the overall mean competitive ability of the full-sibs comprising the progeny. Selection procedures are discussed in the light of this conclusion.     

Optimal regimes of selection for grain yield and harvest index in spring wheat

Summary Alternative strategies of multi-site testing of advanced lines in the northern wheat belt of New South Wales have been evaluated, using genetic parameters for large plot grain yield and hill plot harvest index estimated from dryland and irrigated trials at regional sites during 1975–1981. The average pairwise genetic correlation of large plot grain yields recorded at different sites within years was 0.45±.03, with a mean repeatability within trials of 0.56±.05. Harvest index measured in 20-grain hill plots in 1978 showe genetic correlations of 0.98±.08 with plot yield at the same site, and 0.39±0.06 with plot yield assessed at other sites in the same year.The genetic correlation between harvest index in hill plots and total biological yield in large plots at the same site was 0.84±.13, the relationship showing no evidence of curvilinearity. Selection for harvest index in hill plots is therefore expected to lead to an increase in biological yield as well as grain yield in the breeding populations studied. Quantitative genetic theory suggests that the response to selection for grain yield can be increased by approximately 40% with an initial screening using hill plot harvest index at three sites instead of one, and reallocation of resources in the first stage of large plot yield assessment to include 6–8 sites, rather than dryland and irrigated trials at a single location.     

Lack of interplot competition in Swedes (Brassica napus ssp rapifera L.)

Summary An experiment comparing double row plants with four row plots where only the centre two rows were harvested (guarded double row plots) were laid out in two subsequent years. Fresh weight yields, dry matter yields, bulb dry matter content, refractometer index and harvest index were recorded and analyzed statistically. The cultivar x plot type interactions were in none of the cases significant. The increase in error variances when comparing double row plots with guarded double row plots was significant only for harvest index in the first year.Taking into account the low selection intensity when small plots are used, i.e. in early stages of plant breeding programmes, we conclude from these experiments that guarded plots are not necessary when breeding swedes under our growing conditions.     

Adjustment for Competition Between Genotypes in Single-Row-Plot Trials of Winter Wheat (Triticum aestivum)

Several statistical methods were investigated for improving yield estimation for 72 genotypes of winter wheat tested in a single-row-plot (SRP) trial. The different analytical models were compared using several criteria: the residual mean square fit; the standard error of differences of genotype means; the correlations of genotype means with means from six-row-plot (6RP) reference trial; the expected genetic gains relative to 6RP trial from selecting the 10 top yielding genotypes. There was no significant correlation between the unadjusted genotype means for SRP and 6RP. Genotype yields were positively correlated with height in SRP, but this correlation was reversed in 6RP. Using the mean height difference of a plot with its two neighbours as a covariate to adjust for competition in SRP reduced the standard error of difference of genotype means and substantially increased their correlation with the 6RP means. The predicted selection efficiency in SRP trial increased from zero, before adjustment, to 83 % of 6RP trial. Including the difference in heading date and the effect of guards at borders as covariates in the SRP analysis improved the residual mean square fit but had no effect on correlation with 6RP means or selection efficiency. A producer-competitor model in which individual competitor effects were estimated for each genotype gave a substantial improvement in fit over the covariate models but a much lower correlation with 6RP means and selection efficiency. Yield selection in early generation wheat trials based on single-row plots could be considerably strengthened by use of a plot covariate derived from height difference between neighbours.     

Level of partial resistance to leaf rust,Puccinia hordei,in West-European barley and how to select for it

Summary The partial resistance to leaf rust (Puccinia hordei) of 40 West-European spring barley cultivars was measured in plots isolated from one another to reduce inter plot interference. The leaf area affected by leaf rust was also measured in small plots of 0.5 m² adjacent to each other, and on individual plants. The latent period was measured in the seedling stage and the adult plant stage, the infection frequency in the seedling stage only. The cultivars varied widely for partial resistance, many cultivars carrying a considerable level. Both the small adjacent plots and the single plants showed a marked inter plot interference strongly reducing the difference between cultivars. H wever, the ranking order of the cultivars was hardly, if at all, affected. Both latent period and the infection frequency showed large differences between cultivars, the latent period in the adult plant stage being highly correlated (r=0.82) with partial resistance, infection frequency in the seedling stage only rather weakly (r=–0.33).Selection for partial resistance appeared very effective in all stages tested; the seedling, the single adult plant, and the small plot stage. Selection in the small plot stage was the most effective followed by selection in the seedling stage. Selection for partial resistance therefore appears very well possible at all stages of the selection program.     

小麦品种慢叶锈性的研究

小麦慢叶锈品种具有侵染率低、潜伏期长、孢子堆小、产孢量少、严重度低、病害进展曲线下面积小和病害虽流行但产量损失不显著等特点.潜伏期和扬花期平均病害严重度与产量损失的关系最密切,因此测定某一小麦品种的潜伏期(x_1)和平均病害严重度(x_2)(田间感病对照品种发病达50%或95%时),可以作为衡量该品种慢(快)叶锈性的两个指标和选种的依据.用y=94.67-3.10x_1+0.51x_2估测由叶锈造成的小区产量损失(y)有一定可靠性(R=0.96).用聚类分析法把供试品种分为慢锈、中慢、中快和快锈品种类型.苗期和成株期慢叶锈性有一定的吻合性.     

Effects of Limited Border and Harvest Rows and Interplanting Cultivars on Yields of Field-Grown Soybeans*

Under some experimental conditions it may be necessary to limit the area of field experimentation but still provide a large number of treatment replicates. This situation is germane when relatively expensive facilities for treatment application are necessary. Under such conditions researchers may want to (1) restrict the number of border and treatment rows and (2) combine several cultivars of one crop within the same treatment plot. Results of experiments conducted to test the effect of these actions on seed yields of commercial soybean cultivars indicate that with narrow row spacing at least two border rows are necessary to reduce border effects on yield to less than 10%. Also, it is shown that when rows of different varieties are placed adjacent to each other in the same plot, yield interactions may occur. These results suggest that there are practical limits to how small an individual plot may be and that preliminary studies to determine cultivar interactions should be performed prior to implementation of experimental designs which incorporate cultivar interplanting procedures. Nevertheless, the use of small plots and interplanting may be effective methods of experimentation when space is limited.     

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.     

Grain yield and its components in spring barley under row and hill plot conditions

Twenty homozygous barley lines were grown in row and hill plots at two locations in Ontario in 1973. The hill plots were of two spacings –30×30 cm and 45×45 cm between hills. Within each spacing, three seeding rates were used i.e. 15, 25 and 35 seeds per hill. Grain yield and three of its components, namely; number of seeds per spike (NSS), number of spikes per plot (NSP) and seed weight (SW) were studied. It was concluded that both NSS and SW could be evaluated in hill plots. NSS was found to be an important component of grain yield and its relationship with grain yield was unaffected by plot types and locations. SW also remained unaffected by plot types and seeding rates but as a component of grain yield it was the least important of the three components measured. The correlation between SW and grain yield could be changed by locations. NSP was as important as NSS as a component of grain yield, and was highly correlated with grain yield. Unlike NSS, NSP could not be efficiently evaluated in hill plots since its correlation between row and hill plots was generally lower.     

Indirect selection for grain protein and grain yield in winter wheat

Summary The efficiency of the honeycomb selection procedure in selecting outstanding genotypes was observed at two interplant distances (d), i.e. d=100 cm, low density, representing noncompetitive conditions and d=15 cm, high density, representing presence of interplant competition. Progress due to selection among the plants grown with and without competition was established by comparison of the plot performance of offspring from selected plants with that of offspring from plants taken at random. The relation between selection intensity and response to selection was observed to detect a possible negative correlation between competing and yielding ability.So far, the results obtained do not yet allow to make a choice between selection of individual plants in presence or in absence of interplant competition. No significant correlation between single plant yield and plot yield was found at any of the two densities. However, response to selection for yield was higher when selecting at low density supporting Fasoulas' preference for selecting single plants in absence of competition. These results must be taken with caution since seed quality and a biassed sample of random plants exerted an important effect on the obtained response to selection.     

Spaced-plant traits related to seed yield in plots of perennial ryegrass (Lolium perenne L.)

Summary Seed yield in perennial ryegrass is low and selection criteria for high seed production are lacking. Indirect selection in spaced plants would be efficient, but spaced-plant traits need to be identified that correlate with seed yield in drilled plots. Spaced plants were studied of nine perennial ryegrass cultivars with a different seed production when grown in plots. Genotypic variation within cultivars for seed yield components and other traits was assessed in four environments in replicated clonal experiments. Extensive genotypic variation for most traits was present within each cultivar. Based on cultivar means of 25 or 50 genotypes, significant differences among cultivars were found for most traits. Cultivar-year interactions were found for most traits, but no significant cultivar-location interactions were generally found. Spaced-plant traits in general showed poor correlation to corresponding traits in drilled plots. Cultivars with contrasting seed yield in plots could not be distinguished on the basis of their spaced-plant traits and therefore no criteria for indirect selection for seed production in drilled plots could be identified in spaced plants.     

Protein yield of oats as determined by protein percentage and grain yield

Summary Relationships among the traits protein percentage, grain yield, and protein yield of oats were studied with F₂-derived lines in F₃ and F₄ from 27 matings obtained by crossing high-protein with high-yield oat lines. High-protein parents were (a) selections from an Avena sativa bulk, (b) selections from three-way matings in which an initial parent was A. sterilss, and (c) cultivars. High-yield parents were derived from backcross populations involving A. sterilis accessions as donor parents.Significnnt genetic variation existed among F₂-derived lines for grain and protein yield in all matings and for protein percentage in all but one mating.Protein percentage had a highly significant negative correlation with grain yield (r=–0.33^**) when pooled over all matings, but in five, these two traits were not correlated. Overall, protein percentage showed a small negative correlation with protein yield (r=–0.09^*), and protein and grain yields had a high positive association (r=0.98^**). F₂-derived lines with both high protein percentage and high grain yield were obtained.High transgressive segregates for protein percentage occurred in two matings, for grain yield in nine, and for protein yield in 14. Most high transgressive segregates for protein yield were high because of high grain yield only, but in four matings, lines were found where protein yield was increased by concurrent increases in both protein percentage and grain yield.Only a few specific parental combinations between high-protein and high-yield parents produced segregates in which increased protein percentage contributed materially to high-protein yields.Journal Paper No. J-11264 of the Iowa Agriculture and Home Economics Experiment Stn., Ames, Iowa 50011. Project 2447.     

半干旱区不同种植模式对马铃薯淀粉形成及产量的影响

为探明不同种植模式对宁夏南部山区马铃薯淀粉形成及产量的影响,采用单因素随机区组设计,设置露地平作（A1）、露地单垄单行（A2）、露地单垄双行（A3）、半膜单垄双行（A4）和全膜单垄双行（A5）5个处理,研究了不同种植模式对宁夏南部山区马铃薯淀粉形成酶活性、淀粉含量和产量的影响。结果表明,淀粉积累后期A5处理的总淀粉含量较A1、A2、A3和A4处理分别提高34.5%、26.1%、18.5%和12.7%。淀粉积累过程中,淀粉形成酶ADPG-PPase、UDPG-PPase、SSS、SBE和GBSS活性对马铃薯支链淀粉、直链淀粉和总淀粉的积累有直接或间接影响,与马铃薯块茎总淀粉含量的相关系数分别为0.691、0.264、0.514、0.629和0.130。不同种植方式对马铃薯产量有明显影响;A5处理产量最高,A4处理次之,分别较A1处理增产83.8%和62.9%。在宁夏半干旱区,全膜单垄双行种植模式在马铃薯块茎淀粉积累、淀粉形成酶活性提高和增产方面有明显优势。