Cultivar Blends Research Articles

Blend Response and Stability and Cultivar Blending Ability in Oat

Genetic diversity in cropping systems can provide buffering against varying environmental conditions. Therefore, cultivar blends may have greater and more stable yields than their pure‐line components. Optimization of cultivar blend development requires knowledge of the relative importance of pure‐line yield potential, blend response, and cultivar interactions to blend yield. Grain yield and volume weight of oat (Avena sativa L.) pure‐line cultivars and cultivar blends were measured in eight Iowa environments in order to compare their productivity and stability and to estimate genetic components of blend yields. In one experiment, five early‐maturing cultivars were grown as pure lines and as all possible two‐ and three‐way cultivar blends. In a second experiment, ten midseason‐maturing cultivars were grown as pure lines and as all possible two‐way blends. Grain yield was 3% greater (P < 0.05) and volume weight was 1% greater (P < 0.05) in blends than in pure lines in the early‐maturity experiment; however, pure line and blends did not differ in the midseason‐maturity experiment. Blends had more stable (P < 0.05) yields than pure lines in the early‐maturity experiment only. Modified diallel analysis was used to partition the variation among two‐way blends into general yielding ability (GYA) and true general competitive ability (TGCA) of each component genotype, and specific competing ability (SCA) interaction between blend components. General yielding ability variation was significant, whereas variation for neither TGCA nor SCA was significant. Oat genotype responses to blending were sufficiently consistent across blending partners that superior blends can be selected based on pure‐line evaluations of early‐maturing cultivars.

Effect of Extraction Conditions on Yield, Composition, and Viscosity Stability of Barley β‐Glucan Gum

ABSTRACTCereal β‐glucan can function as a thickener, but endogenous β‐glucanase enzymes of the grain cleave β‐glucan, reducing its viscosity. Although different extraction techniques have been developed, the viscosity stability of β‐glucan gum has not been reported. The objective of this study was to investigate the effect of extraction treatments on the yield, purity, and viscosity stability of barley β‐glucan (BBG) gum. A regular barley cultivar, Condor, and a waxy cultivar blend were extracted at pH 7–10 and 55°C for 0.5 hr. Four extraction conditions were evaluated: 1) extraction at high pH with no additional heat treatment; 2) boiling of extract; 3) prior refluxing of flour with 70% ethanol; and 4) treatment of extract with thermostable α‐amylase for purification. Viscosity of extracts was monitored for ≥24 hr at 25°C. The highest β‐glucan purities were achieved with a boiled Condor extract at pH 7 (81.3% db, 4.1% yield) and with refluxed waxy barley extracted at pH 8 and treated with α‐amylase and (79.3% db, 5.1% yield). Gums extracted without subsequent heat treatment or prior refluxing of flour had high protein (>17%) and starch (>24%) impurities, respectively. The viscosity of gums obtained without heating was unstable. Prior refluxing treatment was not sufficient to stabilize final extracts. Boiling extracts resulted in stable but low viscosity. Reflux followed by purification treatment produced the highest stable viscosity for 0.5% solutions of both Condor (64 mPa sec‐1, pH 7) and waxy (48.8 mPa sec‐1, pH 8) extracts. Stable BBG gum with high viscosity can be obtained using thermal treatments in combination with high pH. The potential use of such gums as thickeners in food systems needs to be assessed.

Dollar Spot Severity as Influenced by Trinexapac‐ethyl, Creeping Bentgrass Cultivar, and Nitrogen Fertility

AbstractDollar spot (Sclerotinia homoeocarpa F.T. Bennett) is a widely distributed and destructive pathogen of turfgrass in the United States. A 2‐yr field study was conducted at Columbus, OH, to determine the influence of a plant growth regulator, creeping bentgrass (Agrostis stolonifera L.) cultivars, and N fertility on dollar spot severity. ‘Crenshaw’ creeping bentgrass was seeded alone or in a 50:50 blend by weight with ‘Penncross’ creeping bentgrass. Plots were fertilized at 0, 24.4, or 48.8 kg N ha−1 per application. One‐half of each plot received trinexapac‐ethyl (TE) [4‐(cyclopropyl‐α‐hydroxymethylene)‐3,5‐dioxo‐cyclohexanecarboxylic acid methyl ester] at 0.8 L ha−1. The TE and fertilizer treatments were initiated in May 1995 and 1996 with four subsequent applications made at 30‐d intervals. Initially, the cultivar blend reduced the rate of dollar spot development compared with Crenshaw alone; however, neither the blend nor Crenshaw provided commercially acceptable dollar spot suppression throughout the study. Both TE and N fertilization significantly (P ≤ 0.05) reduced dollar spot severity over the 2‐yr period. Trinexapacethyl applied alone effectively suppressed dollar spot activity, but efficacy increased with increasing N rates. Dollar spot symptoms decreased and thatch thickness increased at elevated N levels. During this 2‐yr study, interactions between TE and N fertility resulted in a significant (P ≤ 0.05) reduction in dollar spot severity. Thus, on golf course fairways where dollar spot may be severe, incorporation of these two treatments into a turfgrass management program will enhance dollar spot suppression and reduce fungicide inputs.

Use of wheat cultivar blends to improve grain yield and quality and reduce disease and lodging

Cultivar blends can provide a measure of disease control due to host diversity. The diversity of cultivar blends also may be useful for improving agronomic performance and end-product quality. This paper reports on the performances of blends (0:1, 1:2, 1:1, 2:1, and 1:0) of two fall-sown hard red spring wheat cultivars, Yolo (high grain yield, low susceptibility to septoria tritici blotch and leaf rust, good lodging resistance, poor grain quality) and Serra (high grain yield, high susceptibility to septoria tritici blotch and leaf rust, high susceptibility to lodging, excellent grain quality). The blends were grown in several environments in California for 3 years. The taller Serra was more competitive than Yolo in the various blends. Spike populations of Serra often were larger in blends than expected from the proportion of seed sown. Spikes of Yolo in blends had fewer spikelets than spikes of Yolo in sole crop Yolo, while spikes of Serra in blends had more spikelets than spikes of Serra in sole crop Serra. Blends had advantages over sole crops in several respects. When disease pressure was moderate or high, blends had less leaf rust and septoria tritici blotch than sole crop Serra, but more disease than sole crop Yolo. When lodging occurred, blends had less lodging than sole crop Serra. Overall, there were no significant differences in yield among the blends and sole crops of Serra or Yolo. The blends produced grain protein and baking quality equivalent to sole crop Serra and better than sole crop Yolo. The 2:1 Yolo:Serra blend was the optimum blend and is an attractive alternative to sole crop Yolo or sole crop Serra for wheat growers in the Sacramento Valley of California.

Avaliação da competição intergenotipica em misturas de cultivares de soja

Para avaliar os efeitos da competição intergenotípica em misturas de cultivares de soja - Glycine max (L.) Merrill - foi conduzido um experimento em Capão do Leão, RS, no ano agrícola de 1989/90. Os tratamentos foram os estandes puros de IAS 5, Ivorá, Bragg, BR 8 - Pelotas e Ivaí e as combinações de Bragg com os demais cultivares, nas proporções de 20, 35, 50, 65 e 80%. O delineamento experimental foi o látice parcialmente balanceado 5x5, com quatro repetições. A competição intergenotípica foi quantificada pela variação percentual = 100 (PM - PEP)/ PEP, onde PM é a média do caráter em mistura e PEP é a média do caráter em estande puro. As misturas produziram, em média, 3,8% mais que a média dos componentes em estande puro. Duas misturas, IAS 5 + Bragg e BR 8-Pelotas + Bragg, proporcionaram acréscimos no rendimento em todas as proporções de misturas. Concluiu-se que a competição intergenotípica pode ser utilizada no melhoramento da soja, visando a obtenção de misturas com rendimento e desempenho superior. Respostas diferenciadas à competição intergenotípica foram observadas em diferentes misturas e proporções e, proporção e características contrastantes entre os cultivares como capacidade de ramificação, altura de planta, ciclo de maturação e período de florescimento devem ser consideradas para a formação de misturas superiores.

Interactions Among Mowing Height, Nitrogen Fertility, and Cultivar Affect the Severity of Rhizoctonia Blight of Tall Fescue

The effects of three mowing heights (3.8, 6.4, and 8.9 cm) and three nitrogen fertility regimes (0, 24.4, and 48.8 kg N per ha per month) were assessed on epidemics of Rhizoctonia blight in four cultivars and one cultivar blend of tall fescue in 1993 and 1994. Significant differences in disease severity were observed among mowing heights, fertility regimes, and cultivars or blend in each year. In addition, significant cultivar x mowing height interactions were detected in both years, and significant cultivar x fertility interactions occurred in 1993. The cvs. Mojave and Rebel II exhibited significantly more disease than the other cultivars or blend late in the 1993 study. Analysis of interactions revealed that disease was significantly greater on these cultivars than on others at fertility regimes of 0.0 and 24.4 kg N per ha, and at mowing heights of 3.8 and 6.4 cm. In 1994, Mojave again exhibited significantly more disease than the other cultivars or blend at the 3.8 cm mowing height near the peak of the epidemic, and Rebel II was the only cultivar that displayed significantly more disease at the 6.4 cm height than at the other heights tested. Across cultivars, severity of Rhizoctonia blight was significantly greater at the 8.9 cm mowing height than at the 3.8 cm height during epidemic peaks in 1993. The opposite was observed in 1994. Each cultivar or blend exhibited significantly more disease in fertilized than in nonfertilized plots by at least one of the dates on which significant cultivar x fertility interactions were detected in 1993. In 1994, data from nonfertilized plots was withheld from analysis due to an epidemic of white blight that interfered with assessment of Rhizoctonia blight. However, significantly higher levels of disease were observed in plots treated with 48.8 kg N per ha per month than in those treated with 24.4 Kg N.

Influence of Resistant and Susceptible Cultivar Blends of Hard Red Spring Wheat on Wheat Stem Sawfly (Hymenoptera: Cephidae) Damage and Wheat Quality Parameters

Use of resistant and susceptible cultivar blends of hard red spring wheat ( Triticum aestivum L.) were investigated over a 3-yr period as a method to suppress wheat stem sawfly, Cephus cinctus Norton, damage. Blends provided inconsistent protection against stem cutting. Differences in estimated harvestable yield were only detected in 1 year. Total yield and milling and baking qualities of blends were not significantly different from those of monocultures. Blends may be useful in situations where the potential for damage by wheat stem sawfly is low to moderate.

The physiological causes of mixing effects in cultivar mixtures: A general hypothesis

A model is presented explaining those mixing effects in cereal cultivar blends that cannot be attributed to reduced disease levels but are thought to result from improved compensatory reactions to environmental stress in cereal cultivar blends. Cultivars are characterized by the slopes b and deviation mean squares s d 2 of linear regressions of their individual pure stand performance on the means of all pure cultivars. It is assumed that a cultivar 1 which yields less than expected in a particular environment does not utilize all growth factors available. The amount of growth factors not utilized is postulated to be taken up by the other mixture component which then produces more than expected in pure stand. It is hypothesized that this additional ‘compensatory’ yield is what is usually named the mixing effect. Two variants of the hypothesis; namely, one-sided and two-sided compensation, are investigated using results from field experiments with winter barley.

Relationships among Charcoal Rot Infection, Yield, and Stability Estimates in Soybean Blends

Charcoal rot [Macrophomina phaseolina (Tassi) Goid] of soybean [Glycine max (L.) Merr.] commonly affects plants grown in the western midwest of the USA. No control measures have been reported. This study measured the effects of cultivar blends and rates of planting on charcoal rot infection and agronomic traits to determine if blends provide a greater protection against the disease and broader adaptation to environments. Six blends and four pure lines in maturity groups III and IV were tested in replicated plots across eight locations. Measurements taken on each plot included seed yield, height, lodging, plant population, and amount of charcoal rot infection. The relationship of these traits with stability estimates were considered. Reducing planting rate from 30 seeds m−1 (387 500 seeds ha−1) to 20 seeds m−1 (258 000 seeds ha−1) significantly lowered infection levels without reducing yield. Stage of reproductive growth was associated linearly with infection level. There was no significant genotype effect for infection when stage of reproductive growth was used as a covariate. Infection levels were correlated with response (bi), relative performance over environments. Response and biological estimates of stability were significantly correlated with one another. Deviations from response, r2, and ecovalance were also significantly correlated. The positive association of growth stage and infection suggests planting full‐season cultivars as a method of reducing charcoal rot. There was no benefit in blending pure lines either in increased yield or decreased charcoal rot infection.

Individual Crown Selection for Resistance to Freezing Stress in Winter Oats1

In recent years, crown freezing tests have been used to classify germplasm of small grain crops for resistance to freezing stress, a major component of winter hardiness. Selection has been based, however, on large numbers of crowns, and techniques for individual plant selection have not been developed. Our objective was to develop a system for growing and hardening winter oats (Avena byzantina K. Koch and A. saliva L.) that will provide uniform expression of the freezing resistance trait and facilitate accurate individual crown selection.A technique of growing plants in individual tubes under controlled conditions of light, temperature, and moisture was developed. Individual crowns were frozen in capped vials on rotating shelves in a freezing chamber. Crowns that survived severe freezing stress and regenerated new roots were saved as selections.Effectiveness of the technique was tested by applying two cycles of crown selection to a four cultivar blend. After cycles 1 and 2, the mean injury scores of the population were 95.6 and 100%, respectively, of the most hardy component cultivar. In a second experiment, crowns of an F6 bulk population were frozen and only 16 out of 640 survived. In subsequent tests of these lines, nine were equal to the hardy parent and 13 were equal or superior to the population mean. Thus, our crown selection technique provided a degree of precision that should be useful in breeding for increased resistance to freezing stress and improved winter hardiness.

Cultivar blends for buffering against curly top and leafspot diseases of sugarbeet

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Estimation and Utilization of Inter‐cultivar Competition in Peanuts1

Competition among three peanut (Arachis hypogaea L.) cultivars: ‘NC 5,’ ‘NC 17,’ and ‘Florigiant,’ was measured in replicated hill and row‐plot field designs for purposes of predicting optimum proportions of the components in seed blends. The three cultivars are adapted to the Virginia‐North Carolina peanut belt, but differ in maturity and growth habit. Competition was determined by calculating the coefficients of regression for mean plant, fruit, and seed characters on numbers of competing plants or rows.Three‐year trials provided evidence of inter‐cultivar competition. Fruit yield, fruit number, and plant weight of NC 17 were found to increase (overcompensate) significantly over that of pure stands when grown in competition with Florigiant. Coefficients tended to be negative, small in magnitude, and nonsignificant when Florigiant was in competition with NC 17. NC 5 and NC 17 frequently had reduced numbers, sizes, and weights of fruit when grown in competition with each other. Overcompensation was not found when the coefficients for the regression of NC 17 performance on number of competing plants or rows of Florigiant were summed with coefficients based on reciprocal arrangements of the cultivars.Yields of cultivar blends could not be predicted using data from competition tests.