Cultivar Blends Research Articles

Blend ratios and mixtures of brown patch susceptible and resistant tall fescue cultivars

AbstractBrown patch (Rhizoctonia spp.) is a major disease of turf‐type tall fescue (TF) [Schedonorus arundinaceus (Schreb.) Dumort., nom. cons.]. Many cool‐season turfgrass lawns consist of species mixtures or cultivar blends, but the exact proportion of resistant cultivars in blends and mixtures to effectively reduce disease has not been well documented. A field study was conducted in West Lafayette, IN, and Blacksburg, VA, during 2022 and 2023 to determine the brown patch severity of various blend ratios (0%, 25%, 50%, 75%, and 100% by weight) using a brown patch susceptible and resistant TF cultivar. Additionally, mixtures (90% and 10% by weight, respectively) of TF and Kentucky bluegrass (Poa pratensis L.) with a susceptible and resistant TF cultivar were evaluated. Seasonal appearance/turf quality and brown patch severity were visually determined, and area under the disease progress curve (AUDPC) was calculated. Turf quality and brown patch severity were similar at both locations. Additionally, blends and mixtures containing ≥75% of the resistant cultivar maintained higher average visual quality across both locations compared to the susceptible cultivar alone. Between the two mixtures, the inclusion of a resistant TF cultivar maintained higher canopy density and increased the proportion of TF at both locations. Blends and mixtures containing ≥75% of a resistant cultivar reduced brown patch AUDPC by 71% and 83% in 2022 and 2023, respectively, when compared to the 100% susceptible cultivar. This field study reinforces the importance of selecting resistant TF cultivars to reduce seasonal brown patch symptoms in cool‐season turfgrass lawns.

Determining the optimal ratio of resistant to susceptible bentgrass cultivars to reduce dollar spot severity

AbstractDollar spot, caused by Clarireedia spp., is the most prevalent disease on creeping bentgrass golf fairways. Interseeding newer dollar spot‐resistant cultivars into susceptible bentgrass stands could reduce dollar spot severity and the need for resultant fungicide use. This study was conducted to determine the optimal ratio of resistant to susceptible cultivars in a blend that will result in dollar spot reduction. Greenhouse experiments were conducted on cultivar blend ratios (0%, 10%, 25%, 50%, 75%, 90%, 100%) of dollar spot‐resistant (Pure Select, 007XL, Coho) and susceptible (Penncross) bentgrass challenged with inoculation of two Clarireedia spp. isolates. Disease severity was determined using visual estimates and digital image analysis. Dollar spot severity was significantly influenced by the Clarireedia isolate, with a fungicide‐resistant isolate being more aggressive and producing more disease than a sensitive one. Dollar spot severity was highest on Penncross alone, with no statistical differences observed among the resistant cultivar monostands. Mean disease severity of the blended cultivar ratios was divided into three statistically different groups—low resistance (10% and 25%), medium resistance (50% and 75%), and high resistance (90% and 100%). Compared to Penncross, blending a 10% resistant cultivar reduced AUDPC (area under the disease progress curve) values by 2% and 3% in Experiments 1 and 2, respectively, while blending a 90% resistant cultivar yielded 20% and 32% reductions. These results indicate dollar spot severity decreases as the ratio of the resistant cultivar in a stand increases, and blending resistant cultivars into susceptible has the potential for reducing disease.

Diversity, composition, and freedom to choose drive the effects of St. Augustinegrass cultivar blends on an herbivorous insect

AbstractWarm‐season turfgrasses are conventionally produced and maintained as cultivar monocultures, which leaves them less resilient to pest attack than more diverse plantings. Recent evidence has indicated that mixing St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze] cultivars can provide pest management benefits compared with cultivar monocultures. Research in other systems has shown that the effects of plant diversity on herbivores often depends on the number and identity of plant species present. Host plant diversity can affect herbivore fitness via postconsumptive physiological effects or before consumption by influencing herbivore behavior or plant defenses. To investigate the mechanisms by which St. Augustinegrass cultivar diversity and composition affect an insect herbivore, six cultivars were mixed to create two levels of cultivar diversity, and fall armyworm life history traits were tracked under no‐choice diet mixing conditions and conditions where the larvae could forage among mixed cultivars. These experiments demonstrated that specific cultivar blends can reduce herbivore fitness and herbivory, and that the effects on fall armyworm fitness are likely driven by insect–plant interactions rather than postconsumptive physiological effects. The results will inform pest management strategies in warm‐season turfgrass production and management, adding to the literature focused on the effects of intraspecific plant diversity.

Cultivar blends: A strategy for creating more resilient warm season turfgrass lawns

Cultivar blends: A strategy for creating more resilient warm season turfgrass lawns

Required mowing events of transgenic Kentucky bluegrass cultivars compared with conventional turfgrass cultivar blends and species mixtures

AbstractMowing is a labor‐intensive yet important cultural practice to maximize turfgrass health and performance. Selecting cultivars with a slower vertical growth habit can help reduce mowing frequency and improve turfgrass quality (TQ). New transgenic Kentucky bluegrass (Poa pratensis L.) (KBG) cultivars with a dwarf growth habit have been developed by overexpressing the gibberellin 2‐oxidase pathway. However, the impact of this overexpression on the number of required mowing events and mowing frequency in the field is unknown. Therefore, the primary objective of this research was to quantify the required number of mowing events based on the one‐third rule of four transgenic cultivars (‘ProVista’) (PV) and 16 conventional turfgrass cultivars, blends, and mixtures. Over the 2‐yr research period, four PV cultivars in the top statistical group averaged ≤21 mowing events, whereas all other turfgrasses averaged ≥41 mowing events. For mowing frequency, all PV cultivars required an average mowing frequency of ≥20 d, whereas all other turfgrasses required an average mowing frequency of ≤10 d. Although the PV cultivars required half as many mowing events, two of the PV cultivars were consistently in the top statistical group for TQ. The PV KBG cultivars represent new technology for turfgrass genetics with the novel trait of reduced mowing that can benefit the industry by reducing mower emissions, noise, and use, as well as increased TQ and flexibility for turfgrass practitioners, since mowing frequency can be extended.

Mixing warm‐season turfgrass cultivars to reduce weed pressure and increase lawn quality

AbstractSt. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze] is a warm‐season turfgrass widely planted in monoculture throughout tropical and subtropical regions of the world. Monocultures preserve desirable inheritable traits but may predispose turfgrass lawns to pest invasion and reliance on high‐maintenance inputs. Evidence from multiple plant systems suggests that increasing inter‐ or intra‐specific plant diversity increases resilience to biotic and abiotic stress. Here, we tested if mixing St. Augustinegrass cultivars would be a viable approach to reducing weed invasion and increasing turfgrass lawn quality compared with cultivar monocultures. Mixed‐cultivar plantings grew into denser stands of grass, which translated to about 4% less weed cover than cultivar monocultures. Digital image analysis showed that mixtures of four cultivars grew into higher quality turfgrass stands than cultivar monocultures. This study provides novel evidence that cultivar blends may reduce weed pressure and enhance St. Augustinegrass lawn quality, which, combined with other potential resilience benefits, may create a more sustainable approach to warm‐season turfgrass lawn production and management.

The effects of wheat cultivar blend on the content of essential grain minerals

The effects of wheat cultivar blend on the content of essential grain minerals

The effects of wheat cultivar blend on the content of essential grain minerals

In western Europe, not so long ago, wheat was frequently grown in a blend (mixture) of two or more cultivars, which was not common in southeast European countries. However, in recent times again growing wheat cultivars in a blend become more acceptable. Why? There are several advantages to this practice. In a blend, we have the possibility to combine different characteristics of two or more cultivars. For instance tolerance to different diseases, lodging tolerance, to combine characters in negative relation (for instance high yield and good grain protein content), and finally nutritive value of wheat, especially when essential minerals are in question. The last one will be the subject of this communication. Seven high protein wheat lines and one registered cultivars are sown in sixteen wheat 1:1 blends, and the effect of blending was studied with an intention to get a higher concentration of essential minerals and better nutritive value of wheat flour.

Minimal irrigation requirements of Kentucky bluegrass and tall fescue blends in the northern transition zone

AbstractLawns in the cool‐humid region typically consist of mixtures or blends of cool‐season turfgrass species and cultivars. To maintain a desirable aesthetic appearance and maximize seasonal greenness, many lawns receive supplemental irrigation. Turfgrass breeders have developed superior cultivars with reduced water needs, but the exact proportion of these grasses to include in lawn seed blends to reduce irrigation needs has not been well documented. A field study was conducted to determine the irrigation requirements of various blend ratios (0, 25, 50, 75, and 100%, w/w) of drought‐tolerant (DT) and drought‐susceptible (DS) Kentucky bluegrass (Poa pratensis L., KBG) and turf‐type tall fescue [Schedonorus arundinaceus (Schreb.) Durmort., syn. Festuca arundinacea Schreb.; TF] cultivars at two mowing heights (5.1 or 8.9 cm). Supplemental irrigation requirements were determined over a 74‐d deficit irrigation period using a 70% green coverage threshold (GCT70) approach, where 12.7 mm of supplemental irrigation was applied if an individual plot fell below GCT70 using digital image analysis. Total irrigation needs ranged from 66.7 to 176.9 mm, and TF generally required the least irrigation. For KBG, a blend containing ≥75% DT cultivar required the longest time to reach GCT70 (25–33 d), the least irrigation (94–110 mm), and provided the highest overall visual quality. The TF responses were more variable, and the magnitude of differences among cultivar blends was less compared with KBG. These results indicate that where blending of cultivars is desired, the inclusion of cultivars with demonstrated drought tolerance in blends is important for reducing lawn irrigation needs.

Effect of Wheat Cultivars and Blends on the Oviposition and Larval Mortality ofCephus cinctus(Hymenoptera: Cephidae) and Parasitism byBracon cephi(Hymenoptera: Braconidae)

The wheat stem sawfly (Cephus cinctus Norton) is a major historical pest of wheat in the northern Great Plains of North America. The insect spends most of its life as a larva protected inside grass stems so that its management has relied on strategies other than insecticides. We conducted a study in southern Alberta from 2006-2009 to assess the effects of wheat species, cultivar, seeding rate, and blending a resistant and a vulnerable cultivar, on oviposition, larval infestation, and cutting damage. The mortality caused by its primary parasitoid, Bracon cephi (Gahan), was also assessed to investigate the potential benefit of cultivar blends to enhance sawfly biological control. Sawfly laid fewer eggs on plants of the durum cultivar 'AC Avonlea' and on those of the solid-stemmed cultivar 'Lillian' compared to plants of the hollow-stemmed cultivar 'CDC Go.' Larval establishments (infestation) followed a similar pattern to that of oviposition. At these locations there was low cutting damage in most years and to a large extent this was due to mortality inflicted by the parasitoid Bracon cephi (40-60%). However, the remaining mortality was attributed to other factors and host, particularly the inclusion of the solid-stemmed cultivar. Direct and indirect factors likely affected the success of the parasitoid in the crop monocultures and blends, and these mechanisms require further research.

Wheat cultivar blends: A step forward to sustainable agriculture

It is only in the last hundred years or so that crop monoculture has become predominant in industrialized agriculture for field and plantation crops. The reasons were for simplicity of planting, harvesting and other operations, which could all be mechanized, and for uniform quality of the crop product. However, monoculture produced severe disadvantages, such as vulnerability to diseases, pests and weeds, and yield instability, which necessitated, for example, the large-scale use of pesticides, fertilizers and growth regulators. To avoid or reduce some of the problems of monoculture, we need to introduce and manage diversity in better ways. At the highest level, species monoculture is difficult to change, at least in the short term. At the variety level, diversification is easy to manage, in the form of variety mixtures within the field. The idea of purposely blending different varieties of wheat is more than 50 years old and was first proposed and tested to reduce the impact of stem and leaf rust. More recently, this concept has also been expanded to look whether blends improved grain yield and/or grain quality. This article reviews the current knowledge about the mechanisms that account for disease reduction and yield increase in a variety of mixtures. It discusses the various determinants in the adoption of a variety of mixtures and the prospects for and challenges in using a variety of mixtures as a functional diversification strategy. Key words: Disease reduction, diversity, sustainable agriculture, wheat variety mixtures, yield stability. INTRODUCTION Wheat variety blends are seed mixtures of two or more pure varieties. Cultivar mixtures refer to mixtures of cultivated varieties growing simultaneously on the same parcel of land with no attempt to breed for phenotypic uniformity (Mundt, 2002). Wolfe (1985) defined cultivar mixtures as mixtures of cultivars that vary for many characters including disease resistance, but have sufficient similarity to be grown together. Compared to the modern monoculture model, blending wheat varieties is a different approach. Each wheat variety has susceptibilities that can cause fluctuations in yield. For example, some varieties are highly disease resistant but may respond poorly to drought or a variety that is fairly cold-hardy may succumb to certain insect pests. In any environment where stresses occur unpredictably, combining pure varieties that have complementary strengths can help stabilize yields (Cowger, 2007). Variety and species mixtures are not only being used extensively in small-scale subsistence agriculture worldwide but also in large-scale systems. Cultivar blends have been used extensively in small grain production in several European countries (Wolfe, 2001). Currently, 6 to 15% of the wheat production area in the states of Washington, Oregon, and Kansas is planted to blends every year (NASS, 2007). Approximately 17% of the 644 000 ha of soft white common winter wheat seeded in Washington in 1999 consisted of mixtures (WASS, 1999). Part of the mixture production is for animal feed; however, cereal cultivar mixtures in Switzerland, Poland and the US are used for bread and beer production. Most interesting is the fact that the highest quality coffee of Colombia is almost all produced in cultivar mixtures to protect the coffee from the coffee rust disease. These mixtures are perennial and have been successful since 1982 on a large scale (Wolfe, 2001). Superiority of cultivar

Wheat cultivar blends: A step forward to sustainable agriculture

It is only in the last hundred years or so that crop monoculture has become predominant in industrialized agriculture for field and plantation crops. The reasons were for simplicity of planting, harvesting and other operations, which could all be mechanized, and for uniform quality of the crop product. However, monoculture produced severe disadvantages, such as vulnerability to diseases, pests and weeds, and yield instability, which necessitated, for example, the large-scale use of pesticides, fertilizers and growth regulators. To avoid or reduce some of the problems of monoculture, we need to introduce and manage diversity in better ways. At the highest level, species monoculture is difficult to change, at least in the short term. At the variety level, diversification is easy to manage, in the form of variety mixtures within the field. The idea of purposely blending different varieties of wheat is more than 50 years old and was first proposed and tested to reduce the impact of stem and leaf rust. More recently, this concept has also been expanded to look whether blends improved grain yield and/or grain quality. This article reviews the current knowledge about the mechanisms that account for disease reduction and yield increase in a variety of mixtures. It discusses the various determinants in the adoption of a variety of mixtures and the prospects for and challenges in using a variety of mixtures as a functional diversification strategy. Key words: Disease reduction, diversity, sustainable agriculture, wheat variety mixtures, yield stability. INTRODUCTION Wheat variety blends are seed mixtures of two or more pure varieties. Cultivar mixtures refer to mixtures of cultivated varieties growing simultaneously on the same parcel of land with no attempt to breed for phenotypic uniformity (Mundt, 2002). Wolfe (1985) defined cultivar mixtures as mixtures of cultivars that vary for many characters including disease resistance, but have sufficient similarity to be grown together. Compared to the modern monoculture model, blending wheat varieties is a different approach. Each wheat variety has susceptibilities that can cause fluctuations in yield. For example, some varieties are highly disease resistant but may respond poorly to drought or a variety that is fairly cold-hardy may succumb to certain insect pests. In any environment where stresses occur unpredictably, combining pure varieties that have complementary strengths can help stabilize yields (Cowger, 2007). Variety and species mixtures are not only being used extensively in small-scale subsistence agriculture worldwide but also in large-scale systems. Cultivar blends have been used extensively in small grain production in several European countries (Wolfe, 2001). Currently, 6 to 15% of the wheat production area in the states of Washington, Oregon, and Kansas is planted to blends every year (NASS, 2007). Approximately 17% of the 644 000 ha of soft white common winter wheat seeded in Washington in 1999 consisted of mixtures (WASS, 1999). Part of the mixture production is for animal feed; however, cereal cultivar mixtures in Switzerland, Poland and the US are used for bread and beer production. Most interesting is the fact that the highest quality coffee of Colombia is almost all produced in cultivar mixtures to protect the coffee from the coffee rust disease. These mixtures are perennial and have been successful since 1982 on a large scale (Wolfe, 2001). Superiority of cultivar

Grain Yield Performance and Stability of Cultivar Blends vs. Component Cultivars of Hard Winter Wheat in Nebraska

In diverse growing environments, cultivar blends of hard winter wheat (Triticum aestivum L.) are considered as an option over pure cultivars for maintaining grain yield and reducing risk to producers. The objectives of this research were to evaluate the grain yield between blends and their component cultivars over several locations in Nebraska and to compare blend grain yield stability. Two separate experiments of six three‐cultivar blends and their component cultivars tested in a total of 30 environments and three two‐cultivar blends and their component cultivars tested in a total of 20 environments were grown in replicated randomized block designs. All component cultivars and cultivar blends (referred to as lines, hereafter) were evaluated for mean grain yield performance and stability. ‘Pronghorn’‐‘Goodstreak’‐‘Buckskin’ was the sole cultivar blend that significantly increased grain yield when compared with the average of its component cultivars. The grain yield advantage for the mean average cultivar blends varied from 2.2% lower to 1.9% higher with overall advantage of 0.4% yield increase for all the nine cultivar blends. Cultivar blends of ‘Millennium’‐‘Wesley’‐‘Wahoo’, Millennium‐‘Halt’‐Wahoo, and Millennium‐‘Alliance’‐Wahoo were the most stable lines using regression estimates for stability. When compared with the average of component cultivars, cultivar blends were more stable over different environments with little or no reduction in grain yield.

The effect of grape vine cultivars on Lobesia botrana (Lepidoptera: Tortricidae) population levels

The European vine moth Lobesia botrana Denis & Schiff. (Lepidoptera: Tortricidae) is a key pest in the vineyards of Israel and Europe. Traps baited with the female sex pheromone are commonly used to monitor the pest population. However, the role of the vine cultivars on monitoring the moth population using pheromone-baited traps was not yet studied. The present study aimed to identify the effect of grape cultivars on L. botrana adult distribution patterns in the field, in order to achieve a better understanding of the monitored data in respect to male and female’s host preference. The 3-year study in commercial vineyards used four cultivars: Carignan, Emerald Riesling, French Colombard, and Cabernet Sauvignon. The moth population of each generation was estimated from male counts in pheromone traps; three generations were observed in all experimental orchards, each year. Female host choice was studied by monitoring freshly deposited eggs and newly hatched larvae on vines. The study showed a significant effect of cultivar on numbers of trapped males in most years, and a cultivar effect on female host choice. For both males and females and for all phenological stages of the grapes, Carignan and French Colombard attracted the most and Cabernet Sauvignon the fewest specimens. The results show that cultivar blend within the vineyard can affect the distribution pattern of the pest. Knowledge of the expected choice of the female moth, and of the timing of its decision could lead to an improved monitoring system, with the preferred cultivar as an indicator.

Effect of Wheat Stem Sawfly Damage on Yield and Quality of Selected Canadian Spring Wheat

The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), has reached outbreak status at most locations in the southern Canadian prairies. Solid-stemmed wheat, Triticum aestivum L., cultivars, which are less susceptible to damage, remain the primary management option. This article quantifies the effect of wheat stem sawfly damage on grain yield and quality at harvest and determines how cultivar selection affects harvest losses. Solid-stemmed cultivars were compared with hollow-stemmed cultivars and with blends of a 1:1 ratio of each. The hollow-stemmed cultivars with the exception of ‘McKenzie’, which had intermediate levels of stem cutting, were all significantly more susceptible to stem cutting than solid-stemmed cultivars. Cultivar blends had lower damage but were still significantly higher than the solid-stemmed cultivars. The solid-stemmed ‘AC Eatonia’ and ‘AC Abbey’ had the lowest levels of stem cutting and ranked second and third overall for yield in 2001 and 2002. McKenzie ranked first, which reflects its yield potential in combination with its partial resistance to stem cutting. Lower cutting in AC Eatonia, AC Abbey, McKenzie, and the blend of AC Abbey/McKenzie was significantly correlated with lower grain losses. Grain lost at harvest has major economic implications if sawfly pressure is moderate to high and susceptible cultivars predominate.

Effect of Wheat Stem Sawfly Damage on Yield and Quality of Selected Canadian Spring Wheat

The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), has reached outbreak status at most locations in the southern Canadian prairies. Solid-stemmed wheat, Triticum aestivum L., cultivars, which are less susceptible to damage, remain the primary management option. This article quantifies the effect of wheat stem sawfly damage on grain yield and quality at harvest and determines how cultivar selection affects harvest losses. Solid-stemmed cultivars were compared with hollow-stemmed cultivars and with blends of a 1:1 ratio of each. The hollow-stemmed cultivars with the exception of'McKenzie', which had intermediate levels of stem cutting, were all significantly more susceptible to stem cutting than solid-stemmed cultivars. Cultivar blends had lower damage but were still significantly higher than the solid-stemmed cultivars. The solid-stemmed 'AC Eatonia' and 'AC Abbey' had the lowest levels of stem cutting and ranked second and third overall for yield in 2001 and 2002. McKenzie ranked first, which reflects its yield potential in combination with its partial resistance to stem cutting. Lower cutting in AC Eatonia, AC Abbey, McKenzie, and the blend of AC Abbey/ McKenzie was significantly correlated with lower grain losses. Grain lost at harvest has major economic implications if sawfly pressure is moderate to high and susceptible cultivars predominate.

RAPD‐Based Genetic Relationships in Kentucky Bluegrass

Kentucky bluegrass (Poa pratensis L.) is a widely used, facultatively apomictic, cool season turf and forage grass, with many known cultivars. Previously these have been classified on the basis of morphological traits in field tests. However, these determinations are lengthy, sensitive to environmental variations, and there are few traits that can be tested. Molecular markers provide an alternative way to classify these cultivars. Important advantages of molecular markers include lack of sensitivity to changes in environmental conditions, as well as a nearly unlimited potential number of markers and speed of the marker assays as compared with field tests. They can also provide additional information such as the amount of genetic divergence between Kentucky bluegrass cultivars and other genotypes, the amount of agreement between morphological and marker‐based classification, and the amount of genetic variability between seedling replicates of genotypes. Random amplified polymorphic DNA (RAPD) marker data was collected from three replicates each of 123 Kentucky bluegrass cultivars, plant introductions (PIs), experimental breeding lines, and interspecific hybrids between Kentucky and Texas bluegrass (Poa arachnifera Torr.). From these data multidimensional scaling (MDS) plots were created, and ANOVA tests of significant differences between germplasm sources were performed. The PIs were the most genetically divergent from the cultivars, while the interspecific hybrids were not as distinct. Members of two morphological trait‐based types were found to be genetically similar, and there was a wide range of genetic variability among germplasm sources. The genetic divergence of the PIs, combined with their potentially high turf utility reported in earlier studies, indicates their potential as a genetic resource. All but two of the morphological trait‐based types contained genetically diverse individuals, so that cultivar blends of all but these two types would be morphologically similar yet genetically diverse. The rather high within‐cultivar genetic variability could be due to a relatively high proportion of potentially sexually produced off‐types. Thus, this study provides further evidence for the utility of RAPD markers for turfgrass genetics, as well as important genetic information for turf breeders and managers.

Genome‐Wide Genetic Diversity among Components Does Not Cause Cultivar Blend Responses

Genetically diverse plant populations may be better able to exploit ecological resources and reduce interplant competition than genetically homogeneous populations. Cultivar blends can have greater productivity and yield stability than pure lines; however blend effects are not consistent. The varying levels of genetic diversity represented in blends may confound the interpretations and comparisons of the results of different blend studies. We tested the hypothesis that genetic diversity of blend components is related to blend performance by evaluating blends of a set of five early‐maturing and a set of 10 midseason‐maturing oat (Avena sativa L.) cultivars in two separate experiments at eight Iowa environments. Within each experiment, pure lines and all possible two‐way blends were evaluated for grain yield and test weight means and stability and adaptability parameters. The genetic diversity of each blend was estimated by pedigree diversity [1 − coefficient of parentage (COP)], amplified fragment length polymorphism (AFLP)‐derived genetic distances (1 − Dice coefficient), and phenotypic diversity (based on height and heading date differences). Blend response was limited in these experiments and was not correlated with any diversity measure, and blend stability parameters were not consistently related to diversity measures across experiments. We also investigated the relationship between pedigree diversity and blend performance in other crops by computing the coefficients of parentage of cultivar pairs used in previous blend studies in maize, soybean, and wheat. Pedigree diversity was correlated with higher blend response only in two of 10 experiment–environment combinations tested. Genome‐wide genetic diversity alone does not cause positive crop blend responses.

The Influence of Irrigation Frequency and Cultivar Blends on the Severity of Multiple Root Diseases in Sugar Beets.

The effects of cultivar mixtures and two irrigation frequency treatments were evaluated over two seasons for their impact on a complex of sugar beet root diseases in three fields infested with the fungal pathogens Aphanomyces cochliodes, Fusarium oxysporum f. sp. radicis-betae, Rhizoctonia solani, and the viral pathogen Beet necrotic yellow vein virus (BNYVV). Irrigations after emergence consisted of two or five (two 1994 studies) and three or six (1995 study) applications of water for dry and wet treatments, respectively. Cultivar treatments included MH9155, HH67, Ranger, Rhizosen, and four combinations of these same cultivars. Disease progress was monitored through destructive sampling of plants exhibiting foliar symptoms typical of root disease during the season. At harvest, data on root and sucrose yields, sucrose percentage, and a root disease index were collected. No significant irrigation × cultivar treatment interactions were observed. Few significant differences were observed between irrigation treatments involving measured yield components. Reduced irrigations however, resulted in significantly lower disease incidence in all three repeated experiments when cultivar treatments were combined. No added benefits were observed for increasing yield or decreasing root disease by planting mixed cultivars, compared to the same cultivars planted individually. Several regionally adapted cultivars performed as well or better than mixtures under the unusually high levels of disease pressure in test fields. When few alternative options are available, sugar beet growers may still benefit from reducing irrigations, and growing locally adapted cultivars in soils severely infested with root pathogens.

Turf Performance of Mixtures and Blends of Tall Fescue, Kentucky Bluegrass, and Perennial Ryegrass

Various mixtures of tall fescue, Festuca arundinacea Schreb., Kentucky bluegrass, Poa pratensis L., and perennial ryegrass, Lolium perenne L., may be beneficial for turf culture because of genetic diversity and improved tolerance to environmental stresses compared with a single species. Turf-type tall fescue, dwarf tall fescue, Kentucky bluegrass, and perennial ryegrass were seeded as cultivar blends and in all possible combinations as species mixtures in two locations, irrigated and nonirrigated. Turf was mowed at 19 and 51 mm and subjected to an interval of brief, but intensive, simulated traffic. Perennial ryegrass was the dominant species in all mixtures with tall fescue, Kentucky bluegrass, or both. After 5 years, turf-type tall fescue comprised 62% of mixtures with Kentucky bluegrass when averaged over locations. Dwarf tall fescue comprised 48% of mixtures compared with Kentucky bluegrass at 44%. Kentucky bluegrass was more competitive with tall fescue in the irrigated vs. nonirrigated location. Mowing height effected small changes in populations year to year while simulated traffic had little effect on populations at 1 year following treatment. The advantage of mixing species compared with individual species to reduce disease occurrence was evident on several occasions. Our study supports earlier research reports that tall fescue will remain competitive in mixture with Kentucky bluegrass several years after seeding.