Cultivar Mixtures Research Articles

Plasticity of barley in response to plant neighbors in cultivar mixtures

AimsCultivar mixtures can increase productivity through complementarity in resource use, but reported results are often conflicting and the role of plasticity in shaping plant-plant interactions is poorly understood. We aim to determine if individual cultivars show different phenotypic responses when grown in a mixture, whether these responses depend on the neighboring cultivar identity, and how they contribute to variations in productivity and nitrogen (N) use.MethodsFive spring barley cultivars were field-grown in pure stands and in mixtures during 2 years. Plant traits related to development, growth, N use, and reproduction were measured to identify temporal patterns of plastic responses to neighboring plants.ResultsPlants in mixtures were shorter and developed slower early in the season, but later on they grew faster and produced more grain than the corresponding pure stands. Some cultivars showed complementary N accumulation only when grown together with specific neighbors. Mechanisms of improved productivity differed between the individual mixtures.ConclusionsPlastic plant-plant interaction between cultivars is an important driver behind the variability in mixing effects. Results contribute to a better understanding of how productivity in cultivar mixtures is affected by plastic adaptation and differentiation of plant traits, depending on the environment created by neighboring genotypes.

Seed mixture strongly affects species-richness and quality of perennial flower strips on fertile soil

Within the frame of the EU Common Agricultural Policy, most countries subsidise the establishment and maintenance of perennial flower strips on arable land within Agri-Environmental Schemes to provide foraging habitats and refuges for wildlife.In a replicated field experiment, we studied the effects of different types of seed mixtures on the establishment and maintenance of perennial flower strips on fertile arable land in the federal state of Saxony-Anhalt, Germany over seven years. The seed mixtures were commonly applied within recent Common Agricultural Policy funding periods: (1) a low-diversity cultivar standard seed mixture (CULTIVAR), (2) a high-diversity cultivar and native plant mixture (MIX), and (3) a high-diversity native plant mixture (WILDFLOWER). All plots were mulched every year in March and at the beginning of August.The low success of CULTIVAR triggered the massive encroachment of spontaneously established perennial grasses. In MIX, too, cultivars have disappeared after the first year. Both wildflower variants were successful in maintaining a high cover of sown perennial native forbs and a high ratio of established sown species, even after seven years. WILDFLOWER always tended to show better values than MIX. Furthermore, spontaneously establishing species began to spread their cover in MIX in the fifth year, with a very strongly increasing tendency, whereas in WILDFLOWER cover of spontaneously immigrating species stayed satisfyingly low.Using native wildflowers to establish perennial wildflower strips was very effective in maintaining high species diversity within the Agri-Environmental Schemes funding period of five years and beyond. WILDFLOWER was especially successful. On the other hand, CULTIVAR failed completely. On fertile soils in regions with rather low yearly precipitation, mulching twice a year supported the maintenance of perennial wildflower strips.

Increased crop diversity reduces the functional space available for weeds

SummaryThere is a drive to improve the sustainability of agricultural systems including the biodiversity component. Cultivar mixtures offer yield benefits from the same land area, but the mechanisms behind this overyielding have not been completely worked out. One potential mechanism is improved competition with weeds. We use an experimental approach of varying barley (Hordeum vulgare L.) genotypic and phenotypic diversity to test the hypothesis that increases in diversity have an impact on weed growth strategies and community assembly, or if responses are driven by barley performance. There was no effect of increasing barley mixture diversity on weed traits, either in terms of species means or the community‐weighted mean. However, Functional Richness of the weed community decreased with increasing barley mixture diversity mainly as a result of reduced specific leaf area Functional Richness. This pattern was driven by a reduction in species richness of the weed community rather than by reduced variation within species. Whilst barley phenotype had different impacts on weed traits, there were no specific mixtures of phenotypes or genotypes that had consistent effects on community assembly or weed species responses. The competitive exclusion of weed species could have agronomic and environmental benefits, through better targeting or less frequent use of herbicides. Growing crop mixtures is one of many strategies available to improve agricultural sustainability and resilience, and one that has clear benefits.

Effects of expanding functional trait diversity on productivity and stability in cultivar mixtures of perennial ryegrass

Cultivar mixtures can provide a host of beneficial agroecosystem services in annual grain crops; however, it remains unclear whether these same benefits apply to perennial forage cropping systems, or the degree to which beneficial effects depend on the functional trait diversity of the mixtures. We conducted a field experiment across four locations in the Northeast US in which we grew perennial ryegrass cultivar mixtures varying in cultivar number and range of expression of three functional traits (winter hardiness, heading date, and extended growth) and assessed the effects on dry matter yield and inter-annual yield variability. Trait ratings supplied by the seed company were related to observed variation in perennial ryegrass productivity and/or stability at both the individual cultivar and mixture levels. Winter hardiness was associated with greater perennial ryegrass cumulative biomass, and lower interannual stability. In contrast, extended growth was associated with lower cumulative biomass, and both extended growth and later heading date were associated with greater interannual variability. Overall, cultivar richness was negatively associated with perennial ryegrass biomass and stability; however, the best performing mixtures performed as well as the recommended cultivar for the region. When comparing mixtures with equal cultivar richness, functional trait diversity measured as the additive trait range—the summed range of the three traits associated with the cultivars in that mixture—was positively associated with biomass production and over-yielding, but not interannual variability. Cultivar mixtures of perennial ryegrass can lead to improved forage production when specific functional traits are optimized within mixtures. Our results support the growing understanding that efforts to ecologically intensify agriculture through enhancement of crop diversity are more likely to succeed when they explicitly consider the functional traits of the crops involved rather than solely numbers of cultivars or species.

Wheat genotypic diversity and intercropping to control cereal aphids

Increasing intrafield plant diversity has been shown to regulate pest populations. Mixing wheat cultivars and intercropping winter wheat and white clover are both promising agroecological practices. On field experiments over two growing seasons, we combined both practices and examined the impact on aphid populations and on wheat production. Results show that combining intra- and interspecific diversity did not outperform each practice individually in reducing aphid populations. Taken separately, intercropping tended to have lower aphid infestation, while it was intermediate in cultivar mixtures. Yearly variation in climatic conditions impacted wheat and clover development, as well as the appearance of aphid peaks. Wheat yields and grain nitrogen content were reduced in intercropping by 10% and 7%, respectively, but not in cultivar mixtures. Our findings suggest that intrafield diversification may regulate wheat aphids to some extent, but combining two diversification practices did not result in an attractive trade-off between pest regulation and wheat production in real farming conditions.

Growing tall and dwarf rice cultivars in mixture for better weed management and higher yield

Growing two or more cultivars of same crop species in mixture reduces intra-specific competition for natural resources and increases competitive ability of crops against weeds and thus enhances crop yield. The objective of this study was to evaluate the potentiality of growing rice cultivars in mixtures for minimizing weed pressure and increasing rice yield. The experiment was conducted at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh during Aman season (July-December) 2017. Two transplant Aman rice cultivars viz. Binadhan-13 (tall, late- maturing and fine grain aromatic cultivar) and BRRI dhan49 (semi-dwarf, mid-maturing and coarse grain cultivar) were grown following two spatial arrangements viz., alternate row and alternate hill, and nine different cultivar mixture (Binadhan-13:BRRI dhan49) row ratios viz., 1:0, 1:2, 2:1, 2:3, 3:2, 2:4, 4:2,1:1 and 0:1. The experiment was laid out in a randomized complete block design (RCBD) with three replications. Results confirmed the positive influence of spatial arrangement and cultivar mixture ratio on rice productivity. Both the cultivars showed better growth and higher yield when grown in mixture irrespective of ratios compared to their sole culture performances. But cultivar mixture ratio showed no advantages over sole culture in suppressing weeds. Based on the total yield Binadhan-13 and BRRI dhan49 inter-planted in 1:1 row ratio following alternate hill performed the best resulting in 50% and 12% yield advantages over sole culture of Binadhan-13 and BRRI dhan49, respectively. Therefore, growing tall and dwarf rice cultivars in mixture can be adopted as a tool for increasing rice productivity.
 J. Bangladesh Agril. Univ. 17(2): 133–141, June 2019

Evidence for relative grain yield simulation by red color level of beneath-canopy soil at wheat booting phase: An unexpected observation using image processing

Digital cameras are increasingly utilized as a reliable and readily available remote sensing tool in the emerging technology of high throughput phenotyping and agronomic field assessments. In almost every image analysis of green canopies, image segmentation into the vegetation and non-vegetation parts using thresholding is a fundamental step. Therefore, only the vegetation parts of the high resolution images are considered for estimations and the data recorded in the remained pixels will be ignored. In the present study, an accidental observation is described, in which the red color level of the non-vegetation segments of the images taken at the wheat booting phase could simulate the relative pattern of final grain yield. An image archive of heterogeneous wheat canopies (i.e. cultivar mixtures), captured from experimental plots of a field study conducted at the School of Agriculture, Shiraz University, Iran, was analyzed. It was observed that the red color levels of the image background (BRL, mostly composed of soil pixels) were accurately simulating the final grain yields of the treatments, (i.e. very precise mimicry of relative grain yields –RGY– in monocultures, and exact determination of curve extrema and also the direction of fluctuations, in the case of mixtures). Compared with other colors and image-derived criteria evaluated, BRLs had the pattern most similar to the relative grain yields. Moreover, assessments showed the importance of using higher number of replicates in analyses (i.e. 6 vs 3 replications). This observation suggests the red color level of the image-background as a potential novel index for the prediction of wheat grain yield during the preanthesis period; and also the ability of the non-vegetation image segments to provide valuable data for crop remote sensing and image processing studies.

The number of cultivars in varietal winter-wheat mixtures influence aboveground biomass and grain yield in North China

This study evaluated the influence of cultivar number in wheat cultivar mixtures on aboveground biomass and grain yield across two years with different rainfall. Field experiments were conducted in the 2014–2015 (wetter-than-average) and 2015–2016 (drier-than-average) growing seasons in northern China. The study contained either one cultivar (16 × monoculture) or combinations of cultivar mixtures containing two (8 × mixture-2), four (8 × mixture-4), eight (8 × mixture-8) or 16 (1 × mixture-16) wheat cultivars. In the wetter year (2014–2015), grain yield and aboveground biomass in the cultivar mixtures did not differ from the monoculture mean and had no relationship with the number of cultivars across monocultures or cultivar mixtures. However, in the drier year (2015–2016), wheat grain yield and aboveground biomass had a significantly positive relationship with the number of cultivars across monocultures and cultivar mixtures, and both were significantly higher in the cultivar mixtures than the monoculture mean. The higher yields in cultivar mixtures were attributed to higher thousand-grain weights and spike numbers per unit area. The cultivar mixtures had more root biomass and root distribution at depth than the monoculture mean, which contributed to higher water use efficiencies in the drier year. Cultivar mixtures can improve crop performance under water-deficit conditions and are likely to buffer the negative effects of drought on wheat yield under global climate change.

EVALUATION OF THE CULTIVAR MIXTURE STRATEGY AS A SUSTAINABLE TOOL FOR MANAGING WEEDS AND ENHANCING RICE YIELD

The study was conducted to evaluate the potentiality of rice cultivar mixtures as a strategy for managing weeds and increasing the rice yield under different weeding regimes. Two rice cultivars having different plant stature and maturity periods viz. Binadhan-13 and BRRI dhan56 were used in this study. Factors included six cultivar mixture ratios viz. sole Binadhan-13, sole BRRI dhan56, 2:3, 3:2, 2:4 and 4:2 Binadhan-13 to BRRI dhan56, and four weed management practices viz. no, one, two and three weeding. The experimental design was randomized complete block with three replicates. Both the cultivars showed better growth, higher weed suppression and increased yield when grown in mixture irrespective of ratios compared to their monoculture performances. Based on the total rice grain yield, different mixture ratios performed in the order 4:2, 3:2, 2:3 and 2:4 Binadhan-13 to BRRI dhan56. Binadhan-13 and BRRI dhan56 inter-planted in 4:2 row ratio appeared as the best mixture ratio which resulted in 136% and 7% yield advantages and 17% and 24% weed dry matter reduction over sole culture of Binadhan-13 and BRRI dhan56, respectively. Hence, cultivar mixture strategy can be adopted as an effective tool for better weed management and increased yield of rice.

The effect of mixed cultivars plantings on pest abundance and grain yields in rice

A field study was carried out to assess the effects of mixed cultivar plantings on grain yields and on the abundance of pests in rice. Increasing plantation species diversity through cultivar mixtures is often claimed to decrease pest problems while stabilizing or even increasing yield, but the effects on pest abundance of planting rice cultivar mixtures in Indonesia have not been extensively studied. We tested for changes in pest abundance in experimental plots planted with five genetically distinct rice cultivars, combined in two different mixture arrangements (seed mix and row mix). These mixes were cultivated in lowland paddy areas, in replicated randomized block designs, during two growing seasons. Pest abundance was measured weekly in all plots, and rice yields were measured at harvest time. The results showed that the average abundance of pests was reduced in plots planted with cultivar mixes, compared to those planted with monocrops comprised of each of the component cultivars. Plots planted with the seed mix showed consistently reduced brown plant-hopper (Nilaparvata lugens (Stål)) abundance compared to monocrops in each growing season, with a relative reduction in pest abundance of 29.83% at the end of season 1 and 6.61% at the end of season 2, respectively. Plots planted with the row mix consistently showed decreased stem borer abundance compared to monocrops in each growing season, with a relative reduction in pest abundance of 100% at the end of season 1 and 1.4% at the end of season 2, respectively. In terms of yield, plant height proved to be a consistent yield component character, correlating positively with plant yield for both seed mix and row mix in both growing seasons. Our results showed higher average yields –and plant heights--for the mixed genotype plots compared to pure genotype stands in 2013. We found a greater relative increase in the yield of seed mix plots than row mix, measuring 7.26% and 4.63%, respectively in 2013. Among the two types of mixtures, seed mix showed higher overall grain yield. Our findings suggest that rice farmers can both increase yield and decrease pest abundance by planting cultivar mixes.

Grain and straw yield interactions in barley cultivar mixtures

AbstractCultivar mixtures of winter barley and spring barley, together with their component monocultures, were grown in field trials to assess the effect of cultivar combinations on both straw and grain yield. The overall grain yields for all trials were significantly higher for the cultivar mixtures than for the corresponding component monocultures. Also, significant decreases in rhynchosporium disease severity for cultivar mixtures were recorded for most non-fungicide treatments. The size of these responses was often significantly correlated with the component number of the mixtures. The amount of straw produced in mixtures was sometimes changed significantly, but not always in a positive direction and it was only correlated with increasing mixture component number in two environments. No correlation of straw yield potential of cultivars with performance in mixtures was found. Cultivar × cultivar mixture × environment interactions appeared to affect the relative yield of grain and straw differentially and therefore it was not possible to predict the effect of mixtures on the harvest index.

Cultivar Differences and Impact of Plant-Plant Competition on Temporal Patterns of Nitrogen and Biomass Accumulation.

Current niche models cannot explain multi-species plant coexistence in complex ecosystems. One overlooked explanatory factor is within-growing season temporal dynamism of resource capture by plants. However, the timing and rate of resource capture are themselves likely to be mediated by plant-plant competition. This study used Barley (Hordeum sp.) as a model species to examine the impacts of intra-specific competition, specifically inter- and intra-cultivar competition on the temporal dynamics of resource capture. Nitrogen and biomass accumulation of an early and late cultivar grown in isolation, inter- or intra- cultivar competition were investigated using sequential harvests. We did not find changes in the temporal dynamics of biomass accumulation in response to competition. However, peak nitrogen accumulation rate was significantly delayed for the late cultivar by 14.5 days and advanced in the early cultivar by 0.5 days when in intra-cultivar competition; there were no significant changes when in inter-cultivar competition. This may suggest a form of kin recognition as the target plants appeared to identify their neighbors and only responded temporally to intra-cultivar competition. The Relative Intensity Index found competition occurred in both the intra- and inter- cultivar mixtures, but a positive Land Equivalence Ratio value indicated complementarity in the inter-cultivar mixtures compared to intra-cultivar mixtures. The reason for this is unclear but may be due to the timing of the final harvest and may not be representative of the relationship between the competing plants. This study demonstrates neighbor-identity-specific changes in temporal dynamism in nutrient uptake. This contributes to our fundamental understanding of plant nutrient dynamics and plant-plant competition whilst having relevance to sustainable agriculture. Improved understanding of within-growing season temporal dynamism would also improve our understanding of coexistence in complex plant communities.

Impact of crop genetic diversity on a litter consumer

Belowground communities, and especially earthworms, provide numerous services in agroecosystems. In the current context of crop genetic erosion, this study aims at assessing the effect of wheat cultivar diversity on earthworm growth and survival. Our laboratory experiment was divided into two periods: (1) the “feeding period” (4 months), simulating conditions in autumn with cool temperatures and high food availability, and (2) the “non-feeding period” (1 month) simulating conditions in winter with cold temperatures and low food availability because litter had already been consumed without replacement. The aerial biomass of mixtures of wheat cultivars was used as food for earthworms and their growth was measured twice during the feeding period and once during the non-feeding period. We found two major effects on earthworm growth. Increasing the cultivar number (i) increased juvenile earthworm growth and earthworm survival and (ii) decreased adult earthworm growth. A consistent positive effect of nitrogen concentration of the biomass was found on growth and this effect was independent of biodiversity effects. This study suggests that the loss of litter intraspecific genetic diversity has an impact on earthworm populations, probably through mechanisms linked to the variance in edibility or the balanced diet hypotheses. While they remain to be tested in the field, these results suggest that the current losses of crop genetic diversity could potentially impact processes at the community or ecosystem level through a decrease in food quality.

Does genetic diversity of grass improve yield, digestibility, and resistance to weeds, pests and disease infection?

ABSTRACTIntraspecies genetic level diversity has the potential to improve ecosystem functions and services, similar to that by species-level diversity. Although yield, pollination, and pest and disease control have been enhanced by crop genetic diversity, mixing multiple cultivars of grass within a species in an agricultural field have not been fully tested by farmers.We, therefore, tested whether multiple ecosystem functions are increased in a grass mixture of multiple cultivars compared to monoculture and whether this relationship differs with soil fertility. We performed monocultures of four Orchard Grass cultivars and a mixture of these cultivars with and without fertilizer application and examined the aboveground net primary productivity (ANPP), their stability, dry matter digestibility, and resistance to weed, pest, and disease. We found significant differences between cultivars in the second yield and disease lesion area on the leaf, but not between mixed culture and monoculture. Moreover, no significant difference was found in the first and third yields in terms of stability, dry matter digestibility, and leaf damage by insects, although the number of leaves damaged by insects for mixed culture was less than half of that on average for monoculture. Although genetic diversity is not always an important driver of ecological processes due to fluctuation among plots, it may play a role in pest control of agricultural land in the long term.

Genome-wide association study of berry-related traits in grape [Vitis vinifera L.] based on genotyping-by-sequencing markers

ABSTRACTDeciphering the genetic control of grape berry traits is crucial for optimizing yield, fruit quality, and consumer acceptability. In this study, an association panel of 179 grape genotypes comprising a mixture of ancient cultivars, landraces, and modern varieties collected worldwide were genotyped with genotyping-by-sequencing using a genome-wide association approach based on 32,311 single-nucleotide polymorphism (SNP) markers. Genome-wide efficient mixed-model association was selected as the optimal statistical model based on the results of known control loci of grape berry color traits. Many of the associated SNPs identified in this study were in accordance with the previous QTL analyses using biparental mapping. The grape skin color locus was found to be associated with a mybA transcription factor on chromosome 2. Two strong and distinct association signals associated with berry development periods were found on chromosome 16. Most candidate genes of the interval were highlighted as receptor-like protein kinase. For berry weight, significant association loci were identified on chromosome 18, as previously known, and on chromosome 19 and chromosome 17, as newly mapped. Berry flesh texture was newly located on chromosome 16; candidate genes in the interval were related to calcium. Berry flavor was determined on chromosome 5. Genomic regions were further investigated to reveal candidate genes. In this work, we identified interesting genetic determinants of grape berry-related traits. The identification of the markers closely associated with these berry traits may be useful for grape molecular breeding.

Mixing it up – wheat cultivar mixtures can increase yield and buffer the risk of flowering too early or too late

Abstract Mixtures of wheat cultivars of different duration can potentially balance the yield-reducing risks of frost, heat and terminal drought. Cultivar mixtures with contrasting duration were tested across three experiments in Western Australia. Experiment 1 consisted of three sowing dates (early, mid and late), experiment 2 consisted one sowing date and experiment 3 consisted of two sowing dates (early and late). The three experiments and the multiple sowing dates created differences in the exposure to frost, heat and terminal drought risk. Seven treatments were established in each environment, consisting of three commercially-available cultivars (long, mid and short-duration); together with each of the two- and three -cultivar mixtures of these cultivars. In experiment 1 yields of the single cultivars showed the expected pattern with the long duration cultivar having the highest yield when sown early and the short duration cultivar having the higher yield when sown late. There were few differences in yield in experiments 2 and 3. Only a single treatment, a mixture of the long and mid-duration cultivars, was either the highest yielding or not significantly different from the highest yielding across all environments. In experiment 1 there was evidence of over-yielding with the mean of all the mixtures being 6.4% greater (P = 0.043) than the mean of the individual cultivars across the three sowing dates. This research has demonstrated that wheat cultivar mixtures can stabilise the combined risks of frost, heat and drought stress in frost and heat-prone dryland environments, providing growers with a strategy to manage these uncertain risks.

Image-based tracking of ripening in wheat cultivar mixtures: A quantifying approach parallel to the conventional phenology

Developing the quantitative methods independent of the conventional qualitative phenology is a vital necessity for evaluating the temporal trends in the crop growth cycle, particularly in the heterogeneous canopies of cultivar mixtures. A digital camera was used to take ground-based nadir images during two years (2014–15 and 2015–16) of a field experiment conducted at the School of Agriculture, Shiraz University, Iran, for monitoring and quantifying the ripening trends in wheat cultivar mixtures with different ripening patterns grown under two irrigation conditions. The experimental treatments consisted of 4 early- to middle-ripening wheat cultivars and their 10 mixtures, under post-well- and deficit-irrigated conditions, arranged in a randomized complete block design with 3 replicates. Then the images were processed and three image-derived indices including CC (canopy cover), GR [(G-R)/G; RGB color system], and CCGR (CC × GR) were used as the quantifying criteria. The declining trends of these indices during ripening showed strong fits to binomial equations, based on which simple prediction models were suggested and validated. Furthermore, the split linear trends and their slopes were estimated to assess the short-term variations. Some agronomic aspects were also evidenced using the mixtures-monoculture diversions, and the relationship between CC and GR. The frameworks evaluated appear to provide reliable and simple solutions for quantifying the crop temporal trends parallel to the conventional phenology.

Warm-Season Grass Monocultures and Mixtures for Sustainable Bioenergy Feedstock Production in the Midwest, USA

Biomass yield and adaptability to a broad range of environments are important characteristics of dedicated energy crops for sustainable bioenergy feedstock production. In addition to yield potential, the role of species diversity on ecosystem services is also growing in importance as we seek to develop sustainable feedstock production systems. The objective of this study was to compare the biomass yield potential of the commercially available germplasm of native warm-season grasses in monocultures and in blends (mixture of different cultivars of the same species) or mixtures of different species across an environmental gradient (temperature and precipitation) in the Midwest, USA. Warm-season grasses including switchgrass (Panicum virgatum L.), big bluestem (Andropogon gerardii Vitman), indiangrass (Sorghastrum nutans [L.] Nash), sideoats grama (Bouteloua curtipendula [Michx.] Torr.) and Miscanthus × giganteus (Greef and Deu.) were planted in 2009. Biomass was annually harvested from 2010 through 2015 for Urbana, IL and Mead, NE but only in 2010 and 2011 for Ames, IA. The effect of species in monocultures and mixtures (or blends) on biomass yields was significant for all locations. In monocultures, the annual biomass yields averaged over a 6-year period were 11.12 Mg ha−1 and 10.98 Mg ha−1 at Urbana and Mead, respectively, while the annual biomass yield averaged over a 2-year period was 7.99 Mg ha−1 at Ames, IA. Also, the annual biomass yields averaged across the different mixtures and blends at each location were 10.25 Mg ha−1, 9.88 Mg ha−1, and 7.64 Mg ha−1 at Urbana, Mead, and Ames, respectively. At all locations, M. × giganteus and ‘Kanlow N1’ produced the highest biomass yield in monocultures while mixtures containing switchgrass and big bluestem had the greatest mixture yield. The results from this multi-environment study suggest mixtures of different species provided no yield advantage over monocultures for bioenergy feedstocks in Illinois and Nebraska and both systems consistently produced biomass as long as April–July precipitation was near or above the average precipitation (300 mm) of the regions.

Pest suppression in cultivar mixtures is influenced by neighbor-specific plant-plant communication.

Increased plant genotypic diversity in crop fields can promote ecosystem services including pest control, but understanding of mechanisms behind herbivore population responses to cultivar mixtures is limited. We studied aphid settling on barley plants exposed to volatiles from different cultivars, aphid population development in monocultures and two-cultivar mixtures, and differences in volatile composition between studied cultivars. Aphid responses to one cultivar in a mixture were neighbor-specific and this was more important for pest suppression than the overall mixture effect, aphid colonization patterns, or natural enemy abundance. Aphid populations decreased most in a mixture where both cultivars showed a reduced aphid-plant acceptance after reciprocal volatile exposure in the laboratory, and reduced population growth compared to monocultures in the field. Our findings suggest that herbivore population responses to crop genotypic diversity can depend on plant-plant volatile interactions, which can lead to changes in herbivore response to individual cultivars in a mixture, resulting in slower population growth. The impact of plant-plant interaction through volatiles on associated herbivore species is rarely considered, but improved understanding of these mechanisms would advance our understanding of the ecological consequences of biodiversity and guide development of sustainable agricultural practices. Combining cultivars in mixtures based on how they interact with each other is a promising strategy for sustainable pest management.

Mosaics, mixtures, rotations or pyramiding: What is the optimal strategy to deploy major gene resistance?

Once deployed uniformly in the field, genetically controlled plant resistance is often quickly overcome by pathogens, resulting in dramatic losses. Several strategies have been proposed to constrain the evolutionary potential of pathogens and thus increase resistance durability. These strategies can be classified into four categories, depending on whether resistance sources are varied across time (rotations) or combined in space in the same cultivar (pyramiding), in different cultivars within a field (cultivar mixtures) or among fields (mosaics). Despite their potential to differentially affect both pathogen epidemiology and evolution, to date the four categories of deployment strategies have never been directly compared together within a single theoretical or experimental framework, with regard to efficiency (ability to reduce disease impact) and durability (ability to limit pathogen evolution and delay resistance breakdown). Here, we used a spatially explicit stochastic demogenetic model, implemented in the R package landsepi, to assess the epidemiological and evolutionary outcomes of these deployment strategies when two major resistance genes are present. We varied parameters related to pathogen evolutionary potential (mutation probability and associated fitness costs) and landscape organization (mostly the relative proportion of each cultivar in the landscape and levels of spatial or temporal aggregation). Our results, broadly focused on qualitative resistance to rust fungi of cereal crops, show that evolutionary and epidemiological control are not necessarily correlated and that no deployment strategy is universally optimal. Pyramiding two major genes offered the highest durability, but at high mutation probabilities, mosaics, mixtures and rotations can perform better in delaying the establishment of a universally infective superpathogen. All strategies offered the same short‐term epidemiological control, whereas rotations provided the best long‐term option, after all sources of resistance had broken down. This study also highlights the significant impact of landscape organization and pathogen evolutionary ability in considering the optimal design of a deployment strategy.