Cultivar Mixtures Research Articles

Symbiotic interaction between a mixture of Bradyrhizobium japonicum strains and different soybean cultivars

Aim. To study the mutual relations between different soybean cultivars and two Bradyrhizobium japonicum strains after mixed inoculation, to evaluate the impact of the introduced microorganisms on the local rhizobial communities in soil, the formation and functioning symbiotic systems, and productivity of soybean. Methods. Microbiological and serological methods; field experiment, gas chromatography and mathematical-statistical methods. Results. A small- plot field experiment demonstrated that the use of a mixture of B. japonicum 46 and B. japonicum КВ11 strains pro- moted a more even distribution of the local and introduced rhizobia in the nodule populations of 12 soybean cultivars of different geographic origin. There was no domination of particular strains in the nodules, and the symbiotic systems formed were more balanced than the control without inoculation. After inoculation of the above-mentioned mixture, in most cultivars there was a considerable increase in the number of nodules (10–45 % more) and their mass (11–86 % increase). There was also an increase in the level of symbiotic nitrogen fixation with 1.2–4.2 times and an increase in the weight of grain per plant by 6–29 % (depending on the cultivar). The efficiency of a mixture of B. japonicum 46 and КВ11 strains in a preparation Rizogumin was confirmed in extensive field trials with soybean on an area of about 60 thousand ha in different regions of Ukraine. In the background of the local populations of the soybean nodulating bacteria in the areas, the application of the formulated mixture of the two rhizobia strains ensured a stable increase by 15–33 % in the soybean yield as compared with the control without the inoculation. Conclusions. A novel approach was investigated, which lies in the application of a mixture of B. japonicum 46 (genetic group USDA 6) and B. japoni- cum КВ11 (genetic group USDA 123) strains for different soybean cultivars inoculation. Combining these two strains and their introduction into agrocenoses ensured the formation of a balanced symbiotic systems (without clear domina- tion of some strains in the nodules). This was expressed in an intensified nodulation, symbiotic nitrogen fixation, and increased yield of different cultivars of soybeans by 15–33 % as compared to the control (without inoculation).

Wheat cultivar mixtures increase grain yield under varied climate conditions

Scaling current cereal production to meet the globally increasing food demand will be a challenge under climate change. Previous studies have shown that crop diversification, such as intercropping, can increase crop yield, stability, resource-use efficiency and resistance to both biotic and abiotic stresses in agroecosystems. However, more evidence is needed to explain the influence of inter-annual climate variations on crop yield in the context of genetic diversity. Here, we conducted a field experiment over four years in the North China Plain to test the effect of genetic diversity on yield under varied climate conditions. We compared the performance of eight winter wheat cultivars in monocropping with that of mixed cropping of two (mixture-2), four (mixture-4), and eight (mixture-8) cultivars. Our results showed that the yields of all cultivar mixtures were higher than those of their component cultivars in monocropping from 2017 to 2020. In particular, the grain yields of mixture-4 and mixture-8 were significantly increased by 7.37% and 5.94% in the drier years (2017 and 2019), compared with that of the highest yield of local cultivar (LY502). From 2017 to 2020, yield components in wheat mixed cropping had synergetic effects that could offset the tradeoffs among them and obtained an optimized combination at population level. Moreover, the yield stability of all mixtures was higher than the weighted means of monocultures averaged across the four years. The cultivation of mixtures of wheat cultivars effectively alleviated the negative effect of high temperature stress on 1000-grain weight, and improved grain water use efficiency in the drier years. Our findings showed that enhancing wheat genetic diversity at population level can effectively promote grain yield under drought and high temperature, which can be considered as an ecological approach to cope with global climate change towards food security.

Genetic diversity assessment and genome-wide association study reveal candidate genes associated with component traits in sweet potato (Ipomoea batatas (L.) Lam)

The Korean sweet potatoes were bred by various cultivars introduced from Japanese, American, Porto Rico, China, and Burundi. This issue enriched their genetic diversity but also resulted in a mixture of cultivars. For genotyping, we collected and sequenced 66 sweet potato germplasms from different localities around Korea, including 36 modern cultivars, 5 local cultivars, and 25 foreign cultivars. This identified 447.6 million trimmed reads and 324.8 million mapping reads and provided 39,424 single nucleotide polymorphisms (SNPs) markers. Phylogenetic clustering and population structure analysis distinctly classified these germplasms into 5 genetic groups, group 1, group 2, group 3, group 4, and group 5, containing 20, 15, 10, 7, and 14 accessions, respectively. Sixty-three significant SNPs were selected by genome-wide association for sugar composition-related traits (fructose, glucose, and total sugars), total starch, amylose content, and total carotenoid of the storage root. A total of 37 candidate genes encompassing these significant SNPs were identified, among which, 7 genes were annotated to involve in sugar and starch metabolism, including galactose metabolism (itf04g30630), starch and sucrose metabolism (itf03g13270, itf15g09320), carbohydrate metabolism (itf14g10250), carbohydrate and amino acid metabolism (itf12g19270), and amino sugar and nucleotide sugar metabolism (itf03g21950, itf15g04880). This results indicated that sugar and starch are important characteristics to determine the genetic diversity of sweet potatoes. These findings not only illustrate the importance of component traits to genotyping sweet potatoes but also explain an important reason resulting in genetic diversity of sweet potato.

Crop Diversification to Control Rust in Faba Bean Caused by Uromyces viciae-fabae

Uromyces viciae-fabae is a highly specific biotrophic fungus that causes faba bean rust, one of the major diseases affecting this crop. We have assessed the feasibility of using intercropping (faba bean mixed with either pea, wheat or barley) or mixtures of susceptible and resistant cultivars to control rust both under field and controlled conditions. The results of four field intercropping experiments showed a significant reduction in rust severity on faba bean when intercropped with barley (average 22% reduction) but not with the other combinations. This reduction was also confirmed in studies under controlled conditions. The barrier effect of barley appears as the main mechanism explaining rust suppression. Additional experiments under controlled conditions showed that intercropping with barley did not influence the N content of faba bean and that different levels of N nutrition had no impact on rust severity in any case. The cultivar mixture field experiments showed that rust severity in the susceptible cultivar decreased as the proportion of the resistant cultivar in the mixture increased. The importance of the barrier effect of the resistant cultivars was determined in an experiment under controlled conditions. It can be concluded that crop diversification offers great potential to reduce rust in faba bean.

Volatile interactions between specific undamaged barley cultivars affect aphid feeding behavior and performance

Recent studies have demonstrated that cultivar mixtures can reduce aphid plant acceptance and population development. It is still unknown as to which underlying mechanisms may contribute to this phenomenon. We investigated the effects of volatile interactions between undamaged barley cultivars on aphid feeding behavior and performance in the laboratory. Spring barley (Hordeum vulgare L.) cultivar Salome was exposed to volatiles from Fairytale (SeF), Anakin (SeA), or clean air (Se0). We used an electrical penetration graph to test the effect of exposure to neighbor volatiles on the feeding behavior and performance of bird cherry-oat aphids (Rhopalosiphum padi L.). We also assessed aphid relative growth rate, intrinsic rate of increase, and development time on exposed and unexposed Salome plants. Aphids spent significantly longer time on epidermis and mesophyll plant tissues on SeF than Se0, and no difference was observed between SeA and Se0. Significant decreases in the duration of phloem ingestion and phloem sustained ingestion were recorded in SeF showing that volatile-induced effects cause difficulty for aphids to feed. However, no differences in these variables were detected between SeA and Se0. We also observed reduced aphid relative growth rate and intrinsic rate of increase on SeF compared to Se0 and SeA. Our study demonstrated that, in a specific combination, exposure of one barley cultivar to volatiles from another one can change aphid feeding behavior and performance, probably due to changes in host plant properties/quality. Our results provide an insightful explanation of mechanisms responsible for the reduced aphid population development previously observed in the field.

First Report of Pyricularia oryzae Causing Gray Leaf Spot of Perennial Ryegrass (Lolium perenne) in Oregon

Gray leaf spot of perennial ryegrass ( Lolium perenne), caused by Pyricularia oryzae, is a devastating turfgrass disease in many regions of the United States. In 2021, P. oryzae was detected for the first time in Oregon, causing disease on a perennial ryegrass athletic field. This report describes the occurrence of gray leaf spot and pathogenicity testing on the original infected cultivar mixture. The confirmation of this pathogen in Oregon could have management implications for turfgrass managers of the state.

Effects of Pea (Pisum sativum L.) Cultivars for Mixed Cropping with Oats (Avena sativa L.) on Yield and Competition Indices in an Organic Production System.

The benefits of cereal-legume mixed cropping is a sustainable agricultural practice. However, knowledge of the genotypic differences of semi-leafless pea varieties is not enough to help them compete with cereals. In this study, the effects of Lithuania's newest Pisum sativum cultivars ('Egle DS' and 'Lina DS') and, for comparison, a control cultivar ('Jūra DS') established with Avena sativa in mixed cropping system were investigated. Three years of field trials (2018, 2019 and 2020) with four experiments involved three different mixtures of each field pea cultivar with oat. The aboveground biomass of mixed cropped new field pea cultivars was found to be significantly higher: biomass of cultivars 'Egle DS' increased by 17.0% and 'Lina DS' by 7.2% on average compared with the control cultivar 'Jūra DS'. For the mixed cropping system, statistically greater total aboveground biomass was observed with plant ratios of 50% pea + 50% oat and 60% pea + 40% oat compared to peas monocultures. Mixed cropped oat was the dominant species in all tested mixture compositions; however, the highest total grain yield of mixed crops was obtained when new pea 'Lina DS' and 'Egle DS' cultivars were included in the mixtures compared with the control cultivar. The new pea cultivar 'Egle DS' had a greater effect on protein content compared to other tested pea cultivars. In the new pea cultivars 'Lina DS' and 'Egle DS', the higher photosynthetic capacity and aboveground biomass of mixed cropped pea with oat showed mixture effects in the mixed cropped system and could increase total yield compared with pea monoculture. Generally, the new pea cultivars displayed a greater Land Equivalent Ratio (LER) value, resulting in the greatest yield among the mixtures on average for all three years and all four experiments. Future research could optimize the effects of pea cultivar mixtures with cereals to further improve the yield of organic mixed cropping systems.

The genetic diversity-productivity effect in wheat cultivar mixtures at multiple levels

There is abundant evidence that biodiversity promotes ecosystem functions in various ecosystems, and recent syntheses stress the need to promote biodiversity in agroecosystems to enhance productivity and stability in a changing climate. Yet, how we can better manipulate genetic biodiversity to achieve these goals in intensive cropping systems is not well understood. Using a large-scale intensive wheat cropping experiment, we studied the effects of wheat genetic diversity on productivity at multiple levels. The results show that the overyielding effects were achieved in mixed cropping at the population, cultivar, and individual levels, which can be considered as a promising way to enhance food security. In addition, wheat cultivar mixtures were temporally more stable than the monocultures. These point to a combination of the positive and negative effects, including complementarity, selection, and competition, in mixtures that affect the cultivars' collective strategies, which are determined by both the complexity of the mixture and the environmental conditions. Furthermore, we found nonmonotonic genetic diversity-productivity relationships that are consistent at multiple levels, suggesting that increasing the number of cultivars in mixed cropping does not always promote productivity. Our results can be directly interpreted for policy and management in ecological cropping systems.

Multiple scenarios for sexual crosses in the fungal pathogen Zymoseptoria tritici on wheat residues: Potential consequences for virulence gene transmission

Little is known about the impact of host immunity on sexual reproduction in fungal pathogens. In particular, it is unclear whether crossing requires both sexual partners to infect living plant tissues. We addressed this issue in a three-year experiment investigating different scenarios of Zymoseptoria tritici crosses according to the virulence (‘vir’) or avirulence (‘avr’) of the parents against a qualitative resistance gene. Co-inoculations (‘vir × vir’, ‘avr × vir’, ‘avr × avr’) and single inoculations were performed on a wheat cultivar carrying the Stb16q resistance gene (Cellule) and a susceptible cultivar (Apache), in the greenhouse. We assessed the intensity of asexual reproduction by scoring disease severity, and the intensity of sexual reproduction by counting the ascospores discharged from wheat residues. As expected, disease severity was more intense on Cellule for ‘vir × vir’ co-inoculations than for ‘avr × vir’ co-inoculations, with no disease for ‘avr × avr’. However, all types of co-inoculation yielded sexual offspring, whether or not the parental strains caused plant symptoms. Parenthood was confirmed by genotyping (SSR markers), and the occurrence of crosses between (co-)inoculated and exogenous strains (other strains from the experiment, or from far away) was determined. We showed that symptomatic asexual infection was not required for a strain to participate in sexual reproduction, and deduced from this result that avirulent strains could be maintained asymptomatically “on” or “in” leaf tissues of plants carrying the corresponding resistant gene for long enough to reproduce sexually. In two of the three years, the intensity of sexual reproduction did not differ between the three types of co-inoculation in Cellule, suggesting that crosses involving avirulent strains are not anecdotal. We discuss the possible mechanisms explaining the maintenance of avirulence in Z. tritici populations and the potential impact of particular resistance deployments such as cultivar mixtures for limiting resistance breakdown.

Mixtures of Commercial Lentil Cultivars Show Inconsistent Results on Agronomic Parameters but Positive Effects on Yield Stability

Cultivar mixtures are a useful tool to enhance cultivated biodiversity to buffer crop biotic and abiotic stresses. There are multiple pieces of evidence of mixture advantages in terms of pathogen control and increase in yield amount, stability and quality. Lentil represents a founder crop in the Mediterranean, yet it experiences strong yield fluctuations in the face of abiotic stresses. The present study aims to assess the mixing ability of four Italian commercial lentil lines in terms of yield amount and stability, nodule number, total lentil biomass and sensitivity to weeds. Since there is very limited information on lentil genotype traits, two-, three- and four-cultivar mixtures were designed with a trait-blind approach and compared to sole cultivars. The nodule number was mainly influenced by cultivar and weather; no interaction between cultivars was observed. Treatments were differently sensitive to weeds, but the effect of spatial heterogeneity prevailed over that of the cultivar. The average yield stability of all mixtures was significantly higher than pure stands, but in terms of yield amount, individual mixtures either outperformed or were outperformed by pure stands. Against our expectations, cultivar mixtures showed the most advantages in the most productive year: likely, the reason lies in the supposed low genetic diversity of commercial lentil lines in Italy. We encourage further research, taking into account the diversity of Italian lentil landraces, in order to gain a broader genetic base for the implementation of a trait-based approach, which may lead to better-performing mixtures.

Mixtures of rye cultivars to improve forage yield, distribution and nutritive value

The search for forage cultivars that provide higher yields with quality in periods of forage shortage, whether in isolated or mixed management, is essential for livestock stability. Thus, the objective was to evaluate the forage performance and nutritive value of rye cultivars mixtures (BRS Progresso, BRS Serrano and Temprano) from different production cycles compared to the isolated management of rye, dual-purpose wheat cvs. (BRS Tarumã and BRS Pastoreio) and black oat cv. Embrapa 139 Neblina as controls. The experiment was conducted at a randomized complete block design, with four rye associations and the isolated cultivation of wheat, oat, and rye. Dry matter (DM) yield and nutritive value, such as content of neutral detergent fiber (NDF), acid detergent fiber (ADF), and crude protein (CP) content were evaluated for each cut and total values. There was difference (P<0.001) in total DM, the highest yield was in single cultivation as well as mixtures with Temprano. BRS Serrano and BRS Progresso and their mixture had lower leaf blade percentage in the total DM. There were differences (P<0.05) in NDF concentration (55.1 to 70.60%), ADF (15.2 to 34.7%), and CP (27.4 to 36.8%) levels along harvests. Among cultivars, Temprano showed the highest proportion of leaf blades and total DM yield.

Exploiting heterosis of semi-hybrids and heterogeneity of cultivar mixtures to enhance alfalfa crop performance

Alfalfa semi-hybrids (alias free-hybrids or chance-hybrids) of genetically-distant populations may display heterosis, but their actual value is substantially unknown. Higher biomass yield may also derive from heterogeneity in cultivar mixtures. This study aimed to compare three two-way and one three-way semi-hybrids and three two-way physical mixtures issued from putative heterotic populations selected from elite Italian germplasm, Egyptian germplasm and a semi-erect pool from Eastern Europe, Canada and Spanish Mielga, their source populations, and a reference synthetic variety selected from the same pool as the Italian population. We assessed three-year dry-matter biomass yield, final persistence, adaptability and yield stability across eight densely-planted managed environments obtained by the factorial combination of two summer water amounts by two soil types by pure stand (PS) or mixed stand (MS) with forage grasses. Heterogeneity increased yield by 17.0% on average while affecting persistence inconsistently. The advantage over mid-parent value averaged 35.1% for yield and 16.3% for persistence of two-way semi-hybrids, while being 35.6% for yield and 21.1% for persistence of the three-way semi-hybrid. The top-yielding semi-hybrid, issued from Italian and Egyptian material, out-yielded both parent populations, and exhibited 7.4% higher mean yield and greater competitive ability than the reference synthetic variety. PS or MS condition affected plant material × environment interaction for yield or persistence more than summer water availability or soil type, but interaction patterns were mainly quantitative with increasing variation in MS. No manifest plant material variation emerged for yield stability. Based on our results, a semi-hybrid variety type can be valuable for alfalfa.

WINTER WHEAT MIXTURES INFLUENCE GRAIN RHEOLOGICAL AND MIXOLAB QUALITY

This study aims to investigate the effect of a mixture of winter wheat varieties on grain rheological characteristics and the quality of wheat flour analyzed by Mixolab. In the 2019-2020 growing season, a small plots experiment was carried out in an organically certified field in the Czech Republic. The experiment was conducted by randomized complete block design with three replicates, four winter wheat (Triticum aestivum L.) varieties with four mixtures of the same varieties in equal proportions. Based on the results, the expected grain yield was not achieved. The quality of wheat productivity was significantly different among treatments in terms of protein content, wet gluten, sedimentation value, and falling number (P < 0.001). Protein content ranged between 8.04% and 9.85%, mixtures of Butterfly + Lorien and Illusion + Lorien were higher in protein than Illusion and Vanessa varieties and their combination. The highest wet gluten was found under mixtures of Butterfly + Lorien varieties (19.34%) while sowing Butterfly variety gave the highest Zeleny test and falling number compared to other treatments. Butterfly + Lorien and Butterfly + Vanessa mixtures obtained good results for falling number at 250.67 and 272.67 seconds. There were significant differences in rheological quality parameters of winter wheat varieties analyzed by Mixolab including stability, weakening of protein, and starch (P < 0.01 and P < 0.001, except slope gamma). Although the observed benefits were limited to grain yield, mixtures of individual cultivars appear to be a potential tool to improve overall crop performance (grain quality).

Mixing trait-based corn (Zea mays L.) cultivars increases yield through pollination synchronization and increased cross-fertilization

Abiotic stress such as high temperature at flowering is one of many conditions reducing yield of corn (Zea mays L.). Mixing corn cultivars with diverse functional traits increases within-crop diversity and provides a potential means of mitigating yield losses under stress conditions. We conducted a three-year field study to investigate the effects of cultivar mixtures on kernel setting rate, pollen sources, and yield. This study consisted of six treatments, including two high temperature-tolerant (HTT) monocrops of WK702 and DH701, two high temperature-sensitive (HTS) monocrops of DH605 and DH662, and two HTT–HTS mixtures of WK702-DH605 and DH701-DH662. The anthesis–silking interval (ASI) was 0.9–1.6 days shorter in mixtures than in monocrops. Kernel setting rate was increased in mixtures (86.4%–88.7%) compared with those in monocrops (74.7%–84.1%) as a result of synchrony and complementarity of pollination. Grain yields of the HTT–HTS mixtures increased by 13.3%–18.7%, equivalent to 1169 to 1605 kg ha−1, in comparison with HTS corn monocrops. The results of SSR markers showed that cross-fertilization percentage in corn cultivar mixtures ranged from 29.3% to 47.8%, partially explaining yield improvement. Land equivalent ratio (LER) was 1.12 for corn mixtures and the partial land equivalent ratio (e.g., > 0.5) showed the complementary benefits in corn mixtures. The results indicated that mixing corn cultivars with diverse flowering and drought-tolerance traits increased yields via pollination synchrony.

Host mixtures for plant disease control: Benefits from pathogen selection and immune priming.

Multiline and cultivar mixtures are highly effective methods for agroecological plant disease control. Priming‐induced cross protection, occurring when plants are challenged by avirulent pathogen genotypes and resulting in increased resistance to subsequent infection by virulent ones, is one critical key to their lasting performance against polymorphic pathogen populations. Strikingly, this mechanism was until recently absent from mathematical models aiming at designing optimal host mixtures. We developed an epidemiological model to explore the effect of host mixtures composed of variable numbers of single‐resistance cultivars on the equilibrium prevalence of the disease caused by pathogen populations polymorphic for virulence complexity. This model shows that a relatively large amount of resistance genes must be deployed to achieve low disease prevalence, as pathogen competition in mixtures tends to select for intermediate virulence complexity. By contrast, priming significantly reduces the number of plant genotypes needed to drop disease prevalence below an acceptable threshold. Given the limited availability of resistance genes in cultivars, this mechanism of plant immunity should be assessed when designing host mixtures.

The impact of wheat cultivar mixtures on virulence dynamics in Zymoseptoria tritici populations persists after interseason sexual reproduction

AbstractThis study follows on from a previous study showing that binary mixtures of wheat cultivars affect the evolution of Zymoseptoria tritici populations within a field epidemic from the beginning (t1) to the end (t2) of a growing season. Here, we focused on the impact of interseason sexual reproduction on this evolution. We studied mixtures of susceptible and resistant cultivars (carrying Stb16q, a recently broken‐down resistance gene) in proportions of 0.25, 0.5 and 0.75, and their pure stands. We determined the virulence status of 1440 ascospore‐derived strains collected from each cultivar residue by phenotyping on seedlings. Virulence frequencies in the ascospore‐derived population were lower in mixtures than in pure stands of the resistant cultivar, especially in the susceptible cultivar residues, as at t2, revealing that the impact of mixtures persisted until the next epidemic season (t3). Surprisingly, after sexual reproduction the avirulence frequencies on the resistant cultivar residues increased in mixtures where the proportion of the susceptible cultivar was higher. Our findings highlight two epidemiological processes: selection within the pathogen population between t1 and t2 driven by asexual cross‐contamination between cultivars (previous study) and sexual crosses between avirulent and virulent strains between t2 and t3 driven by changes in the probabilities of physical encounters (this study). Mixtures therefore appear to be a promising strategy for the deployment of qualitative resistances, not only to limit the intensity of Septoria tritici blotch epidemics, but also to reduce the erosion of resistances by managing evolution of the pathogen population at a pluriannual scale.

Wheat grain width: a clue for re-exploring visual indicators of grain weight

BackgroundMean grain weight (MGW) is among the most frequently measured parameters in wheat breeding and physiology. Although in the recent decades, various wheat grain analyses (e.g. counting, and determining the size, color, or shape features) have been facilitated, thanks to the automated image processing systems, MGW estimations have been limited to using few number of image-derived indices; i.e. mainly the linear or power models developed based on the projected area (Area). Following a preliminary observation which indicated the potential of grain width in improving the predictions, the present study was conducted to explore more efficient indices for increasing the precision of image-based MGW estimations. For this purpose, an image archive of the grains was processed, which were harvested from a 2-year field experiment carried out with 3 replicates under two irrigation conditions and included 15 cultivar mixture treatments (so the archive was consisted of 180 images including more than 72,000 grains).ResultsIt was observed that among the more than 30 evaluated indices of grain size and shape, indicators of grain width (i.e. Minor & MinFeret) along with 8 other empirical indices had a higher correlation with MGW, compared with Area. The most precise MGW predictions were obtained using the Area × Circularity, Perimeter × Circularity, and Area/Perimeter indices. Furthermore, it was found that (i) grain width and the Area/Perimeter ratio were the common factors in the structure of the superior predictive indices; and (ii) the superior indices had the highest correlation with grain width, rather than with their mathematical components. Moreover, comparative efficiency of the superior indices almost remained stable across the 4 environmental conditions. Eventually, using the selected indices, ten simple linear models were developed and validated for MGW prediction, which indicated a relatively higher precision than the current Area-based models. The considerable effect of enhancing image resolution on the precision of the models has been also evidenced.ConclusionsIt is expected that the findings of the present study, along with the simple predictive linear models developed and validated using new image-derived indices, could improve the precision of the image-based MGW estimations, and consequently facilitate wheat breeding and physiological assessments.

The Central Role of Soil Organic Matter in Soil Fertility and Carbon Storage

The aim of the paper is to give an overview on the chemistry of soil organic carbon (SOC) affecting nutrient availability, the emission of greenhouse gases and detoxifying harmful substances in soil. Humic substances represent the stable part of SOC, accounting for between 50 and more than 80% of organically bound carbon in soil. Humic substances strongly affect the soil solution concentration of several plant nutrients and may increase P-, Fe-, and Cu- solubility, thereby increasing their plant availability. Soil organic carbon, mainly humic substances, can detoxify monomeric Al in acid soils, can strongly bind toxic heavy metals, making them unavailable to the plant roots, and may strongly bind a vast variety of harmful organic pollutants. Increasing SOC is an important goal in agriculture. The inclusion of mixtures of semi-perennial plant species and cultivars may strongly increase SOC and humic substance content in soils. To increase SOC, farmyard manure and its rotted or composted forms are superior compared to the separate application of straw and slurry to soil. The storage of carbon, mainly in organic form, in soils is very important in the context of the emission of greenhouse gases. Worldwide, soils release about 10 times more greenhouse gases compared to fossil fuel combustion. Small increments in SOC worldwide will strongly affect the concentration of atmospheric CO2. The public discussion on soil fertility and greenhouse gas emissionshas been politically controlled in a way that leaves the important and positive contribution of soil organic carbon and mainly humic substances partly misinterpreted and partly underestimated.

Harnessing the Potential of Wheat-Pea Species Mixtures: Evaluation of Multifunctional Performance and Wheat Diversity.

Species mixtures and heterogeneous crop populations are two promising approaches for diversified ecological cropping systems with increased resilience and reduced dependency on external inputs. Inter- and intraspecific diversity were evaluated in combination using 15 wheat (Triticum aestivum) entries, including line cultivars and heterogeneous populations (HPs), from central Europe and Hungary and one winter pea cultivar under organic conditions. Monocultures and wheat mixtures were evaluated multi-functionally for yield, quality, land use efficiency, crop protection, and wheat entry traits. Mixtures increased cereal grain quality, weed suppression, resource use efficiency, yield gain, and reduced lodging. Effects were stronger in 2018/19, which were characterized by dry and nutrient-poor conditions than in 2019/20 when nutrient levels were higher. Wheat entries varied considerably in protein content and yield in both mixtures and monocultures. Under higher nutrient availability, entry-based variation was reduced in both systems, and peas were suppressed. Because of low disease pressure, the wheat entries varied little in terms of disease protection services, and mixture effects on the disease were low. The multi-criteria framework identified stability of yield, yield gains, and quality under high environmental variability of mixtures as clear agronomic advantages with HPs being considerably more stable than line cultivars. Some line cultivars outperformed the HPs in either protein content or yield across environments but not both simultaneously. Trait analysis revealed a possible link between harvest index and reduced competition in mixtures, which can increase yield performance in specific line cultivars. System cultivar interactions were generally very low and highly dependent on environmental conditions. We conclude that while cultivar breeding for mixtures can be successful in monocultures, high environmental variation highlights the necessity of evaluating cultivars in mixtures. In addition, use of intraspecific diversity within interspecific mixed cropping systems can be a valuable addition to further improve mixture performance and its stability under increasing environmental stresses due to climate change.

Plant chemical diversity and its frequency have distinct but complementary effects on insect foraging

Abstract Variability in plant traits such as nutrients and defences can challenge insect herbivores searching for a host plant. Cultivar mixtures are designed to harness this variability to reduce herbivore damage in agroecosystems but have had mixed success. We examine how the spatial frequency of plant trait variability—a fundamental but rarely examined feature of variability—influences insect foraging and survival. We released a generalist herbivore into monocultures of two chemically distinct tomato varieties or dicultures of the two varieties with two spatial frequencies of chemical diversity and tracked herbivore movement and feeding damage. We found the pattern of herbivore feeding damage was more spatially concentrated in both diculture treatments than in either monoculture, indicating that the presence of chemical diversity, regardless of its spatial frequency, influences herbivore foraging. In contrast, total amount of feeding damage was reduced by 25% in dicultures where genotypes were grouped compared to monocultures or dicultures with alternating genotypes, which had similar levels of damage. Similarly, herbivore survival in the low‐frequency diculture was nearly half the survival in the high‐frequency diculture or monocultures. Synthesis and applications. Whereas previous work investigates how the amount of chemical diversity in a plant population influences insect ecology, our results indicate that local spatial distribution of diversity is equally important. A key implication of this work is the potential to design cultivar mixtures spatially, at the movement scale of target organisms, to create more effective pest management landscapes and promote sustainable agriculture.