Variety Mixtures Research Articles

Physical Properties of Three Varieties of High-Oil Canola and One Variety of Low-Oil Canola

<abstract> <bold><sc>Abstract.</sc></bold> Seed major and minor axes of three canola varieties with high oil content (45H29 at 8%, 10%, and 12% moisture content wet basis, and Invigor 5440 and Nex4 105 at 10% moisture content) and one low-oil canola variety (5525 Clearfield at 10% moisture content) were measured at room temperature. Bulk density, angles of repose, and coefficients of friction against four structural surfaces were determined for two varieties of high-oil canola (Invigor 5440 and Nex4 105) and for mixtures of them (at ratios of 1:1, 1:2, and 2:1) at four moisture contents (8%, 10%, 12%, and 14%). The same physical properties were determined for the third high-oil canola (45H29) and for the low-oil canola (5525 Clearfield) at three moisture contents (8%, 10%, and 12%). The four structural surfaces were galvanized steel, plywood, wood-floated concrete, and steel-troweled concrete. Major and minor axes of 45H29 increased with increasing moisture content. Oil content did not affect the axes of canola seeds. Bulk densities were significantly different between Invigor 5440 and Nex4 105. Mixtures of the high-oil canola varieties had bulk density values between those of the canola varieties that were used in the mixtures. Bulk density decreased with increasing oil content. Angles of repose depended more on canola variety and surface properties than on oil content. The coefficient of friction against structural surfaces was not significantly affected by moisture content but was affected by oil content. Bins used to store low-oil canola could also be used to store high-oil canola.

Simple sequence repeat-based identification of Canadian malting barley varieties

Perry, D. J., Fernando, U. and Lee, S-J. 2014. Simple sequence repeat-based identification of Canadian malting barley varieties. Can. J. Plant Sci. 94: 485–496. Practical and reliable means to identify barley varieties are required to provide assurances in segregated grain handling and for quality control in the malting and brewing industry. A set of 10 simple sequence repeat (SSR) markers was selected to differentiate among malting barley varieties grown in Canada. Modification of some PCR primers permitted assembly into two five-marker multiplexes that may be examined simultaneously using an electrophoresis-based DNA analyzer. These markers were surveyed in multiple individual kernels of each of 48 barley varieties grown in Canada, including 31 malting varieties and 17 popular feed varieties. Variation within varieties was common and three general categories of intra-variety polymorphism were recognized: (1) primary biotypes, which were characterized by a fairly even distribution of two alleles at one or more marker loci and complete mixture of allele combinations among the polymorphic loci; (2) uncommon, distinctly different variants; and (3) putative recent SSR mutations. Differentiation among varieties was complete with the exception of one pair of related six-row feed varieties (AC Rosser and AC Ranger) that was indistinguishable and one group of three very closely related two-row malting varieties (CDC Kendall, CDC PolarStar and Norman) that, on an individual-kernel basis, were only partially distinguishable using these markers. Simple, rapid individual-kernel DNA preparation methods were also developed for use in conjunction with the multiplexed markers to provide a convenient, effective and relatively inexpensive tool that may be used for barley variety identification, purity analysis or quantification of variety mixtures.

ASSESSING VARIETY MIXTURE OF CONTINUOUS SPRING WHEAT (TRITICUM AESTIVUM L.) ON GRAIN YIELD AND FLOUR QUALITY IN NORTHEAST CHINA

Wheat (Triticum aestivum L.) variety mixtures represent a relatively unexplored avenue for maintaining yield and improving flour quality. A field experiment was conducted to examine the responses of three spring wheat varieties in pure variety and in variety mixtures under continuous cropping in Northeast China. Three modern spring wheat varieties, along with a three-variety mixture and a two-variety mixture of equal proportions, were planted during the growing seasons of 2006 to 2009. The mixtures were chosen mainly to have complementary traits of yield potential and grain quality. Wheat yield was not affected by continuous cropping but by growing conditions, varieties and variety mixture. Yield stability of 3-variety mixture exceeded that of the pure varieties. The 3-variety mixture consistently out-yielded the means of the respective components (mid-components), with a mean advantage of 0.17 t ha -1 over the different growing conditions. Variety mixture offers greater yield advantages over lower-yield but good-quality variety and improves dough rheological properties and some chemical properties over the higher-yield variety. The 1:1:1 variety mixtures have greater environmental plasticity and potential application in improving flour quality than pure varieties and are therefore recommended for use to Northeast China’s wheat growers even in the absence of severe disease.

Potential of Cowpea Variety Mixtures to Increase Yield Stability in Subsistence Agriculture: Preliminary Results

CowpeaVigna unguiculata(L.) Walp. is an important leafy vegetable and grain legume in Uganda. Unlike in commercial agriculture, where variety mixtures are known to give higher and more stable yields, the performance of cowpea variety mixtures in subsistence agriculture is little known. Mixtures containing up to four cowpea varieties were subjected to all possible 2-way, 3-way, and 4-way combinations. These cowpea varieties and mixtures were grown at three locations in Soroti and Kumi districts in order to assess the relative mixture effect, defined as: Mixture effect (%) = (mixture yield − pure line component average)/pure line component average × 100. Yield data was subjected to one-way ANOVA using the GLM procedure of SYSTAT. PLABSTAT was used to generate ecovalence (Wi) values as a measure of stability with low ecovalence values indicating higher stability. The total cowpea dry matter (DM) yield was in the range of 3.7–6.7 g/m2(leaf) and 12.1–36.7 g/m2(grain), respectively. Mixture effects were between −9.3–14.0% (leaf) and −30.3–21.9% (grain). Yield stability spanned Wi= 0.06–5.30 (leaf) andWi= 4.45–894.84 (grain). The results suggested that yields of cowpea variety mixtures grown in marginal environments were more stable than of single varieties but not all mixtures yielded more than single varieties.

Optimizing Experimental Design Using the House Mouse (Mus musculus L.) as a Model for Determining Grain Feeding Preferences

There is little research evaluating flavor preferences among wheat varieties. We previously demonstrated that mice exert very strong preferences when given binary mixtures of wheat varieties. We plan to utilize mice to identify wheat genes associated with flavor, and then relate this back to human preferences. Here we explore the effects of experimental design including the number of days (from 1 to 4) and number of mice (from 2 to 15) in order to identify designs that provide significant statistical inferences while minimizing requirements for labor and animals. When mice expressed a significant preference between 2 wheat varieties, increasing the number of days (for a given number of mice) increased the significance level (decreased P-values) for their preference, as expected, but with diminishing benefit as more days were added. However, increasing the number of mice (for a given number of days) provided a more dramatic log-linear decrease in P-values and thus increased statistical power. In conclusion, when evaluating mouse feeding preferences in binary mixtures of grain, an efficient experimental design would emphasize fewer days rather than fewer animals thus shortening the experiment duration and reducing the overall requirement for labor and animals.

First Report of Five Viruses Infecting Potatoes in Tanzania.

Potato (Solanum tuberosum L.) is an increasingly important food and cash crop in Tanzania (3). Potato production is concentrated in the southern highlands and mainly carried out by smallholder farmers. A certification system for seed potatoes does not exist in the country. Currently, there is little information about viruses infecting potatoes in Tanzania. In October through December 2011, occurrence of the most common, globally distributed potato viruses, Potato leaf roll virus (PLRV), Potato virus A (PVA), M (PVM), S (PVS), Y (PVY), and X (PVX) (1), was determined in 219 potato plants in 16 fields ranging from 0.2 to 1 ha. Potato crops, 1 to 3 months old, consisted sometimes of mixtures of varieties identified as Arika, Chekundu, Kagiri, Kiazi, Kikondo, Sasamka, or Tigoni by farmers, but could not be independently confirmed. The fields were located in the regions of Mbeya (Kawetele, Kikondo, Umalia, Uyole) and Rungwe (Mwakaleli) ~100 km apart in the southern highlands. Virus-like symptoms observed in most fields included yellowish-green mosaic, leaf rolling, and veinal necrosis. Symptoms in tubers were not studied. Leaves from 10 symptomatic and three symptomless plants were sampled from each field and tested by double antibody sandwich (DAS)-ELISA (1) at ARI-Uyole. Virus-specific antibodies and negative and positive controls were used according to the supplier's instructions (Science and Advice for Scottish Agriculture, Edinburgh, United Kingdom). PVS and PLRV were detected in 55% and 39% of the samples, respectively, and in all fields sampled. PVX and PVM were found in most fields and in 14% and 5% of the samples, respectively. PVA and PVY were only detected in two localities. Co-infection with PVS and PLRV was detected in 14% of the tested plants. Mixed infections involving three or four viruses were detected in 5% of the plants. A total of 20 samples, which were collected from Uyole and Mwakeleli and found to be ELISA-positive for one or several viruses, were pressed on FTA cards (GE Healthcare, Buckinghamshire, United Kingdom), transported to University of Helsinki, and analyzed by reverse-transcription PCR (2) using virus-specific primers designed to amplify the coat protein (CP) encoding region. All ELISA-positive samples tested positive by reverse transcriptase (RT)-PCR. Four and five samples ELISA-negative for PVX or PVA, respectively, were positive when tested by RT-PCR, suggesting that the actual incidence of these viruses may be higher than detected by DAS-ELISA. The PCR products from three to five samples per virus were sequenced without cloning, which reconfirmed detection of PLRV, PVA, PVS, PVX, and PVM (GenBank Accession Nos. KC866618 through KC866622, respectively) and revealed few if any differences among isolates of the viruses. The CP sequences were compared with viruses from other countries and continents (4). CP similarities suggested that viruses might have been introduced to Tanzania through potato trade or through introducing new cultivars without adequate indexing for viruses. These results suggest the need for the development of virus control schemes in potato crops, including the nascent, domestic certified seed potato production in Mbeya.

Are there any Advantages of Genetically Diverse Material in Cereal Breeding Programmes for Organic Farming?

Employing cereal genetic variation in breeding programmes for organic farming is one of the ways to create varieties with higher stability and adaptability. The aim of the study was to compare and evaluate grain yield, quality and other traits of barley pure lines, hybrid populations, variety mixtures, as well as winter wheat hybrid populations and parental varieties, in organic and conventional farming systems. Significant evidence for advantages of using barley mixtures and populations under organic and conventional management systems was not observed. More advantages with respect to yield, adaptability to unfavourable environments and TGW were observed for breeding lines selected for suitability to organic conditions. Combination of distinctive genotypes may result in a fairly stable mixture with average yield above the components. The study confirmed that resistance of winter wheat genotypes to abiotic stress is one of the significant traits that is closely connected with limitation of the wheat productivity in both growing conditions. Yield and grain quality value of winter wheat genotypes was lower under organic conditions compared to a conventional growing system. Advantages of populations were not observed under organic conditions, but significantly higher yield, in comparison to parental varieties, was obtained for two populations in conventional conditions. In general, the yield of populations was intermediate to that of the parents.

Control of foliar diseases in barley: towards an integrated approach

Barley is one of the world’s most important crops providing food and related products for millions of people. Diseases continue to pose a serious threat to barley production, despite the use of fungicides and resistant varieties, highlighting the impact of fungicide resistance and the breakdown of host plant resistance on the efficacy of control measures. This paper reviews progress towards an integrated approach for disease management in barley in which new methods may be combined with existing measures to improve the efficacy of control in the long-term. Advances have been made in genetic mapping of resistance (R) genes and in identifying novel sources of genes in wild barley populations and land races. Marker assisted selection techniques are being used to pyramid R genes to increase the durability of resistance. Elicitors to induce host resistance used in combination with fungicides can provide effective disease control in the field and could delay the evolution of fungicide insensitivity. Traits that may contribute to disease tolerance and escape have been identified and the extent of genetic variation within barley germplasm is being determined. Tools are being developed to integrate the above methods via an assessment of the risk of economic injury occurring from disease to guide decisions on the requirement for fungicide treatment. Barriers exist to the adoption of integrated management approaches from growers and end-users further down the supply chain (e.g. acceptance of variety mixtures) and policy incentives from government may be required for it to be taken up in practice.

Effects of inter-varietal diversity, biotic stresses and environmental productivity on grain yield of spring barley variety mixtures

Varietal seed mixtures tend to increase and stabilize crop yields, yet their application is sparse. Large-scale cultivation of variety mixtures may require a better understanding of how inter-varietal interactions and their interaction with the environment may influence the grain yield of variety mixtures relative to their component varieties. For this purpose, six variety mixtures of spring barley and 14 component varieties were grown in each of 17 trial environments. A total of 28 observed and a priori plant characteristics, including grain yield, disease severity and weed competitiveness, were derived for each component variety in each trial. The relationship between inter-varietal diversity of each characteristic and the mixing effect on grain yield was analysed. Additionally, various types of yield stability were estimated and compared among mixtures and component varieties. One mixture out-yielded all of its component varieties in almost half of the trial environments. Inter-varietal diversity in grain yield potential correlated significantly with mixing effect, as did straw length diversity when weighted with weed pressure. The grain yields of most mixtures were more stable across environments than their component varieties when accounting also for the general response to environmental productivity. Hence, most mixtures adapted slightly better to environmental productivity and were less sensitive to environmental stress than their component varieties. We conclude that the efficacy of variety mixtures may be enhanced by mixing relatively high-yielding varieties differing in responsiveness to environmental productivity.

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

Performance of spring barley varieties and variety mixtures as affected by manure application and their order in an organic crop rotation

In order to obtain a high and stable yield of organic spring barley, production should be optimized according to the specific environment. To test the performance of spring barley varieties under varying cropping conditions, a field experiment was carried out in 2003 and 2004 in a six-field mixed organic crop rotation. We investigated the choice of variety, the order in a rotation, and the application of manure (slurry and farmyard manure; 0 to 120 total-N ha−1) on grain yields of six selected varieties with different characteristics grown in either pure stands or in two spring barley mixtures, each consisting of three varieties. Average grain yield of the barley varieties varied between 3.3 t DM ha−1 and 4.1 t DM ha−1. Grain yields of the two mixtures were 4.0 and 3.6 t DM ha−1, respectively. The varieties/mixtures interacted with crop order and year. Foliar diseases were more severe in the barley following grass-clover with large annual differences in the individual diseases. Despite different rooting depths and nutrient uptake patterns, there was no interaction between variety/mixture and the manure input regarding grain yield. In the 1st year after grass-clover, one of the two mixtures gave higher grain yield than the average yield of the individual varieties in the mixture. This was not the case in the 4th year after grass-clover and for the second variety mixture. Thus, although the present results did not indicate that some barley varieties were better adapted to conditions with low manure input than others, variety mixtures that give a robust and stable organic production may potentially be developed.

Grain yield increase in cereal variety mixtures: A meta-analysis of field trials

Plant ecology theory predicts that growing seed mixtures of varieties (variety mixtures) may increase grain yields compared to the average of component varieties in pure stands. Published results from field trials of cereal variety mixtures demonstrate, however, both positive and negative effects on grain yield. To investigate the prevalence and preconditions for positive mixing effects, reported grain yields of variety mixtures and pure variety stands were obtained from previously published variety trials, converted into relative mixing effects and combined using meta-analysis. Furthermore, available information on varieties, mixtures and growing conditions was used as independent variables in a series of meta-regressions. Twenty-six published studies, examining a total of 246 instances of variety mixtures of wheat ( Triticum aestivum L.) and barley ( Hordeum vulgare L.), were identified as meeting the criteria for inclusion in the meta-analysis; on the other hand, nearly 200 studies were discarded. The accepted studies reported results on both winter and spring types of each crop species. Relative mixing effects ranged from −30% to 100% with an overall meta-estimate of at least 2.7% ( p < 0.001), reconfirming the potential of overall grain yield increase when growing varieties in mixtures. The mixing effect varied between crop types, with largest and significant effects for winter wheat and spring barley. The meta-regression demonstrated that mixing effect increased significantly with (1) diversity in reported grain yields, (2) diversity in disease resistance, and (3) diversity in weed suppressiveness, all among component varieties. Relative mixing effect was also found to increase significantly with the effective number of component varieties. The effects of the latter two differed significantly between crop types. All analyzed models had large unexplained variation between mixing effects, indicating that the variables retrievable from the published studies explained only a minority of the differences among mixtures and trials.

Effects of planting arrangement on the occurrence of tungro virus infection in mixtures of resistant and susceptible varieties

Effects of planting arrangement on the occurrence of tungro virus infection in mixtures of resistant and susceptible varieties

Does resource complementarity or prevention of lodging contribute to the increased productivity of rice varietal mixtures in Yunnan, China?

We conducted an experiment in Gejiu, Yunnan Province of China during the wet season of 2002 to examine the importance of resource complementarity and prevention of lodging in the fast-spreading practice of growing rice varietal mixtures in China to suppress rice blast disease and its associated damage. The hybrid rice variety Shanyou 63 and the glutinous or sticky rice variety Huangkenuo were used to study intra- and inter-varietal competition in the rice intercropping system. The experiment was laid out as a randomized complete block design in four replications with pure stands and mixtures of both varieties at different total planting densities and mixing ratios. In half of the pure stand treatments of glutinous rice a metal frame was installed to prevent lodging. The results showed that resource complementarity between the two rice varieties, resulting from niche differentiation, was marginal and did not greatly enhance the productivity of the rice varietal mixtures. In contrast, prevention of lodging of glutinous rice was identified as an important additional advantage of growing these rice varieties in mixture.

Performance and stability of performance of spring wheat variety mixtures in organic and conventional management systems in western Canada

SUMMARYWheat (Triticum aestivum L.) variety mixtures represent a relatively unexplored avenue for maintaining and stabilizing yield for both organic and conventional producers. The present study examined the responses of three Canadian western red spring wheat varieties in sole crop and in variety mixtures to varying levels of simulated and natural competition, as well as environmental stress at one conventionally and two organically managed locations in central Alberta, Canada, between 2003 and 2005. Three modern hard red spring wheat varieties (Superb, semi-dwarf; AC Intrepid, early maturing and 5600HR, tall), along with 13 two- and three-way variety mixtures, were planted under two levels of simulated weed (Brassica juncea L.) competition at each of the eight location-years. The B. juncea weed competition treatment decreased yields at all locations. Overall yield was lowest at the certified organic farm and highest under conventional management. Sole-crop semi-dwarf Superb and all three Superb–Intrepid mixture entries consistently yielded among the highest, regardless of management system, testing location or competition treatment. The 1:1 and 1:2 Superb–Intrepid mixture entries were the most stable of all entries tested. Early season vigour was strongly associated with yield, with the strongest correlation occurring under low-moisture, low-nutrient, high-competition conditions at the certified organic farm. Spring wheat variety mixtures may provide greater stability with little or no reduction in yield, while providing greater competitive ability.

Developments in breeding cereals for organic agriculture

The need for increased sustainability of performance in cereal varieties, particularly in organic agriculture (OA), is limited by the lack of varieties adapted to organic conditions. Here, the needs for breeding are reviewed in the context of three major marketing types, global, regional, local, in European OA. Currently, the effort is determined, partly, by the outcomes from trials that compare varieties under OA and CA (conventional agriculture) conditions. The differences are sufficiently large and important to warrant an increase in appropriate breeding. The wide range of environments within OA and between years, underlines the need to try to select for specific adaptation in target environments. The difficulty of doing so can be helped by decentralised breeding with farmer participation and the use of crops buffered by variety mixtures or populations. Varieties for OA need efficient nutrient uptake and use and weed competition. These and other characters need to be considered in relation to the OA cropping system over the whole rotation. Positive interactions are needed, such as early crop vigour for nutrient uptake, weed competition and disease resistance. Incorporation of all characteristics into the crop can be helped by diversification within the crop, allowing complementation and compensation among plants. Although the problems of breeding cereals for organic farming systems are large, there is encouraging progress. This lies in applications of ecology to organic crop production, innovations in plant sciences, and the realisation that such progress is central to both OA and CA, because of climate change and the increasing costs of fossil fuels.

The enset (Ensete ventricosum) gardens of Sidama: composition, structure and dynamics of a traditional poly-variety system

The composition and structure of 300 enset gardens from 10 different locations in Sidama were examined. Average size of the gardens was 0.74 ha. The gardens are composed of mixtures of various named enset varieties and different groups recognisable on the basis of ‘sex’ (male and female) and use (cooking and processing). The gardens exhibit high diversity, with a given garden containing up to 24 varieties (mean = 8.2). However, the components are not represented equally. Typically, the gardens consisted of one or two very abundant varieties and a much larger number of less common ones. Enset gardens are dynamic because the number and composition of varieties and different types changed from garden to garden, from location to location and across time. Their composition, structure and dynamics have been influenced by human, socio-economic factors (farm size, land per capita, cropping patterns and size of livestock), temporal circumstances and landscape elements (elevation) in which they are found. The nature, characteristics, organization and functions of Sidama enset gardens are outlined and the importance of maintaining mixtures of varieties for farmers is discussed.

Estimates of phenotypic diversity and breeding potential of Ethiopian wheats

An Ethiopian wheat collection consisting of 293 entries, tetraploids and hexaploids was scored for 14 qualitative or quantitative characters each having two or more phenotypic classes. The pattern of variation of the individual characters varied from region to region. Some characters showed localized concentrations, and others did not have any clear pattern of distribution. A clinal pattern of variation was observed for resistance to powdery mildew. The frequency of resistance increased from north to south, with a concentration of intermediate resistance on the Arussi-Bale Highlands. A low level of diversity was observed for glume pubescence, and an intermediate to a high level of diversity for all the other characters. All estimates of regional diversity were high, and there was no significant difference among them. The genetic potential and the breeding value of Ethiopian wheats are discussed, and variety mixtures are indicated as possible method of natural gene conservation.

Winter wheat variety mixtures as an alternative for sustainable and ecological farming

Winter wheat variety mixtures as an alternative for sustainable and ecological farming