Evolutionary Plant Breeding Research Articles

Deep genotyping reveals specific adaptation footprints of conventional and organic farming in barley populations—an evolutionary plant breeding approach

Sustainable food production for a growing world population will pose a central challenge in the coming decades. Organic farming is among the feasible approaches to achieving this goal if the yield gap to conventional farming can be decreased. However, uncertainties exist to which extend—and for which phenotypes in particular—organic and conventional agro-ecosystems require differentiated breeding strategies. To answer this question, a heterogeneous spring barley population was established between a wild barley and an elite cultivar to examine this question. This initial population was divided into two sets and sown one in organic and the other in conventional managed agro-ecosystems, without any artificial selection for two decades. A fraction of seeds harvested each year was sown the following year. Various generations, up to the 23th were whole-genome pool-sequenced to identify adaptation patterns towards ecosystem and climate conditions in the allele frequency shifts. Additionally, a meta-data analysis was conducted to link genomic regions’ increased fitness to agronomically related traits. This long-term experiment highlights for the first time that allele frequency pattern difference between the conventional and organic populations grew with subsequent generations. Further, the organic-adapted population showed a higher genetic heterogeneity. The data indicate that adaptations towards new environments happen in few generations. Drastic interannual changes in climate are manifested in significant allele frequency changes. Particular wild form alleles were positively selected in both environments. Clustering these revealed an increased fitness associated with biotic stress resistance, yield physiology, and yield components in both systems. Additionally, the introduced wild alleles showed increased fitness related to root morphology, developmental processes, and abiotic stress responses in the organic agro-ecosystem. Concluding the genetic analysis, we demonstrate that breeding of organically adapted varieties should be conducted in an organically managed agro-ecosystem, focusing on root-related traits, to close the yield gap towards conventional farming.

Approaches and Advantages of Increased Crop Genetic Diversity in the Fields

Crop genetic diversity is the most important factor for a long-term sustainable production system. Breeding and production strategies for developing and growing uniform and homogenous varieties have created many problems. Such populations are static and very sensitive to unpredictable stresses. In Nepal, more than 80% of the seed system is informal, which has contributed greatly to creating and maintaining genetic diversity within the field. This paper aims to assess and present the approaches and advantages of increased crop genetic diversity in the fields, based on the experiences of implementing on-farm conservation activities carried out in Nepal for last two decades. Some of the evidence has been derived from an ongoing evolutionary plant breeding (EPB) project being implemented in Nepal. The information is supplemented with field assessments, focus group discussion, and a literature review. The major approaches to increase crop genetic diversity are evolutionary plant breeding, cultivar mixture, landrace enhancement, informal seed systems, the bulk method, diversifying the seed sources, participatory plant breeding, open pollination, etc. EPB and cultivar mixture are very simple and effective approaches to increase crop genetic diversity at field level. The involvement of farmers in these approaches helps to accelerate the population improvement, maintaining the higher degree of genetic diversity. The major advantages of increased crop genetic diversity are seed maintenance by farmers themselves, minimal risk of crop failure, resilience to unpredictable stresses, increased amount of diversified nutrition, production increment, ease of producing organically, etc. However, there are some issues and problems associated with mixtures and intra-varietal diversity; for example, not being able to harvest by machine, maturing at a different date, difficulty in maintaining seeds and registration, etc. Crop genetic diversity should be considered as a sustainable approach for a climate-resilient and self-dependent production system. The higher the genetic diversity in farming land, the more chance of receiving multiple benefits in the agriculture system.

Yield Stability and Quality of Wheat (Triticum spp.) and Barley (Hordeum Vulgare) Populations Evolving under Different Microenvironments: A review

Climate change, human population growth, human health and food security, safety, and sovereignty all demand that the role of biodiversity in plant breeding be revisited. From a biological standpoint, it is possible that populations of diverse plants developed by evolutionary plant breeding will be able to handle the majority of these major issues. Water stress and soil nutrient deficiency may have a negative impact on wheat (Triticum spp.) and barley (Hordeum vulgare) yields and qualities. Drought-tolerant wheat cultivars with high yield and quality potential and improved grain protein content must be developed if food security is to be maintained. Wheat and barley (Triticum spp. and Hordeum vulgare, respectively) are the focus of this research, which aims to examine the stability of evolutionary populations (EPs) in the face of stressful and changeable settings. It's also important to look at how evolved populations stack up against improved varieties in terms of yield and its components. There has not been much progress in making wheat and barley more resistant to drought, especially in Jordan, where the problem is felt the most.

High-throughput estimation of allele frequencies using combined pooled-population sequencing and haplotype-based data processing

BackgroundIn addition to heterogeneity and artificial selection, natural selection is one of the forces used to combat climate change and improve agrobiodiversity in evolutionary plant breeding. Accurate identification of the specific genomic effects of natural selection will likely accelerate transfer between populations. Thus, insights into changes in allele frequency, adequate population size, gene flow and drift are essential. However, observing such effects often involves a trade-off between costs and resolution when a large sample of genotypes for many loci is analysed. Pool genotyping approaches achieve high resolution and precision in estimating allele frequency when sequence coverage is high. Nevertheless, high-coverage pool sequencing of large genomes is expensive.ResultsThree pool samples (n = 300, 300, 288) from a barley backcross population were generated to assess the population's allele frequency. The tested population (BC2F21) has undergone 18 generations of natural adaption to conventional farming practice. The accuracies of estimated pool-based allele frequencies and genome coverage yields were compared using three next-generation sequencing genotyping methods. To achieve accurate allele frequency estimates with low sequence coverage, we employed a haplotyping approach. Low coverage allele frequencies of closely located single polymorphisms were aggregated into a single haplotype allele frequency, yielding 2-to-271-times higher depth and increased precision. When we combined different haplotyping tactics, we found that gene and chip marker-based haplotype analyses performed equivalently or better compared with simple contig haplotype windows. Comparing multiple pool samples and referencing against an individual sequencing approach revealed that whole-genome pool re-sequencing (WGS) achieved the highest correlation with individual genotyping (≥ 0.97). In contrast, transcriptome-based genotyping (MACE) and genotyping by sequencing (GBS) pool replicates were significantly associated with higher error rates and lower correlations, but are still valuable to detect large allele frequency variations.ConclusionsThe proposed strategy identified the allele frequency of populations with high accuracy at low cost. This is particularly relevant to evolutionary plant breeding of crops with very large genomes, such as barley. Whole-genome low coverage re-sequencing at 0.03 × coverage per genotype accurately estimated the allele frequency when a loci-based haplotyping approach was applied. The implementation of annotated haplotypes capitalises on the biological background and statistical robustness.

CONCEPT AND RATIONALE OF EVOLUTIONARY BARLEY BREEDING UNDER CLIMATE CHANGE IN JORDAN

In this study, we reviewed the climate changing and the impact on crop production, and evolutionary breeding as adaptation key to crop resilience. The increasing climate change impact on the agriculture system has renewed interest to the broadest possible germplasm base for a resilient and sustainable food system. Heterogeneous populations developed through evolutionary plant breeding could be the ideal solution to reduce the effects of environment variability on cereal crop planted under low-input conditions.The study assessed the genetic basis of adaptation of a barley population which evolved in different rainfed locations and years in Jordan without any human selection as suggests model of plant breeding strategy to improve food security, nutrition, income and resilience of smallholder farmers in the dryland regions in the climate change scenarios. The study suggests that the breeder can shift the undesirable traits in evolutionary populations by practicing individual selection for specific adaptations, or individual selection from populations showing wide adaptations and high stability. On the other hand, the breeder can overcome the undesirable traits by keeping the highest variations within the population by seed sieving to remove small seed and plant mowing for tallest head.

Utilization of Evolutionary and Participatory Plant Breeding Approaches for Rapid Adoption: The Case of Durum Wheat, Central Parts of Ethiopia

Wheat has been almost the first crop domesticated through evolution, natural selection, hybridization, and artificial selection; directly contributed to the adaptation and development of modern varieties. The role of participatory and evolutionary plant breeding in combination can be utilized as a new approach to cope with the complexity of wheat variety adoption and climate change. This method can be also curiously used to improve food security and nutritional value for the rapidly growing human population to reduce the dependence on inorganic agricultural inputs. The experiment was conducted with the objective; to evaluate different mixtures of durum wheat under local climate to improve the variety adoption process and enhance resilience to climate change. Field trials were conducted on 27 heterogeneous durum wheat populations (mixtures) over two locations for one year to test the use of evolutionary plant breeding combined with participatory farmers' selection for local climate adaptation, nutritional value, and grain yield. The result showed that gender preferences associated with important adaptation traits like spike color, head compactness, and plant height are effective for determining high-yielding wheat variety and founded with better adaptation to changing climate. During an evaluation by farmers; mixtures exhibited compact head (MTOPTI_UNS (25), M10_UNS (27), M10_MS (9), and MTIG_FS (12), white-colored head (M10_UNS (27), M10_MS (9), MTOPTI_UNS (9), MTIG_FS (12), M217_UNS (19), and mixtures with tall plants resistant to lodging (MTOPTI-UNS (25), were more preferred and selected by farmers. Broadly, according to the experiment, mixtures (evolutionary populations) have comparative advantages over modern varieties for enhancing resilience to climate change, nutrition, and better adaptation.

Utilization of Evolutionary Plant Breeding Increases Stability and Adaptation of Winter Wheat Across Diverse Precipitation Zones

Evolutionary plant breeding (EPB) is a breeding method that was used to create wheat (Triticum aestivum L.)-evolving populations (EP), bi-parental and composite-cross populations (BPPs and CCPs), by using natural selection and bulking of seed to select the most adaptable, diverse population in an environment by increasing the frequency of favorable alleles in a heterogeneous population. This study used seven EPs to evaluate EPB in its ability to increase the performance of agronomic, quality, and disease resistance traits and adaptability across different precipitation zones. The populations were tested in field trials in three diverse locations over 2 years. Least significant differences showed the EPs performance was dependent on their pedigree and were statistically similar and even out-performed some of their respective parents in regards to grain yield, grain protein concentration, and disease resistance. Stability models including Eberhart and Russel’s deviation from Regression (S2di), Shukla’s Stability Variance (σi2), Wricke’s Ecovalance (Wi), and the multivariate Additive Main Effects and Multiplicative Interaction (AMMI) model were used to evaluate the adaptability of the EPs and their parents. The BPPs and CCPs demonstrated significantly greater stability over the parents across precipitation zones, confirming the capacity of genetically diverse EP populations to adapt to different environments.

Evolutionary Plant Breeding as a Response to the Complexity of Climate Change.

SummaryClimate change is one of the processes that have already overstepped the safe planetary boundaries, together with the rate of biodiversity loss and human interference with the nitrogen and phosphorus cycles. The three processes are related to agriculture and, as such, to both food safety and food security, and ultimately to human health. Adaptation to climate change is a difficult breeding objective because of its complexity, its unpredictability, and its location specificity. However, one strategy exists, which is based on a more dynamic use of agrobiodiversity in agriculture through the cultivation of evolutionary populations. In this review, we show how the translation into agricultural practice of nearly 100 years of research on evolutionary populations and mixtures is able to address the complexity of climate change while stabilizing yield, decreasing the use of most agrochemicals, thus reducing emissions and producing healthy food.

Concept and rationale of evolutionary plant breeding and its status in Nepal

Nepal has released and registered a total of 623 genetically uniform (mono genotyped) varieties. These varieties were developed by both conventional and classical plant breeding, biotech-assisted plant breeding, and participatory plant breeding methods. However, these varieties have been shown to vary in their yield performance over the years and locations. Smallholder farmers dominate agriculture with 53% of the land-owning households with their land holding size of less than 0.5 ha in Nepal. Farmers are increasingly losing their own saved seeds. There have been impacts of weather variability, often modern crop varieties are not available to suit with these changing conditions. Farmers are looking for crop varieties that can better adapt to these changing conditions, and seeds of which can be saved for the next season planting. Evolutionary Plant Breeding (EPB), which creates and maintains a high degree of genetic diversity (i.e. polymorphic population), is a choice for breeders and farmers for accelerating the development of climate resilient and sustainably high-performance crop varieties. In 2015, the National Gene Bank in Nepal started an EPB program for the local rice variety, Jumli Marshi with the objective of enhancing genetic conservation through creating a dynamic gene pool. An evolutionary population can be compared to a living gene bank, not only in line with bringing greater yield stability, but also greater diversity in aroma, nutritional value and quality. Evolutionary populations have the potential to produce higher yields and perform better than their local or improved counterparts in adverse, or stress conditions. Under stress conditions, evolutionary populations have also been shown to be more resistant to weeds, diseases and pests damage than homogenous crop populations. Based on the source of diversity used in EPB, two different types of populations- Composite Cross population, and Composite Mixtures, population are developed. With the exception of Europe, and only for some crops, existing seed policies do not favor such populations. Therefore, there is a need to revise seed regulations in order to allow the cultivation of a higher degree of genetic diversity.

Yield, yield stability and farmers’ preferences of evolutionary populations of bread wheat: A dynamic solution to climate change

The role of biodiversity in plant breeding needs to be reconsidered to cope with the complexity, location specificity and combined challenges of climate change, human population increase, human health and food security, safety and sovereignty. From a biological viewpoint, heterogeneous plant populations derived from evolutionary plant breeding may address most of these grand challenges. Field trials were conducted over four years and four locations under organic farming conditions to test the hypothesis that evolutionary populations planted in contrasting locations, evolve adapting to the local conditions and becoming distinct from one another. The experiment also included mixtures, landraces and a modern variety of bread wheat. The results show evidence of divergent selection for grain yield under the sole effect of natural selection by which the best performing evolutionary populations yielded as much or more than the commercial variety. Farmers' selection within one of the evolutionary populations was effective in improving yield and yield stability above those of the original population across years and locations. Farmers' preference was not always associated with grain yield and was not gender dependent. We conclude that evolutionary populations are able to gradually evolve, adapting to each environment in which their seed is multiplied, reaching high and stable yield levels thus ensuring income to farmers, both as seed and as grain.

Twenty Four Approaches for Conservation of Non-Orthodox Agricultural Plant Genetic Resources in Nepal

The conservation of plant genetic diversity underpins the future of agriculture, food and nutrition security and is critical to ensure the ability of future generations to cope with global environmental changes. The conservation efforts were more focused on orthodox crop species in Nepal before 2010. About 40% of agricultural plant genetic resources are non-orthodox, either recalcitrant/ intermediate type or vegetatively propagated plant species. Approaches for conservation of non-orthodox plant species differ from that of orthodox crops. Different conservation approaches have been established by National Agriculture Genetic Resources Center, Nepal for conserving non-orthodox agricultural plant species. We applied household survey, literatures survey, field survey, key informant survey and organized focus group discussion for assessing the different conservation approaches. A total of 24 approaches are being considered for conservation of non-orthodox plant species. Approaches under the ex-situ strategy are field genebank, botanical garden, city park, government farm, religious place, in-vitro culture and evolutionary plant breeding; under on-farm strategy are community field genebank, school field genebank, household field genebank, community/ public orchard, village level field genebank, geographical indication and participatory landrace enhancement, and under in-situ strategy are protected area, Ramsar site, world heritage site, community forest and legal protection for conserving non-orthodox plant species in Nepal. Field genebank is the very good approach, and it has been established in about 20 research stations. It should be extended to government farms and agriculture offices to conserve the local APGRs available in their respective command areas. Databases (passport and characterization) have been generated and will be available online to enhance the utilization in breeding, research and production.

Agronomic and quality characteristics of old, modern and mixture wheat varieties and landraces for organic bread chain in diverse environments of northern Italy

Wheat landraces and old varieties could have an important role for food security not only as source of gene readily available for breeders, but also because they perform well in marginal environments and are more resilient as compared to the modern cultivars. The Italian cereal sector suffers from lack of seed companies that breed specifically adapted varieties for organic and biodynamic farms. Participatory and evolutionary plant breeding (PPB and EPB) have been used in this research to (i) evaluate the agronomic characteristics of old, modern and mixture of varieties and landrace of bread wheat (Triticum aestivum spp.) and their adaptability to organic farming in hilly and mountainous areas; (ii) assess the technological, nutritional and functional properties of grains (rheological characteristic, macro and micro elements contents and antioxidants); (iii) explore the consumers’ preferences for breads obtained by old and modern varieties. Between five and seven old (Sieve, Verna, Gentil Rosso, Andriolo, Gambo di ferro, Frassineto and Abbondanza), two mixtures and four modern (Bolero, Blasco, Arabia and Bologna) varieties were tested for two years in between two and three organic farms (FARM1, FARM2 and FARM3) in hilly areas of Piedmont. Agronomic characteristic were strongly affected by locations and years. On average, Bologna, Abbondanza and Arabia, and the two mixtures were the highest yielding varieties. Flour strength (W) varied greatly ranging from 230 in 2011 for Andriolo to 38 in 2012 for Gambo di ferro. Gluten quality, expressed by GI, was found to be almost within the optimal range but was affected by the year. All six bread samples were acceptable to the 233 consumers who scored them, but the bread produced with old wheat varieties, particularly with Andriolo and Gambo di Ferro, was the preferred one. The old varieties and their mixtures yielded less than the modern varieties but with higher stability as shown by the inability of the modern varieties in FARM1 to survive the winter (they were not harvested) while the old varieties reached maturity showing higher robustness, Therefore, the use of old bread wheat varieties and their mixture, assessed with participatory and evolutionary plant breeding, could represent a strategy for local communities to cope with climate change while improving food security and food quality.

Morphological diversity in a barley composite cross-derived population evolved under low-input conditions and its relationship with molecular diversity: indications for breeding

SUMMARYIn order to reduce the environmental impact of agriculture and improve the resilience and sustainability of our food systems, there is an increasing interest in shifting from the present agricultural systems, which are characterized by high external inputs, to low-input productive systems characterized by high resilience and sustainability. Purposely developed varieties are needed for the latter. With the rapid disappearance of landraces, heterogeneous populations such as composite cross populations (CCPs) or line mixtures, developed through evolutionary plant breeding, could be the ideal source of breeding material for the development of new cultivars for low-input productive systems. Parental lines of CCPs should be selected among old breeding lines, varieties or landraces because the specific characteristics required for low-input or organic farming systems might have been lost during selection of modern varieties. In the current scenario of renewed interest in evolutionary plant breeding, the evolution of diversity in heterogeneous populations needs to be better investigated to maximize the advantages that can be obtained by their utilization.The present paper reports on the analysis of 88 barley plants chosen randomly from a CCP, namely AUT DBA (where AUT indicates autumn sowing and DBA is the acronym of the former Department) that was multiplied for 13 years under a low-input management system without any conscious human selection, aiming to investigate the morphological diversity still existing in the population and its potential value as source of breeding material for low-input/organic agriculture and understanding the traits that contributed to the adaptive success of certain groups of individuals.Eighteen plant and spike morphological traits were analysed using bi-dimensional spatial analysis, cluster analysis, non-parametric tests and multivariate approaches. Low lodging and loose smut damage were observed in the CCP where several individuals were superior to the best control for at least one of the four yield-related traits, namely spike weight, number of seeds per spike, weight of seeds in a spike and grain weight. Three morphological clusters were identified using cluster analysis. Clusters 2 and 3 grouped the largest number of CCP individuals which, compared with those in cluster 1, were characterized mainly by heavier spikes with higher seed number, taller culms and early flowering. Interestingly, the plant architecture of all the controls was different from that of the most frequent genotypes in the CCP, showing that low-input systems may require a plant architecture different from the one usually considered as the most suitable for high-input systems. Taking advantage of results from Raggiet al. (2015), phenotypic data were also analysed according to individual genetic group assignment. Results suggest that plant height at the beginning of stem elongation, and days to heading, together with traits related to culm and leaf morphology, could have played a significant role in determining the success of plants from genetic group D, which is the group most represented in the CCP.According to the wide range of morphological diversity existing in the AUT DBA and the high percentage of lines that show favourable combinations of different traits, this population could be a useful gene-pool from which to select lines for breeding activities. Even though further use of the CCP for breeding purposes may be limited by its possible evolution, there are different ways of manipulating the CCP to counteract the undesirable changes without great economic and/or technical efforts. The high number of multi-locus genotypes and the evolutionary responses observed in AUT DBA show that the prediction that phenotypic micro-evolution in natural systems may be limited by low genetic variances in harsh environments and low selection pressure in good environments is not necessarily true for low-input systems.

Evolution of a barley composite cross-derived population: an insight gained by molecular markers

SUMMARYMany studies have highlighted the continuously increasing need for genetic diversity in the field; nonetheless, plant breeding is still predominantly generating uniform cultivars. Evolutionary plant breeding offers the possibility of reconciling agro-biodiversity, high yields and adaptation to climate change. However, the diversity that can be conserved in heterogeneous populations, its evolution and the potential of ‘evolutionary breeding’ in the actual scenario of climate change is still a matter of debate. In the present study, a total of 147 barley individuals, 56 from seven parental populations (PPs) and 91 from the composite cross-derived population (CCP) resulting from their inter-crossing were genotyped at 22 Simple Sequence Repeat (SSR) loci with the objective of obtaining insights into how genetic diversity evolved in the field during 13 years of multiplication. A total of 92 different alleles were detected in the PP and 100 in the CCP. Results showed that the composite individuals are grouped into five major clusters differing for both the number of individuals and the relative level of genetic diversity. The mean values of the most common descriptors of genetic diversity were not significantly different between the parental and the composite populations. However, analysis of molecular variance showed some degree of differentiation between the two populations suggesting that evolution occurred during the years of multiplication and selection effects were detected for some loci. The SSR loci detected as putatively under selection in the present study have already been reported as co-localized with quantitative trait loci for adaptedness traits or tagging genes related to abiotic stress response. According to the current results, evolving crop populations, which have the capability of adapting to the conditions under which they are grown, can be useful in conserving genetic diversity and as sources of genes for breeding purposes in particular in the actual scenario of climate change.

GM Crops, Organic Agriculture and Breeding for Sustainability

The ongoing debate about the use of genetically-modified (GM) crops in agriculture has largely focused on food safety and genetic contamination issues. Given that the majority of GM crops have been produced to respond to the problem of crop yield reductions caused by diseases, insects and weeds, the paper argues that in those cases, the currently used GM crops are an unstable solution to the problem, because they represent such a strong selection pressure, that pests rapidly evolve resistance. Organic agriculture practices provide a more sustainable way of producing healthy food; however, the lower yields often associated with those practices, making the resultant healthy food more expensive, open the criticism that such practices will not be able to feed human populations. Evolutionary plant breeding offers the possibility of using the evolutionary potential of crops to our advantage by producing a continuous flow of varieties better adapted to organic systems, to climate change and to the ever changing spectrum of pests, without depending on chemical control.

Evolutionary Plant Breeding in Cereals—Into a New Era

In evolutionary plant breeding, crop populations with a high level of genetic diversity are subjected to the forces of natural selection. In a cycle of sowing and re-sowing seed from the plant population year after year, those plants favored under prevailing growing conditions are expected to contribute more seed to the next generation than plants with lower fitness. Thus, evolving crop populations have the capability of adapting to the conditions under which they are grown. Here we review the current state of research in evolutionary plant breeding and concentrate on the ability of evolving plant populations to deal with stressful, variable, and unpredictable environments. This resilience of evolving plant populations is seen as a major advantage under the predicted threats faced by agriculture such as global climate change. We have conducted an analysis of the strengths, weaknesses, opportunities and threats of this breeding approach and suggest how its concept can be broadened and expanded. Given the current legal restrictions for realizing the potential of evolutionary plant breeding, we call for a change in legislation to allow evolving crop populations to enter agricultural practice on a larger scale.

Evolution, plant breeding and biodiversity

This paper deals with changes in biodiversity during the course of evolution, plant domestication and plant breeding. It shows than man has had a strong influence on the progressive decrease of biodiversity, unconscious at first and deliberate in modern times. The decrease in biodiversity in the agricultures of the North causes a severe threat to food security and is in contrasts with the conservation of biodiversity which is part of the culture of several populations in the South. The concluding section of the paper shows that man could have guided evolution in a different way and shows an example of participatory plant breeding, a type of breeding which is done in collaboration with farmers and is based on selection for specific adaptation. Even though participatory plant breeding has been practiced for only about 20 years and by relatively few groups, the effects on both biodiversity and crop production are impressive. Eventually the paper shows how participatory plant breeding can be developed into ‘evolutionary plant breeding’ to cope in a dynamic way with climate changes.

Evolutionary plant breeding for low input systems

Heritable variation is at the heart of the process of evolution. However, variation is restricted in breeding for uniform crop populations using the pedigree line approach. Pedigree lines are successful in agriculture because synthetic inputs are used to raise fertility and control weeds, pests and diseases. An alternative method promoted for exploring the value of variation and evolutionary fitness in crops is to create composite cross populations. Composite cross populations are formed by assembling seed stocks with diverse evolutionary origins, recombination of these stocks by hybridization, the bulking of F1 progeny, and subsequent natural selection for mass sorting of the progeny in successive natural cropping environments. Composite cross populations can provide dynamic gene pools, which in turn provide a means of conserving germplasm resources: they can also allow selection of heterogeneous crop varieties. The value of composite cross populations in achieving these aims is dependent on the outcome of mass trials by artificial and natural selection acting upon the heterogeneous mixture. There is evidence to suggest that composite cross populations may be an efficient way of providing heterogeneous crops and of selecting superior pure lines for low input systems characterized by unpredictable stress conditions.