Robust seed systems, emerging technologies, and hybrid crops for Africa

The tricot approach: an agile framework for decentralized on-farm testing supported by citizen science. A retrospective

Matching crop varieties to their target use context and user preferences is a challenge faced by many plant breeding programs serving smallholder agriculture. Numerous participatory approaches proposed by CGIAR and other research teams over the last four decades have attempted to capture farmers' priorities/preferences and crop variety field performance in representative growing environments through experimental trials with higher external validity. Yet none have overcome the challenges of scalability, data validity and reliability, and difficulties in capturing socio-economic and environmental heterogeneity. Building on the strengths of these attempts, we developed a new data-generation approach, called triadic comparison of technology options (tricot). Tricot is a decentralized experimental approach supported by crowdsourced citizen science. In this article, we review the development, validation, and evolution of the tricot approach, through our own research results and reviewing the literature in which tricot approaches have been successfully applied. The first results indicated that tricot-aggregated farmer-led assessments contained information with adequate validity and that reliability could be achieved with a large sample. Costs were lower than current participatory approaches. Scaling the tricot approach into a large on-farm testing network successfully registered specific climatic effects of crop variety performance in representative growing environments. Tricot's recent application in plant breeding networks in relation to decision-making has (i) advanced plant breeding lines recognizing socio-economic heterogeneity, and (ii) identified consumers' preferences and market demands, generating alternative breeding design priorities. We review lessons learned from tricot applications that have enabled a large scaling effort, which should lead to stronger decision-making in crop improvement and increased use of improved varieties in smallholder agriculture.

The seed sector development in low-income countries: Lessons from the Malawi seed sector policy process

Introduction

External conditionalities have shaped public policy development in borrowing nations. This has been through top-down policy support programs, an example being the policy reforms under the structural adjustment program. Under the seed sector reforms Malawi committed to the Southern Africa Development Community and the Common Market for Eastern and Southern Africa harmonized seed regulations technical agreements.

Methods

To contribute to the debate, we analyzed the Malawi seed sector policy process by investigating three questions: What were the leading events? Who were the stakeholders involved, and their roles? Which factors influenced the policy process? Qualitative tools were employed based on policy process theory using the Kaleidoscope Model. We used stakeholder inception, planning, feedback workshops, and key informant interviews (N = 17). This data was complemented by grey literature as secondary information. Snowball sampling was used to identify key informant interview participants based on the saturation principle. Narrative analysis focusing on content, structure, and dialogic context was used.

Results

Our results show a strong external influence on the seed sector policy process. This began after independence when development partners supported the establishment of the public agricultural research system to improve production for food security and export. Failure to achieve the earlier objectives resulted in economic reforms aimed at private sector-led seed sector development based on market-oriented policies. The increase in the private sector's role called for adopting and enacting regulatory policies and legislation that used policy transfer theory. International financial institutions, multinational companies, and regional economic communities led this process. Our evidence suggests that the civil society community in Malawi contested the policies for not recognizing farmers' rights. This affected the domestication process of the harmonized seed regulations technical agreements.

Discussion

Therefore, we recommend critical consideration and embracing of existing domestic social, political, and technical conditions to support economic policy reforms. This would help reduce unintended consequences and improve inclusivity. Governments may need to play an interlocutory role for the various actors in the policy domain during the domestication process.

Incorporating male sterility increases hybrid maize yield in low input African farming systems

Maize is a staple crop in sub-Saharan Africa, but yields remain sub-optimal. Improved breeding and seed systems are vital to increase productivity. We describe a hybrid seed production technology that will benefit seed companies and farmers. This technology improves efficiency and integrity of seed production by removing the need for detasseling. The resulting hybrids segregate 1:1 for pollen production, conserving resources for grain production and conferring a 200 kg ha⁻¹ benefit across a range of yield levels. This represents a 10% increase for farmers operating at national average yield levels in sub-Saharan Africa. The yield benefit provided by fifty-percent non-pollen producing hybrids is the first example of a single gene technology in maize conferring a yield increase of this magnitude under low-input smallholder farmer conditions and across an array of hybrid backgrounds. Benefits to seed companies will provide incentives to improve smallholder farmer access to higher quality seed. Demonstrated farmer preference for these hybrids will help drive their adoption.

Seed hybridization technology improves maize yield in African smallholder farming conditions.

Transcriptional gene silencing in bread wheat (Triticum aestivum L.) and its application to regulate male fertility for hybrid seed production

Transcriptional gene silencing (TGS) can offer a straightforward tool for functional analysis of plant genes, particularly in polyploid species such as wheat, where genetic redundancy poses a challenge in applying mutagenesis approaches, including CRISPR gene editing. In this study, we demonstrate efficient TGS in wheat, mediated by constitutive RNA expression of a promoter inverted repeat (pIR). pIR-mediated TGS of two anther-specific genes, TaMs45 and TaMs1, abolished their function resulting in male sterility. Whilst TGS of TaMs45 required transcriptional silencing of all three homoeologs, a B-genome-specific pIR for TaMs1 was sufficient to confer male sterility. We further show that the pIRs effect TGS of TaMs45 gene through DNA methylation of homologous promoter sequence, successfully suppressing transcription of all three homoeologs. Applying pIR-mediated TGS in wheat, we have generated a dominant male fertility system for production of hybrid seed and demonstrated the efficacy of this system under greenhouse and field conditions. This report describes the first successful TGS in wheat, whilst providing a dominant negative approach as alternative to gene knockout strategies for hybrid wheat breeding and seed production.

Demand-side challenges to increase sales of new maize hybrids in Kenya

In Eastern and Southern Africa, as the public sector has retreated from maize seed production and the private sector has emerged to fill the resulting void, a key issue for researchers, governments and private donors has been the capacity of privately owned, typically small scale, seed businesses to effectively produce and distribute hybrid seed. Roughly two decades on, research and development programming continues to focus on supply side issues in supporting the maize seed industry to bring new varieties to farmers. Motivated by thinking on agri-food value chains, this article explores the potential for achieving a stronger demand orientation in programming to support the maize seed industry, a requirement for varietal turnover. In 2019 data were collected in Kenya from i) 80 agro-dealers on their relations with seed businesses and their marketing of maize seed, ii) 466 farmers on their seed choice and engagement with agro-dealers and iii) 8 seed companies on their distribution and sales strategies. Results confirmed the overarching supply-push orientation of the industry, characterized by limited innovation and risk taking, weak collaboration between actors, low margins for retailers, and limited investments in seed marketing. Farmers showed weak appetite for acquiring new seed products, preferring instead to purchase seeds that they knew from experience. Better strategies for building seed value chains will require deeper insights on stakeholders needs and strategies, to include the capacity of seed businesses and retailers to innovate in business management and marketing.

The political ecology of seed security in the Northern Ghanaian Savannahs

Seed security is being promoted as a means of achieving productivity, food security, and resilience among smallholders. This has resulted in notions that vulnerabilities among smallholders in Africa are the outcomes of inadequate adoption of improved seeds. What these perspectives have neglected is: How politics mediate access to seeds? and Whether and how politics influence farmers' perception of seed security? This study draws upon a case study of Northern Ghanaian Savannahs to examine politics and seed security among smallholders. The logistic analysis shows that the presence of recurring conflicts significantly determines how farmers perceived vulnerability to seed insecurity. Thus, farmers from relatively peaceful villages were 4.705 times more likely to rate themselves as not vulnerable to seed insecurity compared to their counterparts experiencing recurring conflicts. Analysis further shows that smallholder vulnerabilities to seed insecurity are constructed at the intersection of historical ethnic conflicts and neoliberal policies in ways that contest the dominant narratives. Key for achieving seed security is a better understanding of how local and macro politics influence perceptions and mediate access to healthy and desirable seeds.

Technological advances in maize breeding: past, present and future

Maize has for many decades been both one of the most important crops worldwide and one of the primary genetic model organisms. More recently, maize breeding has been impacted by rapid technological advances in sequencing and genotyping technology, transformation including genome editing, doubled haploid technology, parallelled by progress in data sciences and the development of novel breeding approaches utilizing genomic information. Herein, we report on past, current and future developments relevant for maize breeding with regard to (1) genome analysis, (2) germplasm diversity characterization and utilization, (3) manipulation of genetic diversity by transformation and genome editing, (4) inbred line development and hybrid seed production, (5) understanding and prediction of hybrid performance, (6) breeding methodology and (7) synthesis of opportunities and challenges for future maize breeding.

Developing and deploying climate-resilient maize varieties in the developing world

In sub-Saharan Africa (SSA) and Asia maize yields remain variable due to climate shocks. Over the past decade extensive progress has been made on the development and delivery of climate-resilient maize. In 2016 over 70000 metric tonnes of drought-tolerant maize seed was commercialized in 13 countries in SSA, benefiting an estimated 53 million people. Significant progress is also being made with regard to the development and deployment of elite heat-tolerant maize varieties in South Asia. Increased genetic gain in grain yield under stress-prone environments, coupled with faster replacement of old/obsolete varieties, through intensive engagement with seed companies is essential to protect maize crops grown by smallholders from the changing climates in SSA and Asia.

Concurrent modifications in the three homeologs of Ms45 gene with CRISPR-Cas9 lead to rapid generation of male sterile bread wheat (Triticum aestivum L.)

Hexaploid bread wheat is not readily amenable to traditional mutagenesis approaches. In this study, we show efficient utilization of CRISPR-Cas system and Next Generation Sequencing for mutant analysis in wheat. Identification and manipulation of male fertility genes in hexaploid bread wheat is important for understanding the molecular basis of pollen development and to obtain novel sources of nuclear genetic male sterility (NGMS). The maize Male sterile 45 (Ms45) gene encodes a strictosidine synthase-like enzyme and has been shown to be required for male fertility. To investigate the role of Ms45 gene in wheat, mutations in the A, B and D homeologs were produced using CRISPR-Cas9. A variety of mutations in the three homeologs were recovered, including a plant from two different genotypes each with mutations in all three homeologs. Genetic analysis of the mutations demonstrated that all three wheat Ms45 homeologs contribute to male fertility and that triple homozygous mutants are required to abort pollen development and achieve male sterility. Further, it was demonstrated that a wild-type copy of Ms45 gene from rice was able to restore fertility to these wheat mutant plants. Taken together, these observations provide insights into the conservation of MS45 function in a polyploid species. Ms45 based NGMS can be potentially utilized for a Seed Production Technology (SPT)-like hybrid seed production system in wheat.

Diallel genetic analysis for multiple traits in eggplant and assessment of genetic distances for predicting hybrids performance

Evaluation and prediction of the performance of hybrids is important in eggplant (Solanum melongena) breeding. A set of 10 morphologically highly diverse eggplant parents, including nine inbred S. melongena and one weedy S. insanum accessions, were intercrossed according to a half-diallel mating design without reciprocals to obtain 45 hybrids. Parents and hybrids were evaluated for 14 morphological and agronomic conventional descriptors and 14 fruit morphometric traits using Tomato Analyzer. Genetic distances among parents were estimated with 7,335 polymorphic SNP markers. Wide ranges of variation and significant differences were observed in the set of 55 genotypes for all traits, although the hybrids group had significantly higher vigour and yield than parents. General and specific combining abilities (GCA and SCA) were significant for most (GCA) or all (SCA) traits, although a wide variation was obtained for GCA/SCA ratios. Many relevant traits associated to vigour and yield had low GCA/SCA ratios and narrow-sense heritability (h2) values, while the reverse occurred for most fruit shape descriptors. Broad-sense heritability (H2) values were generally high, irrespective of GCA/SCA ratios. Significant correlations were found between traits related to size of leaf, flower and fruit, as well as among many fruit morphometric traits. Genetic distances (GD) among parents were coherent with their phylogenetic relationships, but few significant and generally low correlations were found between GD and hybrid means, heterosis or SCA. The results provide relevant information for developing appropriate strategies for parent selection and hybrid development in eggplant and suggest that GD among parents have limited value to predict hybrid performance in this crop.

A single point mutation in Ms44 results in dominant male sterility and improves nitrogen use efficiency in maize

Application of nitrogen fertilizer in the past 50 years has resulted in significant increases in crop yields. However, loss of nitrogen from crop fields has been associated with negative impacts on the environment. Developing maize hybrids with improved nitrogen use efficiency is a cost-effective strategy for increasing yield sustainably. We report that a dominant male-sterile mutant Ms44 encodes a lipid transfer protein which is expressed specifically in the tapetum. A single amino acid change from alanine to threonine at the signal peptide cleavage site of the Ms44 protein abolished protein processing and impeded the secretion of protein from tapetal cells into the locule, resulting in dominant male sterility. While the total nitrogen (N) content in plants was not changed, Ms44 male-sterile plants reduced tassel growth and improved ear growth by partitioning more nitrogen to the ear, resulting in a 9.6% increase in kernel number. Hybrids carrying the Ms44 allele demonstrated a 4%-8.5% yield advantage when N is limiting, 1.7% yield advantage under drought and 0.9% yield advantage under optimal growth conditions relative to the yield of wild type. Furthermore, we have developed an Ms44 maintainer line for fertility restoration, male-sterile inbred seed increase and hybrid seed production. This study reveals that protein secretion from the tapetum into the locule is critical for pollen development and demonstrates that a reduction in competition between tassel and ear by male sterility improves grain yield under low-nitrogen conditions in maize.