A decade of Tropical Legumes projects: Development and adoption of improved varieties, creation of market‐demand to benefit smallholder farmers and empowerment of national programmes in sub‐Saharan Africa and South Asia

Abstract This article highlights 12 years (2007–2019) of research, achievements, lessons learned, challenges and gaps in discovery‐to‐delivery research in legumes emanating from three projects, collectively called Tropical Legumes (TL) with a total investment of about US$ 67 million funded by the Bill & Melinda Gates Foundation. These projects were implemented by three CGIAR centres (ICRISAT, CIAT and IITA) together with 15 national agricultural research system partners in sub‐Saharan Africa and South Asia. The TL projects together with some of their precursors and complementary projects from other agencies, facilitated the development of 266 improved legume varieties and the production of about 497,901 tons of certified seeds of the target legume crops in the focus countries. The certified seeds have been planted on about 5.0 million ha by more than 25 million smallholder farmers in the 15 countries and beyond, producing about 6.1 million tons of grain worth US$ 3.2 billion. Furthermore, the projects also trained 52 next generation scientists that included 10 women, by supporting 34 Masters degrees and 18 PhD degrees.


| CHI CKPE A -ADAP TATI ON TO DROUG HT AND HE AT S TRE SS E S
In the face of diminishing rainfall and increasing temperatures globally, developing drought-and heat-tolerant chickpea varieties becomes imperative considering that chickpea is one of the important legume crops largely grown by smallholder farmers who are more susceptible to climate variability and change. Therefore, efforts were made to develop several early-maturing (drought escaping) varieties with improved drought tolerance by selecting for grain yield under moisture stress conditions. Similarly, selection for pod set in the crop subjected to heat stress during the reproductive stage has helped in developing heat-tolerant varieties. In parallel, significant advances were made in decoding the chickpea genome (Varshney, Song, et al., 2013), sequencing several hundred germplasm lines and varieties , developing genetic and physical maps and identifying quantitative trait loci (QTLs) including "QTL-hotspot" region containing QTLs for several drought tolerance traits. Some of these efforts were partially supported by TL projects as well as the CGIAR Generation Challenge Programme. In the TL projects, the "QTL-hotspot" region was also introgressed into several popular cultivars using marker-assisted backcrossing (MABC) and introgression lines giving significantly higher yield than the popular cultivars (Thudi et al., 2014;Varshney, Gaur, et al., 2013).
Similarly, molecular breeding has been used successfully to develop resistant lines for Fusarium wilt and ascochyta blight resistance (Mannur et al., 2019;Pratap et al., 2017;Varshney, Mohan, et al., 2014). During the three phases of the project, 28 chickpea varieties were developed and released and 259,552 tons of certified seeds of modern improved varieties were produced and planted on about 2.2 million ha ( Table 1). Some of these achievements have been presented in detail by Gaur et al. (2019) in this issue.

| COMMON B E AN -MARK E T-DRIVEN B REEDING AND G ENDER-RE S P ONS IVE PARTICIPATORY VARIE TAL S ELEC TION
Guided by market-driven approaches to develop client preferred common bean varieties, significant efforts were made to address the production constraints and develop multi-trait common bean varieties.
In parallel, the genome sequence of common bean became available from a US-led consortium (Schmutz et al., 2010). Molecular markers for several traits were developed (Mukankusi-Mugisha et al., 2019) and used for selection in breeding programmes to develop varieties resistant to key diseases and insect pests. In brief, 104 common bean varieties were developed and released and 96,530 tons of certified seed were produced and planted on about 965,302 ha (Table 1). Some of these achievements have been presented by Mukankusi-Mugisha et al. (2019). The authors have also highlighted the efforts to utilize modern genomic tools to increase scale, efficiency, accuracy and speed of breeding. In addition, adoption of gender-responsive participatory variety selection that led to the release of several market preferred varieties in 31 African countries has been highlighted.
F I G U R E 1 Tropical Legumes (TL) crops and geographies. Phases I and II of TL II projects conducted research and development activities on six legume crops, namely chickpea, common bean, cowpea, groundnut, pigeonpea and soybean. The TL III project focused on four crops, i.e., chickpea, common bean, cowpea and groundnut.  Through the support of the TL projects, 29 cowpea varieties were developed and 20,353 tons of certified seeds were produced and planted on about 508,825 ha (Table 1). These efforts have been highlighted by Boukar et al. (2019) in this special issue.

| G ROUNDN UT -ADVAN CE S IN G ENOMIC S AND IMPLEMENTATI ON OF INTEG R ATED B REED ING APPROACHE S
Low groundnut yields in Asia and Africa can be attributed to various production constraints, leading to less production and low income for smallholder farmers. Advances made under TL and associated projects led to a better understanding of the groundnut genome, discovery of genes/variants for traits of interest and the integration of marker-assisted breeding for selected traits. Under TL projects, EDITORIAL NOTE a total of 76 groundnut varieties were developed and released and 101,634 tons of certified seed were produced and planted on about 1 million ha by 2017 (Table 1). The integration of genomic tools in the breeding process accompanied by increased precision of yield trialling and phenotyping is expected to increase efficiency and enhance genetic gain for the released improved groundnut varieties. There are already several success stories of development of improved lines for resistance to foliar diseases (Pasupuleti et al., 2016;Varshney, Pandey, et al., 2014) and for high oleic acid content (Bera et al., 2018;Janila et al., 2016).

| PI G EONPE A -AN AMALG AM OF B REED ING AND G ENOMI C RE S E ARCH
Pigeonpea was part of the legume crops portfolio in two phases of the project (TL II Phases I and II), during which 19 improved pigeonpea varieties and hybrids were developed and released and 5,686 tons of certified seed were produced and planted on about 227,450 ha (Table 1)

| SOYB E AN -PUB LI C S EC TOR B REED ING FOR CULTIVAR DE VELOPMENT IN THE AFRI C AN TROPI C S
Cultivated soybean is the number one oil and protein supplier for animal and human nutrition. It accounts for about 84.5% of the world's grain legumes trade (Abate et al., 2011). Although SSA accounts for less than 2% of the global production, it constitutes an important component in smallholder cropping systems. In SSA, soybean has made comparable contribution to the growth in production with annual growth rates of 3.0% in area and 3.5% in yield. Despite these positive trends, average soybean yields in Africa (1.2 tons/ha) are much lower than the global average of about 2.5 tons/ha. The low yields are due to a number of production constraints including low adoption of improved varieties and poor agronomic practices. Two phases of TL projects, together with other associated projects, facilitated the development and release of 10 improved varieties and the production of 14,146 tons of certified seeds that replaced old varieties on about 188,607 ha (Table 1). Chigeza et al. (2019) provide an overview of current soybean breeding in SSA and an update on the accomplishments of the IITA soybean breeding programme.

| FABA B E AN -B REED ING FOR B I OTIC AND AB I OTI C S TRE SS E S
Although faba bean (Vicia faba) was not part of the TL projects, we

| MARKE T-LED OP TI ON S TO SC ALE UP LEG UME S EEDS IN DE VELOPING COUNTRIE S
Smallholder farmers need not only improved varieties, but also connection to markets so that they can generate more income.
Therefore, TL projects invested in this direction as well. It fostered innovative public-private partnerships in joint testing of innovative market-led seed systems, skills and knowledge enhancement and

| INTEG R ATI ON OF G ENOMIC S , G ENE TIC S , B REED ING AND S EED SYS TEMS TO ACCELER ATE G ENE TI C G AIN S
The article by Ojiewo et al. (2019) highlights the importance of continuous genetic improvement for enhanced productivity, production, quality and adoption of higher yielding cultivars to enhance their sustainable and timely availability, accessibility and affordability. It discusses exploring of plant genetic resources and their genetic characterization, trait discovery based on genome sequences and large-scale marker resources available and pre-breeding approaches. The authors also highlight the value of diagnostic markers for early generation selection and molecular breeding by providing the current status of their availability and usage. A detailed account is given of the deployment of molecular breeding for developing superior lines. Finally, the authors provide a road map to develop better varieties rapidly by integrating different genomic, genetic and breeding approaches. Adoption of decision support tools may help achieve greater scale . In addition, improved cultivars of the legume crops are also more responsive to improved crop management for high productivity, making them increasingly more relevant to reducing hunger in the areas they are traditionally grown and consumed.

| IMPAC T ON THE G ROUND
During Phases I and II of the project, disseminated improved varieties were adopted on at least 4.0 million hectares and more than US$ 2.6 billion was generated from the project and investment partners. This is far above the total TL II (Phase I and Phase   On the other hand, in Tanzania, adoption of improved groundnut varieties is estimated at 19% nationally before correction through DNA fingerprinting data. However, the seed system works through about 400 farmer research groups linked to seed companies as contract seed producers, together with training and the adoption of integrated crop management practices have contributed to increased  Finally, for sustainable legume production, it is not enough to generate new high yielding market preferred varieties and seed production; instead, it is equally important to have a well trained next generation of breeders. With this objective, TL projects have trained 34 Masters degree and 18 PhD degree students including 10 females and 42 males (Table 2). The time has come to turn to sequence-based breeding in these legume crops. Furthermore, while the integration of genomic information and deployment of modern breeding approaches such as sequence-assisted breeding  and speed breeding (Watson et al., 2018) can accelerate the development of superior varieties, it is crucial to have a strong seed delivery system in SSA and SA so that farmers can have access to improved varieties . The pace at which old varieties are replaced by new ones needs to be accelerated.

| SUMMARY AND OUTLOOK
Adopting appropriate agronomic practices while cultivating improved varieties will help in realizing the full potential of genetics and breeding and in delivering more produce to farmers. At the same time, providing farmers access to markets will fetch them more income to improve their livelihoods. Subsequently, market feedback should go back in the loop to define traits in the development of market-led and climate resilient varieties. The future of legumes breeding is bright and promises to benefit smallholder farmers in SSA and SA.

KEYWORDS
breeding, food security, genomics, legumes, seed system Organization.

FU N D I N G I N FO R M ATI O N
Bill and Melinda Gates Foundation, Grant/Award Number: OPP1114827

CO N FLI C T O F I NTE R E S T
The authors declare that they have no conflicts of interest.