Current and projected eco-geographic adaptation and phenotypic diversity of Ethiopian teff (Eragrostis teff) across its cultivation range
Introduction
Teff (Eragrostis tef (Zucc.) Trotter) is a C4 annual cereal crop of the Poaceae family widely grown in the Horn of Africa (Costanza et al., 1979; D’Andrea, 2008). Its grain is valued for traditional food preparations including enjera, the fermented flatbread ubiquitous in Ethiopian and Eritrean kitchens, and its fine straws are used for construction of mud-walled houses as well as for animal feed in the smallholder farming system diffused in the region. Teff is considered indigenous to Ethiopia and features tremendous phenotypic diversity in the upper East African Rift Valley region (Harlan, 1971; Vavilov, 1951). Its gene pool is contributed by thousands of landraces that local farmers have been growing for millennia, currently covering about one third of the land area dedicated to cereals in Ethiopia(Central Statistical Agency, 2016). Teff is grown at relatively high elevations under rainfed agriculture achieving yields in the range of 1–2 ton · ha−1, substantially lower than those of other cereals commonly grown in the region including maize and wheat (Cochrane and Bekele, 2018). Yet teff is often preferred over other cereals because of its superior marketability and cultural relevance (Ketema, 1997; Minten et al., 2018).
Teff landraces have broad adaptation, and are grown in a number of agroecologies spanning from vertisols prone to waterlogging to non-vertisols with low moisture stress (Abewa et al., 2014; Haileselassie et al., 2011; Ketema, 1997). The evolution of the teff genepool is ongoing in smallholder farmer fields, where natural selection meets and interacts with human selection in shaping crop diversity (Bellon and Van Etten, 2014). Little is known about trait-environment correlations existing in teff germplasm, although adaptation may have emerged from local cultivation conditions as it is the case in other cereal crops (Lasky et al., 2015). Local farmers are indeed very aware of climate constraints to cultivation of teff germplasm (Felix et al., 2018). Precipitation and temperature are arguably the climate features most critical to Ethiopian agriculture, as they affect organic matter decomposition, cycling of nutrients, and vegetative production (; Zhang and Yan, 2014). The climate change scenarios projecting the Earth system towards a dramatic increase of temperatures (Steffen et al., 2018) threaten marginal agroecosystem with abiotic and biotic stresses potentially altering their productivity and function (Tubiello et al., 2007). Teff accessions collected in challenging environments may then be a valuable genetic resource for developing new varieties with adaptation traits supporting the sustainable intensification of Ethiopian agriculture in the wake of climate change.
Teff breeding has been burdened by lack of knowledge and by the inherent difficulty in conducting crosses between different accessions. Teff is a strict autogamous species, with outcrossing frequency between 0.2% and l.0%. Moreover, its remarkably small florets open for a limited time, typically early in the morning (6:45−7:45 a.m.) (Berhe, 1975). Regardless, in recent years teff genetic resources have been systematically characterized with the aim of conducting modern breeding on this crop (Assefa et al., 2011; Cannarozzi et al., 2018; Girma et al., 2014; Teklu and Tefera, 2005). In these regards, a number of diversity studies have been conducted on teff germplasm using morphological (Assefa et al., 1999; Jifar et al., 2015; Kefyalew et al., 2000) and molecular markers (Assefa et al., 2003; Zeid et al., 2012), yet describedonly a limited share of the variability overall available in Ethiopian teff. In order to support crop improvement tackling both present and future needs, the vast allelic diversity available in locally adapted genetic resources must be fully considered. Once characterized for their bioclimatic and phenotypic diversity, collections of genetic resources may be valorized by designing appropriate germplasm conservation strategies, as well as by including those collections in breeding programs (Mengistu et al., 2018). Climate prediction scenarios may be then used to derive scenarios of future habitat suitability (De Sousa et al., 2019) and to foster assisted gene flow (Aitken and Bemmels, 2016).
Typically, smallholder farmers grow mixtures of teff accessions, and this is reflected by the heterogeneity of the genetic materials maintained in the gene banks (Ketema, 1997). In the past five decades, the Ethiopian Biodiversity Institute (EBI) has collected and conserved thousands of teff accessions from across the country. This vast ex situ collection is the most comprehensive assembly of teff diversity available to date and represents most of the genetic variation of Ethiopian teff available globally. In this study, we performed a phenotypic and bioclimatic characterization of 3850 Ethiopian teff accessions sourced at the EBI, discussing their diversity on the landscape. We then used our findings to develop a species distribution model providing an outlook of future scenarios of teff distribution in Ethiopia.
Section snippets
Plant materials and data curation
This study focuses on 3850 teff accessions representing the entire active ex situ collection of teff available at the EBI (https://www.ebi.gov.et/) in 2016. About 1 g of seeds was obtained from each accession. The geographic information system program QGIS 3.0.3 (QGIS Development Team, 2019) was used to map accessions for which passport data was available. GPS coordinates of accessions having gazetteer information were manually derived at the highest precision possible using Google Maps (Google
Teff distribution and bioclimatic diversity
For all analyses pertaining teff geographic distribution, a sub-collection comprising 2084 accessions with sampling information was utilized. These accessions were sampled throughout the country in the years 1967–2015 at altitudes varying from 902 to 3090 m.a.s.l., and latitudes and longitudes varying between 05°03′00″ N and 15°13′00″ N; and 34°22′00″ E and 42°34′00″ E, respectively (Fig. 1, Table S2).
Ethiopian teff accessions are cultivated in a broad range of environments (Table 1, Fig. S1).
Teff diversity and current adaptation
The marked environmental variability of Ethiopia (Mamo, 2005; Simane and Struik, 1993) adds with the rainfed agriculture conducted in the country in causing substantial fluctuations in crop production (Ray et al., 2015; Yamusa et al., 2015), teff included. Previous reports from national yield trials reported that the most suitable areas for teff cultivation are located at altitudes of 1700−2200 masl, where the annual rainfall amounts to 750–850 mm and mean temperature ranges between 10 °C and
Conclusions
Climate change is already influencing agriculture in several ways. Changes in temperature and precipitation as well as weather and climate extremes are increasing pressure on agroecosystems, degrading natural resources and threatening food production. This study is a starting point for designing new strategies for the sustainable improvement of teff. The phenotypic and pedoclimatic characterization of the whole working germplasm collection at EBI provided a thorough description of the most
Author contributions
MD and MEP designed the study. ABW and CA conducted data analysis. EAD, YGK, and CF supported data analysis and field characterization. ABW and MD drafted the paper. MD and CA produced figures.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
We are grateful to the Ethiopian Biodiversity Institute for providing the genetic materials included in this study and allowing access to passport information supporting data curation. This work was supported by the Doctoral Programme in Agrobiodiversity at the Scuola Superiore Sant’Anna, Pisa, Italy
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