Crop adaptation to climate change in the semi-arid zone in Tanzania: the role of genetic resources and seed systems
© Westengen and Brysting; licensee BioMed Central Ltd. 2014
Received: 4 November 2013
Accepted: 17 January 2014
Published: 1 February 2014
Rural livelihoods relying on agriculture are particularly vulnerable to climate change. Climate models project increasingly negative effects on maize and sorghum production in sub-Saharan Africa. We present a case study of the role of genetic resources and seed systems in adapting to climatic stress from the semi-arid agroecological zone in Tanzania.
Crop adaptation, switching to more drought-tolerant crop species or varieties, is an important adaptation strategy within a diverse portfolio of livelihood responses to climatic stress. Crop adaptation involves the adoption of improved maize varieties combined with continued use of local varieties of both maize and sorghum. Regression modelling shows that households receiving the extension service and owning livestock are more likely to switch to drought-tolerant varieties as a response to climatic stress than those without access to these assets. The seed system in the study area consists of both formal and informal elements. The informal channels supply the highest quantities of both sorghum and maize seeds. Recycling of improved varieties of maize is common and the majority of households practice seed selection. Detailed assessment of the three different categories of genetic resources – local, improved and farmer-recycled varieties – reveals that drought tolerance is more frequently reported as a reason for growing local varieties than for growing improved varieties of maize and sorghum. The significantly later maturity reported for local varieties compared to the improved varieties bred to have a short growing cycle indicates that households distinguish between drought-tolerance and drought-avoidance traits.
Seed system perspectives on crop adaptation offer insights into the complex ways crop adaptation is realized at the livelihood level. The integration of informal and formal seed system elements is important for the adaptive capacity of agriculture-based livelihoods. Our findings highlight the value and importance of location-specific information about crop variety use for arriving at realistic recommendations in impact and adaptation studies.
KeywordsAdaptation Agriculture Seed systems Genetic resources Maize Sorghum
Adaptation to climate change is a major issue in the current food security discourse [1, 2]. Livelihoods in developing countries depending on agriculture are particularly vulnerable to changes in the mean and variability of climate and the need for adaptation is highlighted in crop impact studies from sub-Saharan Africa (SSA) [3, 4]. Adaptation options in agriculture involve changes at the farm management level as well as changes in the policy and institutional decision environment . In the portfolio of common on-farm and non-farm livelihood adaptation strategies, crop adaptation (changing to crop species or varieties that are resistant to climatic stress) is among the most cited adaptation measures [3–10]. The important role that crop adaptation has achieved in the discourse is illustrated by a United Nations General Assembly resolution from 2009, which ‘underlines the importance of … making crops more tolerant to environmental stress, including drought and climate change’ . Despite the general agreement about the importance of crop adaptation there are diverging views in the adaptation literature about how this adaptation option can be realized at the livelihood level.
The need to adapt crops to changing environmental conditions is not new, rather it is the most fundamental co-evolutionary relationship between crops and humans since the dawn of agriculture [12, 13]. Crop adaptation in the Darwinian sense is the evolution of crops to become better suited to their environments. In traditional agriculture, adaptation is an interplay between natural selection and selection by farmers. In modernized agriculture, which has been rapidly spreading in the developing world with the Green Revolution since the 1960s, the science of plant breeding has largely replaced the farmer’s role in crop development . Conventional plant breeding can briefly be defined as crossing plants with desired characteristics and selecting offspring combining those desirable characteristics to produce so-called improved varieties. The technology and the political economic context are different, but genetic diversity is the raw material for adaptation both in on-farm crop development and in professional plant breeding. This role of crop diversity is reflected in the term genetic resources, which encompasses seeds, plants and plant parts useful in crop breeding, research or conservation for their genetic attributes . In traditional agriculture, genetic resources for adaptation are sourced from the farmer’s own field or through gifts and trade with other farmers, and sometimes through gene flow from other varieties or wild relatives of the crop. In modernized agriculture, the plant breeders act as intermediaries between the genetic resources and the farmer, and the genetic resources used to breed new varieties are normally sourced from genebanks and genetic stocks.
The terms informal and formal seed systems are used to distinguish between the two different sources of genetic resources [16, 17]. In SSA’s smallholder agriculture, most seeds are sourced through the informal seed system and only a small proportion of the seeds planted every year are sourced through formal market channels with direct links to plant breeding [18, 19]. However, farm saving and recycling of improved varieties is common [20–22]. Socio-economic work from Mexico has demonstrated that recycling and hybridization between landraces and improved varieties of maize is a deliberate strategy used by smallholder farmers to combine desirable traits from improved and local varieties, a phenomenon known as creolization [23, 24]. Thus, the distinction between the formal and informal seed systems is not clear-cut. Development initiatives aiming at replacing the informal seed system with formal seed systems modelled after those found in industrialized countries have been questioned and challenged in recent seed system literature [25–28].
Vermeulen et al. , in a review of options to support agriculture and food security under climate change, point out that while we know much about what regions and crops are likely to be sensitive to climate change, there is limited scientific knowledge about how current farming systems can adapt. This gap arguably reflects methodological and epistemological differences between two scholarly traditions dealing with agriculture in a climate change context. The first is impact oriented and the other studies the vulnerability and capacity of affected livelihoods [29, 30]. While there is no clear-cut boundary between the two literatures, their difference is apparent in the Intergovernmental Panel on Climate Change (IPCC) report from Working Group II on Impacts, Adaptation and Vulnerability where the two literatures are reviewed by different expert groups in different chapters [6, 32]. The impact-oriented literature projects yield loss in the largest food crops and focuses on the consequences for regional and national food security, often with a view to recommending targeting of adaptation measures [3, 6, 33, 34]. The literature on capacity and vulnerability commonly applies a livelihood and poverty perspective on adaptation [32, 35, 36] and typically treats coping and adaptation as objects for empirical research. The difference in starting point (crop impact vs socio-economic impact) often leads to differences in recommendations with regard to how crop adaptation can be realized in developing countries. The impact-oriented literature projects shifts in crop climates that are likely to make the current crop varieties unsuitable and commonly arrives at recommending breeding and dissemination of stress-tolerant and climate-ready varieties. On the other hand, the focus on local conditions and safety nets in the vulnerability and capacity studies often leads to an emphasis on the adaptive importance of local crops and traditional knowledge.
We here present a study of crop adaptation in an area where households experience climate stress and cultivate crops for which climate change models project adverse effects on future yield. This paper is a contribution towards bridging the gap between different scholarly traditions on climate change adaptation. We apply a combination of the livelihood approach and seed system perspectives when addressing the following research questions: (a) Is crop adaptation an important adaptation strategy? (b) What livelihood factors are associated with practicing on-farm adaptation activities in general and crop adaptation in particular? (c) What is the role of genetic resources and seed systems in crop adaptation?
Study site and impact projections
Impact projections for maize and sorghum yields vary according to the scale and model used. At the regional SSA scale, Schlenker and Lobell  coupled historical crop production data with predictions for temperature and precipitation changes from 16 climate change models under the A1b emission scenario of the IPCC, and projected aggregate production losses of 17% for sorghum and 22% for maize by mid-century. For Tanzania, the nationally projected impact of a 2°C seasonal temperature increase is an 8.8% reduction of sorghum yield and 13% for maize in the same period . Thornton et al.  ran the biophysical crop model CERES-Maize  with a fine spatial resolution (10 arc-minute grids or ~18 km resolution) across East Africa, and predicted that the semi-arid region in Tanzania is one of the areas where maize yields are likely to be reduced by 20% or more. The villages in the current study are located in areas where maize production is predicted to be adversely affected (Figure 1).
Theoretical framework and statistical methods
We used a livelihood approach [43, 44] to study adaptation and assess the relative importance of crop adaptation in light of the institutional context and other adaptation options accessible to the households. Drawing on the seed system literature [17, 25, 27], we study seed systems as the institutions that mediate access to genetic resources. Furthermore, we analyze the association between different categories of genetic resources and a range of production and consumption variables, drawing on the socio-economic literature on the benefits of different types of crop varieties [24, 45].
We used both qualitative and quantitative methods when collecting and analyzing the data. We conducted key informant interviews of actors in the formal seed system in the area of research as well as with villagers and authorities in the villages included in our case study. The quantitative analysis is based on a random sample of 320 households in two villages, who were interviewed using a structured questionnaire with both closed and open-ended questions. The questionnaire consisted of four sections: a section on asset status, a section on stress factor ranking, a section on coping activities in times of stress and a section on the seed system and varieties used. In the section on coping activities we asked if households were practicing any of the activities on a list of coping activities and if the reason was climatic stress or other stressors. The list was based on coping activities documented in the literature [22, 46, 47] and elicited in the initial qualitative phase of data collection. We used logistic regression models with the common on-farm coping activities (practiced by more than 15% of the households due to climatic stress) as response variables and a set of livelihood factors as explanatory variables. In these models the log odds of the activities were modeled as a linear combination of the explanatory variables. The explanatory variables included in our model were chosen based on hypotheses of either positive or negative associations with the response variables based on findings in other quantitative adaptation studies [10, 48, 49]. To account for asset status we included human capital variables (household size and the sex, age and education of the household head), financial capital variables (annual income and a dummy variable for livestock ownership), an institutional dummy variable on the extension service on cropping and a village effect dummy variable. The modeling was coded in R  and the models were evaluated with a Wald test from the Analysis of Overdispersed Data package .
The seed system part of the survey was formulated first by asking about sources of seeds and planting material for all crop species cultivated and second by asking in detail about area allocation and quality aspects of the different varieties of maize and sorghum. First, we classified the different seed sources as either formal or informal based on the seed system typology outlined in Sperling et al. . Second, we classified the different varieties as belonging to one of the three genetic resource categories: local, improved or farmer-recycled. The classification was based on information provided by the household on the variety cultivated and cross-checked with information on variety names and history from key informant interviews with farmer groups, extension workers and plant breeders. The term ‘local varieties’ is used to distinguish the varieties said to have a long history in the area from the improved varieties produced in the formal seed system. For sorghum we could have used other terms such as ‘landrace’ or ‘traditional variety’, but in the outcrossing crop maize, which is subject to gene flow from recently introduced varieties, these terms are problematic and we chose to use the same terminology for both crops. Farm-saved improved varieties re-used on a farm in two seasons or more were classified as farmer-recycled. We tested the correlation between crop switching and the area cultivated to the different categories using the non-parametric correlation test Spearman’s rho (ρ). Finally, we analyzed the deviance between local and improved varieties with regard to a range of production and consumption variables using a chi-square test.
Results and discussion
Livelihoods under stress
Determinants of adaptation
Regression models for on-farm coping activities practiced by households with livelihood factors as explanatory variables a
Shift cropping area
Switch to drought-tolerant variety
Switch to drought-tolerant species
Sex of household head
8.145 × 10-1**
−3.489 × 10-2
−9.470 × 10-2
−4.035 × 10-1
6.545 × 10-1*
9.329 × 10-1**
Age of household head
−6.419 × 10-3
−2.961 × 10-3
−1.244 × 10-3
−8.348 × 10-3
−6.811 × 10-3
−2.073 × 10-3
4.804 × 10-1
−2.739 × 10-1
1.001 × 10-1
−1.753 × 10-1
9.645 × 10-2
−9.479 × 10-2
1.203 × 10-2
−9.705 × 10-3
4.775 × 10-2
2.682 × 10-2
−1.095 × 10-2
1.589 × 10-1**
9.324 × 10-1*
7.656 × 10-1*
1.069 × 10-1
2.780 × 10-1
−2.906 × 10-8
1.925 × 10-8
8.799 × 10-11
5.494 × 10-8
7.887 × 10-8
7.698 × 10-8
2.388 × 10-3
8.177 × 10-1**
2.184 × 10-1
8.109 × 10-2
6.252 × 10-1*
−1.855 × 10-1
7.638 × 10-1**
−6.596 × 10-1*
8.010 × 10-1**
5.785 × 10-1*
2.861 × 10-2
9.071 × 10-1**
P = 0.00017
P = 0.011
P = 8.8 × 10-5
P = 0.017
P = 1.7 × 10-13
P = 1.8 × 10-7
Before further discussion of the livelihood factors associated with crop adaptation, it is useful to consider what kind of genetic resources are used by the respondents who answered that they had switched to a drought-tolerant variety as a response to climatic stress. While the intention was to capture all kinds of variety switches, it appears that for maize the respondents understood the question as whether they have switched to an improved drought-tolerant variety. Two findings support this conclusion: (1) the significant positive association with households receiving the extension service in the regression model and (2) the significant positive correlation between this activity and the area allocated to improved varieties (ρ = 0.19, P < 0.001). In comparison, the area allocated to local varieties is negatively correlated with the same activity (ρ = −0.17, P < 0.01). Thus, rather than capturing all kinds of adaptive switches, the question apparently mainly captures the adoption of improved varieties.
In this study we did not find the typical human capital factors usually associated with adoption of improved varieties, such as household size and the sex, education and age of the household head , to be significantly positively associated with crop adaptation. Out of the two financial capital variables included, annual income and possession of livestock, only the latter positively affected the probability of undertaking crop adaptation. Interestingly, the same pattern was found for wealth indicators in a scoping study for drought-tolerant maize done by the International Maize and Wheat Improvement Centre (CIMMYT) in East Africa . The same study found that neither the length of education nor the sex of the household head affected the purchasing of improved varieties in Tanzania, while these factors significantly enhanced the likelihood in other countries in SSA. A study from Ethiopia  found that larger households headed by older males with more education and higher income were more likely to undertake crop adaptation. A study from Malawi  similarly found that larger households headed by males and experiencing climate-related shock were more likely to purchase seeds. The lack of positive association between the household’s human capital and crop adaptation in this study indicates that institutional factors play a larger role. This is confirmed by the positive association between receiving the agricultural extension service and switching to drought-tolerant varieties. The government’s extension service is promoting improved varieties of both sorghum and maize in the villages studied and some of the varieties are promoted as drought-tolerant. Prior to the growing season, during which this study was undertaken, improved maize varieties were sold through the extension service at subsidized rates in Mangae and improved sorghum was distributed by the extension service in Laikala under a seed aid program. The subsidized and free distribution of improved varieties is supposed to target the poorest and most needy households. This probably explains why receiving the extension service seems to ‘trump’ other factors that normally influence the likelihood of cultivating improved seeds. The important role of participation in government programs is observed in several studies of determinants of adoption of improved varieties from other areas [45, 64].
The role of the seed system
Proportion of maize and sorghum seeds sourced from different supply channels in Mangae and Laikala
Seed source (percentage)a
Production and consumption variables reported by households in Mangae and Laikala for each field a
Local (n = 156)
Improved (n = 189)
Farmer-recycled (n = 60)
Local (n = 290)
Improved (n = 56)
Farmer-recycled (n = 7)
Reason for growingb
Biotic stress resistance
The scores given by households to the two production variables, maturity and drought resistance, reveal a complexity in the perception of traits relevant for withstanding climatic stress. Local varieties of both sorghum and maize are reported to have a significantly longer maturity period than improved ones. Since a short time for maturation is generally considered a valuable drought-resistance trait [62, 66], this is apparently contradictory to the finding of no significant difference between the average household scores given to local and improved varieties for this trait. A possible explanation can be found in the scientific definition of drought resistance, which is commonly defined as encompassing both drought avoidance and drought tolerance. Varieties that do not avoid drought and need a long growing period to mature might still be relatively drought resistant because they are able to tolerate drought.
The local varieties of sorghum in the study area take 5 to 7 months to mature and the local varieties of maize take more than 3 months. The improved varieties of sorghum and maize have considerably shorter maturation periods: from 120 days down to only 90 days for the earliest maturing varieties of both crops. The maize variety kito, which has a short maturation period, was recommended by the extension service due to the late onset of rains in the growing season when this study was conducted. However, short maturation period varieties are not necessarily the most robust varieties if drought strikes before flowering and grain filling [67, 68]. Because of the unpredictable rains early in the growing season, drought escaping varieties such as kito might actually be less drought resistant than other improved and local varieties. This can explain why varieties with other physiological traits that are important for withstanding drought are favored by the households in Mangae and Laikala. The most commonly improved maize varieties are staha and TMV1, which were released by the public Tanzania Agricultural Research Organization. Neither are short maturation period varieties according to CIMMYT, which classifies staha as a very late maturing variety and TMV1 as an intermediate to late maturing variety . The observation that short maturation period not necessarily is a reason for choosing a variety to cope with abiotic stress has also been observed in other studies of farmers’ perceptions. In a study from Chiapas, Mexico, Bellon and Taylor  observed that while a short growing period was perceived as a positive trait associated with improved maize varieties, resistance to drought was a positive trait only attributed to local varieties. In a later study from the same area, drought resistance was ranked as one of the more important traits and one that was given a significantly higher rank for local compared to improved varieties .
The complexity in the perception of drought resistance is also apparent for sorghum in the study area. The sorghum variety wahi is, like the maize kito, an example of an improved short maturation period variety promoted by the formal seed system with very limited adoption among farmers. A short maturation period is a breeding target for sorghum in SSA because the day-length sensitivity common in local varieties is considered a production constraint . The day-length-sensitive local varieties shift from vegetative to reproductive growth when the days shorten to a critical period, regardless of the date of planting. This trait has mixed implications for coping with and adapting to climatic stress. Its primary function is to ensure that grain matures under dry conditions, which is important for avoiding grain rot, mold and other diseases . Thus, day-length sensitivity is an adaptation to the temporal habitat of the local varieties, and together with local preferences in taste and end-product use, this adaptation probably goes a long way to explaining the low adoption of improved sorghum among smallholders in the region. However, day-length sensitivity makes local varieties vulnerable to shifts in the normal seasonality. The photoperiod stays the same even if the climate conditions change and this raises questions about the adaptive potential of the local genetic resources as well as about the ability of the seed system to deliver this adaptation in a timely manner. The spatial scope of informal seed systems in providing farmers with appropriate genetic resources to adapt is beginning to attract research informed by climate projections . Our results suggest that the temporal scope of seed systems warrants more research in this context.
Seed system perspectives and adaptation
There is mounting evidence that agriculture in SSA will have to adapt to the adverse effects of climate change and much attention from development practitioners and scholars is directed towards the question of the means of adaptation. It is generally agreed that the genetic resources of important food crops are key assets for adaptation in rural households, but different research outlooks lead to different conclusions about what kind of genetic resources best allows farmers to adapt. In an agricultural modernization perspective, crop adaptation is commonly framed as a question of the public and commercial development of improved varieties, and farmers’ crop adaptation options are framed as the adoption of new technology. This framing of crop adaptation does not represent the current reality in subsistence agriculture in SSA, where most of the seeds planted are uncertified and sourced through informal seed system channels.
Framing crop adaptation with a livelihood approach captures the complex resource access situation faced by rural households in the semi-arid zone in Tanzania. The results presented here confirm that climatic stress is already a major stress factor in the livelihoods of people living in the area and that crop adaptation is among the more important responses used by households. Crop adaptation involves adoption of improved maize varieties combined with continued use of local varieties of both maize and sorghum, which despite their late maturity are valued for their drought tolerance. The seed system in the study area consists of both formal and informal elements, but the informal elements are the most important supply channels. All genetic resource categories are subject to on-farm selection and hybridization, and farmer selection may lead to incremental on-farm crop adaptation. Our findings support the view that the integration of informal and formal seed system elements will be important for agriculture-based livelihoods in meeting the challenges ahead [25–27].
This study highlights two important methodological challenges in impact and adaptation studies. First, the use of generic variety data in modeling crop impact on a large geographical scale may be problematic because of the diversity between crop varieties with regard to drought avoidance and drought tolerance traits. Biophysical crop models often fail to capture that varieties sourced through informal seed channels dominate smallholder agriculture in SSA. No single variety can represent the diverse situations in a single village, let alone in studies making projections at the national or regional level. The second methodological challenge is relevant for the small, but growing body of regression model-based adaptation studies in which a ‘switch to a drought-tolerant variety’ is used as a response variable. People’s understanding of what a drought-tolerant variety constitutes is likely to be influenced by national and international development actors’ promotion of improved varieties under this banner. In this study households’ perceptions of the characteristics of and reasons for growing the different genetic resource categories reveal that local and recycled varieties play a role in adaptation to drought stress that was left undetected in the regression modeling. The perceptions of the varieties observed here are not objective measurements, but they are nevertheless important in understanding actual decision-making by farmers . Different attributes of the varieties influence the use and allocation of land to local, improved and farmer-recycled varieties. Our findings highlight the value and importance of location-specific information about crop variety use for arriving at realistic recommendations in impact and adaptation studies. Seed system perspectives of crop adaptation offer insights into the complex ways crop adaptation is realized at the livelihood level and can contribute to increase knowledge of how farming in SSA can and will adapt to a changing climate.
International Maize and Wheat Improvement Centre
Intergovernmental Panel on Climate Change
This work was supported through a grant from the University of Oslo. We are grateful to Jans Bobert and Khamaldin Mutabazi from the project Resilient Agro-landscapes to Climate Change in Tanzania for invaluable support and advice during the fieldwork. We thank Philip K Thornton for providing the yield projection data used in Figure 1. We acknowledge Sokoine University of Agriculture for granting the research permit. We are grateful for the key information and advice we obtained from academic staff at Sokoine University, as well as the many actors in the formal seed sector. Special thanks go to the late maize breeder Alfred Moshi, who provided key insights into breeding and the adoption of improved maize in the study area. Many thanks are also due to Philip Daninga and the excellent group of MSc students who assisted with the fieldwork. Finally we would like to express our gratitude to the people and leaders of Mangae and Laikala villages for their willingness to participate in this study. This manuscript was improved by critical and insightful comments from Trygve Berg, Desmond McNeill and two anonymous reviewers.
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