Modern maize varieties going local in the semi-arid zone in Tanzania

Abstract

BackgroundMaize is the most produced crop in Sub-Saharan Africa, but yields are low and climate change is projected to further constrain smallholder production. The current efforts to breed and disseminate new high yielding and climate ready maize varieties are implemented through the formal seed system; the chain of public and private sector activities and institutions that produce and release certified seeds. These efforts are taking place in contexts currently dominated by informal seed systems; local and informal seed management and exchange channels with a long history of adapting crops to local conditions. We here present a case study of the genetic effects of both formal and informal seed management from the semi-arid zone in Tanzania.ResultsTwo open pollinated varieties (OPVs), Staha and TMV1, first released by the formal seed system in the 1980s are cultivated on two-thirds of the maize fields among the surveyed households. Farmer-recycling of improved varieties and seed selection are common on-farm seed management practices. Drought tolerance and high yield are the most important characteristics reported as reason for cultivating the current varieties as well as the most important criteria for farmers’ seed selection. Bayesian cluster analysis, PCA and FST analyses based on 131 SNPs clearly distinguish between the two OPVs, and despite considerable heterogeneity between and within seed lots, there is insignificant differentiation between breeder’s seeds and commercial seeds in both OPVs. Genetic separation increases as the formal system varieties enter the informal system and both hybridization with unrelated varieties and directional selection probably play a role in the differentiation. Using a Bayesian association approach we identify three loci putatively under selection in the informal seed system.ConclusionsOur results suggest that the formal seed system in the study area distributes seed lots that are true to type. We suggest that hybridization and directional selection differentiate farmer recycled seed lots from the original varieties and potentially lead to beneficial creolization. Access to drought tolerant OPVs in combination with farmer seed selection is likely to enhance seed system security and farmers’ adaptive capacity in the face of climate change.

Crop adaptation to climate change in the semi-arid zone in Tanzania: the role of genetic resources and seed systems

“…In another paper we explore the consequences of this seed management in more depth using single nucleotide polymorphisms to study genetic diversity and differentiation in the local maize seed system in one of the villages in this study [65]. The assessment of households' reasons for cultivating the different genetic resource categories and their perceptions of consumption and production qualities casts more light on the complexity of crop adaptation (Table 3).…”

Genetic diversity of maize accessions for maizelethal necrosis disease resistance

“…In addition, since 1974 to 2000, maize researchers under maize research program in Tanzania have managed to utilize some potentials from maize germplasm sourced from in and outside the country to release a number of varieties (Kirway et al, 2000). Some of those were able to be adopted because they possessed some traits prefered by the community as well as being connected to the existing farming practices (Westengen et al, 2014). The characteristics of those released varieties extends from plant characteristics, yield performance, disease resistance/ tolerance etc; this gives an indication that maize germplasm present an opportunity for making genetic enhancement against maize production challenges.…”

How an improved sorghum variety evolves in a traditional seed system in Mali: Effects of farmers’ practices on the maintenance of phenotype and genetic composition

“…In most of Africa these informal systems still ensure between 80 and 100% of farmers' seed supply, as highlighted by Louwaars and de Boef (2012). Seed is saved on-farm (recycled), with the aim of reproducing the variety phenotype or adapting a population to the farmer's needs, whether it be maize in Central Mexico, pearl millet in India or organic bread wheat varieties in France (Louette and Smale, 2000;Perales et al, 2003;vom Brocke et al, 2003;Dawson et al, 2012;Westengen et al, 2014). Louette and Smale (2000) showed that farmer phenotype-based selection in traditional maize systems was the key to maintaining the typical ear characteristics of a maize variety under the presence of gene flow.…”

“…Farmers' seed selection and management can especially influence the genetic composition of the variety in open-pollinated crops such as pearl millet and maize (Morris et al, 1999;vom Brocke et al, 2003;Warburton et al, 2010;Lakis et al, 2011;Westengen et al, 2014). Using SNP markers, Westengen et al (2014) recently showed that the formal system seed of improved open pollinated maize varieties differentiated significantly from farmer recycled seeds of the same varieties in Tanzania.…”

“…Using SNP markers, Westengen et al (2014) recently showed that the formal system seed of improved open pollinated maize varieties differentiated significantly from farmer recycled seeds of the same varieties in Tanzania. The authors attributed the changes in farmer recycled seed to possible hybridization and directional selection for drought tolerance.…”