The role of genetic variation from traditional landraces and wild species in the improvement of cultivated plants has been well recognized (Thomas and Mathur, 1991; Rao and Bramel, 2000). However, the value of plant genetic resources largely depends on richness of the collection, extent of characterization/evaluation and access to information and the germplasm itself. Evaluation of germplasm for response to biotic and abiotic stresses and identification of farmer and market preferred traits are key factors in its effective utilization for improved crop productivity (Manyasa et al., 2008). Investment in studies to determine the genetic diversity is important, for this knowledge enables proper organization and
# Finger millet georefence sites Lakes
District boundary
N
70 0 70 140 210 Kilometers
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# GU L U
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MU KO NO KIT G U M
APA C MA SI ND I
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PAD E R AR UA
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IG AN G A MO Y O
AD JU M A NI
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TO RO RO MBA L E
KA MW E N G E
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NT U NG A M O KA BAR O L E BU N DI BU G YO
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KA PCH O R WA
KA NU N G U
BU SI A SIR O N KO
KIS O RO
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Key
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development of improved parents and new cultivars. Morphological and agronomic traits have been widely used in the characterization and evaluation of various crops (Rick and Holle, 1990; Kaemer et al., 1995) and help understand the agronomic value of the germplasm and define potential divergent heterotic groups for use in hybridization (Ortiz et al., 1998). Use of morphological traits therefore increases the understanding of genetic variability within the germplasm thus enabling its proper management and utilization for breeding and production. Morphological characterization is relatively easy, reliable and low in cost. Genetic markers have become useful in enhancing the understanding of the diversity of natural variation especially in species where appropriate polymorphic markers are available. Over the last decade, a number of DNA markers have been developed and used in the study of crop genes, genome and genetic diversity. Therefore, agro-morphological evaluation and molecular analysis of germplasm are useful in diversity determination because they provide complementary information and increase the resolution of genetic diversity analysis (Dida et al., 2008).
1.4.1 Diversity studies in finger millet
The East African region being the primary centre of finger millet diversity boasts of a wider genetic base for the crop and large germplasm collections are held in the countries’ genebanks. These East African germplasm pools however, remain largely uncharacterized and hence unutilized (Kisandu et al., 2007;
Oduori and Kanyenji, 2007; Wanyera 2007). In Uganda, the civil strife in the 1970s and early 1980s led to loss of some landraces (Wanyera personal Communication). The ex-situ collection at the National Semi-Arid Research Institute (NASARRI) has been reduced from the original 2000 to 1000 accessions due to circumstances beyond the breeder’s control (Wanyera, personal communication). Even at global level, Upadhyaya (2010) reported that only 1% of the total germplasm has been used in crop improvement largely due to lack of data and information yet many germplasm lines evaluated have been found to be superior for specific traits and utilized either for breeding or direct release as cultivar.
Moreover, to be able to discern and appreciate diversity and adaptation for production and productivity of the germplasm, there is need to characterize and evaluate the germplasm within countries of collection and/or in similar target production agro-ecologies.
Cultivated finger millet is reported to have a narrow genetic base (Dida et al., 2007). However, phenotypic variation has been observed by many authors in a number of germplasm collections assessed.
Using 150 accessions from Africa and Asia, Hilu and de Wet (1976a) reported variability in vegetative, floral and seed morphology based on eco-geographical origin and were able to distinguish three eco-geographical races namely African highland race, lowland race and the Indian race. The variability
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observed was mainly contributed by flag leaf sheath length, flowering culm branches, culm diameter and seed colour. In Ethiopia, Bezaweletaw et al. (2006) characterized 66 accessions and found high variability among the accessions for all agronomic traits. High variability for productive tillers was also reported by Ganapathy et al. (2011) and Reddy et al. (2009). Phenotypic diversity was recorded in 2000 accessions from East Africa and India and effectively used to group the material into six races namely africana, spontenea-wild types, elongate, plana, compacta and vulgaria (Reddy et al., 2009). The variability reported indicates the potential for finger millet improvement through selection.
The use of molecular markers to study diversity in finger millet has been limited due to the limited understanding of the finger millet genome and unavailability of adequate polymorphic markers (Dida et al., 2007). The finger millet genome has only recently been studied and a few markers identified.
Upadhyaya et al. (2008) used 20 Simple Sequence Repeat (SSR) markers to characterize over 900 finger millet accessions at ICRISAT-India, revealing 231 alleles and identifying unique alleles distinguishing accessions from East Africa, southern Africa and south Asia. Although Dida et al. (2008) reported the availability of more than 200 SSR markers in finger millet suitable for mapping critical traits, they only reported the successful use of 45 of the markers for finger millet diversity studies. The 45 markers were used together with phenotypic data on 79 accessions from India and Africa and found three groups based on origin namely African, Asian and African x Asian hybrids with low variability in Asian accessions suggesting that they originated from a small genepool. Sinha and Pande (2010) using six homologous and seven heterologous SSR primer pairs found homologous primer sets more appropriate as they revealed high polymorphic alleles. Random amplified polymorphic DNA (RAPD) markers have also been used in finger millet diversity studies revealing high polymorphism in African landraces and low polymorphism in Indian landraces and improved lines (Fakrudin et al., 2000). The low diversity in improved types could be due to genetic loss through selection over time. Other researchers among them Gupta et al. (2010), Das et al. (2006), Salimath et al. (1995), Babu et al. (2007) and Kumari and Pande (2010) also reported successful use of RAPD markers to study diversity in finger millet. Because of low variability within cultivated finger millet types a large number of highly variable markers such as SSRs are required for molecular analysis (Dida et al., 2007). The SSRs have a high level of allelic diversity as a result of the variable number of repeat units within their structure, making them valuable tools for diversity studies (Morgante and Olivieri, 1993). They are often multi-allelic and can be multiplexed and automated for high-throughput genotyping (Tommasini et al., 2003). They are also characterized by hyper-variability, abundance and reproducibility and are co-dominant hence are able to identify heterozygotes which makes them a suitable option for mapping and molecular characterization (Morgante and Olivieri, 1993; Saghai- Maroof et al., 1994).
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