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region are long season types that mature when the rains are ending; a key trait as drying and threshing are usually done in the fields. This is corroborated by Gopal Reddy et al. (2009) in studies done in India who found accessions from Tanzania to be the latest maturing among collections from East Africa. Production areas in Kenya and Uganda have bimodal rainfall patterns with each season lasting three to four months hence cultivars used are relatively early and drying and harvesting are done in the homesteads. Specific agro-ecological adaptation was detected in the germplasm. At Alupe the best yielding accessions were from northern Uganda, eastern Uganda, and western Kenya. The similarity in these accessions was in their duration to flowering (they flowered in about 75 days) and had good resistance to leaf, neck and finger blast. The relatively high blast tolerance in Ugandan accessions could be as a result of farmer awareness about the disease (hence selection against susceptible cultivars) coupled with research intervention leading to promotion and adoption of improved blast tolerant cultivars.
At the low altitude Kiboko research station, accessions from the eastern and western sub-regions of Uganda performed best and were relatively early (71-77 days to flower). The lower 1000 grain mass at Kiboko could be attributed to moisture stress especially at grain filling particularly in late maturing accessions. The best performing accessions at the cool high altitude Lanet location were from the Rift valley sub-region where Lanet is also situated. Genotypes adapted to this location are usually late flowering but importantly they are also cold tolerant as low temperatures usually occur at the crop flowering stage thus affecting pollen viability. In finger millet low temperature has been reported to affect pollination and fertilization processes (Bandyopadhyay, 2009). This was evident at Lanet where partial sterility was recorded in early maturing check cultivar KNE 479 and several other accessions which effectively reduced grain yield. This is not unique to finger millet. Low temperatures have been reported to affect many crops at various stages of growth and development. In sorghum (Sorghum bicolor) low night temperatures (<13°C) during flag leaf formation induce male sterility and reduce pollen viability (McLaren, 1997) and possibly stigma receptivity (Osuna-Ortega et al., 2000).
Uganda is presumed to be the centre of origin for finger millet (Hilu et al., 1979) hence higher variability was expected to be found in the country’s collections. However the variability in these accessions was relatively lower across most of the quantitative traits compared to accessions from Kenya and Tanzania.
This trend could be attributed to: low variability in finger millet production agro-ecologies hence cultivars used are relatively similar (Personal observation in 210 during collection of the germplasm used in this study); more research intervention relative to Kenya and Tanzania hence more use of improved cultivars (ICRISAT, 2013) leading to a narrow genetic base; more commercialization of finger millet with end-users preferring specific cultivars; and diversity loss during the war in the 1970s (N. Wanyera
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personal communication). Conversely, more variability was detected in the Tanzanian accessions where there has been less research intervention and so most of the cultivars currently used are unimproved landraces and are expected to have a wider variability. The high overall mean diversity indices detected in this study for quantitative traits reflects the potential breeding value of the germplasm. Gopal Reddy et al.
(2009) reported lower diversity indices (0.492) for quantitative traits of germplasm sourced from East Africa but also recorded high diversity in finger length, plant height and days to flowering. The low diversity detected could have been due to the germplasm used and/or the environment under which evaluation was carried out. Overall Ugandan accessions performed better agronomically across locations than the other accessions which could be due to the more improved genotypes in the collection compared to the Tanzanian accessions for instance which were mostly landraces.
2.5.3 Principal component and cluster analyses
Based on differential traits loadings on PC1 and PC2 the delineation of the variability in the accessions was based on peduncle length, panicle exertion, plant height, leaf sheath length, grain yield and leaf blade length. Earlier research by Bezawelataw et al. (2006) and Bharathi (2011) also corroborated these findings. High contribution of grain yield to the variability between accessions was also reported by Lule et al. (2012) while Dhanakodi (1988) found most contribution to be from leaf length. The 66.1% of total variability accounted for by the six PCs was higher than the 59.63% reported by Bharathi (2011) on seven PCs but less than 91.5% by three PCs reported by Gopal Reddy et al. (2009). However, lack of a distinct delineation pattern between the countries of origin for the first two PCs was indicative of the close relationship between the three countries’ germplasm. This finding agrees with earlier studies by Gopal Reddy et al. (2009) and Lule et al. (2012) who analyzed a set of finger millet accessions from Burundi, Ethiopia, Kenya, Tanzania and Uganda and found that accessions from East Africa, viz. Kenya, Tanzania and Uganda were closely related. Quantitative traits play a key role in adaptation to environments. Most of the agro-ecologies where finger millet is grown in East Africa receive above average rainfall. This therefore means that a number of different genotypes could be grown in a single agro-ecology which essentially explains the similarity in adaptation for several of the genotypes assessed.
However from the Shannon diversity indices, trait variances and cluster distances, it was evident that higher diversity exists in Tanzanian accessions relative to Kenyan and Ugandan accessions. This diversity must be exploited for finger millet improvement. Since most of the germplasm in the Tanzanian genebank remains uncharacterized (Kisandu et al., 2007), efforts should be made to characterize the germplasm to ascertain its true value for effective conservation and utilization. Inter-and intra-cluster distances obtained
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could form a basis for selection of diverse parents for target trait improvement. Accessions with similar agronomic traits will always group together irrespective of region of origin. The cross country and sub- region cluster patterns could also be as a result of seed exchanges between farmers either through relatives, markets and/or relief food/seed coupled with cross cutting agro-ecologies, cultures and end uses.
However, selections within countries and sub-regions for agro-ecological adaptation and end use could be the reason for the high variability recorded within countries and sub-regions. The high frequency of similarity in accession names across the sub-regions in Uganda also suggested that probably the landraces used were fairly similar thus narrowing the genetic diversity. In the cluster analysis, the low representation of minicore accessions in clusters three, five and six may be an indication of the existence of diversity in this germplasm collection not yet represented in the global collection which should be carefully identified and included in future minicore constructions.