Abstract
Analysis of spatial diversity, temporal diversity and coefficient of parentage (COP) were carried out along with measurements of agronomic and morphological traits to explain on-farm diversity of modern varieties or landraces of wheat (Triticum aestivum L. and Triticum durum L.) grown by farmers in Ethiopia. Farm level surveys showed low spatial diversity of wheat where only a few dominant varieties appeared to occupy a large proportion of wheat area. The five top wheat varieties were grown by 56% of the sample farmers and these varieties were planted on 80% of the total wheat area. The weighted average age of wheat varieties was high with an average of 13.8 years for bread wheat showing low temporal diversity or varietal replacement by farmers. The COP analysis showed that average and weighted diversity of bread wheat was 0.76 and 0.66, respectively variance component analysis showed significant variations for agronomic characters such as plant height, grain yield, and yield components (kernels spike-1, thousand seed weight) among modern varieties and/or landraces. The principal component analysis explained better the variation among varieties and landraces. Cluster analysis based on agro-morphological traits grouped modern varieties and landraces into separate clusters. The present study describes the diversity of wheat crop available on the farm using different indicators. The variation among modern varieties and landraces offered opportunities for using genotypes with desired agronomic characters in plant breeding to develop varieties suitable for different agro-ecological zones in the country. Key words: Ethiopia, wheat, genetic diversity, spatial diversity, temporal diversity, coefficient of parentage, landraces.  
Highlights
Crop genetic diversity refers to variation within a plant, within a crop, between crops of the same species and between different crop species (Almekinders et al, 1995)
The diverse agro-ecology and long history of association with the wheat crop and its production under a variety of socio-economic and cultural situations led to the evolution of highly diverse forms of landraces which could be of practical benefit for crop improvement
The Ethiopian highlands are considered the centers of diversity of tetraploid wheats where a considerable wealth of genetic variability and diversity still exists on the farm
Summary
Crop genetic diversity refers to variation within a plant, within a crop, between crops of the same species and between different crop species (Almekinders et al, 1995). It is argued, that the definition of diversity across disciplines could be problematic because the criteria and scales for measurements and their relationships are weak (Smale et al, 1996). Spatial diversity indicates the number of varieties grown or the proportion of area occupied by each variety per unit farm, area, community or region. Temporal diversity indicates changes in crop varieties (or sequential varietal releases by plant breeders) assessing changes taking place over time through introduction or withdrawal of varieties by individual farmers or farming communities. At present a combination of different approaches and tools are used to analyze the genetic diversity of crops (Duvick, 1984; Brennan and Byerlee, 1991; Smale et al, 1996)
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