This article addresses processes of livelihood diversification among pastoralists in the rangelands of northern Kenya and southern Ethiopia. The objectives of the article are threefold: (1) to suggest a theoretical framework for addressing income diversification among pastoralists with reference to current literature and databases; (2) to present a case study on pastoral income diversification based on preliminary field research in northern Kenya and southern Ethiopia; and (3) to summarize current understandings of pastoral diversification while pointing to additional empirical research needs. By showing how comparative analyses in the region have been constrained by theoretical and data deficiencies, the article explores ways in which income diversification differs by what are termed conditional, opportunity, and local response variables. Climate, distance to market towns, gender, wealth, and education are attributes covered by these variables and discussed in the article. The conceptualization and case study provide useful bases for conducting comparative research on pastoral diversification in East Africa specifically, and in sub-Saharan Africa generally.

Cinnamoyl CoA-reductase (CCR) and caffeic acid O-methyltransferase (COMT) catalyze key steps in the biosynthesis of monolignols, which serve as building blocks in the formation of plant lignin. We identified candidate genes encoding these two enzymes in perennial ryegrass (Lolium perenne) and show that the spatio-temporal expression patterns of these genes in planta correlate well with the developmental profile of lignin deposition. Downregulation of CCR1 and caffeic acid O-methyltransferase 1 (OMT1 ) using an RNA interference-mediated silencing strategy caused dramatic changes in lignin level and composition in transgenic perennial ryegrass plants grown under both glasshouse and field conditions. In CCR1-deficient perennial ryegrass plants, metabolic profiling indicates the redirection of intermediates both within and beyond the core phenylpropanoid pathway. The combined results strongly support a key role for the OMT1 gene product in the biosynthesis of both syringyl-and guaiacyl-lignin subunits in perennial ryegrass. Both field-grown OMT1-deficient and CCR1-deficient perennial ryegrass plants showed enhanced digestibility without obvious detrimental effects on either plant fitness or biomass production. This highlights the potential of metabolic engineering not only to enhance the forage quality of grasses but also to produce optimal feedstock plants for biofuel production.

A molecular marker-based map of perennial ryegrass (Lolium perenne L.) has been constructed through the use of polymorphisms associated with expressed sequence tags (ESTs). A pair-cross between genotypes from a North African ecotype and the cultivar Aurora was used to generate a two-way pseudo-testcross population. A selection of 157 cDNAs assigned to eight different functional categories associated with agronomically important biological processes was used to detect polymorphic EST-RFLP loci in the F(1)(NA(6) x AU(6)) population. A comprehensive set of EST-SSR markers was developed from the analysis of 14,767 unigenes, with 310 primer pairs showing efficient amplification and detecting 113 polymorphic loci. Two parental genetic maps were produced: the NA(6) genetic map contains 88 EST-RFLP and 71 EST-SSR loci with a total map length of 963 cM, while the AU(6) genetic map contains 67 EST-RFLP and 58 EST-SSR loci with a total map length of 757 cM. Bridging loci permitted the alignment of homologous chromosomes between the parental maps, and a sub-set of genomic DNA-derived SSRs was used to relate linkage groups to the perennial ryegrass reference map. Regions of segregation distortion were identified, in some instances in common with other perennial ryegrass maps. The EST-derived marker-based map provides the basis for in silico comparative genetic mapping, as well as the evaluation of co-location between QTLs and functionally associated genetic loci.

key variables: leaf appearance rate, leaf elongation rate, and leaf lifespan. The expression of each of these traits is Quantitative trait loci (QTLs) for a number of agronomically imunder both genetic and environmental control (Lemaire portant traits of perennial ryegrass (Lolium perenne L.) were identiand Chapman, 1996), and leaf development in Lolium fied by means of a reference molecular marker-based genetic map. Replicated phenotypic data was obtained for a number of field-assessed has been demonstrated to be under genetic control in a morphological and developmental traits as well as the winter hardinumber of studies (Edwards and Cooper, 1963; Rhodes, ness-associated characters of winter survival and electrical conductiv-1973; Hazard et al., 1996). Structural characteristics of ity. Marker-trait association analysis was performed by a number of plants such as tiller number, leaf number, and leaf size methods, and a high degree of congruence was observed between the are the result of these morphogenetic traits, and their respective results. QTLs were detected for morphological traits such measurement in breeding programs allows a dissection as plant height, tiller size, leaf length, leaf width, fresh weight at of the complex herbage yield trait as well as predictions harvest, plant type, spikelet number per spike and spike length, as well of the response to grazing. as the developmental traits of heading date and degree of aftermath Different ecoclimatic regions, or pastures under difheading. A number of traits were significantly correlated, and coinciferent grazing regimes, may provide alternative selecdent QTL locations were identified. No significant QTLs for winter survival in the field were identified. However, a QTL for electrical

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