Morphological and agronomic variation in north African and Arabian alfalfas

A long history of cultivation in desert regions of the Middle East has led to the evolution of diverse ecotypes of very nonwinterdormant alfalfa (Medicago sativa L.). However, relatively little is known about variation among alfalfa ecotypes from different regions of the Middle East. Relationships between extant Middle Eastern ecotypes and elite nondormant alfalfas are also not well understood. Both of these factors confound the use and conservation of this germplasm resource. The objective of this study was to develop and use practical numerical analysis procedures to describe variation in representative Middle Eastern alfalfa ecotypes and improved nondormant germplasm. Agronomic and morphological data were collected in southern Arizona over a 2-yr period from 25 ecotypes from North Africa and the Arabian Peninsula and seven elite cultivars or populations bred in North America using primarily Middle Eastern germplasm. Data were taken on forage yield, stem elongation rate, maturity, response to salinity, aphid population, frost damage, leaf area and shape, internode number and length, and stem and leaf pubescence. These data were subjected to principal components and average linkage cluster analysis. This resulted in classification of the populations evaluated into six phenotypically distinct geographical groupings: northeastern Africa (including all elite populations), the central portion of the Arabian Peninsula, Oman, Yemen, southwestern Saudi Arabia, and the Siwa Oasis in Egypt. Eight country or regional clusters were resolved in further analysis. Significant regional variation was observed within the germplasm evaluated but ecotypes from neighboring countries were generally closely associated. All elite germplasm fell within one cluster and significant divergence from the phenotype common in elite nondormant cultivars and North African ecotypes was observed in germplasm from more isolated regions, especially in southern Arabia. This suggests that only a relatively small portion of the range of variability in Middle Eastern alfalfas has been used in formal breeding.