Inheritance of Root Traits in Alfalfa

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Root growth patterns influence nutrient uptake, productivity, and persistence in alfalfa (Medicago sativa L.). Inheritance of traits affecting root growth patterns in alfalfa are not well understood. Objectives of this research were to determine the affects of plant spacing and geographic location on root traits in alfalfa, to determine the inheritance of seven root morphological traits of alfalfa, and to evaluate the association between root traits, fall dormancy, and seedling year herbage yield. Progenies of diallels and design II matings were planted during May 1991 at two locations in 30‐cm rows with 2.5 cm between plants within the row. Plants were evaluated for seedling year herbage yield and fall dormancy. During October 1991, they were dug and evaluated for taproot diameter (TD), lateral root number (LRN), lateral root diameter (LRD), lateral root position (LRP), fibrous mass (FRM), percentage of determinate taproots (PDT), and determinate taproot position (DTP). Border effects were determined by evaluating single plants from the ends of the plots separately from plants in the middle of the plots. Extra space on plot borders affected root morphology, but few progeny × border interactions were found. Location affected root morphology, and a few location × cross interactions were observed for TD and LRP. Additive genetic effects were important in controlling inheritance for TD, LRN, LRD, LRP, and FRM. These traits had moderate (45) to high (87) heritabilities. genetic variances were detected for PDT or DTP. Taproot diameter was the root trait most highly correlated with fall dormancy (0.46–0.50) and seedling year herbage yield (0.61–0.75). Selection for LRN, LRD, and FRM at one location with uniform plant spacing should be successful. Multiple location selection programs may be more appropriate for TD and LRP.