Root growth patterns influence nutrient uptake, productivity, and pers
istence in alfalfa (Medicago sativa L.). Inheritance of traits affecti
ng root growth patterns in alfalfa are not wed understood. Objectives
of this research were to determine the affects of plant spacing and ge
ographic location on root traits in alfalfa, to determine the inherita
nce of seven root morphological traits of alfalfa, and to evaluate the
association between root traits, fall dormancy, and seedling year her
bage yield. Progenies of diallels and design II matings were planted d
uring May 1991 at two locations in 30-cm rows with 2.5 cm between plan
ts within the row. Plants were evaluated for seedling year herbage yie
ld and fall dormancy. During October 1991, they were dug and evaluated
for taproot diameter (TD), lateral root number (LRN), lateral root di
ameter (LRD), lateral root position (LRP), fibrous root mass (FRM), pe
rcentage of determinate taproots (PDT), and determinate taproot positi
on (DTP). Border effects were determined by evaluating single plants f
rom the ends of the plots separately from plants in the middle of the
plots. Extra space on plot borders affected root morphology, but few p
rogeny x border interactions were found. Location affected root morpho
logy, and a few location x cross interactions were observed for TD and
LRP. Additive genetic effects were important in controlling inheritan
ce for TD, LRN, LRD, LRP, and FRM. These traits had moderate (45) to h
igh (87) heritabilities. No 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 sp
acing should be successful, Multiple location selection programs may b
e more appropriate for TD and LRP.