EVALUATION OF STEM, STRENGTH OF ALFALFA (MEDICAGO-SATIVA L) GENOTYPES

Stem strength, as an estimate of forage intake potential, could be a u seful selection parameter in alfalfa (Medicago sativa L.) breeding pro grams, but there is little information on sampling techniques or the e ffect of tissue weakening by bacterial or fungal incubation. This stud y investigated the effect of stem position (top, middle, bottom) and i ncubation with a water control, Ruminococcus flavefaciens or Neocallim astix MC-2 on stem shear strength of four alfalfa genotypes, Stem diam eter was closely associated with shear force in all treatments and was used as a covariate in statistical analyses. Shear strength increased from the top to the bottom of all genotypes regardless of incubation. Both bacterial and fungal incubation reduced (P<0.01) shear strength, with the fungus reducing shear strength to the greatest extent, Genot ype differences (P<0.05) across incubation treatments were detected in the bottom stem portions only, There were no genotype X incubation tr eatment interactions within any stem position, but genotype X position effects (P<0.01) were detected in the water incubation control, The b ottom sections of alfalfa showed the largest differences and would pro vide the best sample material to estimate forage intake potential. Ste m diameter should be used as a covariate.