Effects of intraspecific competition on growth and seed yield of contrasting sulla genotypes.

Sulla (Hedysarum coronarium L.) is a short-lived perennial legume native to the Mediterranean basin, where it is grown extensively as a 2-year forage crop. Seed is often obtained as a secondary product from second-year crops established to produce forage. Very little information is available on seed yield capacity in the first year of the crop cycle and on the influence of agronomical techniques on the reproductive process. The present study aimed to evaluate the effect of intraspecific competition on dry matter accumulation (both in epigeic organs and in taproots) and seed production in the first year of a crop cycle for two contrasting genotypes. Two field trials were carried out in a Mediterranean environment during the 2003/2004 and 2004/2005 growing seasons. The experiment was set up as a split-plot design with four replications. The treatments were as follows: 1) genotype: Gangi or Resuttano (both originated from inside Sicily but differed in terms of growth rate during the 2 years of the cycle); and 2) intraspecific competition realized by means of two plant densities: 100 and 600 plants/m2. The results showed that in the first year of the cycle, the two landraces had very different behavior: Resuttano tended to accumulate C reserves in taproots, whereas Gangi used the photoassimilates mainly for epigeic growth and the gamic reproduction process. As a result, Gangi produced about 550 kg/ha seed, whereas Resuttano had a negligible seed yield. The increase in intraspecific competition increased above- and belowground biomass at the beginning of flowering irrespective of genotype but had no effect on crop growth or seed yield at maturity.