L. Pecetti, E. Piano and M. Romani

Istituto Sperimentale per le Colture Foraggere, viale Piacenza 29, 26900 Lodi, Italy

The interest for grazing-tolerant alfalfa varieties has recently increased in Europe with the growing demand for sustainable agriculture, multi-purpose utilization systems, and environmental protection. The breeding program established at the Forage Research Institute in Lodi, Italy, relied on the acquired evidence that plant attributes such as prostrate or semi-erect growth, deep-set crown, creeping-rootedness, and rhizomatous habit confer grazing tolerance, and are widespread in the taxa of the Medicago sativa complex. In the framework of this selection, 31 half-sib progenies from genotypes preliminarily selected for deep-set crown and plant spreading ability were subjected to continuous grazing from June through October in the second and third year after establishment. The genotypes originated from base materials previously categorized into four morphological models, according to top-growth habit and vigor (Piano et al., 1996). One model (D2) was creeping-rooted and three were rhizomatous, with rhizome aptitude decreasing, and erectness increasing from D1 to D3 to D4. The most represented D3 model was further split into two sub-groups approaching, respectively, the less vigorous D1 and the more vigorous D4 models, and coded as D3-lv and D3-hv. Persistence was recorded after each season of grazing as percent ground cover assessed by a grid method based on Bouton and Smith (1996) and with reference to a tolerant (Alfagraze) and an intolerant (Equipe) check. Differences among progenies for persistence (already evident after one season of grazing) were mostly related to the morphological models. There was significant variation among rhizomatous types, the D1 and D3-lv models being most persistent and the D3-hv and D4 models the least. The creeping-rooted D2 model showed the lowest persistence and did not differ from the intolerant, upright check (Table 1). Yield potential assessed before imposing the grazing (spring 1997) was substantially directly related to plant vigor and erectness, and inversely related to final persistence. After two cycles of grazing, the most yielding progenies were the high-persisting, prostrate, and rhizomatous D1 and D3-lw types. After the grazing pressure, these progenies approached the biomass production of the tolerant check Alfagraze (98% and 94% of the check value, respectively) (Table 1). The results suggest that rhizomatous types are generally better persisting and yielding under continuous grazing than creeping-rooted types. Among rhizomatous types variation exists in relation to plant morphology, which can be exploited to select varieties combining persistence with adequate yield.

References

Bouton, J.H. and S.R. Smith, Jr. (1996). Standard Tests to Characterize Alfalfa Cultivars. P A-8. NAAIC.

Piano E., P. Valentini, L. Pecetti and M. Romani (1996). Euphytica 89: 279-288.

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