The effect of age of the sward on the relationship between water-soluble carbohydrate accumulation and drought survival in two contrasted populations of cocksfoot (Dactylis glomerata L.)


Dr F. Volaire, Institut National de Recherches Agronomiques. LEPSE, 34060 Montpellier cedex 1. France.


In Mediterranean drylands, drought survival is a major factor of persistence of perennial forage grasses. In the island of Corsica, plant survival and changes in water-soluble carbohydrate (WSC) content were investigated in first- and second-year swards of two populations of cocksfoot: Lutetia, a drought-sensitive cultivar, and KM2, a drought-resistant Mediterranean population. When subjected to a moderate drought under a rain-shelter. Lutetia died whereas KM2 recovered with low mortality. The sensitivity of survival to the date of defoliation is emphasized. In first-year swards, WSC content in entire tiller bases at the end of the drought was four times greater in KM2 than in Lutetia and was correlated with differential recovery in the two populations. Conversely in second-year swards, no relationship between WSC content in entire tiller bases and recovery was found. However, WSC content in the youngest living enclosed leaves of KM2 accumulated to reach 63% of dry matter (DM) whereas in Lutetia WSC fell below 30% of DM; this factor might be associated with its survival. In both tiller bases and enclosed leaves, sucrose content and the content of large fructans tended to increase over the summer, whereas monosaccharide content declined. Enclosed leaves are the main survival organs: their role as a sink for translocated material (sucrose) and as a site of fructan accumulation is discussed.