Relation Entre la Teneur en Sucres Réducteurs des Tissus du Tournesol (Helianthus annuus L.) et leur Invasion par Macrophomina phaseolina (Tassi) Goid.

Relation between the amount of reducing sugars in sunflower tissues and their invasion by Macrophomina phaseolina (Tassi) Goid. Reducing sugars (R.S.) were measured with Bernfeld colorimetric method. In the roots, the amount of R.S. increased up to a maximum, then decreased from the beginning of flowering, and remained constant, at a very low level, from the outset of seed maturation. The same evolution was observed, with a delay of one week, in stem bases, but the amounts of R.S. were a little higher. Roots, and thereafter, stems, were invaded by Macrophomina phaseolina only after the minimum level of R.S.was reached. Varietal differences were observed, in a collection of sunflower hybrids, in response to invasion by M. phaseolina. R.S. levels in stem bases were higher in the resistant than in the susceptible hybrids.