Effect of plant genotype on the efficacy of stimulators of plant defences in two horticultural pathosystems
Abstract: Four stimulators of plant defences (SPD) were tested on two pathosystems: powdery mildew (PM) due to Podosphaera xanthii on melon and downy mildew (DM) due to Bremia lactucae on lettuce. More than 450 accessions of melon were screened for the stimulation of their defence reactions by a formulation with laminarin, BION® 50WG and CalFlux and more than 400 accessions of lettuce with BION, Calflux and a formulation with yeast extract (ABE IT 56). In the PM/melon pathosystem, only BION was able to induce resistance; in the majority of the accessions resistance was not activated but some accessions fully susceptible to PM in the control sprayed with water were very well protected by BION. In the DM/lettuce pathosystem, the three tested SPD could induce resistance, but again BION was the most effective. Close to half accessions of the 300 susceptible to Bl: 25 and a quarter of the 110 accessions tested with Bl: 26 were well protected against the tested strain by BION and some of these were also protected by CalFlux (13% and 14%, respectively) and few by ABE IT 56 (10% and 4%, respectively). In both pathosystems, the induced resistance seems to be strain-specific as some accessions were protected against one strain and not protected against another strain; nevertheless some promising accessions were protected against both strains.