The Eff icacy of Resistance Inducing Agents for the Control of Sunflower Broomrape (Orobanche cumana

The resistance inducing agent 1, 2, 3-Benzothiadiazole-7-carbothioic acid S-methyl ester (BTH) has been demonstrated in triggering defence reactions in crop plants against bacterial, fungal and viral pathogens but also against parasitic weeds of the genus Orobanche. In this study, pot experiments were conducted under greenhouse conditions to evaluate the efficacy of different concentrations of BTH and other resistance inducing agents in order to control Orobanche cumana in sunflower (Helianthus annuus). The elicitors were applied on sunflower plants (cv. HA 89) grown in pots as soil drenching three times in intervals of 14 days. Evaluation of disease appearance as well as biochemical analysis were conducted as described elsewhere. BTH applied in a concentration of 10 mg/pot resulted in a complete inhibition of infestation of sunflower roots with O. cumana. However, the weight and size of the sunflower heads were diminished by about 70% in contrast to CK (non-parasitized and untreated control). BTH at 5 mg/pot reduced about 87% of total number of O. cumana. In this concentration no significant effect on sunflower head weight was observed. With the exception of dichloro-isonicotinic acid (DCINA) none of the other agents tested had a significant effect on the infestation with O. cumana. DCINA applied at 3 and 10 mg/pot reduced the total number of O. cumana by 66% and 100%, respectively. However, the development of sunflower heads was completely inhibited. The results show that the commercially available resistance inducing agent BTH is able to decrease infection with O. cumana when given as soil drench. Applied in low concentration the compound even does not reduce the productivity of the crop. This control method can contribute to an integrated management of the parasitic weed O. cumana.