Induced Resistance Against Plasmopara helianthi in Sunflower Plants by DL-β-Amino-n-butyric acid

Sunflower piants treated with the nonproteiti amitio add, DL-jS-attiino-n-butyric acid (BABA) were protected agaittst infection with Plasmopara helianthi. Soil drenches at the highest rates (150-250 ttig/kg soil), applied one day before the inoculation induced high levels of protection (80-83%) against the disease and more than 90% control was observed when BABA was applied at 300 mg/kg soil. However, at this concentration phytotoxic symptoms were observed. This compound also provided a curative activity when applied one day post-inoculation. BABA had no antifungal activity in vitro against P. hetianthi. The effect of BABA on zoosporangia germination was evaluated by treating pre-germinated seeds with the compound solution and the zoosporangia suspension for 3 h. Then, seeds were sown and the percentages of infected plants were determined. The other two aminobutyric acid isomers (a and g) were ineffective against downy mildew. The mechanisms by which DL-^-amino-n-butyric acid protect sunflowers against downy mildew awaits more detailed elucidation.