Phytogard® and DL-β-amino butyric acid (BABA) induce resistance to downy mildew (Bremia lactucae) in lettuce (Lactuca sativa L)

Downy mildew of lettuce (Bremia lactucae) is a serious disease. An alternative to chemicals is the application of disease resistance inducers. The aim of this study was to test whether DL-beta -amino butyric acid (BABA) and Phytogard (R) (K2HPO3) could induce resistance in downy mildew susceptible plants. Aqueous solutions of BABA (0, 10, 20, 30, 50, 80, 100 mM) and Phytogard(R) (0.0, 5.8, 29.0, 40.6, 58.0 and 87.0 ppm) were sprayed on seven-day-old seedlings 0, 3, 7 and 15 days before or 1-3 days after inoculation with B. lactucae. Results obtained showed that Phytogard(R)- and BABA-induced resistance was dose-dependent. At 40.6 ppm for Phytogard(R) and 10 mM for BABA, complete protection was obtained. Both compounds had a curative effect and the induced resistance lasted for at least 15 days. It was also shown that both compounds induced systemic resistance in lettuce against downy mildew. Phytogard(R) at 40.6 ppm completely inhibited spore germination while BABA at 20 mM did not. Pathogenesis related (PR) protein analysis showed that BABA induced weak accumulation of PR-2, but not PR-1, PR-5 and PR-9. Phytogard(R) induced none of these proteins. The use of these two compounds to protect lettuce from B. lactucae is discussed.