Abstract
The use of chemical inducers for the development of host resistance is an alternative approach to plant disease management and is assumed to be much more environmentally sound than traditional pesticides. Five chemical inducers, salicylic acid, oxalic acid, ascorbic acid, dipotassium hydrogen phosphate (KH2PO4), and calcium chloride (CaCl2), all at concentrations of 10 mM, and an untreated control treatment were applied by seed soaking to compare their effectiveness in inducing resistance against chocolate spot disease (Botrytis fabae Sard.) in faba bean under greenhouse and field conditions, and to investigate whether use of these chemicals in this way is associated with a reduction in plant growth and yield under field conditions. A field experiment was conducted over 2 years (2007 and 2008) using a randomized complete block design with 4 replications. Results indicated that, under greenhouse and field conditions, KH2PO4 and CaCl2 treatments were either moderately or less effective in reducing disease severity of chocolate spot. However, both inducers significantly increased the growth and yield of faba beans under field conditions compared with the untreated control treatment. The greatest reduction in disease severity of chocolate spot under greenhouse and field conditions was observed in treatments of ascorbic acid and oxalic acid. The decrease in disease severity ranged from 70.6% to 79.9% for oxalic acid and from 68.1% to 80.2% for ascorbic acid, as compared with the untreated control under greenhouse conditions. Under field conditions, the decreases in disease severity with ascorbic acid and oxalic acid treatments relative to the untreated control were 79.4% and 71.3% on day 30, 62.4% and 41.8% on day 45, and 60.1% and 41.1% on day 60, respectively. The treatments of salicylic acid and oxalic acid produced the lowest values for growth and yield parameters. These results led to the conclusion that, for field application of chemical inducers to develop host resistance, it is important to study their effects on growth and yield in addition to their ability to control diseases.