Interactive effects of Indole- 3-butyric acid (IBA) and salicylic acid (SA) on growth parameters, bulb yield and allicin contents of garlic (Allium sativum) under drought stress in field

Field trial was conducted to study the impact of 0 and 100 ppm Indole 3-butyric acid (IBA) and 0, 0.1 and 0.5 mM salicylic acid (SA) on growth and biochemical parameters, bulb yield and allicin contents in a local garlic cultivar under drought stress in Iran. Drought reduced all parameters recorded but allicin percentage. SA increased leaf area, root number, plant fresh weight, bulb weight, diameter and length, clove number and weight and brix and the effect of 0.5 mM SA was more pronounced. IBA increased total carothenoid, root and shoot fresh weight, bulb diameter and brix, but reduced anthocyanins. However, interaction of drought and SA was significant for total chlorophylls, anthocyanins, membrane permeability, root length and clove weight and 0.5 mM SA was more effective under drought and to lesser extends under non-drought stress conditions. IBA was more effective in clove number and total caratenoids when SA was applied whereas allicin contents, clove weight and membraine stability were improved in the absence of SA. Futhermore, IBA was highly effective in almost all parameters recorded only under non-drought stress and was ineffective under drought stress. The Three factor interaction was significant for plant height, final bulb yield and allicin yield. Under non-drought stress, SA was more effective when IBA was not used, whereas under drought stress, SA was equally effective under presence or absence of IBA. However, under non-drought stress, the highest amount of bulb yield and allicin yield was achieved from 100 ppm IBA+ 0.5 mM SA which was 41% and 47% over the control, respectively, whereas under drought stress, 0.5 Mm SA produced the highest bulb yield and allicin yield which was 50% and 67%, respectively over the corresponding control. It is concluded that, a combination of SA and IBA is effective for promotion of growth and bulb yield under non-drought stress whereas, under drought stress, IBA is ineffective and SA is able to promote growth and bulb yield.