Effect of Vesicular Arbuscular Mycorrhizal Fungi on Papaya (Carica papaya L.) Plant Underwater Stress Conditions

Seedlings of papaya (Caricapapaya L.) were transplanted to pots with or without an vesicular arbuscular mycorrhizal (VAM) fungus Glomus mosseae. After 3 months, half the plants were subjected to water stress by withdrawing irrigation. The leaf water potential (LWP) was measured during 20 days of water-stress treatment and then the plants were harvested. Root ethylene and I-aminocyclopropane-I-carboxylic acid (ACC) concentrations were measured and plant fresh weight determined. The LWP decreased during the water-stress treatment and this decrease was more severe in the non-VAM plants. Plant fresh weight was higher for VAM than non-VAM plants under both conditions. Under well irrigated conditions, the ethylene concentration in the roots was increased by the presence of VAM although there was no significant difference between VAM and non-VAM roots in ACC levels. ACC increased in both VAM and non-VAM roots under water-stress conditions. The water-stress treatment resulted in marked increase in ethylene concentration in non-VAM roots but the concentration in VAM roots was slightly lower normal conditions.