EFFECT OF BENZOIC ACID AND MYCORRHIZA ON MENTHA VIRIDS PLANTS GROWN UNDER DIFFERENT IRRIGATION LEVELS

The response of spearmint plants growth, volatile oil production and volatile oil constituents to benzoic acid (BZA) treatments and inoculation by mycorrhizal fungi under different irrigation levels was studied. Three levels of soil moisture 30%, 60% and 100% field capacity (FC) were used. BZA was applied at three rates 0, 150 and 300 ppm, while Arbuscular Mycorrhizal fungi (AMF) were used at 1g/1kg soil. Results showed that benzoic acid (300ppm) or mycorrhizal fungi were capable to alleviate the deteriorative effect of drought stress. The plants which irrigated with 100% FC and treated by AMF or BZA at 300 ppm recorded an improvement in growth characters in term of plant height, fresh and dry weights and volatile oil yield. Meanwhile, the highest volatile oil percentage during the two seasons were recorded at 60% FC with mycorrhizal fungi followed by benzoic acid at 300 ppm treatment. It was noticed that, the vegetative growth, oil  production and oil yield increased when the plants were treated by mycorrhizal fungi or BZA at 300 ppm and irrigated at 60% FC compared to those plants irrigated by 100% FC and untreated. Proline content was increased in plants under drought stress (30% FC) and untreated. The lowest values of proline content were found in the plants irrigated by 100% FC and treated by either benzoic acid or mycorrhizal fungi. Also, data showed that, dehydrogenase enzyme activity was the best under the highest level of field capacity (100% FC) with inoculation by mycorrhizal fungi. On the other hand; catalase enzyme activity was superior under the lowest level of FC (30%). AMF colonization infection on roots of spearmint plants increased with high level of FC (100%). AMF spores recorded significant increases under different levels of field capacity after harvesting period particular with mycorrhizal treatment followed by BZA (300ppm) treatment. It is of interest to mention that treating spearmint plants with benzoic acid and mycorrhiza induce mitigation effect on the harmful effect of stress condition.