Physiological response of Garlic (Allium sativum) to elevated tropospheric ozone in high altitude region of Western Ghats, Tamil Nadu, India

Abstract

A pot culture study was conducted at Horticultural Research Station, Ooty, to assess the effect of ground-level ozone on physiology in garlic plants and find out suitable remedial measures against ground-level ozone. The potting soil was acidic with very low salt concentration, very high in organic carbon, medium in nitrogen, phosphorus and high in potassium. Elevated ozone levels (150ppb and 200ppb) had significantly reduced the garlic plant chlorophyll content, stomatal conductance, photosynthetic rate, pungency and total soluble solids. The highest chlorophyll content (33.97µmolm-2) was observed under ambient ozone level(T1), and lowest chlorophyll content (12.68µmolm-2) was observed in elevated ozone exposure at 200 ppb(T3), highest stomatal conductance (0.45mmol m-2s-1) was recorded in Ambient Ozone level+foliar spray 3%Panchagavya(T4), and lowest stomatal conductance (0.11mmolm-2s-1) was observed in elevated ozone exposure at 200 ppb(T3).Since the elevated ozone had a significant reduction in photosynthetic rate in garlic, lowest was observed (0.82µmolCO2 s-1m-2) in T3-Elevated ozone exposure at 200 ppb and the highest photosynthetic rate (3.02µmolCO2 s-1m-2) was observed in treatment T4-Ambient Ozone level+foliar spray 3%Panchagavya after a week. When coming to quality of garlic bulbs, highest pungency content was found in Ambient Ozone level+foliar spray 0.1%Ascorbic acid and lowest was observed in Elevated ozone exposure at 200 ppb(T3) furthermore, in observing garlic quality where total soluble solids (TSS) showed that the treatment Ambient Ozone level+foliar spray 3%Panchagavya (40.00°Brix) as highest and treatment Elevated ozone exposure at 200 ppb(T3) recorded the lowest. Thus, tropospheric ozone has detrimental impact on physiological responses, which will reduce crop growth and yield. The ozone protectants helped in scavenging the O3 from apoplast of the crops. Among the ozone protectants, neem oil acted as a good ozone scavenger followed by ascorbic acid and panchagavya to improve the physiological response of garlic plants under elevated tropospheric ozone levels.