A rapid and reliable screening method for rice ozone tolerance was developed to enhance evaluation technique in determining the reaction of tolerant and susceptible genotypes at the early stage of growth. Plant growth parameters were measured to evaluate ozone effects on the growth of seedlings which can be later used as criteria for ozone tolerance. Plants were subjected to 0.3 and 1 ppm ozone using 15 and 30 day-old seedlings with 7 h exposure per day for 10 days. Our results show that the tolerant, moderately tolerant and susceptible cultivars can be classified at higher ozone concentration with younger seedlings by the leaf bronzing score after 10 days. Thus, screening for ozone tolerance could be done using 1 ppm concentration. For rapid screening, direct seeding and younger seedlings at 15 days are most desired to reduce time of growing in the pots or trays. Shoot dry weight was significantly reduced in the ozone-treated seedlings compared with the control plants. Higher reduction of shoot biomass was observed in 15 day-old seedlings at 34 - 66% and 38 - 54% in 0.3 and 1 ppm, respectively compared with 12 - 24% and 28 - 48% in the 30 day-old seedlings.
Key words: Fumigated chamber, leaf bronzing, ozone screening, rice.
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