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This study presents the first experimental evidence of the sensitivity of rice plants to ambient air pollution from the Southeast Asian tropical region. Two widely adopted local cultivars of rice (Oryza sativa L.), MR84 and MR185, were grown in open top chambers ventilated with charcoal-filtered air and non filtered air, and in adjacent open plots on the campus of University Putra Malaysia. This is located on the south side of the Klang Valley, a rapidly developing area embracing Kuala Lumpur and other satellite cities, but where agriculture remains important The experimental period was from October 2000 to January 2001, corresponding to the main rice growing season in peninsular Malaysia. Adverse impacts on rice growth and yield were observed and were attributed to phytotoxic levels of ambient ozone. There was a clear difference in the sensitivity of the two selected cultivars. A yield reduction of 6.3% was observed for cultivar MR185 (p < 0.01) which was largely due to an increase in grain sterility, whilst the yield reduction for cultivar MR84 was not statistically significant. The reasons for these differing responses are discussed, and a comparison of the present findings with crop responses to ozone found under European conditions suggests a higher sensitivity in our study crops. With increasing industrialisation and urbanisation, this study highlights the need for further examination of the sensitivity of a wider range of crops and cultivars to ambient air pollution in this region, and also points to the potential for appropriate cultivar selection to ameliorate impacts. [ABSTRACT FROM AUTHOR]

The phytotoxic risk of ambient air pollution to local vegetation was assessed in Selangor State, Malaysia. The AOT40 value was calculated by means of the continuously monitored daily maximum concentration and the local diurnal pattern of O3. Together with minor risks associated with the levels of NO2 and SO2, the study found that the monthly AOT40 values in these peri-urban sites were consistently over 1.0 ppm.h, which is well in exceedance of the given European critical level. Linking the O3 level to actual agricultural crop production in Selangor State also indicated that the extent of yield losses could have ranged from 1.6 to 5.0% (by weight) in 2000. Despite a number of uncertainties, the study showed a simple but useful methodological framework for phytotoxic risk assessment with a limited data set, which could contribute to appropriate policy discussion and countermeasures in countries under similar conditions.

Plants of soybean (Glycine max L.) were grown with and without the ozone protectant EDU (N-[2-(2-oxo-1-imidazolidinyl)ethyl]-n2 phenylurea) at a suburban site, a remote rural site and a rural roadside site around the city of Lahore, Pakistan. The development and yield of the plants was determined in two experiments--one immediately post-monsoon and one in the following spring (pre-monsoon). Concentrations of nitrogen dioxide and photochemical oxidants were measured at each site. The effect on yield of EDU at the suburban site (47 and 113% increase in seed weight per plant relative to the untreated plants in the post- and pre-monsoon experiments, respectively) was similar to the effects of filtration on yield on soybean in a parallel open-top chamber study at the same site (77% increase relative to plants subjected to unfiltered air for the pre-monsoon experiment). Effects of EDU on yield were greater at both rural sites than at the suburban site in both experiments, and greater in the spring experiment (182% at the remote rural site and 285% at the rural roadside site) than in the post-monsoon experiment (94% at the remote rural site and 170% at the rural roadside site); oxidant concentrations were also greater at the rural sites than at the suburban site, and greater in the spring experiment than the post-monsoon experiment. The results imply that ozone may be causing significant crop losses in rural areas around Lahore; however, the geographical extent of the problem, and the implications for peri-urban agriculture around other cities of south Asia are uncertain.