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Relation of Crop Maturity and Physiology to Air Pollution Incited Bronzing of Phaseolus vulgaris. Jerry H. Haas, Research Station, Canada Department of Agriculture, Harrow, Ontario. Phytopathology 60:407-410. Accepted for publication 25 September 1969. DOI: 10.1094/Phyto-60-407.

Bronzing symptoms of white beans (Phaseolus vulgaris) are necrotic stippling of the upper leaf surface followed, in 2-3 days, by chlorosis and then abscission of leaves. Natural fumigation does not always result in necrosis. The disease occurs late in the growing season. Within a relatively uniform crop, damage is often not uniform. Crop maturity (stage of development) regulates the time of symptom expression, and crop vigor its severity. Leaf area per plant begins decreasing at “full bloom”, and bronzing occurs about 10 days later, or 59 days after seedling emergence in most plot areas and about 1 week later in others. Dry matter production, before symptoms, is negatively correlated with disease severity. It is suggested that carbohydrate depletion of leaves predisposes them to airborne-oxidant-incited necrosis, chlorosis, and defoliation.