Comparative Etiological and Epidemiological Studies on Rust Diseases of Phaseolus vulgaris and Macroptilium atropurpureum

Abstract

Collections of rust on Phaseolus vulgaris and Macroptilium atropurpureum from Australia and South America were examined. Telia of Siratro rust were not observed. Urediniospores of the Siratro rust encompassed a broader range in size than those of bean rust (Urornyces appendiculatus) but were generally within the accepted range for that species. The walls of the Siratro rust urediniospores were significantly thicker than those of the bean rust urediniospores and were outside the given range. Although the Siratro rust produced small (160 μm) sporulating uredinia on the bean rust differential cultivar Golden Gate Wax, all members of the bean rust differential set were classified as resistant to it.

The pathogens (Siratro rust and bean rust race egh) on their respective hosts showed significantly different responses to dew period temperature for infection. The pattern of response to the different post dew period temperatures was also significantly different, although the optimal temperature range for maximum infection in this stage was the same. Optimal environmental conditions for maximum disease development during the pre-penetration stage of the disease cycle were 20°C and 24 h of dew for Siratro rust and 15-20°C and 24 h of dew for the bean rust. The optimal temperature range for maximum disease development for the Siratro and bean rust pathogens in the post-penetration stage of infection was 20-26°C. While maximum numbers of uredinia developed on bean at 14-24°C this temperature range resulted in the latent period and generation of time being extended by one day in comparison to those at 20-26°C and 24-32°C.