Majestic potatoes planted in soil naturally infested with Streptono,ces scabies were trickle irrigated to prevent infection of the tubers except during consecutive 7-day periods in the first eight weeks when tubers were developing (28 May to 23 July).During each interval without irrigation, lesions of scab affected an average of 4 internodes on the tubers but the later water was withheld, the closer to the apex of the tubers was the infection at final lifting. The tubers with most area scabbed were those unwatered between 11 and 18 june, the third week from tuber initiation, when the first-formed internodes, which expand more than later-formed ones, became infected.
Urediospores of U. viciae-fabae (broad bean rust) germinated well in the range 5-26 mC, with fastest germination at 20 mC. Exposure to 30 mC gave poor germination and damaged the spores. Infection of Vicia faba leaves depended on a moisture film. At 20 mC some infection occurred with only 4 h leaf wetness, but longer wet periods up to 24 h gave increased infection. At lower temperatures, the infection process was slower and final pustule numbers were smaller. Spore germination was delayed by daylight and by all artificial light sources that contained far-red (700-800 nm) wavelengths. The delay was increased at higher light intensities. When spores were subjected to alternating periods of light and darkness, it was found that 40 min of darkness was sufficient for the irreversible induction of germination at 20 mC.
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