Improvement of genetic potential in safflower (Carthamus tinctorius) against Pythium species would be an efficient means of control of this major seed and seedling fungal pathogen. The type and content of reaction for plant to pathogen could be severely affected by environmental conditions such as temperature. In this study seed rot and seedling damping-off of fourteen safflower genotypes that came from different origins, were evaluated using Pythium ultimum infected and sterile paper towels at temperatures 10, 15, 20, 25 and 30°C. Both factors including the temperatures and the genotypes and their interaction affected seed germination of safflower. The results showed that temperature had a significant effect on number of normal and diseased seedlings in Pythium-infected media. Among the five different levels of treated temperatures, the lowest number of normal seedlings occurred at 25 and 30°C, and the lowest number of diseased seedlings were also observed at 10 and 15°C. There was a considerable difference among the fourteen studied genotypes for number of normal seedlings and number of diseased seedlings in infected media under laboratory conditions. The effect of genotype × temperature interaction on both number of normal seedlings and number of diseased seedlings was no significant. Cultivar CW-74 had the lowest, and cultivars LRV-51-51 and LRV-55-259 had the highest number of normal seedlings under Pythium-infected conditions. And also, Line 34072 had the lowest, and cultivar CW-74 had the highest number of diseased seedlings in Pythium-infected media. In fields infesting with P. ultimum, sowing safflower seed when temperature is more than 15°C is likely to have poor stand establishment due to seed rot and seedling damping-off. Therefore it is advisable to plant safflower early when soil temperature is cool.
Key words: Pythium ultimum, zoospore, seed, seedling, rot.
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