Screening Tomato Lines for Late Blight (Phytophthora infestans) Resistance Under Conventional and Organic Systems

Late blight caused by Phytophthora infestans is a serious foliar disease in tomato. This disease caused severe damage on tomatoes throughout much of the USA during the summer of 2009. While conventional crops could be managed by scheduled spraying of fungicides, tomato production under organic conditions was a challenge. The objective of this research was to evaluate tomato lines and hybrids grown in a conventional system without fungicides and under organic conditions with approved fungicides to help identify suitable ones for organic production systems. We evaluated 100 tomato genotypes, including breeding lines and hybrids, derived from multiple resistance sources under conventional systems in two locations (Mills River and Waynesville, NC). A sub-set of 20 genotypes consisting of breeding lines, hybrids, and heirloom tomatoes were also evaluated under an organic production system for late blight resistance.  The genotypes were scored for late blight in a scale from 0 to 5, 0 indicating no disease at all whereas 5 indicating fully covered with the disease. From the conventional set of experiment, 35 lines did not show any symptoms of late blight at all whereas additional 37 had some symptoms scoring less than or equal to 1. Results from the organic set of experiment were in agreement with the one from conventional. Superior performance of some of the breeding lines and hybrids for horticultural traits along with high level of resistance to the late blight in both experiments indicated that the list of genotypes from this experiment may provide the foundation for further development of late blight resistant tomato in future.