Vulnerability of US maize germ plasm to phaeosphaeria leaf spot

Phaeosphaeria leaf spot (PLS) is a potentially important maize disease that has recently appeared in the continental United States in winter breeding nurseries in southern Florida. To better predict the potential of this newly introduced disease to inflict damage on the U.S. maize crop, 64 public and private inbred lines and 80 proprietary commercial maize hybrids representing the genetic diversity in the U.S. maize crop were evaluated for resistance to PLS in the 1996-97 and 1997-98 winter nursery seasons. Plots were evaluated for PLS severity (0 to 9 scale) at the early to mid dent stages of kernel development. Relatively few hybrids or inbreds were free from PLS at this growth stage. inbred lines related to B73 were particularly susceptible to PLS. Relatively few commercial hybrids were as severely diseased as a susceptible check hybrid, indicating that U.S. maize production is not particularly vulnerable to damage from PLS at this time. However, the susceptibility of several widely used parental inbred lines makes PLS a potential concern to the seed industry should it become established in areas of hybrid seed production.