Downy mildew disease progress in resistant and susceptible cucumbers tested in the field at different growth stages

Abstract

Downy mildew, caused by the oomycete pathogen Pseudoperonospora cubensis (Berkeley & Curtis) Rostov, is a major foliar disease of cucumber.Ten years after the reemergence of P.cubensis, downy mildew continues to be a major threat to cucumber production in the United States.Cucumber accessions with high levels of resistance have been identified.Development of cultivars with high levels of resistance remains an important objective of cucumber breeding programs.We tested a set of cucumber cultigens, including highly resistant PI accessions and susceptible control lines, to observe the effect of plant age on resistance.Cultigens responded differently to disease across plant developmental stages.In general, older plants had more disease symptoms, even those classified as resistant, such as PI 197088.However, PI 330628 and PI 605996 held their resistance even at late developmental stages.It is possible that these lines were resistant at late stages due to other factors, such as their rapid, indeterminate growth, that allows them to outgrow the disease.However, although PI 197088 appears to have a rapid, indeterminate growth habit, it did not have more resistance at later stages of plant maturity.Regardless of the mechanism involved, plant breeders should use the genetic resistance in PI 330628 and PI 605996 over PI 197088.