Survey of the pathogen of Alternaria late blight reveals different levels of carboxamide fungicide resistance on the main pistachio producing regions of California

Authors:
  • PLPaulo Lichtemberg
    Paulo Lichtemberg
  • RPRyan Puckett
    Ryan Puckett
  • DFDaniel Felts
    Daniel Felts
  • YLYong Luo
    Yong Luo
  • LDLorene Doster
    Lorene Doster
  • DRDavid Rodriguez
    David Rodriguez
  • TMThemis Michailides
    Themis Michailides
Open Access
Publisher website
Google Scholar
Abstract
Alternaria late blight (ALB), caused mainly by the fungal pathogen Alternaria alternata, is an important pistachio disease that causes severe tree defoliation and fruit shell staining. Its control relies on multiple fungicide sprays, including carboxamide fungicides. In 2015, we surveyed 35 orchards representing nine pistachio producing counties of California to determine the current situation of Alternaria resistance to four widely used carboxamide fungicide active ingredients. This survey showed that isolates collected in the northern (Tehama, Glenn and Colusa counties) and southern (Tulare, Kings and Kern counties) Central Valley presented higher frequencies of carboxamide resistance than isolates collected from orchards in the central region (Fresno, Madera and Merced counties). The number of carboxamide usages in a year is the main factor determining elevated resistance. By extracting the A. alternata DNA and sequencing the carboxamide target genes, we evaluated the prevalence of specific molecular alterations (mutations) associated with carboxamide fungicide resistance. Finally, we identified cross-resistance patterns among different carboxamide fungicides, leading to recommendations about combinations to avoid.

This publication has 9 references indexed in Scilit: