Season-Long Dynamics of Spinach Downy Mildew Determined by Spore Trapping and Disease Incidence

Abstract

Peronospora effusa is an obligate oomycete that causes downy mildew of spinach. Downy mildew threatens sustainable production of fresh market organic spinach in California, and routine fungicide sprays are often necessary for conventional production. In this study, airborne P. effusa spores were collected using rotating arm impaction spore trap samplers at four sites in the Salinas Valley between late January and early June in 2013 and 2014. Levels of P. effusa DNA were determined by a species-specific quantitative polymerase chain reaction assay. Peronospora effusa was detected prior to and during the growing season in both years. Nonlinear time series analyses on the data suggested that the within-season dynamics of P. effusa airborne inoculum are characterized by a mixture of chaotic, deterministic, and stochastic features, with successive data points somewhat predictable from the previous values in the series. Analyses of concentrations of airborne P. effusa suggest both an exponential increase in concentration over the course of the season and oscillations around the increasing average value that had season-specific periodicity around 30, 45, and 75 days, values that are close to whole multiples of the combined pathogen latent and infectious periods. Each unit increase in temperature was correlated with 1.7 to 6% increased odds of an increase in DNA copy numbers, while each unit decrease in wind speed was correlated with 4 to 12.7% increased odds of an increase in DNA copy numbers. Disease incidence was correlated with airborne P. effusa levels and weather variables, and a receiver operating characteristic curve analysis suggested that P. effusa DNA copy numbers determined from the spore traps nine days prior to disease rating could predict disease incidence.

Spinach Growers Value Host Resistance and Synthetic Fungicides in the Fight against Downy Mildew

“…In the future, surveys can be conducted to explore producer's willingness to pay and adopt alternative management practices, like resistant seeds developed with CRISPR technology (Kock et al 2019), spore trapping (Choudhury et al 2016a), mixes of resistant and susceptible varieties (Choudhury et al 2016b), oospore seed thresholds (Choudhury et al 2017a), and organic pesticides (Choudhury et al 2015a;Choudhury et al 2017b). These studies could be conducted online or in person.…”

Rapid detection of rice disease using microscopy image identification based on the synergistic judgment of texture and shape features and decision tree–confusion matrix method

“…The image method cannot realize real‐time warning of field crop diseases. Because of the improvement and popularization of spore trap devices, airborne fungal spores are commonly collected by these devices . Therefore, a spore trap combined with the image method is widely used for real‐time warning of field crop diseases.…”

“…Because of the improvement and popularization of spore trap devices, airborne fungal spores are commonly collected by these devices. [10][11][12] Therefore, a spore trap combined with the image method is widely used for real-time warning of field crop diseases. Li et al 13 captured the urediniospores of Puccinia striiformis f. sp.…”

Research Advances in Adopting Drip Irrigation for California Organic Spinach: Preliminary Findings

“…Downy mildew on spinach is a widespread and very destructive disease in California. It is a disease that is the most significant issue facing the spinach industry, and crop losses can be significant in all areas where spinach is produced [8]. Peronospora effusa is an obligate oomycete that causes downy mildew of spinach.…”

“…Like all downy mildew pathogens, P. effusa requires cool and wet conditions for infection and disease development [8,10]. The California industry is known for using very high planting densities and a large number of seed lines per bed [10].…”