‘Candidatus Phytoplasma asteris’ subgroups display distinct disease progression dynamics during the carrot growing season

Marjorie Garcia,Kurt Lamour,Benjamin Z. Bradford,Justin Clements,Weijie Huang,Agnieszka Zwolinska,Shannon Piper,Russell L. Groves,Saskia Hogenhout

doi:10.1371/journal.pone.0239956

Abstract

Aster Yellows phytoplasma (AYp; ‘Candidatus Phytoplasma asteris’) is an obligate bacterial pathogen that is the causative agent of multiple diseases in herbaceous plants. While this phytoplasma has been examined in depth for its disease characteristics, knowledge about the spatial and temporal dynamics of pathogen spread is lacking. The phytoplasma is found in plant’s phloem and is vectored by leafhoppers (Cicadellidae: Hemiptera), including the aster leafhopper, Macrosteles quadrilineatus Forbes. The aster leafhopper is a migratory insect pest that overwinters in the southern United States, and historical data suggest these insects migrate from southern overwintering locations to northern latitudes annually, transmitting and driving phytoplasma infection rates as they migrate. A more in-depth understanding of the spatial, temporal and genetic determinants of Aster Yellows disease progress will lead to better integrated pest management strategies for Aster Yellows disease control. Carrot, Daucus carota L., plots were established at two planting densities in central Wisconsin and monitored during the 2018 growing season for Aster Yellows disease progression. Symptomatic carrots were sampled and assayed for the presence of the Aster Yellows phytoplasma. Aster Yellows disease progression was determined to be significantly associated with calendar date, crop density, location within the field, and phytoplasma subgroup.

Highlights

Understanding the progression of pathogen infections resulting in disease phenotypes in agricultural crops is critically important for determining effective pest management strategies
Aster Yellows disease progression increased over the growing season and was dependent upon initial planting density
Disease incidence gradually increased throughout the season until October, Aster Yellows phytoplasma subgroups display distinct disease dynamics during the growing season when it increased exponentially, reaching an average of 4.5 ± 1.8% and 4.3 ± 1.9% in the high-density planting, and an average of 11.0 ± 5.9% and 8.2 ± 2.2% in the low-density planting (Fig 1 and S3 Table)

Summary

Introduction

Understanding the progression of pathogen infections resulting in disease phenotypes in agricultural crops is critically important for determining effective pest management strategies. This small, wall-less prokaryote can infect more than 350 different species of plants including vital agricultural crops resulting in multiple host-dependent disease phenotypes [1,2,3]. The AYp pathogen causes Aster Yellows (AY) disease This pathogen is vectored by multiple leafhopper species [1,2,3]. Aster Yellows phytoplasma subgroups display distinct disease dynamics during the growing season effector is responsible for enhanced colonization by insect vectors on plants [15], a phenotype that is dependent on SAP54 interaction with RAD23 [15]. Our overarching goal was to investigate the disease progression of AY within a carrot field, emphasizing the spatial and temporal dynamics of AY incidence and the composition of SAP effectors genes associated with AYp strains found in infected plants. The findings provide insight into the movement and colonization of AYp in a carrot field and will lead to a better understanding of disease progression and management

Ethical statement

Results

Discussion and conclusions