Population dynamics of Rhizoctonia, Oculimacula, and Microdochium species in soil, roots, and stems of English wheat crops

Matthew Brown,Rumiana V Ray,Linda K Nielsen,James W Woodhall,Daniel Tomlinson,Arifa Farooqi

doi:10.1111/ppa.13329

Matthew Brown, Rumiana V Ray + Show 4 more

Open Access

https://doi.org/10.1111/ppa.13329

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Abstract

AbstractThis study aimed to elucidate the population dynamics of Rhizoctonia, Oculimacula, and Microdochium species, causing the stem base disease complex of sharp eyespot, eyespot, and brown foot rot in cereals. Pathogen DNA in soil, roots, and stem fractions, and disease expression were quantified in 102 English wheat fields in two seasons. Weather data for each site was collected to determine patterns that correlate with assessed diseases. Oculimacula spp. (66%) and R. solani AG 2‐1 (63%) were most frequently detected in soil, followed by R. cerealis (54%) and Microdochium spp. (33%). Oculimacula spp. (89%) and R. cerealis (56%) predominated on roots and soil but were not associated with root rot symptoms, suggesting that these species used soil and roots for survival and as inoculum source. M. nivale was more frequently detected than M. majus on stems up to GS 21–30 and co‐occurred on plant samples with O. acuformis. O. yallundae had higher DNA concentration than O. acuformis at the lower 5 cm basal region at GS 37–45. R. cerealis predominated in the upper 15 cm above the base beyond stem extension. Brown foot rot by Microdochium spp. was favoured by cool and wet autumns/winters and dominated in English wheat. Eyespot and sharp eyespot disease index by Oculimacula spp. and R. cerealis, respectively, correlated with wet/humid springs and summers. Results suggested that stem base pathogens generally coexisted; however, their abundance in time and space was influenced by favourable weather patterns and host development, with niche differentiation after stem extension.

Highlights

The stem base disease (SBD) complex of wheat consists of three components: eyespot, brown foot rot (BFR), and sharp eyespot (Nicholson & Turner, 2000)
This is the first study to quantify the dynamics of a range of fungal species and diseases in soil, root, and stem fractions of English wheat crops and as such provides novel information on the incidence of economically important wheat pathogens, and the risk of their associated diseases
The novel finding of this study is that the predominant Rhizoctonia spp. in soil of English wheat crops was R. solani anastomosis groups (AGs) 2-1, occurring on average in 63% of fields

Summary

| INTRODUCTION

The stem base disease (SBD) complex of wheat consists of three components: eyespot, brown foot rot (BFR), and sharp eyespot (Nicholson & Turner, 2000). Isolates of R. solani attack young roots of their hosts (Harris & Moen, 1985), and the most recent study has shown that AG 2-1 is capable of reducing the number of primary roots, root volume, and root surface area on 6-day-old wheat seedlings (Sturrock et al, 2015) Environmental factors such as meteorological conditions influence the development of fungal pathogens in soil and in planta and alter root and stem base disease development and severity. The aim of this study was to define the population dynamics of Oculimacula, Microdochium, and Rhizoctonia spp. as the principal pathogens causing SBD in soil and on stems of naturally infected English winter wheat crops during two seasons. The individual objectives were to (a) determine the incidence and severity of diseases on the roots and stems of winter wheat crops; (b) quantify targeted species of Rhizoctonia spp., Oculimacula spp., and Microdochium spp. at different developmental stages of the crop using quantitative real-time PCR (qPCR); and (c) identify meteorological factors that influence disease severity and pathogen DNA accumulation in soil and in planta

| MATERIALS AND METHODS

Findings

| DISCUSSION