Effect of northern corn leaf blight severity on Fusarium ear rot incidence of maize

Maryke Craven,Belinda Janse Van Rensburg,Henry A Njom,Liesl Morey,Adrian Abrahams

doi:10.17159/sajs.2020/8508

Maryke Craven, Belinda Janse Van Rensburg + Show 3 more

Open Access

https://doi.org/10.17159/sajs.2020/8508

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Abstract

Northern corn leaf blight (NCLB) caused by Exserohilum turcicum and Fusarium ear rot caused by Fusarium verticillioides, are economically important maize diseases in South Africa. The effect of induced plant stress by NCLB on F. verticillioides ear rot and fumonisin production is unknown. Four field trials were conducted during 2016/2017 and 2017/2018 (November and December planting dates) at the Agricultural Research Council – Grain Crops in Potchefstroom (South Africa). Three maize cultivars with varying resistance levels to NCLB were selected (IMP50-10B – susceptible, BG3292 – moderately susceptible, DKC 61-94BR – resistant). NCLB severities were created through eight treatments: TMT1 – maximum control (three fungicide applications); TMT2 – standard control (two fungicide applications) and TMT3 – natural control (not inoculated or sprayed). The remaining treatments were inoculated with a cocktail of five NCLB races (Race 3, 3N, 23, 23N and 13N): TMT4 (five weeks after planting / WAP); TMT5 (five and six WAP); TMT6 (five, six and seven WAP); TMT7 (six and seven WAP); and TMT8 (seven WAP). Maize ears were naturally infected with F. verticillioides. Fifteen random plants were labelled at dent stage and NCLB severity (%), area under the disease progress curve, ear rot diseased area, ear rot severity (%), ear rot incidence (%) and total fumonisins (FB1+FB2+FB3; ug/kg) were established. Low levels of cob rot severity and fumonisins were obtained in all four trials. NCLB severity did not affect ear rot related parameters measured. Mean fumonisin levels were below the South African tolerance levels. Fumonisin concentrations differed significantly between cultivars but was not affected by NCLB severity or the cultivar x treatment interaction. Significance:  This is the first study to investigate the effect of NCLB severity as a predisposing factor of ear rot incidence and severity of maize. The study confirmed that ear rot incidence and severity are not impacted by secondary stressors induced by NCLB, and that the cultivation of NCLB-resistant varieties would not bring about lower ear rot incidences.

Highlights

Northern corn leaf blight (NCLB), caused by Exserohilum turcicum (Pass.) K.J
The current study reports on the observed influence of northern corn leaf blight severity on F. verticillioides ear rot infection and fumonisin production in the grain of three South African maize hybrids with varying NCLB disease resistance in the field
As environmental conditions during the flowering period determine the potential for ear rot development, reigning conditions during this period were of interest in the current study

Summary

Introduction

Northern corn leaf blight (NCLB), caused by Exserohilum turcicum (Pass.) K.J. Leonard and E.G. Typical yield losses attributed to the disease generally range between 15% and 30%, but yield losses of up to 50% have been documented.[2,3] A potential yield reduction of 2–8% exists for every 10% increase in disease severity.[4,5]

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