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

Maryke Craven; Liesl Morey; Adrian Abrahams; Henry A. Njom; Belinda Janse van Rensburg

doi:10.17159/sajs.2020/8508

Authors

Maryke Craven Grain Crops, Agricultural Research Council, Potchefstroom, South Africa https://orcid.org/0000-0001-7352-2414
Liesl Morey Biometry Unit, Agricultural Research Council, Pretoria, South Africa
Adrian Abrahams 1.Grain Crops, Agricultural Research Council, Potchefstroom, South Africa; 2.Department of Biotechnology and Food Technology, University of Johannesburg, Johannesburg, South Africa http://orcid.org/0000-0002-5657-7760
Henry A. Njom Grain Crops, Agricultural Research Council, Potchefstroom, South Africa https://orcid.org/0000-0001-5153-107X
Belinda Janse van Rensburg Grain Crops, Agricultural Research Council, Potchefstroom, South Africa https://orcid.org/0000-0002-5458-2187

DOI:

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

Keywords:

AUDPC, Exserohilum turcicum, fumonisin, Fusarium verticillioides, HPLC

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.