A detached leaf assay to rapidly screen for resistance of maize to Bipolaris maydis, the causal agent of southern corn leaf blight

Elizabeth Aregbesola,Sarah Hearne,Gbolagade Jonathan,Ranajit Bandyopadhyay,Titilayo Falade,Alejandro Ortega-Beltran

doi:10.1007/s10658-019-01870-4

Abstract

Southern corn leaf blight (SCLB), caused by the fungus Bipolaris maydis, is a disease that significantly affects maize productivity across the globe. A detached leaf assay (DLA) was developed to rapidly assess maize resistance to SCLB. Several experiments were conducted to: (i) identify a highly virulent B. maydis isolate; and to determine the most appropriate (ii) phytohormone to maintain viability of maize leaf tissue, (iii) leaf age for the assay, and (iv) inoculum concentration. Once optimized, the DLA was compared with screenhouse and field experiments. Use of DLA required a maximum of 28 days for resistance assessment, in contrast to screenhouse and field tests at a minimum of 33 and 72 days, respectively. DLA positively correlated with screenhouse (r = 0.48, P = 0.08) and field experiments (r = 0.68, P = 0.008). Assessments of diverse B. maydis strains and host genotypes indicated that the DLA could be used to detect both highly virulent SCLB strains and highly resistant maize genotypes. Here we report that DLA is a rapid, reliable technique to screen maize resistance to SCLB. Use of this tool in maize breeding programs can speed up the process of identification of sources of resistance to multiple variants of SCLB.

Highlights

SLB15 was selected to both optimize the detached leaf assay (DLA) and to assess resistance of 14 maize open pollinated variety (OPV) to B. maydis using DLA, screenhouse, and field experiments
Detached leaf assays are useful tools to screen crop cultivars to diverse diseases (Rajkumar et al 2005; Boydom and Dawit 2013; Arraiano et al 2001; Felsenstein et al 1998; Zandjanakou-Tachin et al 2013; Weihmann et al 2016; Degani and Cernica 2014); Twizeyimana et al 2007a; Moročko et al 2006) and insect pests (Maharijaya et al 2011; Sharma et al 2005)
Reliable DLA to screen maize genotypes for resistance to southern corn leaf blight (SCLB), a disease caused by the fungus B. maydis

Summary

Introduction

In sub-Saharan Africa (SSA), maize (Zea mays L.) provides well over 50% of the caloric intake of millions of people (van Ittersum et al 2016). In tropical regions of SSA, maize production is frequently affected by southern corn leaf blight (SCLB), a foliar disease caused by the fungus Bipolaris maydis The other races of B. maydis are Race O and Race C. The former is a more successful saprophyte and prevails across the globe (Fisher et al 1976). Losses associated with SCLB considerably impact livelihoods of farmers, food and feed sectors, and trade in countries where maize is a staple, including several SSA countries

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