Infection of Maize by Clavibacter michiganensis subsp. nebraskensis Does Not Require Severe Wounding

Abstract

Goss’s bacterial wilt and leaf blight of maize is caused by Clavibacter michiganensis subsp. nebraskensis. Infested residue is the primary source of inoculum and infection occurs via wounds caused by sand blasting, hail, or wind damage. The pathogen survives as an epiphyte on maize leaves and, because the disease has been observed on plants in the field with no obvious wounding, we wondered whether infection by epiphytic C. michiganensis subsp. nebraskensis and disease development could occur in the absence of severe wounding. Consequently, greenhouse experiments were done to evaluate disease development in the absence of wounding in ambient and increased humidity conditions. Maize plants at the V4 to V5 crop development stage were spray inoculated with a suspension of C. michiganensis subsp. nebraskensis (108 cells ml−1). Leaf blight incidence was assessed on whole plants and individual leaves; epiphytic populations of C. michiganensis subsp. nebraskensis were monitored by dilution plating of leaf washes; and epiphytic C. michiganensis subsp. nebraskensis colonization was visualized using scanning electron microscopy (SEM). Goss’s leaf blight symptoms were observed on nonwounded plants in ambient (37.0% plant incidence) and increased humidity conditions (60.0% plant incidence). Populations of epiphytic C. michiganensis subsp. nebraskensis survived and increased on maize leaves, particularly at increased humidity. We observed C. michiganensis subsp. nebraskensis colonizing maize leaves in localized sites that included epidermal junctions, cuticle depressions, in and around stomata, and at the base of trichomes. Single cells and aggregates of C. michiganensis subsp. nebraskensis were observed within substomatal chambers using SEM. These data indicate that severe wounding is not necessary for C. michiganensis subsp. nebraskensis infection of maize, and stomata or trichomes may serve as entry points for the bacterium.

Identification of Loci That Confer Resistance to Bacterial and Fungal Diseases of Maize

“…The bacteria colonize the xylem, and vascular wilt symptoms can develop in susceptible lines ( Mbofung et al 2016 ; Jackson et al 2007 ; Schuster 1972 ). The bacteria usually enter the leaves through wounds, but can also enter through natural openings in the absence of wounding in high-humidity conditions ( Mallowa et al 2016 ). First identified in 1969, GW is now found throughout the midwestern United States and Canada ( Malvick et al 2010 ; Howard et al 2015 ; Singh et al 2015 ; Schuster 1972 ; Mueller et al 2016 ; Jackson et al 2007 ).…”

Genome‐Wide Analysis and Prediction of Resistance to Goss's Wilt in Maize

“…he bacterium overwinters in infected crop residue on the soil surface, where it relies on splashing rain for dissemination (Schuster, 1975). he pathogen is nonmotile (Vidaver and Mandel, 1974) and most likely to infect through wounded or damaged tissue; however, disease development has been observed in unwounded plants under high humidity conditions (Mallowa et al, 2016).Goss's wilt is endemic from Louisiana, USA, to…”

Identification of Quantitative Trait Loci for Goss's Wilt of Maize

“…nebraskensis overwinters in infected crop residue on the soil surface (Schuster, 1975). Infection occurs most readily through wounded or damaged tissue; however, disease development can occur in unwounded plants subjected to high‐humidity conditions (Mallowa et al, 2016). Hail damage and sand blasting both cause the type of mechanical injury necessary for infection, but splashing water is often necessary to move the pathogen, as Cmn is nonmotile (Vidaver and Mandel, 1974; Jackson et al, 2007).…”