Pathogenic behaviour of Cephalosporium maydis and C. acremonium

Abstract

S U M M A R YCephalosporium maydis infects young maize plants easily, but as plants age fewer are infected and none after approx. 50 days from sowing. The mesocotyl and seminal, fibrous and adventitious roots are attacked, especially when there is damage or much inoculum. Most penetration occurs where roots are elongating and emerge from the mesocotyl or from fibrous roots. At first the fungus grows superficially on roots, producing hyphae with short, brown, thick-walled, and swollen cells. After penetrating, the fungus spreads towards the xylem, where it grows slowly at first but after 5 weeks grows faster upwards.C. acremonium causes black-bundle disease of maize. It seems to infect plants growing in unfavourable conditions but the details remain uncertain. The percentage of plants infected was not related to the amount of inoculum and the fungus may not be a primary parasite. The sterile culture filtrate of the fungus produces vascular discoloration and wilt of maize seedlings.

Plant growth hormones suppress the development of Harpophora maydis, the cause of late wilt in maize

“…Indeed, H. maydis behave both as a hemi-biotroph and necrotroph. The pathogen is spread throughout the host; by flowering (anthesis at 9-10 weeks), it is distributed throughout the stalk and many vessels are blocked with hyphae and a dark gumlike substance (Sabet et al 1970). So the pathogen is gradually suffocating the host by filling the xylem, causing vascular occlusion.…”

“…First symptoms appear approximately 60 days after sowing (Sabet et al 1970) and include drying out of the lower leaves. Later, drying out ascends upwards in the plant and causes leaf yellowing and dehydration, color alteration of the vascular bundles to a yellow-brown hue and then the appearance of red-brown stripes on the lower internode .…”

Diagnosis and Control of <i>Harpophora maydis</i>, the Cause of Late Wilt in Maize

“…First symptoms appear approximately 60 days after sowing [20] and include the development of light green stripes on the leaves; the stripes become translucent, and the entire leaf rolls inward from the edges. Later, drying-out ascends upwards in the plant and includes leaf yellowing and dehydration, color alteration of the vascular bundles to a yellow-brown hue and then the appearance of redbrown stripes on the lower internode, the symptoms advancing to the fifth internode or further [12].…”

“…Spread within a field is often associated with mechanical operations such as cultivation that moves soil. H. maydis can persist on corn stubble for 12 -15 months [20,25]. Sclerotia are produced under low humidity, which ensures long-term survival of H. maydis (up to 15 months) in no-till residues on the soil surface.…”

“…Some fungicides that were tested worked well in pots but failed in field experiments [32], while others achieved promising success [32]. Since H. maydis is a poor saprophytic competitor [20], various attempts at biological control by inoculating corn seed with competitive or antagonistic organisms (Macrophomina phaseolina, Trichurus spiralis, Bacillus subtilis, Pseudomonas fluorescens, Verticillium tricorpus) have been evaluated [29,33,37,38]; however, success on a field scale has not been demonstrated consistently. Today, there is no available effective chemical or biological method for controlling late wilt in Israel.…”