Diseases of Corn (2)

Common rust
Causal organism: Puccinia sorghi Schweinitz, Basidiomycotina
The most general rust disease occurring severely in Hokkaido and Tohoku Districts, the northern part of Japan. The disease occurs severely under cool and wet conditions. It produces orange to brown, oval uredinia of 2-5mm in length and 1-2mm in width on the both sides of the infected leaf abundantly around the silking stage. The surface of uredinia tears and they expose and scatter urediniospore for transmission. Later the stroma become blackish and produce telutospores in it. Some kinds of creeping sorrel are known as alternate hosts. The pathogen is classified into many races according to their reactions on corn lines, the races occurring in Japan are unknown.

Crazy top
Causal organism: Sclerophthora macrospora (Saccardo) Thirumarachar, Shaw et Narasimhan, Mastigomycotina
Fungal disease that causes rosette or malformation of the infection plants. It often shows severe symptom such as extreme increase of tillers at the upper nodes, curling of leaves, hyperplasia and malformation of tassels, phyllody of ears, etc. The sign of the disease is white powders produced on the infected leaf after raining. These are mass of zoosporangia of the causal organism and they germinate and release zoospore in water and spread. The host range of the causal organism is wide and it can infect more than 140 kinds of garamineous plants such as rice and wheat.

Epicoccum leaf spot
Causal organism: Epicoccum nigrum Link, Imperfect fungi
Little occurrence has been reported only in Hokkaido, the northern part of Japan.

Eye spot
Causal organism: Kabatiella zeae Narita et Y.Hiratsuka, Imperfect fungi
Fungal disease occurring severely in the cool region. The disease produces abundant lesions that are ash white with brown border, circle, and 1-3 mm in length on the leaf and sheath. It is characteristic that faint yellow, water-soaked halo is formed around the lesion. The disease occurs severely where the wind blows hard and makes leaves injured. The pathogen grows comparatively well at the low temperature. Host range is narrow.

Fusarium stalk rot
Causal organism: Fusarium graminearum Schwabe s.str., F. oxysporum Schlechtendahl, Imperfect fungi
Fungal disease first occurred in Oct 2012 in Hokkaido, the most northern area of Japan. It causes wilting of whole plant at the yellow ripe stage. At the beginning, the roots turn red and then the amount of roots dicrease with some proliferation and the ear of infected plant hangs down like as Pythium root rot. Because the inside of the culm become hollow and soften with white to pink mold, it is difficult to cut and harvest the plants by machines. Causal organism are F. graminearum and F. oxysporum known to cause Gibberella stalk rot and Fusarium root rot, respectively abroad. The pathogenicity of F. graminearum is far stronger compared with F. oxysporum in results of inoculation tests. Reaction of resistance to the pathogens is distictly different among corn varieties.

Gibberella ear rot
Causal organism: Gibberella zeae (Schweinitz) Petch, G.fujikuroi (Sawada) Ito, Ascomycotina
Fungal disease making the heads moldy and occurring especially in warm regions. It occurs from the end of summer to autumn and the mold of faint red or salmon flesh color is often produced in the ear. It becomes a purplish black and advances to the pith of the ear when the disease progresses severely. There are two kinds of causal organisms (G.zeae reported in a lot of cereals and F. verticillioides) in Japan. The latter produces the alkaloid, fumonisine, which is considered to cause lung edema of pig, and white brain syndrome of horse and gullet cancer of human.

Northern leaf blight
Causal organism: Setosphaeria turcica (Luttrell) Leonard et Suggs, Ascomycotina
Important fungal disease causing leaf blight mainly in the cool regions. The occurrence of the disease increases under the cool and wet conditions. If occurring severely, the whole crops of the field are damaged and killed. It occurs mainly after the silking stage and lesions are yellowish brown to gray, spindle shape, 3-10cm in length on the leaf. When the lesion become old, the center part comes to be moldy, blacking and to split easily there along the leaf veins. Conidia of the pathogen disperse by wind and rain and spread. Although the races are differentiated according to the resistance genes of corn, those occurring in Japan are unknown.

Northern leaf spot (=Helminthosporium leaf spot)
Causal organism: Cochliobolus carbonum Nelson, Ascomycotina

race 3

Spot-causing fungal disease occurring increasingly mainly in the cool region. The disease begins to occur around the rainy season and stripe lesions are produced along the midrib abundantly. Lesions are ash white with brown border, 0.5-3cm in length and 0.1-0.5cm in width. Lesions expand and fuse when occurring severely, and the infected leaf withers. The symptom in the picture is caused by race 3 of the pathogen, and the race is mainly occurring in Japan. Race 2 which produces short stripe is occurring a little, but no occurrences of race 1 which produces round lesions in specific corn lines have been reported in Japan.

Pythium root rot
Causal organism: Pythium graminicola Subramanian, Mastigomycotina
The important fungal disease which causes wilting of whole plant at the yellow ripe stage. At the beginning, the roots turn brown and then the whole plant withers around the yellow ripe stage. It is characteristic that the ear of infected plant hangs down. Because the inside of the culm become hollow and soften, it is difficult to cut and harvest the plants by machines. Causal organism is Mastigomycotina and their zoospore swim in water and spread. Since the fungi can infect various kinds of gramineous crops and weeds, these plants are considered to be primary inocula of the disease.

Pythium stalk rot
Causal organism: Pythium aphanidermatum (Edson) Fitzpatrick, Mastigomycotina
Fungal disease which occurs sporadically in Kanto and Tohoku Districts. The disease begins to occur at the stage of plant about 1 meter in height at the end of June. The surface of the culm just upper the ground at first discolors to shade brown and water-soaked, and soon the rot extends to inside of the culm rapidly. Brown and spindle-shaped lesions are sometimes produced on the surface of the culm. The culm softens and rots and the whole plant twists and falls down. The pathogen produces zoosporangia on the infected tissue and release zoospores for an epidemic. A young plant just after heading often infected especially under high temperature (30 or more) and high humidity condition.

Rhizoctonia root rot
Causal organism: Rhizoctonia solani Kuhn AG-2-2, Basidiomycotina
Fungal disease which causes root rot and damage such as lodging. The disease is occurring in Kyushu Districts, the southern part of Japan. The lesion is brown to blackish brown, sinks in the center part, and produced on the crown and prop root. The infected plant easily lodges or falls down by weak wind or rain. Since it becomes difficult to cut and harvest by machines, the yields decrease in results. The causal organism can infect various plants and cause root rot symptom and is confirmed to infect also sorghum causing a similar symptom.

Return to top