Corn stunt disease

Corn stunt disease is considered a major disease of maize (Zea mays) in the Americas. Although it is probably caused by a complex of pathogens, Spiroplasma kunkelii seems to be the major component of this disease. S. kunkelii is transmitted by leafhoppers in the field (mainly by Dalbulus maidis).

S. kunkelii is reported as a major disease limiting maize production and causing economic damage in Central and South America. In recent years, its incidence has increased in many tropical and sub-tropical maize-growing areas. For example studies carried out in Argentina from 1991 to 2001, showed that the disease has largely spread across the northern part of the country, since its initial discovery in the north-east. In the Tucumán province, it was showed that S. kunkelii caused yield reductions varying from 50% to 90% (with an average of 70%) and that infected plants produced 3 times less grain (in weight). In the USA where the disease was formerly considered sporadic, corn stunt has been observed every year in the central valley of California since 1996, and in 2001, an outbreak there was reported to have caused economic losses of more than 5 million USD.

Symptoms
Infected maize plants are stunted and show chlorotic stripes on the leaves. They have much shorter internodes with a proliferation of secondary shoots, thus giving the plants a short and bushy appearance. Infected plants often show reddish purple leaf margins. Ears are small and poorly filled. Symptoms may vary according to climatic conditions, maize cultivar and the presence of other pathogens.

Control
Disease control is difficult in the field, and there is little information about effective methods against the insect vector or about the availability of resistant/tolerant maize varieties.