Maize wallaby ear disease (MWED), an important plant disease which was reported in Queensland, Australia for the first time, has broken out in Sichuan, Guizhou provinces and Chongqing district since the 1980s. In Nanchong Sichuan, the total area covered by MWED and the yield loss of maize is 10,600 hectares and 4,800,000 kg in 1988 respectively, and in Guizhou province it reached to 824 hectares in 1999. Subsequently, the disease has broken out in Chongqing district on several occasions and caused serious economic losses in the production of maize. The biological and ecological characteristics and the transmission of virus by Cicadulina bipunctella(Mats) as well as the development and control methods of MWED are reviewed in this paper.
MWED is transmitted effectively by three leafhoppers C.bipunctella, C.bimaculata(Evans) and Nesoclutha pallida(Evans). Plants with a severe infection have a stiff and erect appearance and develop numerous galls often covering all secondary veins on most or all leaves. These plants rarely recover, but die early or remain severely stunted and yield very little or no grain. Other than the leafhoppers transmitting MWED, the development of the disease is also influenced by temperature, humidity and maize varieties. The optimum conditions for the disease are (28±1)℃,RH 75%～90%, and most varieties are susceptible. The MWED disease index has a peak which lasts for almost 20 days from the last 10 days of May to the first 10 days of June in each year. It is still not clear whether the disease agent is a virus or an insect toxin.
C.bipunctella, the dominant species transmitting MWED in China, has 5 nymph instars and overwinters as adults. The population on gramineous crops and weeds shows such behavior as high preference to illumination and preference to green leaves. It has three generations per year in northern Sichuan and brings on the reduction of output for maize mainly by the overwintering generation and the first generation. The density of C.bipunctella in Nanchong Sichuan has two peaks and the spatial distribution of the population shows either clumped or uniform patterns during the period of maize growth. The temporal and spatial dynamics of the leafhopper are influenced by temperature, humidity as well as its host plants. C.bipunctella transmits MWED effectively except the 1st instar nymph. From adults the disease agent of MWED is passed to their offspring through eggs. The acquisition feeding period of C.bimaculata is 7d and the inoculation feeding period of C.bipunctella is approximately 10min. The transmission rate of adults is above 90%, and the capacity of transmission of the disease agent has two peaks which appears in the first 2 days and from the fourteenth to the sixteenth day of the adult period after eclosion.
Based on the research on MWED and its vector leafhopper, it is understood that virus original, susceptible maize varieties and vector leafhoppers are essential for the occurrence of the disease. When the three requirements are met, the disease will develop and spread rapidly. In order to decrease the losses caused by MWED, measures such as planting resistant varieties, controlling the quantity of vector leafhopper and reducing the disease agent should be addressed especially in areas with severe infection.