Viral synergism and its role in management of maize lethal necrosis disease

Maize lethal necrosis disease (MLND) in Kenya has been reported to be caused by a coinfection between a non-potyvirus Maize chlorotic mottle virus (MCMV) and a potyvirus Sugarcane mosaic virus (SCMV). The control of the disease in Kenya has been a challenge owing to the synergistic interactions that exist between the two viruses. This study, sought to determine the stage of synergism between the two viruses and its role in influencing the severity of the disease. Three maize hybrids were grown in a greenhouse and were mechanically inoculated with MCMV, SCMV and MCMV+SCMV at the vegetative stage, V4-5. The synergism was studied for a period of 90-days and double-antibody sandwich (DAS)-ELISA was used to estimate the viral titer of MCMV and SCMV under individual and co-infection states of maize plants. The results showed that the viral titers of the two viruses in both single and double infection followed a normal curve. Synergistic effect was observed between the 21- and 28-days post-inoculation (dpi). A significant increase in the titers of MCMV was observed at this time in days, while that of SCMV was more or less constant. Also, the study revealed that viral titers of SCMV in both individual and co- infected maize plants remained constant; while the viral titers of MCMV in co- infected maize increased significantly as compared to the individual infections. Furthermore, there was a positive correlation between increased symptom severity and synergism. Based on these results, SCMV plays a major role in the severity and spread of MLN disease in the South-Rift region.   Key words: Maize lethal necrosis, maize chlorotic mottle virus, Sugarcane mosaic virus, maize virus diseases.