Infectivity of Maize Chlorotic Mottle Virus from Contaminated Maize Seeds

Abstract

Seeds have been identified as major sources of introduction and spread of pathogens, with viruses being detected in the seed and also on the seed coat. In this study, the infectivity of Maize chlorotic mottle virus (MCMV) through seeds was investigated. Maize seeds that had tested positive for MCMV previously using double antibody enzyme-linked immunosorbent assay (DAS-ELISA) and real-time reverse transcription polymerase chain reaction (real time RT-PCR) were obtained from various sources. The seeds were soaked in phosphate buffer overnight and the solution used to inoculate maize seedlings. The whole seed was also ground and mixed with the buffer and used for inoculation of seedlings by hand rubbing. Visible MCMV symptoms were observed on less than 2% of the 547 seedlings inoculated with the seed soak and seed extract from contaminated seed 28 days after inoculation and this was confirmed using DAS-ELISA. Use of real time reverse transcription polymerase chain reaction revealed infectivity of MCMV from one of the seed sources used. The mean cycle threshold (Ct) values of samples that showed infectivity ranged from 28.21 to 29.40 cycles. The means were significantly different (P<0.001) from the other samples tested, the healthy and negative controls. When compared to seedlings inoculated with MCMV-infected leaf sap, there was visible development of symptoms associated with MCMV infection, with a severity score of three and Ct values as low as 11.53. The results show evidence of infection of MCMV on maize seedlings caused by virus present in seed extract. Despite rare occurrence of infectivity, the presence of viable virus may cause spread of the virus in the field, leading to development of maize lethal necrosis disease where a cereal potyvirus is present.