Identification of natural weed hosts of Cucumber mosaic virus subgroup-I and the absence of seed transmission in weed hosts in Pakistan

Abstract

ABSTRACT Every year in Pakistan the Cucumber mosaic virus (CMV) severely damages tomato crops, but little is known about the epidemiology of this disease. Tomato fields with a high incidence of CMV were tested to determine the range of potential natural alternative weed hosts of CMV. A total of 553 symptomatic leaf samples from 36 plant species representing 19 families were analysed for the presence of CMV subgroup-I and subgroup-II using triple antibody sandwich enzyme-linked immunosorbant assay (TAS-ELISA) and reverse transcription polymerase chain reaction (RT-PCR). CMV subgroup-I was detected for the first time in nine plant species: Chenopodium album, Calotropis procera, Heliotropium indicum, Cornopus didymus, Convolvulus arvensis, Melilotus indica, Galium aparine, Nicotiana plumbaginifolia and Withania somnifera. Back indexing with leaf extracts of naturally infected TAS-ELISA- and RT-PCR-positive plants of all of these weed species produced severe symptoms in tomato plants of the susceptible variety Nagina. Grow-out testing proved the absence of seed transmission of CMV subgroup-I in TAS-ELISA- and RT-PCR-positive weed species. This information is useful for reducing early CMV infection by eradicating these weed species, thereby reducing virus reservoirs and the vector aphid population. However, the TAS-ELISA and RT-PCR tests proved the absence of CMV subgroup-II in the tested samples.