Isolation, identification and molecular characterisation of an isolate of Zucchini yellow mosaic virus occurring in KwaZulu-Natal, South Africa

Abstract

Zucchini yellow mosaic virus (ZYMV) is an economically important virus infecting cucurbits and has a worldwide distribution. In the Republic of South Africa, ZYMV has been reported as a major limiting factor to cucurbit production. The aim of this study was to identify, isolate and partially characterise a ZYMV isolate from KwaZulu-Natal (KZN). On the basis of host reactions, electron microscopy, serology, and size of the coat protein, a potyvirus infecting cucumber, squash, pumpkin and melon samples collected from farms around KZN was positively identified as ZYMV. Mechanical inoculation of test plants showed that the virus host range was limited to the cucurbits. Mottling, vein banding and blistering of leaves, and distortion of fruit were the main symptoms observed on field and inoculated hosts. Flexuous virus particles, 720–780 nm long, were observed under the electron microscope from purified virus samples. In ultra-thin leaf sections, infected plant cells contained pinwheel and scroll-type inclusion bodies. An enzyme-linked immunosorbent assay test using antibodies specific to ZYMV following single-lesion virus isolation gave a positive reaction. The size of the potyvirus coat protein was shown to be about 35.7 kDa using sodium dodecyl sulphate–polyacrylamide gel electrophoresis. Nucleotide sequence analysis of the partial coat protein gene of the ZYMV isolate from KZN revealed 95–98% sequence identity with isolates occurring in central Europe and the Indian subcontinent, and 90–93% identity with isolates from Singapore and Taiwan. These high levels of sequence identity indicate that the KZN isolate is a variant of ZYMV. We propose the name ZYMV-KZN for the virus strain we have identified.