Botryosphaeria species associated with grapevine decline in Western Australian vineyards

To determine the Botryosphaeria species involved in grapevine decline in Western Australia a survey was conducted on five grape growing regions, Swan District, Margaret River, Manjimup, Pemberton and Geographe. Sixteen vineyards were sampled for symptoms including bleached canes, vines with limited or no bud burst and wedge and half moon shaped internal lesions. Four Botryosphaeria species, B. obtusa, B. australis, B. rhodina and B. stevensii were found to be associated with grapevine decline in Western Australia. This is the first recording of B. australis and B. stevensii associated with grapevines in Western Australia. Botryosphaeria species are widespread on Western Australia grapevines with a total of 62.5% of the vineyards having at least one Botryosphaeria species isolated. Of the Botryosphaeria species, B. obtusa was the most commonly isolated, with 51 isolates from 6 vineyards, followed by B. australis with 37 isolates from 8 vineyards, B. rhodina with 3 isolates from 2 vineyards and a single isolate of B. stevensii from vineyard 13. Identifying the Botryosphaeria isolates to species level was difficult based on morphological characteristics. Colony morphology was often found to look similar and had an ability to change on different substrates, while the conidia of several species were also similar in shape, size and pigmentation. Combining the morphological characteristics with DNA sequencing techniques provided an accurate and reliable form of identification. Botryosphaeria australis was characterised by the production of a yellow pigment in culture. B. obtusa and B. stevensii both produce brown conidia with septa but generally the width of B. obtusa conidia is less than 10um wide, while those of B. stevensii average 12um. B. stevensii has the largest conidia of all four Botryosphaeria species associated with grapevines in Western Australia. Distinct vertical striations are also present on B. rhodina conidia. A key to identify the Botryosphaeria species associated with grapevines in Western Australia has been provided. Vegetative compatibility tests were used to determine the genetic diversity of B. australis and B. obtusa isolates associated with grapevine decline in Western Australia. A total of 20 VCGs were found among the 31 B. australis isolates, which represents a maximum genetic diversity of 38%. Pemberton had the highest genetic diversity of B. australis isolates with 100%. A total of 28 VCGs were obtained among 46 B. obtusa isolates, which represents a genetic diversity of 45%. Pemberton had the highest genetic diversity of B. obtusa isolates with 43%. The maximum genetic diversities of 38 and 45% are intermediate to high when compared to the genetic diversities of other species. There is a lack of information regarding the genetic diversity of Botryosphaeria species. A pathogenicity trial was conducted to determine whether any of the four Botryosphaeria species, B. australis, B. obtusa, B. stevensii and B. rhodina were pathogenic to healthy, rooted grapevine cuttings of two grapevine cultivars grown in Western Australia, Red Globe and Shiraz. There was a significant (p<0.05) between the pathogenicity of the Botryosphaeria isolates. B. australis was the most pathogenic species, followed by B. rhodina and B. stevensii. B. obtusa did not produce lesions on any of the canes and it is possible that B. obtusa has an endophytic part of its lifecycle on grapevines in Western Australia. There was also a significant (p