Black Scab of Jojoba (Simmondsia chinensis): an emerging disease in Australia caused by Elsinoe australis

Black scab disease of jojoba (Simmondsia chinensis) (Link) C. K. Schneider caused by Elsinoe australis Bitanc. & Jenkins was first reported in Australia in 2012. While this pathogen has been reported on citrus in other countries, it has not been previously found on any crop within Australia. E. australis is on the watch list of Plant Health Australia as a serious threat to the Australian citrus industry. However, its time and mode of entry into Australia''s jojoba plantations remains unknown. Jojoba is a desert plant and has emerged as a viable cash crop in Australia. Its unique features indicate that it could be a part of farming system well-adapted to climate change while providing a diversified income. However, the economically viable Australian jojoba industry is under threat from E australis.The Department of Agriculture WA reported in 1995 that USA, Argentina, Mexico and Israel had been the major producers of jojoba '' due to increasing world demand '' over the previous 15 years. Australia contributed approximately 10 percent of the total world production with only 300 hectares of land under cultivation of jojoba. According to the Australian Bureau of Statistics (1996), in 1994''95 Australia''s production of jojoba seeds was approximately seven tonnes, which produced roughly three tonnes of oil. The price of jojoba oil varies from $30 to $50 per litre depending upon processing and the quality of the oil. Price fluctuations in Australia in 1994''95 saw jojoba''s value drop to $15 per kilogram from a record price of $37 per kilogram in the early nineties. Today, the United States remains the major supplier of jojoba oil. Jojoba is considered to be comparatively free from diseases. However, some fungal species such as Pythium, Phytophothora, Fusarium, Verticillium and Alternaria, and bacteria such as Burkeholderia, have been reported to have attacked jojoba in Australia (Ash et al., 2005). In 2007, jojoba wilt was observed in plantings (originating from vegetative propagation) at the end of the second and third year after planting which was caused by Fusarium oxysporum (Hazanovski, & Erlich, 2007). Two major diseases, collar rot caused by Fusarium oxysporum and leaf spot of jojoba caused by Burkeholderia andropogonis, were reported for the first time in Australia in 2003 and 2004 (Albiston et al., 2003; Cother et al., 2004). In order to develop successful disease management strategies for E. australis, studies related to its host''pathogen interactions, genetic diversity and epidemiology have been undertaken. Surveys of the incidence and severity of black scab of jojoba were under taken in 2010, 2011 and 2012. One hundred percent disease incidence was found in all the surveyed locations (Hillston, Forbes and Condobolin). The susceptibility of various cultivars of jojoba to black scab caused by E. australis is unknown. In this study, five jojoba cultivars '' Waradgery, Wadi Wadi, Barindji, Guyambil and Dadi Dadi '' collected from five major affected locations in NSW and Southern Queensland (Hillston, Forbes, Bourke, Condobolin and Goondiwindi) were screened for their tolerance to the pathogen. Although none of the cultivars showed complete tolerance to the pathogen, the Wadi Wadi cultivar demonstrated moderate tolerance. Waradgery was found to be the most susceptible cultivar. The results were further validated through an informal survey sent to jojoba growers in the five locations. This study has reported for the first time the intra-specific variation of the nuclear ribosomal loci between Australian E. australis jojoba isolates. PCR amplified Internal Transcribed Spacer (ITS1, 5.8S and ITS2) fragments from five representative jojoba isolates, were sequenced to demonstrate their close relatedness to the natsudaidai and sweet orange pathotypes of E. australis (anamorph Sphaceloma australis Bitanc. & Jenkins., 1935).