Cotton leaf curl disease (CLCuD) is caused by a complex of different begomoviruses and DNA-β satellite molecules. Both the viruses and the satellites are transmitted by the Silverleaf whitefly (SLW). CLCuD is responsible for serious economic losses to cotton production in several areas where it occurs. For example, CLCuD cost the Pakistan industry an estimated US$5 billion between 1992 and 1997. CLCuD represents a serious biosecurity risk to the Australian industry. Early detection of the disease if introduced into Australia is vital to minimise economic losses. This is, through containment to limit disease spread, eradication if feasible or early implementation of management packages if eradication is not feasible.

Begomoviruses are considered one of the major emerging viral threats to crop production worldwide (Mansoor et al. 2006; Varma and Malathi 2003). The number of begomoviruses causing CLCuD has risen from only a few species in 1992 to at least six species, with about 30 different genomic sequence variants within those six species, in 2008 (Fauquet et al. 2008). A similar emergence of different DNA-β satellites has also been observed. The continual succumbing of CLCuD-resistant cotton varieties to the disease in Pakistan and India indicates an ongoing emergence of new virus species and/or DNA-β satellites. Several of these viruses and DNA-beta satellites also infect and cause disease in a range of vegetables and ornamentals, including tomato, chilli, capsicum, cucurbits and hibiscus and as many of these plants species are susceptible to more than one begomvirus, there is opportunity for the emergence of new begomoviruses. This is because multiple virus infections within the one host plant can facilitate a genetic mixing between the different virus species, leading to emergence of new species with altered host ranges and pathogenicity. Given, new begomoviruses or DNA-β satellites, may arise in plant species other than cotton, the viruses of concern to the cotton industry are not just those currently associated with CLCuD, but should also include potential emergence of new species in other plant species. Hence detection and management of CLCuD will involve multiple commodities (eg vegetables and ornamentals) and not be limited to cotton.

Many begomovirus species, several of which potentially cause CLCuD, are present in countries to the immediate north of Australia, such as Indonesia. Establishment of begomoviruses in northern Australia could occur in native vegetation or weeds, including native and endemic Gossypium and Hibiscus species, or in vegetable crops, and once established represent a significant threat for spread to southern cropping areas. Incursions of these viruses could occur through importation of infected plant material, or in virus-laden whiteflies associated with the movement of people, plant material or in tropical cyclones.

Within the last 5 years, Australia had two incursions of whitefly-transmitted viruses, including the begomovirus, Tomato yellow leaf curl virus (TYLCV). The incursion of the two viruses in distinctly different Australian growing regions and their presence at multiple locations demonstrates the existence of multiple entry and spread pathways. Abutilon mosaic virus (AbMV), another begomovirus, has been present in Australia for decades. The ornamental industry sells infected Chinese lantern (Abutilon spp., family Malvaceae) plants as a variegated form due to the symptoms induced by the virus. The presence of this virus in a widely distributed ornamental species highlights a significant risk pathway for virus introduction and spread. Thus, a review of the regulations governing the importation of ornamental species are imported in Australia and what restrictions apply to these imports is paramount to thoroughly analyse the risk for introduction of biosecurity threats such as CLCuD.