Worldwide, virus diseases, especially Cotton leaf curl disease (CLCuD) cause serious economic losses to cotton production. For example, CLCuD cost the Pakistan industry an estimated US$5 billion between 1992 and 1997. CLCuD is not known to occur in Australia and is a significant biosecurity risk for the industry. The disease is caused by a complex of different begomoviruses and DNA-/3 satellite molecules. Okra, hibiscus and papaya are alternative hosts of the CLCuD complex. However, the survival of the disease between cotton seasons is not fully understood and other alternative weed and crop hosts may also harbour the disease. The CLCuD complex is transmitted by the silverleaf whitefly, which is widespread and abundant in many Australian cotton production areas. In countries to the immediate north of Australia, there is a range of plant species infected with various begomoviruses and DNA-/3 satellites, many of which may have the potential to cause CLCuD. Therefore, establishment of CLCuD, in native and endemic Gossypium and Hibiscus species present in northern Australia is a risk.

The major outcome of this project was a draft contingency plan for CLCuD. The plan contains details on how to detect, contain and eradicate or manage the disease if introduced to Australia. The plan is available for comment by the industry, thus providing opportunity for industry input on what aspects are included in an emergency response for CLCuD. Furthermore, the industry was provided with training on the symptoms of the disease and how to find it which will assist in early reporting and subsequently improve the chance of containment and eradication or management of the disease if introduced.

Alternative CLCuD hosts were clarified within the project including the identification of two new crop hosts, melon and capsicum, and two new native gossypium hosts, Gossypium sturtinanum and Gossypium robinsonii.

Surveys of commercial cotton and native gossypium provided confidence that CLCuD is not present in Australia. It also allowed a thorough evaluation of endemic viral diseases and confirmation that the endemic strain of TSV is not causing economic damage to Australian cotton. CBTD was regularly detected at low levels but during the 2011 season was causing economic damage on a number of properties. This recent outbreak allowed opportunity to evaluate the disease under highly conducive conditions and thereby enhance knowledge on its management. Multiple samples were collected to confirm ratoon cotton as an important disease reservoir.

Preliminary results on characterisation and epidemiology of the polerovirus(es) causing CBTD has highlighted the complexity of the disease. Symptomology, causal agents and disease reservoirs all require clarification. Some of these issues will be addressed in the current CRDC project DAQ1201.