This project aimed to examine the possible impact of tobacco streak virus (TSV) on the

Australian cotton industry. TSV is transmitted by thrips and causes a newly emerging disease which has had a significant impact on grain crops, especially sunflower and mungbean, in Central Queensland since ca. 2004.

This one year scoping study has established that cotton is susceptible to field infection

with TSV within the Emerald cotton production area, with infected plants being found at

several locations. Results from field surveys indicated that TSV did not cause significant

disease or losses in CQ cotton in the 2007/2008 season, with most field crops inspected

having less than 1% of plants affected by mild symptoms, often only consisting of single,

diffuse necrotic lesions on one leaf of infected plants.

More severe symptoms were occasionally observed in field infected plants which

included dark purple necrotic, spreading lesions on leaves, sometimes forming numerous diffuse ring spots. On plants with numerous necrotic lesions the upper leaves sometimes also displayed chlorotic mottle and deformed, down-curled leaves. Higher levels of infection were only observed in volunteer cotton plants near parthenium infestations.

A total of 13 cotton varieties/lines have been screened for resistance/susceptibility to

TSV in glasshouse tests. Results indicate that all lines are susceptible to TSV, with all

displaying mild symptoms on inoculated leaves. However, almost all lines tested had

apparently healthy growth after the initial localised symptoms.

Parthenium is suspected to be the key alternative host of TSV in central Queensland and results from this study have shown that TSV infected parthenium is present at several locations throughout the Emerald cotton production area. Crop hygiene with effective control of flowering parthenium in and around crops (particularly when crops are young) is likely to be a key control method to minimise the risk of TSV entering crops.

While results from this scoping study indicate that TSV may not cause significant

disease or losses in central Queensland cotton crops, the study was conducted during an unseasonally wet cropping cycle and many questions remain unanswered about what factors cause systemic infection, what insect vectors are involved in transmission and the extent of disease damage during a “normal” season.