This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

Tomato spotted wilt virus (TSWV) occured sporadically in potato crops in Australia, sometimes causing severe losses. Very little was known about the disease in potato making it difficult to determine the underlying factors responsible for the disease. Part of the problem stemmed from the sporadic nature of the disease in potato, which made it hard to find a consistent data set for analysis, at the desired level of aggregation, both for disease incidence and intensity as the variables to be explained and for explanatory variables.

As part of a continuing effort to deepen the researchers insights into the ecology and epidemiology of TSWV in potato crops, surveys were conducted from June 2001 to March 2004 in commercial potato fields in South Australia, Victoria and Tasmania. Mathematical models were developed to predict onion and tomato thrips (the only two known vector thrips species found in potato crops) population fluctuations. The models were used as a hazard prediction for integrated TSWV disease management.

Among the most significant factors affecting the epidemiology of virus diseases was the inherent susceptibility of the cultivars being grown. The reaction of twenty-seven potato cultivars, with diverse genetic backgrounds, to TSWV were studied for two seasons in both glasshouse and field conditions, consistent with normal commercial growing practices, and to evaluate the effects of infections at different stages of plant growth. Variations in susceptibility to infection were exhibited by potato cultivars and were conditioned by the age of the plant at the time of infection as measured by symptom expression, shoot and tuber infections.

Viral movement restriction was a common natural resistance mechanism to infections in many infected plants. To further understand the observed resistance to both infection and virus systemic invasion in potato, the effects of temperature and its interaction with plant age at the time of inoculation on foliar and tuber infections of TSWV, and symptom expression in two commonly commercially grown potato cultivars Shepody (susceptible) and Russet Burbank (tolerant) was studied. Overall, there were variations in the virus movement patterns in early versus late inoculations at different temperatures used.

Factors that influenced thrips dispersal determined if and when. Onion thrips preferences and performances on host plants were examined, in both choice and non-choice assays, to gain insights into the relative importance of different potential TSWV transmission patterns. Thrips raised on either TSWV-infected potato, tomato or D. stramonium, fed and reproduced preferentially on some test plants. Thrips did not reproduce on potato cultivars Bismark and Tasman and on the weed, C. album, confirming non-preference for these plants and suggested the involvement of some non-contact cues involving antibiosis or antixenosis.

Insecticide trials across three seasons indicated the potential of both pre-plant and foliar treatments to reduce disease spread in Tasmania (where onion thrips was the only known TSWV vector active in potato). In contrast, a trial in South Australia where both onion and tomato thrips were present indicated little benefit of insecticide treatment.

In summary, the results from the above studies, collectively, contributed to uncover some ecological relationships and patterns of both TSWV and its vector thrips that could be integrated with plausible mechanisms to explain the epidemiology of the virus in potato crops and advance the rationale for future research in this direction.