INSIGHTS INTO THE EPIDEMIOLOGY OF CHLOROTIC STREAK DISEASE AS DETERMINED BY MULTIPLE FIELD ASSESSMENTS

DURING ANNUAL RATOON stunting disease (RSD) seedbed inspections at Harwood, assessments of the relative prevalence of chlorotic streak disease (CSD) were recorded on a scale of 0 (none evident) to 3 (highly prevalent). Over a three-year period (2012–2014), these assessments were made for 32 varieties growing in 1106 seedbeds. Additionally, the degree of crop uniformity was recorded (0 = even, 3 = highly uneven), as uneven distribution of CSD in a field can lead to a patchy presentation of the crop. There was variation in the level of CSD and crop unevenness among varieties, while there was significantly less CSD present in 2014 than the preceding La Niña-defined years. When crop classes were sorted into fallow plant, replant, ratoon from fallow plant and ratoon from replant, there were no significant differences in the level of CSD present among classes, while the degree of crop unevenness increased across that series, indicating that other factors influence crop uniformity. CSD was significantly less prevalent in dual row configurations; however, this may be influenced by grower practice in regards to variety adoption, clean seed uptake and drain management. This approach to CSD assessment was readily adopted by RSD survey teams and has facilitated improved epidemiological knowledge of a poorly understood disease.