Symptoms

Chlorotic streak is a systemic disease of unknown cause and is characterised by yellow to creamy-white leaf streaks with irregular waxy margins. These streaks, usually 2-6mm wide, may be short or may extend the fully length of the leaf blade.

Streaks in the early stages of development are usually fragmented, but as they age they become more regular and take on a yellow hue. Necrotic areas frequently develop along the centre of the streak. Streaks appear similar on both sides of the leaf blade. More than one leaf streak may occur on a single leaf. Heavy symptom development may be accompanied by wilting and shoot death leading to variable plant stands.

Longitudinal slicing of diseased stalks reveals reddened vascular bundles through the node and a short distance inter the internode region.

Cause
The causal agent has not been identified, though some evidence suggests it is a virus. The disease is transmitted in planting material and by flood waters.

Distribution
The disease is distributed widely throughout Queensland but is worse in flood-prone areas. The worst-affected mill areas include Rocky Point, Macknade and Victoria, though wetter parts of northern Queensland and New South Wales regularly suffer yield losses from the disease.

Assessment of Severity
Timing and inspections
Soil temperatures of 30^oC favour symptom expression of the disease while lower temperatures may lead to a temporary absence of symptoms. For this reason, especially in southern Queensland, inspections should coincide with high soil temperature in the November to March period.
Assessing severity
In recording diseased areas, note is made only of moderate to severe disease. A few diseased shoots in a block are of no real consequence for crop yield and are not recorded in routine disease assessments. It is suggested that diseased stalk populations of 5% be the threshold for disease records.

History of Incidence
Chlorotic streak apparently took some time to spread through the state. The first pathology survey of northern Queensland showed that the disease was endemic in the area before it was first recognised as a disease (1929). As the disease is favoured by flooding and wet conditions, high level of disease have occurred during high rainfall periods (for example the 1970s).