From Dagmar Hanold, School of Agriculture, Food and Wine, University of Adelaide
In her article on the premature death of eucalyptus trees, Wendy Zuckerman cites a paper claiming that the eucalypt tree disease Mundulla Yellows (MY) is caused by environmental factors (11 September, p 44).
However, my colleagues and I published a paper in an earlier issue of the same journal which shows that MY is actually a contagious disease of unknown aetiology (). We outlined many clear descriptors that distinguish it from environmental causes of eucalypt yellowing. For example, the disease is defined by a progressive succession of symptoms through clearly described disease stages; it is irreversibly lethal and may affect a single tree in a group of healthy ones. Furthermore, symptoms have been transferred by inoculation from MY-affected trees to healthy eucalypt seedlings.
Taking into account these descriptors, environmental yellowing by definition is not MY, and continued use of the term for a whole range of disorders has been a cause for much time-wasting and futile discussions.
Adelaide, South Australia
