Abstract

In recent years, Queensland ginger growers have sometimes found it difficult to establish crops. Seed-pieces either rot within a few weeks of planting or young plants grow poorly, shoots become yellow and eventually die. Surveys aimed at determining the cause of the problem showed that rhizomes designated for planting material were invariably infected by Fusarium oxysporum f. sp. zingiberi (Foz). The pathogen was also isolated from fungicide-treated seed-pieces that were ready for planting, and from newly planted seed-pieces. The soft-rot bacterium Erwinia chrysanthemi was also recovered from rotting seed-pieces but nearly always in association with Foz. It was not involved in the disease under normal soil moisture conditions, but rotting often occurred when seed-pieces were inoculated with both E. chrysanthemi and Foz and planted in wet soil. Experiments with biocides confirmed that Foz was the main cause of poor emergence, as only fungicides effective against Foz (i.e. carbendazim and benomyl) reduced the percentage of seed-pieces that rotted in the ground. Poor crop establishment appears to be a more severe form of a disease than has been present in the Queensland ginger industry for many years. Changes in farming practices are probably responsible for the increased disease severity, as vegetative compatibility studies suggested that a more virulent form of Foz has not recently been introduced.