Impact of inoculum density of Fusarium oxysporum f. sp. zingiberi on symptomatic appearances and yield of ginger (Zingiber officinale Roscoe)

Ginger (Zingiber officinale Roscoe) is an important horticultural crop valued for its medicinal and culinary properties. Fusarium yellows, caused by the ascomycete fungus Fusarium oxysporum f. sp. zingiberi (Foz), is a devastating soil-borne disease of ginger. It has curtailed ginger production in Australia and around the world, leading to significant economic losses. An integrated approach is required to manage soil-borne diseases such as those caused by Foz. However, little is known about the influence of Foz inoculum on disease severity. This study aimed to establish a minimum threshold level of spores per gram of soil required for plant infection and to develop and evaluate a pot inoculation method for screening large numbers of plants in a controlled environment. To achieve this, the dominant Australian ginger cultivar Canton was inoculated with 10(1), 10(3), 10(5), 10(6) and 10(7) microconidia g(−1) soil. The inoculum density was positively associated with leaf and stem yellows, and rhizome discolouration, and negatively associated with root length and rhizome weight. The lowest threshold required for plant infection was 10(1) microconidia g(−1) soil, which may provide an important basis for outbreaks of Foz in the field. This finding adds significantly to our knowledge of the impact of soil health on ginger production, thereby contributing to the integrated management of Foz. When used at a high dose, this method can facilitate reliable and accurate screening of Foz-susceptible ginger genotypes in a controlled environment.