Version 1: Determination of the lowest infection threshold for ginger (Zingiber officinale Roscoe) by Fusarium oxysporum f. sp. zingiberi and its impact on yield

Ginger (Zingiber officinale Roscoe) is an important horticulture 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. Little is known about the influence of Foz inoculum dosage 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 suitability in genetic studies on Foz resistance. To achieve this, the dominant Australian ginger cultivar ‘Canton’ was inoculated with pre-determined amounts of colony-forming unit (cfu), ranging from 0 in control, to treatments with 10, 10³, 10⁵, 10⁶, and 10⁷ cfu per gram of soil. The inoculum dosage positively correlated with leaf and stem yellows, and rhizome discolouration, and negatively correlated with root length and rhizome weight. The lowest threshold required for plant infection was 10 cfu per gram of soil, which may provide an important basis for outbreaks of Foz in the field. This finding adds significantly to the knowledge base on ginger soil health and contributes 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.