First report of Fusarium proliferatum causing root rot of Gerbera in China

In January 2018, gerbera plants showed root rot symptoms were found in a greenhouse at Guizhou Horticultural Institute in Guiyang city, Guizhou Province in southwest China. Morphological and molecular identifications confirmed the isolation of Fusarium proliferatum. The pathogenicity was verified with Koch’s postulates. To our knowledge, this is the first report confirming root rot of gerbera caused by Fusarium proliferatum in China.

Gerbera (Gerbera jamesonii, family Asteraceae), also known as Transvaal Daisy, Barberton Daisy or African Daisy, is the fifth most popular cut flowers and potted plants with great commercial value around the world (Terri et al. 2006;Bhatia et al. 2009). Gerbera is a genus of ± 30 species of perennial herbs distributed largely through Africa, Madagascar and extending into China (Hind 2007).
In the winter of 2018, we noticed approximately 30% of gerbera plants showed the root rot symptoms in a greenhouse located at Guizhou Horticultural Institute in Guiyang city, Guizhou Province in southwest China. In the advanced stage of the disease, the roots, crown and stems of these plants were all in black and rotten, with their epidermis peeling off. The leaves and stems of infected plants were chlorotic and wilted.
Diseased root pieces (3 × 3 mm) of gerbera plants were surface-disinfected with 75% ethanol for 30 s and 0.5% NaClO for 3 min and washed three times with sterilized water. The disinfected pieces were dried and incubated on potato dextrose agar (PDA) at 25 °C for 7 days inside a dark chamber.
Koch's postulates were checked by using 1-month-old gerbera healthy plants under controlled conditions. F. proliferatum strain FZJf3-1 inoculum (1 × 10 6 conidia/ml in sterile distilled water) was produced from PDA cultures, and a 25 ml suspension was used to inoculate five potted plants which were grown in sterilized soil. Control plants were inoculated with sterile distilled water. They were incubated at 28 °C and a 12:12 dark/light photoperiod. After 49 days, plants with root rot, leaf and stem chlorosis were observed in inoculated pots while control plants inoculated with sterile water did not show any of the disease symptoms (Fig. 1c,  d). F. proliferatum was reisolated from the symptomatic tissues of infected plants and shown to be genetically identical to the original inoculated strain FZJf3-1, fulfilling Koch's postulates.
So far, in China, the main Fusarium pathogens causing root rot are reported by the complex of the F. oxysporum and F. solani species. In this study, we found that the gerbera root rot was due to F. proliferatum. F. proliferatum is a cosmopolite saprophytic species, but it is also known to be a pathogen causing root rot on garlic (Leyronas et al. 2018), codonopsis (Gao et al. 2017), alfalfa (Cong et al. 2016.), soybean (Díaz Arias et al. 2011) and blueberry (Pérez et al. 2011). To our knowledge, this is the first report confirming root rot of gerbera caused by F. proliferatum in China.