First Report of Fusarium Crown and Root Rot Caused by Fusarium solani on St. John's-Wort in Argentina

Abstract

Since 2001, 15 to18% of commercial plantings of the medicinal plant St. John's-wort (Hypericum perforatum L.) in Buenos Aires Province, Argentina were affected by a new disease. Disease symptoms of crown and root rot, wilting, chlorosis, and necrosis of the leaves appeared in circular-to-irregular shaped sectors of 12- to 14-month-old plants. Symptoms began with foliage turning yellow followed by an irregular, brown necrosis of the leaf margins. Lesions coalesced to form large necrotic areas causing a severe defoliation of the basal and upper leaves. A soft rot affected the crown and roots causing a complete maceration of these tissues. Infected plants broke off easily because the crown region and the roots were destroyed. As the disease developed, a dark brown discoloration girdled the stems that progressed above the soil line to the apex. The infected stems became dry and breakable. Finally, the affected plants died. Segments (1 cm long) were taken from roots and rotted crowns of diseased plants, dipped in 70% ethanol, surface sterilized with NaOCl (1%) for 1 min, and rinsed in sterile water. Each segment was blotted dry and placed on potato dextrose agar. Plates were incubated in the dark at 26°C for 4 to 7 days. The predominate fungus isolated from the diseased tissue was identified as Fusarium solani (Mart.) Sacc. (1). Koch's postulates were completed by dipping the roots of seedlings in a 2 × 106 conidia per ml suspension of a single spore isolate for 45 min. Plants were repotted (20 inoculated and 10 controls) in a sterilized soil mix (soil/sand 2:1) and held in the greenhouse at 23 to 26°C. Characteristic symptoms identical to the original developed on 90% of inoculated plants within 2 weeks after inoculation. Symptoms included wilt and collapse, crown and root rot, and death of the plants. The fungus was recovered from symptomatic tissues. Control plants dipped into distilled water remained healthy. The experiment was repeated, and the results were identical to the first inoculations. To our knowledge, this is the first report of St. John's-wort as a susceptible host of F. solani. Reference: (1) P. E. Nelson et al. Fusarium species. An Illustrated Manual for Identification. Pennsylvania State University Press, University Park, 1983.

Fungal Pathogens in Grasslands

“…Soil-borne fungal diseases have been reported from commercially grown medicinal herbs and turf grass species found in natural grasslands ( Smiley et al., 2005 ). Furthermore, soil-borne fungal diseases have also been identified in commercial monocultures of dicots found in grasslands ( Gaetán et al., 2004 ). However, this knowledge has not been found to provide very much insight into fungal-plant interactions of highly diverse grassland ecosystems ( Ampt et al., 2019 ).…”

Linking ecology and plant pathology to unravel the importance of soil-borne fungal pathogens in species-rich grasslands

“…For instance, R. solani and Fusarium spp. were found in Plantago lanceolata (ribwort plantain) and Fusarium solani in Hypericum perforatum (St John's Wort) commercial plantings (Gaetán et al 2004;Zimowska 2013). Although this evidence stems from forb species, these have been cropped as monocultures and such insights may, therefore, not directly be translated to plantpathogen associations in species-rich grasslands.…”

Deciphering belowground plant-fungal interactions to understand the effects of biodiversity on disease risk

“…For instance, R. solani and Fusarium spp. were found in Plantago lanceolata (ribwort plantain) and Fusarium solani in Hypericum perforatum (St John's Wort) commercial plantings (Gaetán et al, 2004;Zimowska, 2013). Although this evidence stems from forb species, these have been cropped as monocultures and such insights may, therefore, not directly be translated to plant-pathogen associations in species-rich grasslands.…”