First Report of Southern Blight on Valeriana officinalis Caused by Sclerotium rolfsii in Brazil

Abstract

Valeriana officinalis L. (valerian, garden valerian) is a perennial herbaceous plant in the Valerianaceae family, commonly used as a medicinal herb in the treatment of insomnia and nervousness. In May 2019, at Botucatu city in Sao Paulo state (22°53′25″S, 48°27′19″W), 80% of production of valerian plants from a grower were observed to show symptoms typical of southern blight that included leaf wilt and the presence of sclerotia in rotted tissue. Symptoms on infected plants began with yellowing of older leaves from the base to the apex that was accompanied by a brown rot in which sclerotia were formed. The suspect fungal pathogen was tentatively identified as Sclerotium rolfsii (teleomorph Athelia rolfsii) based on its morphological characters and the signs and symptoms of the fungus. Efforts to isolate the fungus for use in pathogenicity tests were made by surface disinfecting infected tissue for 1 min in 70% alcohol and then 2 min in 2% NaOCl, followed by immersion in sterile distilled water. Tissue pieces were then placed in plates containing potato dextrose agar and maintained at 25°C. White mycelia and sclerotia formed in these plates after 7 to 14 days. Sclerotia were brown, ellipsoid in shape, and ranged from 0.82 to 1.8 cm in diameter (average 1.42 cm, n = 100). These dimensions were similar to those obtained by Erper et al. (2019) from S. rolfsii that infected candyleaf in Turkey. A culture of our valerian isolate was deposited in the collection of the Biological Institute of Sao Paulo under accession number MMBF 04/20. Pathogenicity tests were conducted on healthy 2-month-old valerian plants in a greenhouse maintained at 25°C and 95% relative humidity (RH) for 3 days and at 25°C and 70% RH the following 8 days. Sclerotia were incorporated into the soil near four plant stem repetitions as the method of inoculation, and four noninoculated valerian plants were the control. Disease symptoms began to appear 3 days postinoculation, sclerotia formed after 9 days, and plant death occurred within 11 days. Symptoms on inoculated plants were the same as those observed on the original diseased specimens, and control plants remained healthy. S. rolfsii was reisolated from sclerotia produced on inoculated plants, thus confirming Koch’s postulates. DNA for molecular identification was extracted from our isolate of S. rolfsii using the cetyltrimethylammonium bromide method according to Doyle and Doyle (1987). This was followed by a polymerase chain reaction using primers ITS1/ITS4, which amplify part of the internal transcribed spacer region (White et al. 1990). The amplicon obtained (GenBank accession no. MT023434) was bidirectionally sequenced and shared 97.05% sequence identity with A. rolfsii (593/611 nucleotide identity, MH854711). S. rolfsii is known to infect many economically important plants (Tu and Kimbrough 1978). It has been reported from Japan on Valeriana radix (Morita et al. 2015), in India on V. jatamansi (syn. V. wallichii) (Khosla 2014), and in Korea on V. fauriei (Kwon et al. 2010). In Brazil, other medicinal plants such as Taraxacum officinale (dente de leao) (Severino et al. 2014) and Plantago major (tanchagem) (Dias-Arieira et al. 2014) have been reported to be susceptible to infection by S. rolfsii. To our knowledge, this is the first report of the occurrence of S. rolfsii on valerian in Brazil.