First Report of Basal Rot Caused by Sclerotinia sclerotiorum on Calibrachoa hybrida

Abstract

Calibrachoa (Solanaceae) is a plant genus typical of open environments that occurs in both the Pampas and the high-altitude grasslands of southern Brazil (Fregonezi et al. 2012). Calibrachoas (mini petunias) are hybrids developed from native germplasm, with increasing importance in the ornamental plant market. During October 2019, basal rot was observed in plants of C. hybrida cv. INTA 06575 grown in a propagation greenhouse in Hurlingham, Buenos Aires. Those symptoms caused the darkening and withering of the leaves (incidence of 10 %). White mycelial mats containing sclerotia of 2 to 8 mm in diameter were evident on the base of the wilted plants and the nearby soil surface. Pieces of symptomatic stem tissues were surface-disinfested in ethanol 70% for 1 min, sodium hypochlorite (2 g Cl/L) for 1 min, washed with distilled water for 1 min, and placed on potato dextrose agar (PDA) plates. The plates were incubated in the dark for 5 days at 23°C and individual colonies were transferred to new plates of PDA to obtain pure cultures. The colonies developed white cottony mycelium, and a ring of large black sclerotia at the periphery of the plates. No teleomorph was observed. Based on the morphology of the colony, sclerotia, and microscopic observations, the pathogen was identified as Sclerotinia sclerotiorum (Lib.) de Bary (Mordue and Holliday 1976). A representative isolate was deposited in the Entomopathogenic Fungal Culture Collection of Argentina, CEPAVE as CEP 785. Genomic DNA was extracted and the internal transcribed spacer (ITS) region of rDNA was amplified with the primers ITS1/ITS4 (White et al. 1990). The resulting sequence was deposited in GenBank (Accession No. MT177216) and the BLASTn search showed 100 % of identity with those of S. sclerotiorum (ex. MG931017, KX781301). The pathogenicity of the isolate was confirmed by placing plugs of 10 mm2 obtained from a 7-day-old culture grown on PDA,on the stem bases of 12 healthy potted calibrachoas 2 months old. Those segments were wrapped with moistened sterilized cotton (Choi et al. 2017). Four plants with sterile PDA plugs served as controls. Each plant was placed inside a polyethylene bag, and all of them were kept in a growth chamber at 20°C. All the inoculated plants had their leaves discolored after five days, and wilted after thirteen days. Sclerotinia sclerotiorum was consistently re-isolated from rotten stem bases, thus fulfilling Koch’s postulates. Control plants did not develop symptoms. To our knowledge, this is the first report of S. sclerotiorum causing basal rot on Calibrachoa hybrida (Farr and Rossman 2020) in Argentina, and in the world.

Ceratobasidium sp. AG-A, ROOT PATHOGEN OF Calibrachoa hybrida

“…Regarding the incubation period, it differs among these three host pathogen interactions. In fact, leaf symptoms were evident at 5 days for S. sclerotiorum (Borrelli et al, 2020), 6 days for Ceratobasidium sp., and 6 days for F. oxysporum (unpublished), while plant death occurred at 10 days for Ceratobasidium sp., 13 days for S. sclerotiorum (Borrelli et al, 2020) and 16 days for F. oxysporum (unpublished). Knowledge of the presence of pathogens is essential for the development and implementation of proper disease management strategies.…”

“…Crop surveys conducted on a regular basis in these ornamental crops identified Sclerotinia sclerotiorum (Borrelli et al, 2020) and Fusarium oxysporum (Borrelli et al, 2021) as calibrachoa soilborne pathogens. In October 2019, plants of calibrachoa INTA 06575 grown in a polyethylene greenhouse in Hurlingham (Buenos Aires, Argentina) showed sudden wilt (Fig.…”

Leaf spots of calibrachoa caused by Nigrospora oryzae

“…To date, Calibrachoa mottle virus (CbMV) (Liu et al, 2003), Tobacco mild green mosaic virus (TMGMV) (Sabanadzovic et al, 2009), Podosphaera xanthii (Brielmaier-Liebetanz et al, 2015), Phytophthora nicotianae (Lin et al, 2018), Potato virus Y (PVY) (Tombion et al, 2019), Alternaria porri (Nishikawa and Nakashima, 2020), and Sclerotinia sclerotiorum (Borrelli et al, 2020), have been reported to infect calibrachoa plants in different countries. The development of new cultivars includes disease surveys.…”