Preliminary report on stem and root rot, a novel disease of cultivated Mursalitza mountain tea (Sideritis scardica Griseb.), first observed in Bulgaria

Abstract

A new disease of commercially cultivated Mursalitza mountain tea (Sideritis scardica Griseb.) was discovered and diagnosed for the first time in Bulgaria. Disease symptoms included yellowing and stunting, stem and root rot, sudden wilt and premature death on predominantly young newly replanted seedlings and less frequently on mature one- and two-year-old plants. Disease incidence increased throughout the season and in 2021 the disease totally caused 35% and 45% crop losses in the two surveyed fields. All isolates obtained from symptomatic plants were identified by microscopic observation of their morphological characteristics as Fusarium culmorum (Wm.G.Sm.) Sacc. and Fusarium oxysporum Schlecht. emend. Snyder and Hansen. Pathogenicity of all isolates was confirmed on 30-day-old Mursalitza mountain tea seedlings grown in pots with artificially inoculated soils. All inoculated plants showed symptoms identical to those observed on “naturally” infected plants grown in the surveyed field sites. The inoculated pathogens were consistently reisolated from symptomatic tissues. Further efforts are needed to evaluate the full range of biotic and abiotic components involved in the etiology of the stem and root rot, which results in early decline of the crop; an effective disease control program should be designed and implemented. Commercial and semi-commercial cultivation is an important means of protection for indigenous populations of Mursalitza mountain tea in the country. Hence, apart from the economic losses; the disease is likely to compromise the conservation of this endangered botanical species and to impede the restoration of its natural habitats in the wild.