First Report of Meloidogyne incognita Infecting Stachys byzantina in Brazil

Stachys byzantina C. Koch (Lamiaceae alt. Labiatae), commonly known as lamb's ear, is an important medicinal plant with anti-inflammatory, antitumor, anticancer, antispasmodic, sedative and diuretic properties (Asnaashari et al. 2010). This plant is widely consumed in Europe and Asia as aromatic teas. In Brazil, it is an unconventional food plant, nonetheless, its medicinal properties have been recognized as well as its production. In May 2019, in a Sao Paulo State municipality, Jaboticabal, (21°14'38.7"S 48°17'10.6"W), S. byzantina plants presented reduced growth and chlorotic leaves associated with root galls. In the phytopathological clinic, 7,983 eggs and juveniles of Meloidogyne sp. were counted in 10 g of the plant roots. In 100 cm³ of soil surrounding the plant, 532 second-stage Meloidogyne sp. juveniles (J2) were found. Morphological, enzymatic and molecular identification of the nematode species found were performed (Fig. S1). For morphological analysis, perineal pattern of females (n = 10) and labial region of males (n = 10) were analyzed. In the perineal region of females, a high and trapezoidal dorsal arch with thick striations was observed, whereas the males presented the trapezoidal labial region with the prominent labial disc in relation to the sub-median lips and transverse streaks in the head region, typical characteristics of M. incognita (Kofoid and White, 1919) Chitwood 1949. (Netscher and Taylor 1974; Eisenback and Hirschmann 1981). The esterase enzyme profile, obtained individually from 8 females, was compatible with phenotype I1 [Rm (x100) = 46.25], also associated with M. incognita (Esbenshade and Triantaphyllou 1985). Molecular analysis was realized (n = 3) by applying the primers Finc/Rinc (Zijlstra et al. 2000) in the DNA of individual females, which resulted in the amplification of an amplicon of 1200 bp specific for M. incognita. Pathogenicity testing was conducted in a greenhouse by inoculation of 5,000 eggs and juveniles from the original population into S. byzantina seedlings (n = 4). After 90 days, the inoculated plants, unlike the non-inoculated ones, exhibited symptoms similar to those initially observed in the field. The nematodes were extracted from the roots of the inoculated plants, quantified, and the identity of M. incognita was confirmed. The average reproductive factor obtained was 136.6, confirming the pathogenicity of M. incognita to S. byzantina. Thus, this is the first report of M. incognita associated with S. byzantina in Brazil and in the world. Lamb's ear is a horticultural plant, and its high reproductive factor to M. incognita can also result in damage to the subsequent crops. In addition, Lamb's ear is propagated vegetatively and this favors the spread of nematodes to other areas. This new report is important in order to alert producers to realize the proper management of this nematode in S. byzantina.

Keywords: Causal Agent; Crop Type; Field crops; Lamb’s ear; Meloidogyne incognita; Nematodes; Pathogen detection; Root-knot nematode; Stachys byzantina; Subject Areas.