First Report of Meloidogyne Morocciensis Infecting Hops (Humulus Lupulus)

Abstract Humulus lupulus (Cannabaceae) is a climbing herbaceous plant with perennial production, intended mainly for the brewing industry. H. lupulus is widely cultivated in temperate regions; hop cultivars have shown good adaptation in regions of Brazil. In a hop-growing area in São Mateus, the state of Espírito Santo, leaf wilting and galling of the root system was observed. Soil and root samples were taken to the laboratory and processed, and the nematodes extracted from the Meloidogyne genus were identified by morphology, morphometry, and biochemical analysis. According to the results, the species identified in the hop roots was Meloidogyne morocciensis. This is the first report of H. lupulus as host of M. morocciensis.


Abstract
Humulus lupulus (Cannabaceae) is a climbing herbaceous plant with perennial production, intended mainly for the brewing industry. H. lupulus is widely cultivated in temperate regions; hop cultivars have shown good adaptation in regions of Brazil. In a hop-growing area in São Mateus, the state of Espírito Santo, leaf wilting and galling of the root system was observed. Soil and root samples were taken to the laboratory and processed, and the nematodes extracted from the Meloidogyne genus were identified by morphology, morphometry, and biochemical analysis. According to the results, the species identified in the hop roots was Meloidogyne morocciensis. This is the first report of H. lupulus as host of M. morocciensis.
Hop (Humulus lupulus L.) is a climbing herbaceous plant (Fig. 1A) belonging to the Cannabaceae family, native to temperate regions. Flowers of this plant are mainly used in the brewing industry for conferring aroma and flavor to beer, but since it has secondary metabolites with significant biological activities (Astray et al., 2020), the plant is also applied in medicine and can be used in the treatment of diseases, such as insomnia, stress, and anxiety (Kyrou et al., 2017). Although Brazil is a country with a tropical climate, H. lupulus has adapted in regions with a mild climate and shows good plant development (Durello et al., 2019). Nematodes were extracted from soil using the method of Jenkins (1964) and from roots using the method of Coleen and D'Herde (1972). For the identification of Meloidogyne species, the morphology of female perineal patterns was used (n = 10), morphometry of juveniles (n = 20), and by esterase phenotypes obtained by electrophoresis gel (n = 8). Eggs and juveniles were counted on Peter's slides to quantify the population found in the samples.
According to the results of the analyses, it was possible to identify the species as Meloidogyne mococciensis Rammah and Hirschmann, 1990 and as a parasite of the hop plants. The estimated population of eggs and juveniles was 864/100 cm 3 in soil and 2,763/g root. The perineal patterns found exhibit oval-to-square shapes, with moderately separated dorsal arches and continuous and separate coarse striations, similar to that found by Machaca-Calsin et al. (2021) (Fig. 1G).

JOURNAL OF NEMATOLOGY
measurements obtained from the second-stage (J2) juveniles correspond to those of the species M. morocciensis. The esterase isoenzyme phenotype was characterized as A3 by PAGE (Fig. 1F) in the esterase identification method (Carneiro et al., 2008).
Meloidogyne morocciensis is a species less frequently found worldwide when compared to traditional species such as M. javanica and M. incognita. In Brazil, this nematode has been found in beetroots (Machaca-Calsin et al., 2021), peach trees (Silva et al., 2020), tomato plants ( Barros et al., 2018), and soybean (Dalla Nora et al., 2020). Based on the results of the species identification analyses, this is the first report of M. morocciensis on hop roots. We observed that infected hop plants showed developmental damage, such as reduced growth, chlorosis on leaves, and nodules on roots. The disease could reduce hop production and affect other crops reported to be hosts of economic importance in Brazil, such as soybeans and tomatoes. Thus, we recommend hop growers in Brazil, especially in the northern region of Espírito Santo, to take care and avoid the spread of this nematode to other agricultural crops and to other regions of the country.