Hospedabilidade de rosa-do-deserto, Adenium obesum, a Meloidogyne spp. e identificação e transmissão de viroses afetando a ornamental no Ceará

Abstract

The desert rose (Adenium obesum), a species from the Apocynaceae family, is highly valued in landscaping for its diversity and the beauty of its flowers. Due to the growing interest in its cultivation and the scarcity of studies related to nematodes and viruses, this study aimed to: 1) investigate the susceptibility of A. obesum to infection by five species of root-knot nematodes (Meloidogyne); and 2) identify the viruses associated with this ornamental plant in nurseries in the state of Ceará and their transmission methods. To achieve this, 60-day-old potted desert rose seedlings were inoculated with 5,000 eggs of Meloidogyne incognita, M. javanica, M. arenaria, M. enterolobii, and M. konaensis. After 80 days of inoculation, the plants were removed from the pots, and the root system was analyzed for the presence of galls and egg masses, as well as for the quantification of the number of eggs and subsequent calculation of the reproduction factor (RF). Few galls and egg masses were found, along with an RF below 1.0, indicating poor host suitability of the desert rose to the five inoculated root-knot nematodes. The ‘Santa Clara’ tomato plants, used as positive controls, showed a high number of galls (>200) and egg masses (>100) with RF ranging from 35 to 125, confirming the viability of the inoculum. In addition to the nematode host suitability study, the research sought to investigate the viruses associated with symptoms of mottling and mosaic observed in A. obesum plants from nurseries in municipalities of Ceará. For the virus study, 90-day-old healthy desert rose plants were inoculated via sap and grafting using leaves and discs from infected plants. After the appearance of viral infection symptoms, the plant material was sent to the Phytopathology Laboratory of the “Luiz de Queiroz” School of Agriculture – Esalq/SP for pathogen identification. Laboratory analysis, using electron microscopy and molecular techniques (RTPCR), identified the presence of Cucumber mosaic virus (CMV) and a new virus from the genus Potexvirus, provisionally named Desert rose mottle virus (DRMoV), in isolated or mixed infection. Mechanical inoculations in fabaceae and cucurbitaceae with leaf extracts from desert rose plants with mixed infections resulted in infection by CMV only. The practice of grafting, commonly used in desert rose nurseries, may contribute to the spread of these viruses in ornamental seedlings, posing a risk to the health of the commercialized plants. It was concluded that A. obesum is a poor host for the tested Meloidogyne species but is affected by CMV and Potexvirus.