Infection by Meloidogyne javanica does not breakdown resistance to the defoliating pathotype of Verticillium dahliae in selected clones of wild olive

Host-plant resistance is the most practical, long-term and economically efficient disease control measure for Verticillium wilt in olive caused by the soil-borne fungus Verticillium dahliae, and it is the core of the integrated disease management. In Spain, Verticillium wilt has become a main concern for the olive industry because of the widespread occurrence of a highly virulent, defoliating (D) pathotype. Available V. dahliae-resistant olive cultivars show incomplete resistance to the D pathotype and do not satisfy consumers’ demand for high yields and oil quality as well as suitability for new environments and cultural practices in modern olive production in Spain. Highly resistant rootstocks would be of paramount importance for production of agronomically-adapted and commercially-desirable olive cultivars. Nevertheless, the validity of resistant rootstocks grafted with Verticillium wilt-susceptible olive cultivars in soils highly infested with the D pathotype would be increased if the resistance is demonstrated stable in coinfection with plant-parasitic nematodes, such as root-knot nematodes. In this work, wild olive clones ‘Ac-4’, ‘Ac-13’ and ‘Ac-18’ previously developed as highly resistant to D V. dahliae were tested for infection response by the root-knot nematode Meloidogyne javanica alone and jointly with D V. dahliae under controlled conditions optimal for Verticillium wilt in olive. The three wild olive clones showed resistance to D V. dahliae under high inoculum levels in soil and also when plants were co-infected by both pathogens. However, all clones were susceptible to M. javanica, although ‘Ac-13’ and ‘Ac-18’ showed a degree of tolerance to the used inoculum level. Nevertheless, coinfected plants with M. javanica and D V. dahliae reduced the nematode reproduction rate in ‘Ac-13’ and ‘Ac-18’, but increased that in ‘Ac-4’, suggesting that different resistance mechanisms to D V. dahliae might be operating in these clones were acting also on M. javanica reproduction.