Verticillium wilt evaluation of olive breeding selections under semi-controlled conditions
Genetic resistance is the most recommended measure to control verticillium wilt in olive (VWO), a vascular disease caused by the soil-borne fungus Verticillium dahliae, which has promoted in recent years the development of olive breeding programs aiming at obtaining new resistant and highly yielding cultivars. Screening has been commonly performed under controlled condition in grow chamber after artificial inoculation at the early stage of breeding programs, but additional evaluation is necessary to confirm previous results as well as testing for additional agronomic traits. In this work, 20 breeding selections initially classified as resistant to the disease have been re-evaluated in artificially infested soils under natural environmental conditions. The maximum disease incidence (52.6%) was reached at 26 months after planting and the disease intensity index reached the maximum value of 38.5% at 29 months after plant. Nine breeding selections consistently confirm previous results of resistance to V. dahliae infection but contradictory results, compared to previous evaluation under controlled condition in grow chamber, were obtained for the rest of selections tested, which underlines the need of long-term experimentation under natural environmental conditions. Additional positive agronomic traits such as early bearing was also observed for some of the resistant selections, while variability for plant vigor was found. Some of them seems highly promising for releasing as new cultivars once characterization for other important agronomic traits is completed in future works.