Verticillium Wilt Evaluation of Olive Breeding Selections Under Semi-Controlled Conditions

Abstract

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.

Assessment of Maternal Effects and Genetic Variability in Resistance to Verticillium dahliae in Olive Progenies

“…Once we discarded the existence of the maternal effect, this study focused on selecting the crosses that maximize the percentage of seedlings resistant to Verticillium wilt. Interestingly, one of the demonstrated results from our study was the wide variability in the resistance level of the offspring, which is consistent with previous studies [ 10 , 11 , 32 ]. In an olive-breeding program, two strategies can be followed.…”

“…In addition, how and in what proportion these resistant cultivars are able to transfer resistance to their offspring is not well known. Indeed, it is worth mentioning the wide variability of the resistance level in offspring, even finding resistant genotypes in olive progenies from crosses in which both genitors were susceptible [ 10 , 11 , 32 ].…”

“…Following this strategy, resistant genotypes are always found. The second alternative strategy is to select genotypes with good agronomic characteristics under field conditions, perform clonal propagation, and then evaluate their resistance by artificial inoculations and evaluations in infested fields [ 10 , 32 ]. In this last case, as already mentioned, it must be taken into account that the possibility of finding disease-resistant genotypes within these available genotypes of agronomic interest could be low.…”

Wild Olive Genotypes as a Valuable Source of Resistance to Defoliating Verticillium dahliae

“…Therefore, new genotypes with long-lasting resistance to V. dahliae are needed as cultivars or rootstocks for adequate control of Verticillium wilt in olive plantations. Breeding programs have been developed with the aim of identifying resistant cultivars ( Arias-Calderón et al, 2015a , b , c ; Serrano et al, 2021 ) although satisfactory planting material with appropriate agronomic traits and long-term resistance are not available yet. Several breeding cycles could be necessary to obtain new cultivars with improved agronomic performance.…”

Unveiling Differences in Root Defense Mechanisms Between Tolerant and Susceptible Olive Cultivars to Verticillium dahliae

“…Six olive varieties were chosen for this study, three of them classified as tolerant (Frantoio, Empeltre and Changlot Real) and the other three as susceptible (Picual, Hojiblanca, and Lechín de Sevilla) to VWO (López-Escudero et al, 2004 ; Trapero et al, 2012 , 2015 , 2018 ; Garcia-Ruiz et al, 2014 ; Gómez-Lama Cabanás et al, 2015 ; Serrano et al, 2021 ; Valverde et al, 2021 ). Five-month-old olive plants contained in polyvinyl chloride (PVC) pots (11 x 11 x 12 cm) filled with a peat-based substrate containing the universal slow-release fertilizer Osmocote Exact standard 12–14 M (1g/L) (ICL Specialty Fertilizers-Iberia, Murcia, Spain) and calcium carbonate (0.5 g/L), with a final pH of 7.5 ± 0.5, were purchased in a commercial nursery located in Córdoba province (southern Spain).…”