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

Abstract

Resistance to the defoliating pathotype of Verticillium dahliae has been evaluated in a pool of 68 wild genotypes of olive belonging to the SILVOLIVE collection. Resistance was evaluated by assessing symptom severity using a 0–4 rating scale, estimating the relative area under the disease progress curve (RAUDPC), determining the percentage of dead plants (PDP), and measuring the evolution of morphological parameters in inoculated plants over time. In addition, the density levels of V. dahliae in the stem of root-inoculated genotypes have been quantified by means of quantitative real-time PCR at 35 and 120 days after inoculation (dai). Fifteen genotypes (22%) were cataloged as resistant to V. dahliae (i.e., disease parameters did not significantly differ from those of the resistant cultivar Frantoio, or were even lower). Resistant genotypes are characterized by presenting fewer symptoms and a lower amount of V. dahliae DNA at 120 dai than at 35 dai, indicating their ability to control the disease and reduce the density of the pathogen. The rest of the evaluated genotypes showed variable levels of susceptibility. Overall analysis of all genotypes showed high correlation between symptomatology and the amount of V. dahliae DNA in the stem of inoculated genotypes at 120 dai, rather than at 35 dai. However, correlation at 120 dai was not observed in the set of resistant genotypes, suggesting that resistance to defoliating V. dahliae in olive is based on the occurrence of different mechanisms such as avoidance or tolerance. These mechanisms are valuable for designing breeding programs and for the identification of target genes and resistant rootstocks to better control Verticillium wilt in the olive grove.

Antifungal effects of volatile organic compounds produced by Trichoderma koningiopsis T2 against Verticillium dahliae

“…Due to the stable dormant structure microsclerotia, long-term variability, and coevolution with host plants ( Ju et al, 2020 ; Höfer et al, 2021 ; Starke et al, 2021 ), controlling the spread of Verticillium wilt in plants remains challenging using currently available methods, such as chemical control, genetic breeding, and optimization of the cropping pattern ( Ostos et al, 2020 ; Ramirez-Gil and Morales-Osorio, 2021 ; Zhang Y. L. et al, 2021 ). Disease resistance breeding is limited by a long breeding cycle and a lack of natural resistance resources, and chemical control has no beneficial effect on the control of soil-borne diseases ( Diaz-Rueda et al, 2021 ; Hanika et al, 2021 ; Sunico et al, 2022 ). With the social pressure to make agriculture more sustainable while maintaining a healthy environment, the identification of new strategies that can reduce the use of chemicals is necessary.…”

The Status of Genetic Resources and Olive Breeding in Tunisia

“…Wild olive forests are native to Tunisia and wild/feral olive forms can be found in natural and agrarian ecosystems [65]. This germplasm appears promising for resistance to defoliating Verticillium [85] and root-knot nematodes [86], as well as drought tolerance [87]. In addition, it is considered a resource for improving olive oil's quality.…”

Avoidant/resistant rather than tolerant olive rootstocks are more effective in controlling Verticillium wilt

“…'Picual' grafted onto micropropagated wild olive genotypes one year after their exvitro acclimatization. The different rootstocks used in this study were selected according to their different levels of resistance to Verticillium wilt, previously characterized by Dıáz-Rueda et al (2021). Six genotypes were identified as low susceptible to Verticillium wilt (GUA3, CEH3, AMK27, ACO15, AMK5 and DHO6A).…”

“…Quantification of the amount of V. dahliae DNA in the inoculated plants was carried out at 35 and 120 dai by qPCR using the primers and TaqMan probe designed by Bilodeau et al (2012) and following the procedure described by Dıáz-Rueda et al (2021). Results were expressed as means ± standard errors of the V. dahliae:cox ratios (ng V. dahliae DNA • ng plant DNA -1 ), previously defined as mean normalized quantity (MNQ) in Garrido et al (2009).…”