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Downy mildew evaluation in wild rocket genotypes [Diplotaxis tenuifolia (L.) DC.] under field and controlled conditions

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Downy mildew evaluation in wild rocket genotypes [Diplotaxis tenuifolia (L.) DC.]
under field and controlled conditions
Introduction
Wild rocket (Diplotaxis tenuifolia) belongs to the Brassicaceae family is a much appreciated and healthy baby-
leaf native to the Mediterranean region. Wild rocket downy mildew (DM) is a devastating foliar disease, especially
in temperate climates, caused by the oomycete Hyaloperonospora spp. that can affect plants at all stages. The
objective of our study is to compare seedling and adult plants DM resistance in a group of D. tenuifolia
accessions, to determine whether seedling resistance tested in controlled environment is a good indicator of adult
plant behaviour in the field.
P.S. Coelho1, A.L. Pereira1, J. Reis2, C. Carranca1, V.R. Lopes3and J.M. Leitão2
1INIAV, Oeiras, Portugal; 2MED & CHANGE, FCT/UAlg, Faro, Portugal; 3INIAV/BPGV, Braga, Portugal Contact: paula.coelho@iniav.pt
Funding: This research was supported by project REMIRUCULA - “Resistance characterization to downy mildew in wild rocket crop” (PTDC/ ASP-PLA/28963/2017) and
FCT I.P., through the R&D Unit "GREEN-IT - Bioresources for Sustainability" (UIDB/04551/2020 and UIDP/04551/2020).
Fig. 1. Adult wild rocket DM evaluation in a polytunnel.
Table 1. Adult plant evaluation to downy mildew disease in the field.
Plant material: Forty D. tenuifolia accessions from different origins were tested in a commercial producer located at
Odemira (Vitacress Portugal, SA). Growth conditions: The plants were grown in a field trial (polytunnel) during the
period from October to December 2021 and were naturally infected with Hyaloperonospora spp. (Fig. 1). Screening
method: Seedlings were evaluated in a previous study (data under publication) with 14 days using 0-6 classes in
controlled environment. Adult plants were assessed 71 days after sowing using 0-5 classes, taking into account
the number of infected leaves per plant and the size of sporulating Hyaloperonospora spp. lesions (small ≤Ø1cm
and large 1cm) (Fig. 2).
Fig. 2. Comparison of seedling and adult plant DM resistance.
Materials and Methods
Results
Twenty-eight wild rocket commercial varieties and 12 collected accessions from other origin (prospecting
missions and gene banks) were evaluated (Table 1).
Sixteen accessions were identified with an interesting downy mildew resistance response in adult phase.
In general, similarly to other brassicas, wild rocket accessions were more susceptible at seedling than at adult
stage. No resistant accessions at seedling stage and susceptible at adult plant were identified.
On the contrary, two accessions with a highly susceptible response at seedling stage presented a resistant and a
partially resistant response at adult phase, respectively, accessions no.10 and 6.
Conclusions and perspectives
Our results suggest that downy mildew resistance observed at the seedling stage is a good indication of wild
rocket resistance behaviour at field adult plant.
It is important to increase the resistance of varieties to pests and diseases, ensuring the production of healthy
and safe food, less dependent on chemical products. The accessions classified as resistant at seedling stage
(14 days) exhibited a good DM resistance as adult plants and can be further exploited in breeding programmes
to downy mildew resistance.
Phenotypic categories of
DM evaluation Commercial
variety Collected
accession Total no. of
accessions
Resistant (R) 11 516
Partially Resistant (PR) 6 2 8
Susceptible (S) 8 4 12
Highly Susceptible (HS) 3 1 4
A significant coefficient of correlation was observed
(r=0.628, P=0.000) between seedling and adult
plant DM resistance.
Fig. 2. Downy mildew in wild
rocket (Highly Susceptible).
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