Resistance of Strawberry Cultivars and the Effects of Plant Ontogenesis on Phytophthora cactorum and P. nicotianae Causing Crown Rot

Abstract

Phytophthora crown rot (PhCR) is an important disease of strawberry worldwide. Phytophthora cactorum is the most common causal agent, however, P. nicotianae was also recently reported in the U.S. causing PhCR. Therefore, the goals of this study were to evaluate the resistance of strawberry cultivars from Florida and California, and to study the etiology of the two Phytophthora species causing PhCR. Sixteen strawberry cultivars were evaluated over three Florida seasons for susceptibility to P. cactorum, and P. nicotianae. Inoculations at different days after transplanting (DAT) were also carried out to evaluate the ability of both species to cause PhCR at different phenological stages of the plant. Plant wilting and mortality were assessed weekly, and disease incidence, and the area under the disease progress curve were calculated. Cultivars Sensation® Florida127, WinterstarTM FL 05-107, and Florida Radiance were susceptible, whereas Florida Elyana, Camarosa, Fronteras, Sweet Charlie, and Strawberry Festival were highly resistant to both Phytophthora species. However, some cultivars exhibited stronger resistance to one species over the other. P. cactorum caused more PhCR when plants were inoculated at transplanting, 45, and 60 DAT, whereas P. nicotianae only caused disease when inoculated at transplanting. These results emphasize the importance of screening for disease resistance to guide management recommendations in commercial strawberry production as well as the need for proper pathogen identification since cultivar susceptibility might differ. Varying susceptibility to P. cactorum and P. nicotianae at different growth stages emphasizes the importance of considering both plant and pathogen biology when making management recommendations.

Harnessing underutilized gene bank diversity and genomic prediction of cross usefulness to enhance resistance to Phytophthora cactorum in strawberry

“…The frequency of PhCR‐resistant cultivars worldwide could obviously be greater than what we are reporting here. Although that seems improbable (Mangandi et al., 2017; Marin et al., 2022; Nellist et al., 2019), thorough sampling and screening of non‐UCD modern cultivars is needed to address this question (Figure 2; Supplemental File S1).…”

“…The genetic variation previously uncovered for resistance to PhCR in strawberry has been quantitative with broad‐sense heritability estimates in the 0.40–0.66 range and narrow‐sense heritability estimates in the 0.26–0.39 range; hence, a significant fraction of the phenotypic variation previously observed for resistance to PhCR has been nongenetic (Denoyes‐Rothan et al., 2004; Mangandi et al., 2017; Nellist et al., 2019; Shaw et al., 2006). Although several sources of resistance to this disease have been reported, a high percentage of the previously tested cultivars and other genetic resources worldwide appear to be susceptible, gene‐for‐gene resistance has not been discovered, and breeding for resistance to this pathogen has been challenging (Mangandi et al., 2017; Marin et al., 2022). Here we explore the feasibility of increasing resistance to PhCR through the application of genome‐informed breeding approaches, particularly genomic selection and parent selection using genomic‐estimated breeding values, genetic variances, and usefulness criteria (Allier et al., 2019; Goddard et al., 2010; Heffner et al., 2009; Lehermeier et al., 2017).…”

The devastating oomycete phytopathogen Phytophthora cactorum: Insights into its biology and molecular features

“…An understanding of the molecular mechanisms by which resistance is conferred will be of critical value to growers, breeders, and scientists, as well as a thorough understanding of the pathogen populations. (Hill & Hausbeck, 2008;Jeffers et al, 2004;Marin et al, 2021Marin et al, , 2022Marin et al, , 2023Mei et al, 2015). Generally, they can provide sufficient protection when applied alone.…”

Identification of sequence mutations in Phytophthora cactorum genome associated with mefenoxam resistance and development of a molecular assay for the mutant detection in strawberry (F. × ananassa)

“…Management of both diseases is based on the combination of resistant cultivars, cultural practices, and chemical applications 7 , 8 . Resistant cultivars may be available, but chemical applications have been widely used since most cultivars are mainly bred and selected based on fruit quality and yield and not for resistance to Phytophthora 9 . Although azoxystrobin is labeled for LR, and phosphite products for both diseases, mefenoxam is the most widely used chemical to manage PhCR and LR 10 .…”