Ontogenic Resistance to Uncinula necator Varies by Genotype and Tissue Type in a Diverse Collection of Vitis spp.

Abstract

Berries of grapevine (Vitis spp.) have a limited window of susceptibility to Uncinula necator, the causal agent of grapevine powdery mildew, until the onset of ontogenic resistance approximately 2 to 3 weeks postbloom. This phenomenon has been demonstrated in several cultivars of V. vinifera and in V. labruscana ‘Concord’, which all exhibited a similar duration of susceptibility. To identify genetic variation for ontogenic resistance, we screened a diverse collection of Vitis species and interspecific hybrids maintained in the USDA-ARS cold-hardy Vitis germplasm collection in Geneva, NY. Of the 79 genotypes whose fruit clusters were screened for susceptibility to powdery mildew under field conditions, 50 exhibited a high level of constitutive resistance to powdery mildew and did not develop more than trace levels of disease when inoculated, irrespective of the stage of berry development at inoculation. Twenty-four genotypes exhibited a significant gain of resistance as berries aged. This ontogenic resistance was conserved across four species and several interspecific hybrids of Vitis spp., although the timing of the onset of ontogenic resistance varied by genotype. The mechanism of ontogenic resistance was examined for four genotypes. Similar to previous studies, ontogenic resistance greatly reduced the incidence of successful penetration. Despite the broad conservation of ontogenic resistance across species, one genotype (V. rupestris ‘R-65-44’) remained susceptible past the onset of ripening, over 1 month later than reported previously for V. vinifera and V. labruscana. Variation in the resistance phenotype was observed among the rachis, pedicels, and berries within clusters of the majority of genotypes studied. The genetic variation in ontogenic resistance, in particular the discovery of a genotype in which berries remain susceptible as they mature, will facilitate further study of the inheritance and molecular basis of ontogenic resistance.

Susceptibility to downy mildew (Plasmopara viticola) and powdery mildew (Erysiphe necator) of differentVitiscultivars and genotypes

“…The result of the present study shows that differences in susceptibility to downy mildew and powdery mildew exist among Vitis cultivars/genotypes, as previously reported (Staudt and Kassemeyer, 1995;Cadle-Davidson, 2008;Gee et al, 2008). Differences in susceptibility were also seen between different species of Vitis, as earlier mentioned by several authors (Yu et al, 2012;Boso et al, 2014).…”

“…Susceptibility of V. labrusca cultivars studied very limited numbers and these studies have highlighted that there may be differences between the cultivars (Cadle-Davidson, 2008;Gee et al, 2008;Wu et al, 2011). It is reported that even different ecology also affect resistance to powdery mildew disease (CadleDavidson et al, 2011).…”

Grapevine powdery mildew (Erysiphe necator): a fascinating system for the study of the biology, ecology and epidemiology of an obligate biotroph

“…Ontogenic resistance is broadly conserved across Vitis spp. (Gee et al ., 2008), but berries of less susceptible Vitis species and Vitis interspecific hybrids appear to express it 1–2 weeks earlier than those of V. vinifera (Gadoury et al ., 2001; Gee et al ., 2008). Diffuse powdery mildew colonies develop on berries as they transition to an ontogenically resistant state (Fig.…”

“…Conidial attachment, germination and appressorium formation were not affected by berry age. However, successful penetration of berries, formation of haustoria and development of secondary hyphae often declined to either nil or trace levels once ontogenic resistance was fully expressed in older berries (Ficke et al ., 2003; Gee et al ., 2008). The progress of E. necator was halted by ontogenic resistance in many cases before the formation of visible penetration pores.…”

Molecular strategies to enhance the genetic resistance of grapevines to powdery mildew

“…If we could determine the molecular/genetic basis of ontogenic resistance to powdery mildew in grape berries, it may be possible to use this information to manipulate broad‐spectrum, durable resistance to powdery mildew in other highly susceptible grapevine tissues. Recent work by Gee et al. (2008) has identified a strategy via which the determination of the mechanism of ontogenic resistance might be achieved.…”