Leaf Trichomes as an Effective Structure for Disease Resistance: The Case of Grapevine Downy Mildew

Abstract

Leaf trichomes confer pest resistance. Dense trichomes could also present a physical barrier to microorganisms, such as grapevine downy mildew caused by Plasmopara viticola on grape. Zoospores of P. viticola swim in water and enter stomata. Some wild Vitis accessions such as V. labrusca and V. cinerea have highly hydrophobic, dense, prostrate trichomes on the lower leaf surface that repel water and enhance resistance to downy mildew. Quantitative trait loci for leaf trichome density have been identified on LGs 5, 7, 8, and 15 of grapevine. A major locus on LG 5 was found in V. vinifera 'Muscat of Alexandria,' which has few leaf trichomes. Hairless alleles on LG 5 in historical V. vinifera cultivars reduce trichome density in the progeny of V. labrusca origin. Applying information on these loci in breeding programs would allow the introduction of this natural physical barrier against pathogenic microorganisms into cultivars.

Leaf Polyphenolic Profile as a Determinant of Croatian Native Grapevine Varieties’ Susceptibility to Plasmopara viticola

“…Opposed to this, in the case of resistant genotypes (class 7 and 9), low density levels of the trichomes are present. Subsequently, no correlation between the density of the trichomes and resistance to P. viticola was determined suggesting that this feature does not have a major effect on the resistance level of specific genotypes, in contrast to some previous studies (Kortekamp and Zyprian, 1999;Kono and Shimizu, 2020).…”

“…Apart from constitutive and induced chemical compounds that provide a certain level of tolerance to parasitic microorganisms, resistance to P. viticola can be associated with the synthesis of physical barriers, such as callose and lignin appositions ( Toffolatti et al, 2012 ). Moreover, hydrophobic trichomes on the abaxial leaf sides reduce the retention or repel water drops, thus preventing the encystment of P. viticola zoospores ( Kono and Shimizu, 2020 ), a step that is essential for the pathogen development inside a leaf tissue and further fructification ( Rossi and Caffi, 2007 , 2012 ). This morphological feature is an example of passive resistance, whereas active responses involve hypersensitivity and synthesis of specific secondary metabolites ( Buonassisi et al, 2017 ).…”

“…To prevent the diseases caused by pathogens, plants use sophisticated defense mechanisms that can be either constitutive or inducible defenses ( Muganu and Paolocci, 2013 ). While the constitutive defense is referred to as a preexisting and continuous resistance ( Kono and Shimizu, 2020 ), the induced defense is triggered by a pathogen attack and recognition and includes the perception of plant tissue signals resulting from pathogen infection ( Muganu and Paolocci, 2013 ). Constitutive defense includes preformed physical barriers present on the plant surface (leaf hairs, wax layers, rigid cell walls, and the number and the activity of stomata) or chemical compounds, such as antimicrobial secondary metabolites ( Lattanzio et al, 2006 ).…”

Characterization of VOCs Emitted by Foliage of Grapevine cv. Isabella for Prospecting Innovative Cropping Systems

“…Isabella, were emitted at a similar rate in both diurnal and nocturnal collection times in the first experiment (Table 1). Notably, Isabella leaves are characterized by the presence of dense trichomes [65] and cuticular waxes [66], which might have contributed as storage structures for terpene emissions, as reported in other species [67,68]. Terpenes play multiple roles in mediating antagonistic and beneficial interactions among organisms [69,70] and are involved in plant-to-plant communication and signaling [71].…”

“…These pathogens are relevant during the springtime, and bunch rot also constitutes a main concern during berry ripening. They are affected by morphological (i.e., trichomes, bunch compactness) [65,91], anatomical (i.e., cuticle wax) [66], and physiological (i.e., degree of stomatal opening) [92] traits, secondary metabolites including VOCs [1,6,7,27].…”