Leaf Cutin Monomers, Cuticular Waxes, and Blackspot Resistance in Rose

Abstract

<jats:p>The fungal pathogen <jats:italic>Diplocarpon rosae</jats:italic> causes rose blackspot disease, a serious problem for roses (<jats:italic>Rosa</jats:italic>) in the managed landscape. To prevent this disease, homeowners and professional growers often apply chemical fungicide. However, increased use of fungicides poses an environmental hazard and an economic burden to the user. New landscape rose cultivars like ‘Knockout’ possess increased disease resistance, but the biological basis for this resistance is still unknown. To investigate the potential role of leaf cuticle in blackspot resistance in rose, five rose cultivars known to vary greatly in blackspot resistance were examined for variation in the major lipids of the leaf cuticle, specifically the monomers of the cutin polyester and the free cuticular waxes. This is the first report of cutin monomers in the <jats:italic>Rosa</jats:italic> genera. The rose cultivars selected for this study were ‘Knockout’, ‘Mister Lincoln’, ‘Garden Party’, ‘Purple Passion’, and ‘Bicolor’. ‘Knockout’ and ‘Garden Party’ had significantly lower total cutin monomer amount per leaf area than the other cultivars, whereas the most cutin monomers were observed on ‘Purple Passion’, ‘Bicolor’, and ‘Mister Lincoln’. Five major cutin monomers (mostly hydroxylated 16 carbon fatty acids) dominated the cutin profiles of both adaxial and adaxial surfaces of all cultivars, with the 10,16-dihydroxy hexadecanoic acids being most abundant. The proportion of 10,16-dihydroxy hexadecanoic acids was slightly higher in the adaxial than abaxial leaf cuticles of all cultivars. Correspondingly, other cutin monomers were relatively lower in the adaxial cuticle, except 16-hydroxy hexadecanoic acid that differed little. Uniquely, this is the first report of cutin monomer composition of isolated abaxial and adaxial leaf cuticles of any plant. Total leaf cuticular wax amounts were lowest on ‘Purple Passion’ and ‘Knockout’, intermediate in ‘Mister Lincoln’ and ‘Garden Party’, and highest on ‘Bicolor’, with alkanes as the most abundant wax class. Consistent with previously published disease susceptibility ratings, our visual scores showed that ‘Knockout’ was most resistant to blackspot pathogen infection with a visual disease rating score of 1.0, followed by ‘Mister Lincoln’ at 1.8, ‘Garden Party’ at 5.4, ‘Bicolor’ at 7.5, and ‘Purple Passion’ with the most visible disease damage at 8.8. Regression analysis revealed that the alkane and ester proportions were most closely associated with blackspot disease susceptibility ratings, being inversely (R<jats:sup>2</jats:sup> = 0.63, <jats:italic>P</jats:italic> = 0.05) and directly (R<jats:sup>2</jats:sup> = 0.81, <jats:italic>P</jats:italic> = 0.05) correlated, respectively. More studies on the role of cuticle in rose susceptibility to blackspot are now clearly warranted.</jats:p>

Exploring Complex Ornamental Genomes: The Rose as a Model Plant

“…Some of the resulting genotypes showed a 13-43% reduction in black spot disease symptoms. As for the other fungal diseases, research has also been done in detail on the disease development in the leaves (Blechert and Debener, 2005;Gachomo and Kotchoni, 2007) and the effects of the thickness and composition of the leaf cuticle on the resistance to D. rosae (Goodwin et al, 2007). In this study, Goodwin and coworkers examined five cultivars for natural infections with black spot in the field.…”

Responses of physiological indexes and leaf epicuticular waxes of Brassica napus to Sclerotinia sclerotiorum infection

“…Needles from a resistant selection of eastern white pine had a significantly higher percentage of stomata that were occluded with wax, and fewer germ tubes penetrating stomata than needles from a susceptible selection (Smith et al, 2006). Alkane and ester proportions in rose leaf cuticular wax were most closely associated with blackspot disease susceptibility ratings (Goodwin et al, 2007).…”

Resistance of rose varieties to black spot

“…Гудвин С.М. зі співавторами встановили, що найбільш стійкими проти збудника чорної плямистості були сорти Knockout із візуальним балом ураження 1,0 та Mister Lincoln' з балом 1,8 [14]. Мюллер Д.С.…”