Peach Rusty Spot Is Caused by the Apple Powdery Mildew Fungus, Podosphaera leucotricha

Abstract

Jankovics, T, Dolovac, N., Bulajic, A., Krstic, B., Pascal, T, Bardin, M., Nicot, P C, and Kiss, L. 2011. Peach msty spot is caused by the apple powdery mildew fungus, Podosphaera leucotricha. Plant Dis. 95:719-724.Peach rusty spot, an economically important disease of peach (Prunus pérsica var. pérsica), appears as necrotic spots on fruit. The etiology of the disease is still not well understood, although it has long been suspected that the causal agent is the apple powdery mildew pathogen, Podosphaera leucotricha. This work confirmed this hypothesis based on cross-inoculation experiments and analysis of rDNA internal transcribed spacer sequences polymerase chain reaction amplified from rusty spot and peach powdery tnildew lesions. Cross-inoculations of apple and peach leaves with P. leucotricha and P. panno.sa, the causal agent of peach powdery mildew, showed that (i) young peach fruit, up to 5 cm in diameter, developed symptoms typical of rusty spot following inoculation with P. leucotricha: (ii) leaves of 'Jonagold' apple seedlings developed powdery mildew infections when inoculated by touching young rusty spot lesions to their surfaces; (iii) P. leucotricha sporulated on young peach fruit up to 5 cm in diameter; and (iv) peach leaves and young shoots were not susceptible to P. leucotricha, whereas P. pannosa infected all the green parts of peach. A field experiment revealed that there was only a 2-to 3-week period of time during early peach fruit development when the epidermis was susceptible to P. leucotricha. An outcome of this study is that now a clear distinction can be made between the symptoms caused by P. pannosa and P. leucotricha on peach.

Susceptibility of Peach Cultivars to Rusty Spot and Characterization of Susceptibility Groups

“…The positive correlations between both disease measures and ripening date in this study agrees with observations in other locations showing significant yield losses from rusty spot in late-maturing cultivars (Jankovics et al, 2011). However, because rusty spot epidemics occur much earlier in the growing season, between the shuck-split and pithardening stages, the association with late ripening does not appear to be direct (Furman et al, 2003a).…”

“…Furthermore, because all selections were evaluated under the same environmental conditions in each year, the quantitative data collected in this study allowed direct comparisons of relative susceptibility. Although similar quantitative comparisons of cultivar disease levels have not been previously conducted, rusty spot has been reported to occur on a variety of peach cultivars, including 'Rio-Oso-Gem', 'Summer Queen', 'Goldeneast', and 'Loring' (Daines and Trout, 1977); 'Jerseyqueen' (Furman et al, 2003a); and most recently 'Summerset', 'Suncrest', and 'Fayette' (Jankovics et al, 2011). In each of these studies, the severity of disease development and/or level of yield loss was observed to be high, indicating that these cultivars have a high degree of susceptibility.…”

“…Subsequent field studies examining disease gradients in peach orchards adjacent to apple orchards provided further support for P. leucotricha as the causal agent (Daines and Trout, 1977;Ries and Royse, 1978). Recent molecular-based research examining the rDNA internal transcribed spacer sequences of fungal thallus from rusty spot lesions has confirmed the pathogen to be P. leucotricha (Jankovics et al, 2011).…”

“…Rusty spot is an important disease of peach (Prunus persica L. Batsch) that occurs in many fruit-growing regions of the world (Dolovac et al, 2009;Grove, 1995b;Jankovics et al, 2011). Although the disease was first described in 1941, early attempts to identify the causal agent were thwarted as a result of sparse pathogen growth on fruit (Blodgett, 1941).…”

Australia: A Continent Without Native Powdery Mildews? The First Comprehensive Catalog Indicates Recent Introductions and Multiple Host Range Expansion Events, and Leads to the Re-discovery of Salmonomyces as a New Lineage of the Erysiphales

“…Our arguments for this hypothesis are presented below. Host range expansions appear to be frequent events in the evolution of some powdery mildews (Vági et al, 2007;Kirschner, 2010;Jankovics et al, 2011;Takamatsu, 2013a;Menardo et al, 2016;Beenken, 2017;Frantzeskakis et al, 2019a), and these could explain a number of "accidental" hosts of these fungi in different parts of the world. The genetic and genomic background of such rapid evolutionary processes has been partly revealed in obligate biotrophic plant pathogens (for reviews, see Frantzeskakis et al, 2019a;Thines, 2019).…”