Development ofErysiphe pulchra, the causal agent of powdery mildew, on leaf disks of susceptible and resistant flowering dogwood (Cornus florida)

Abstract

Understanding the relative contribution of the different resistance components is necessary to develop selection schemes and accelerate resistant-cultivar development. This study was conducted to investigate spore germination, infectionstructure formation, and fungal development of Erysiphe pulchra, the causal agent of powdery mildew, on leaf disks of six cultivars or lines of flowering dogwood (Cornus florida) with different levels of resistance. The cultivars and lines tested were grouped into the following three resistance categories: highly susceptible ('Cherokee Daybreak' and MW 94-60), moderately susceptible ('Cherokee Princess , and resistant ('Cherokee Brave' and 'Karen's Appalachian Blush'). Percentages of spore germination and secondary-appressoria formation were not significantly different among the cultivars and lines. Significantly less percent germinated conidia with branched hyphae were observed on resistant cultivars than on the moderately susceptible cultivar or line, which was less than on the highly susceptible cultivar or line. Infection efficiencies were significantly different among cultivars and lines in the three resistance categories, except that there were no differences between 'Cherokee Princess' and the resistant cultivars. Resistant cultivars supported shorter latent periods than moderately and highly susceptible cultivars or lines, but no differences in latent period were detected between the later two resistance categories. The recently released 'Karen's Appalachian Blush' expressed higher levels of resistance to powdery mildew than did 'Cherokee Brave', as indicated by the longer latent period and reduced relative sporulation of the pathogen. Résumé : Comprendre la contribution relative des différents éléments de la résistance est nécessaire pour établir des plans de sélection et accélérer le développement de cultivars résistants. La présente recherche fut menée pour étudier la germination des spores, la formation des structures d'infection et le développement fongique de l'Erysiphe pulchra, agent responsable de l'oïdium, sur des rondelles de feuilles de six cultivars ou lignées de cornouiller (Cornus florida) en fleurs possédant différents degrés de résistance. Les cultivars et lignées testés étaient regroupés selon trois catégories de résistance : très sensibles ('Cherokee Daybreak' et MW 94-60), moyennement sensibles ('Cherokee Princess' et MW 95-25) et résistants ('Cherokee Brave' et 'Karen's Appalachian Blush'). Les pourcentages de germination des spores et la formation d'appressoria secondaires n'étaient pas significativement différents parmi les cultivars et lignées. Le pourcentage de conidies germées avec hyphes ramifiées observé chez les cultivars résistants fut significativement moins élevé que ceux du cultivar et de la lignée moyennement sensibles, eux-même moins élevés que ceux du cultivar et de la lignée très sensibles. L'efficacité de l'infection fut significativement différente parmi les cultivars et lignées dans les trois catégories de résistance, sauf entre 'Chero...

Assessment of resistance components of bigleaf hydrangeas (Hydrangea macrophylla) toErysiphe polygoniin vitro

“…In contrast, spore germination was not different between resistant and susceptible cultivars for Oidium lycopersicum Cooke & Massee on Lycopersicon species (Huang et al 1998), E. pisi DC on sweet pea (Pisum sativum L.) (Poulter et al 2003;Viljanen-Rollinson et al 1998), Sphaerotheca fuliginea (Schlechtend.:Fr.) Pollacci on melon (Cucumis melo L.) (Cohen and Eyal 1988;Floris and Alvarez 1996;Kuzuya et al 2003;Pérez-Garcia et al 2001), E. polygoni DC on mungbean (Vigna radiate (L.) Wilczek) (Reddy et al 2001), and Erysiphe pulchra on flowering dogwood (Cornus florida L.) (Li et al 2006). The results of the present study indicate that resistance mechanisms in bigleaf hydrangea were not involved prior to the penetration attempt of the fungus on host leaf surfaces.…”

“…Restriction or inhibition of hyphal growth on resistant cultivars has been reported in several powdery mildew pathosystems (Floris and Alvarez 1996;Huang et al 1998;Kuzuya et al 2003;Poulter et al 2003). On the other hand, non-hypersensitive resistance responses can also restrict disease development and reduce spore production by preventing haustorium formation (Niks 1986) or by restricting colony growth (Carver and Carr 1978;Li et al 2006). Partial resistance is characterized as continuous variation in fungal sporulation (Niks and Rubiales 2002;Parlevliet 1992).…”

“…Partial resistance is characterized as continuous variation in fungal sporulation (Niks and Rubiales 2002;Parlevliet 1992). Infection efficiency, latent period, and sporulation have been used as components to evaluate partial resistance to plant diseases (Diaz-Lago et al 2003;Li et al 2006;Lindhout et al 1994;Parlevliet 1989;Viljanen-Rollinson et al 1998).…”

“…Formation of haustoria to absorb nutrients and support hyphal growth is necessary for biotrophy establishment. Fungal development can be affected by host resistance at many stages of the infection process (Niks and Rubiales 2002), such as haustorium formation (Martinez et al 2004) and hyphal growth (Carver and Carr 1978;Li et al 2006). Hypersensitive response (HR) that is characterized by rapid death of invaded cells is one of the major resistance mechanisms to restrict fungal development (Adam and Somerville 1996;Cohen and Eyal 1988;Kuzuya et al 2006;Prats et al 2007;Sameshima et al 2004;Vorwerk et al 2007).…”

Evaluation for Resistance to Powdery Mildew in Cornus Species and Hybrids Using a Leaf Disk Assay

“…A cost-and time-effective method is desirable for screening and identifying dogwoods for resistance to powdery mildew. Leaf disk assays have been used to screen for powdery mildew resistance in melon (1,3) and sweet cherry (8), and to investigate resistant components of flowering dogwoods to powdery mildew (5). The objective of this study was to evaluate Cornus species and hybrids for resistance to powdery mildew using an in vitro leaf disk assay.…”