Melon-Powdery Mildew Interactions Reveal Variation in Melon Cultigens and Podosphaera xanthii Races 1 and 2

Abstract

<jats:p>Powdery mildew is a serious disease of melon (<jats:italic>Cucumis melo</jats:italic> L.) worldwide. Twenty-two melon cultigens have been used to define 22 reported races of the pathogen <jats:italic>Podosphaera xanthii</jats:italic> (sect. <jats:italic>Sphaerotheca</jats:italic>) <jats:italic>xanthii</jats:italic> (Castag.) U. Braun &amp; N. Shish. Comb. nov. [syn. <jats:italic>Sphaerotheca fuliginea</jats:italic> (Schlecht. ex Fr.) Poll.]. Discrepancies in the reactions of eight cultigens to populations of <jats:italic>P. xanthii</jats:italic> races 1 and 2 in California, Japan, and Spain revealed genetic differences among them that can be used to differentiate <jats:italic>P. xanthii</jats:italic> race 1 and 2 populations in these countries. Implicit in these results is the existence of previously unknown virulence factors in these populations of <jats:italic>P. xanthii</jats:italic> races 1 and 2 that permit designation of new races of <jats:italic>P. xanthii</jats:italic> on melon. Synthesis of these results with previous reports resulted in the identification of 28 putative races of <jats:italic>P. xanthii</jats:italic> on melon that include eight variants of race 1 and six variants of race 2. Six of the cultigens exhibited resistant blisters in response to heavy infection by <jats:italic>P. xanthii</jats:italic> in field and greenhouse tests.</jats:p>

Gaps and perspectives of pathotype and race determination in Golovinomyces cichoracearum and Podosphaera xanthii

“…Races of Gc and Px have, to date, been differentiated only on melon (Table 2). McCreight (2006) and Lebeda et al (2008) summarized the different genotypes and systems used for CPM race identification and denomination (Tables 2, 3). An overview of the various sets of CPM race differentials is shown in chronological order in Table 2, starting from the appearance of the second race of P. xanthii (in 1938).…”

“…An overview of the various sets of CPM race differentials is shown in chronological order in Table 2, starting from the appearance of the second race of P. xanthii (in 1938). The most frequently used sets of melon differentials include 11 genotypes of C. melo ( Table 2) that can differentiate CPM races originating from melon (McCreight 2006) and other cucurbits, such as cucumber, Cucurbita spp., and watermelon (Lebeda andSedláková 2006, 2010;Lebeda et al , 2007Lebeda et al , 2008. CPM race designations are not uniform, methodical, objective, or meaningful (Table 3), and three methods of race denominations are in use: numbers (e.g., 1, 2, 3), letters (e.g., A, B, C), and combinations of numbers and letters (e.g., 1J, 2F, 2US) ).…”

“…The most frequently used differential set b Bertrand (1991) (3) a large number of new pathotypes and races occur in Czech Republic; (4) Czech CPM populations vary temporally and spatially , 2006, 2010Lebeda et al , 2007. No information on the genetic bases for the pathogenicity of CPM pathotypes or races is currently available at either the molecular or Mendelian level.…”

“…They are also highly variable in their pathogenicity and virulence, as evidenced by the existence of large number of different pathotypes and races (Bertrand et al 1992;Lebeda et al , 2007Lebeda and Sedláková 2006;McCreight 2006) and by their variability in response to fungicides (McGrath 2001;Sedláková and Lebeda 2008).…”

“…There is often a very clear expression of compatibility or incompatibility in host plant-powdery mildew interactions that allows for the classification of pathotypes and races based on the reaction patterns of compatible and incompatible reactions on the differential hosts species or genotypes . A unified, objective system for the determination, denomination, and classification of pathotypes and races on cucurbits remains to be codified (Lebeda and Sedláková 2006;Lebeda et al 2007Lebeda et al , 2008McCreight 2006).…”