Evaluation of Watermelon and Related Species for Resistance to Race 1W Powdery Mildew

Abstract

<jats:p>Powdery mildew [<jats:italic>Podosphaera xanthii</jats:italic> (Castagne) Braun &amp; Shishkoff (syn. <jats:italic>Sphaerotheca fuliginea</jats:italic> auct. p.p.)] is now a common disease on watermelon [<jats:italic>Citrullus lanatus</jats:italic> (Thunb.) Matsum. &amp; Nakai] in the United States. In this study, the entire available U.S. Plant Introduction collection of <jats:italic>Citrullus</jats:italic> Schrad. ex Eckl. &amp; Zeyh. species was evaluated for resistance to <jats:italic>P. xanthii</jats:italic> race 1W. The collection consists of four <jats:italic>Citrullus</jats:italic> species and one <jats:italic>Praecitrullus</jats:italic> Pangalo species [<jats:italic>C. lanatus</jats:italic> var. <jats:italic>citroides</jats:italic> (L.H. Bailey) Mansf., <jats:italic>C. colocynthis</jats:italic> (L.) Schrad., <jats:italic>C. rehmii</jats:italic> De Winter, and <jats:italic>P. fistulosus</jats:italic> (Stocks) Pangalo]. Wild-type accessions tended to be more resistant more often than the cultivated species, <jats:italic>C. lanatus</jats:italic> var. <jats:italic>lanatus</jats:italic>. None were immune, eight of the 1573 accessions exhibited high levels of resistance, and another 86 demonstrated intermediate resistance. Stem and leaf disease severity were weakly correlated (<jats:italic>r</jats:italic> <jats:sup>2</jats:sup> = 0.64, <jats:italic>P</jats:italic> = 0.001). The majority of accessions having resistance were collected in Zimbabwe. Resistance was found in four species.</jats:p>

Species spectra, distribution and host range of cucurbit powdery mildews in the Czech Republic, and in some other European and Middle Eastern countries

“…This species is generally considered to be highly resistant to CPM (Sitterly 1978). Our recent data represent the first report of a GC infection on watermelon in the Czech Republic, and it complements the recent findings of Davis et al (2007).…”

Potential Sources of Resistance to Cucurbit Powdery Mildew in U.S. Plant Introductions of Bottle Gourd

“…The reactions of these differentials have been considered to be consistent worldwide (McCreight, 2006). The melon race 1 in our study could also be designated as race 1M based on suggestions by Davis et al (2007). Recently Davis et al (2007) described race 1W from watermelon and suggested that this race did not infect melons.…”

“…Two days before inoculation, air was blown over leaves of 'Iran H' or squash plants to clear the old conidia and allow new conidia to form. Three weeks after seeding, seedlings were dusted with powdery mildew conidia as described by Thomas et al (2005) and others (Davis et al, 2006b(Davis et al, , 2007. Seedlings were maintained in the greenhouse where conditions were optimal for development of powdery mildew during the winter months.…”

DNA markers and pollen morphology reveal that Praecitrullus fistulosus is more closely related to Benincasa hispida than to Citrullus spp.

“…The US PIs of P. fistulosus were included in several studies that evaluated Citrullus germplasm for disease or pest resistance (Simmons and Levi 2002;Davis et al 2007;Hopkins and Levi 2008) with the idea that the resistant P. fistulosus PIs could be used in breeding programs aimed at enhancing resistance in watermelon cultivars. The results herein confirmed that P. fistulosus is closer to B. hispida and is distant from Citrullus or Cucumis species.…”