Resistance of Cucurbits to Podosphaera xanthii Race 1

Abstract

This study was conducted to establish an efficient screening method to identify cucurbits resistant to powdery mildew. Powdery mildew fungus was obtained from a single lesion of infected cucumber leaf in 2010 at Daejeon. The fungus was identified as Podosphaera xanthii race 1 based on morphological characteristics and resistance responses of four melon differentials. Development of powdery mildew caused by the fungal isolate on 34 commercial cultivars of cucumber was investigated at three plant growth stages in a greenhouse. The degree of resistance of cotyledons of each cultivar to the fungus was not correlated with that of whole plant, but powdery mildew occurrence in the first true leaf was highly correlated with resistance at the level of the whole plant. Based on these results, the first true leaf of cucurbit cultivars can be used for screening of resistance to powdery mildew. In addition, variation of resistance of commercial 12 cucumber and 26 melon cultivars to the powdery mildew fungus due to different growing seasons was tested. In the case of cucumber, the resistance response in some cultivars was influenced by growing season. The resistant cultivars showed higher resistance in the warm season than in the cool season. By contrast, the resistant melon cultivars demonstrated strong resistance in all the tested growing seasons. Interestingly, the tested powdery mildew pathogen, a member of P. xanthii race 1, was not pathogenic on seven cultivars of watermelon (Citrullus lanatus). To follow up on this, diverse race 1 isolates of P. xanthii should be collected and tested.

Identification of a Causal Pathogen of Watermelon Powdery Mildew in Korea and Development of a Genetic Linkage Marker for Resistance in Watermelon (Citrullus lanatus)

“…Although a few studies have identified the causal fungi of powdery mildew in watermelon in Korea (Lee et al, 2010;Kim et al, 2013;Lee et al, 2014), we attempted to characterize the genera and races of the pathogen using previously reported methods for other crops (Bardin et al, 1999;Chen et al, 2008) based on morphological and molecular characters. All morphological characters of the conidia, including the shape, size, and the presence of fibrosin bodies, matched those of P.…”

“…In South Korea, 23 cultivars out of 120 watermelon accessions showed moderate resistance to powdery mildew (Lee et al, 2010). In another trial, 51 commercial cultivars of cucumber (Cucumis sativus), melon (Cucumis melo), and watermelon were screened for resistance to P. xanthii race 1, but this strain was not pathogenic on tested watermelon cultivars (Lee et al, 2014). The authors suggested that the tested P. xanthii race 1 that is infectious to cucumber and melon does not correspond to race 1W, which is infectious to watermelon.…”

Occurrence of Powdery Mildew Caused by New Race 2F of Podosphaera xanthii on Cucumber in Korea

“…, Zitter (1996) race race 1 (Table 1). P. xanthii race race 1 (Zitter et al, 1996), race (Kim , 2016;Lee , 2014). MR-1 6.9% (R) (Fig.…”

“…(Pirondi , 2015) internal transcribed spacer (ITS) ITS1 (5 -TCCGTAGGTGAACCTGCGG-3 ) ITS4 ( 5-TCCTCCGCTTATTGATATGC-3 ) (polymerase chain reaction) . (Lee , 2014).…”

“…4). (Lee , 2014;Zitter , 1996) SE180328 race 2 ( race 2 6 (Cohen , 2004;McCreight, 2006). Race 2 2a 2b (Cohen , 2000;McCreight, 2006…”