Screening of Pumpkin ( Cucurbita spp.) Germplasm for Resistance to Powdery Mildew at Various Stages of Seedlings Growth

Powdery mildew is one of the world’s most widespread and damaging diseases of cucurbits (Kousik et al., 2008). It is caused by several species of the Erysiphaceae including Podosphaera xanthii (syn. Sphaerotheca fulginea) (McGrath and Thomas, 1996; Thomas et al., 1984). This disease acts as a sink for plant photosynthates causing reduction in plant growth, premature foliage loss, and consequently a reduction in yield. The yield loss is proportional to the severity of the disease and the length of time that plants have been infected (Mossler and Nesheim, 2005). It also results the reduced vigor of the seedlings and death of the seedlings in some instances (Kousik et al., 2008). In Korea, S. fuliginea is the most prevalent pathogen of powdery mildew in cucurbits (Shin, 2000). To date, seven races of P. xanthii (syn. S. fuliginea) have been identified using melon (Cucumis melo L.) differentials (Cohen et al., 2004; Pitrat et al., 1998; Thomas et al., 1984). Variability within races 1 and 2 in P. xanthii populations was described using 32 melon cultigens with the potential for the existence of 28 races (McCreight, 2006). Physiological races of this pathogen have not been classified for other cucurbits because of the lack of differentials and fully resistant germplasm (Cohen et al., 2004). A powdery mildew isolate from one cucurbit can infect all other tested cucurbit spp. (Hammett, 1977) and Cohen et al. (2004) has provided detail description of the cucurbit powdery mildew pathogen and race classification system. In the past, screening and selection studies against powResearch Article Open Access Res. Plant Dis. 22(3): 133-144 (2016) http://dx.doi.org/10.5423/RPD.2016.22.3.133