Components of Resistance to Early Blight in Four Potato Cultivars: Effect of Leaf Position

Abstract

Components of early blight resistance were quantified in leaves of different ages in four potato cultivars. The components of resistance: incubation period (IP), lesion number (LN), early blight severity, lesion expansion rate (LER), latent period (LP) and spore production by lesion area (SPLA), were evaluated separately in the lower, middle and upper leaves of four potato cultivars. Plants of cultivar Aracy (resistant), Delta (moderately resistant), Desire´e (susceptible) and Bintje (susceptible) were inoculated with an Alternaria solani isolate at the beginning of the flowering stage. Disease severity varied in different plant parts. In all cultivars, regardless of resistance, the smallest values of LN, and severity were recorded on the upper leaves, suggesting that young tissues are less susceptible. In cultivar Aracy, the IP was long, with small values of LN and LER and consequently, low values of early blight severity in all leaf positions were recorded. Although IP was long in cultivar Aracy, no differences between the moderately resistant cultivar Delta and the susceptible cultivars Bintje and Desire´e could be detected for this component. The IP was only influenced by leaf position in cultivar Aracy. Clear differences in resistance levels among cultivars could be detected regarding LN, severity and LER. However, neither LP nor SPLA were associated with resistance level of cultivars or with leaf position. Analyses according to plant part suggest that evaluations on leaves of the middle third part are most suitable for screening for early blight resistance in potato.

Field resistance of potato cultivars to foliar early blight and its relationship with foliage maturity and tuber skin types

“…Previous field evaluations of EB resistance of potato cultivars have used only one or a few epidemiological variables, such as disease severity at any given time during the epidemic (Brune & Reifschneider, 1989;Brune et al, 1990;Christ, 1991;Reifschneider & Brune, 1992;Brune et al, 1994), the AUDPC (Christ, 1991;Dita-Rodríguez et al, 2006;Simon et al, 2009) and r (Holley et al, 1983). Nazareno et al (1999) suggested that caution must be taken if only one epidemiological variable is used during disease assessment.…”

“…Potato resistance to EB appears to be associated with cultivar maturity, with the late-maturing cultivars tending to be more resistant than early-maturing cultivars (Douglas et al, 1972;Mendoza et al, 1986;Herriott et al, 1990;Pelletier & Fry 1990;Zhang, 2004;Dita-Rodríguez et al, 2006). However, because EB occurs most often during senescence of the host tissues, some cultivars may appear resistant simply because they are late maturing (Herriott et al, 1990).…”

Assessment on early blight of potato in order to compare the two methods<i> in vitro </i>using pathogenic fungi <i>Alternaria solani</i>

“…Disease severity assessments could was done on lower, middle and upper leaves but middle leaf assay is a useful factor for potato cultivars evaluation [1,6]. Therefore in this research was used from middle leaf for resistance level selection.…”

“…Virus free clones of potato cultivars were obtained from the National plant gene bank of Iran. Six cultivars were conducted Ells, Picasso, Maradona, Marfona, Casmos and Desiree that the cultivar Desiree is used as susceptible reference cultivar when screening potato genotypes in Brazil [6,8]. Plantlets were propagated through nodal cutting and kept in growth chamber at 23˚C ± 2˚C, light with a period of 16 h light and 8 h dark.…”

“…The fungicides used to control the disease are expensive and frequently inefficient [4]. Potato resistance to early blight is a quantitative trait, and obtaining successful resistant cultivars is not simple [5][6][7]. It has been observed that resistance to early blight is age-related: early-maturing cultivars are more susceptible than late-maturing cultivars.…”