Variety-specific Epidemiology ofCercospora beticolaSacc. and Consequences for Threshold-based Timing of Fungicide Application in Sugar Beet

Abstract

In Central Europe, fungicides to control leaf spot disease in sugar beet caused by Cercospora beticola are applied based on thresholds of disease incidence (DI, per cent of infected plants). As variety-specific fungicide application was not analyzed to date, the epidemiology of C. beticola and its effect on white sugar yield (WSY) in varieties with different susceptibility were investigated at seven sites in Germany and Austria in 2004 and 2005. All varieties reached the summary thresholds 5 ⁄ 15 ⁄ 45% DI in all environments. Fitting a logistic growth curve to DI revealed significant differences among varieties. At high disease pressure, susceptible varieties reached a considerably higher disease severity (DS, per cent of infected leaf area) at harvest and a larger area under disease progress curve (AUDPC) than resistant varieties. Fitting a logistic growth curve to DS showed an increasing differentiation among varieties with time. The growth rate estimated based on the logistic growth curve was the only variable that performed equally well in differentiating varieties under low and high disease pressure. With increasing disease pressure, varieties differed considerably in WSY, but differences between susceptible and resistant varieties were significant only in some environments. The disease-loss relation between AUDPC and relative WSY was varietyspecific. Resistant varieties had an approximately identical WSY with and without infection and compensated for negative infection effects even at higher AUDPC. Therefore, at high disease pressure, resistant varieties had a higher relative yield compared to susceptible ones. However, our results indicate that there is no need to develop variety-specific thresholds, but resistant varieties reach the established thresholds later than susceptible ones. Consequently, the time of fungicide application can be delayed in resistant varieties. This will help to reduce the use of fungicides to the bare essentials as requested for the integrated crop protection management.

New Generation of Resistant Sugar Beet Varieties for Advanced Integrated Management of Cercospora Leaf Spot in Central Europe

“…Varietal resistance against pathogens often comes along with a yield penalty in the absence of the disease ( Brown, 2002 ). This was also found in several studies with sugar beet (e.g., Miller et al, 1994 ; Mittler et al, 2004 ; Kaiser et al, 2010 ; Gummert et al, 2015 ). Breeding of resistant varieties with high yield performance even without or under low infection pressure is crucial for acceptance in commercial practice.…”

“…It is calculated as the relative difference in white sugar yield (WSY) between the non-treated and healthy fungicide levels and is supposed to describe the tolerance toward CLS ( Ossenkop et al, 2005 ). As resistance against CLS maintains photosynthetic leaf area and thereby reduces yield loss ( Rossi et al, 2000 ), it has been a matter of discussion, whether reduced yield loss can be attributed to tolerance traits or not ( Ossenkop et al, 2005 ; Kaiser et al, 2010 ). Consequently, it has to be evaluated in more detail how CLS resistance and tolerance are connected in sugar beet varieties.…”

Characterization of cytochrome b from European field isolates of Cercospora beticola with quinone outside inhibitor resistance

“…The disease causes a reduction in root harvest weight and extractable sucrose. CLS control measures include the planting of tolerant varieties and crop rotation, but the disease is managed most effectively when combined with timely fungicide applications (Bolton et al, 2012a;Kaiser et al, 2010;).…”

Characterization of CbCyp51 from Field Isolates of Cercospora beticola

“…C. beticola is able to overwinter as stromata in infected sugar beet leaf residue on or directly below the soil surface (14). Control measures for leaf spot include resistant sugar beet varieties and crop rotation but the disease is managed effectively only when combined with timely fungicide applications (10,13,31). The fungus penetrates stomata to gain access to the apoplast (34), where effectors are produced by the invading hyphae that facilitate disease establishment (3).…”