Bacterial diseases of potato.

Bacterial diseases are one of the most important biotic constraints of potato production, especially in tropical and subtropical regions, and in some warm temperate regions of the world. About seven bacterial diseases affect potato worldwide and cause severe damages especially on tubers, the economically most important part of the plant. Bacterial wilt and back leg are considered the most important diseases, whereas potato ring rot, pink eye, and common scab are the minor. Knowledge about zebra chip is extremely rare, as it occurs in a very isolated area and is an emerging disease in New Zealand, Europe, the USA and Mexico. Potato crop losses due to bacterial diseases could be direct and indirect; and they have several dimensions, some with short-term consequences such as yield loss and unmarketability of the produce and others with long-term consequences such as economic, environmental, and social. Some of them are of national and international importance and are the major constraints to clean seed potato production, with considerable indirect effects on trade. This review focuses on Clavibacter spp., Ralstonia spp., Pectobacterium spp., Dickeya spp., Streptomyces spp., and Liberibacter spp. pathogenic to potato, and looks at the respective pathogen in terms of their taxonomy and nomenclature, host range, geographical distribution, symptoms, epidemiology, pathogenicity and resistance, significance and economic losses, and management strategies. Nevertheless, the information collected here deal more with diseases known in developed and developing countries which cause severe economic losses on potato value chain

A new integrated pest management (IPM) model for cercospora leaf spot of sugar beets in the Po Valley

Cercospora leaf spot (CLS), caused by the fungus Cercospora beticola, is the most economically important foliar disease of sugar beets in Italy. It can be controlled with the integrated use of resistant varieties, cultural practices and foliar fungicides. Environmental conditions strongly influence the activity of C. beticola in the field and can be used to guide fungicide applications once the relationships are understood. To assist growers in making profitable decisions regarding the application of foliar fungicides for CLS control, a predictive model, developed by Minnesota and North Dakota State University was adjusted to Italian conditions and evaluated. The model was designed to predict the time of sugar beet infection by C. beticola was likely to occur based on hourly temperature and relative humidity data. CLS control is currently based on treatments scheduled using a \u201ccalendar\u201d program. This system recommends to start fungicide applications on fixed date and continue regularly every 18-20 days. Three years of field trial evaluation of the CLS prediction model at several experimental sites, compared with the calendar program, has resulted in a savings of two fungicide treatments (corresponding to 170 \u20ac/ha) without a significant loss of yield. For control of CLS, multiple applications of the same fungicide during a growing season are unfortunately common. This practice provides the target fungus with the conditions to evolve resistance. Sensitivity assays of C. beticola to DMI and QoI fungicides were carried out on isolates collected in 2009 and 2010 in northern Italy by the University of Bologna and North Dakota State University respectively. Isolates principally came from trial plot but also from commercial sugar beet fields and were tested towards tetraconazole and difenoconazole, pyraclostrobin and tri-floxystrobin using radial growth and spore germination assays. All samples collected in 2009 showed EC50 values for QoI ranging from 0.0008 to 0.2195 μg/ml. The percent range with EC50 values >1 for isolates collected in 2010 for tetraconazole was 44%, for difenoconazole 84%, for pyraclostrobin 27% and for trifloxystrobin 34%. From a samples of isolates with EC50 values >1 μg/ml, the range of EC50 values (μg/ml) for tetraconazole was 3.4-70.0, for difenoconazole 2.0-69.5, for pyraclostrobin 1.5-43.6, and for trifloxystrobin 3.8-77.1

Fungal, oomycete, and plasmodiophorid diseases of potato.

This chapter discusses the major potato diseases worldwide: late blight, early blight, wart, and powdery scab. Late blight, caused by the oomycete Phytophthora infestans, continues to be the main biotic constraint of potato production. Annual losses have been estimated to be about €6.1 billion, with major consequences to food security, especially in developing countries. Symptoms of the disease can be seen in leaves (water-soaked light to dark brown spots), stems (brown spots), and tubers (slightly depressed areas with reddish-brown color). High humidity and mild temperatures are essential for disease development and, under optimal conditions, the disease can destroy a field in a few days. Phytophthora infestans evolves continuously, mainly through recombination and migration from other areas. Thus, monitoring of P. infestans populations is critical for the design of effective management strategies. Fungicides remain as the most common tactic for late blight management, but environmental considerations are increasing the pressure to use host resistance, sanitation, and other measures. New solutions being developed to manage late blight include, among others, smart phone-based decision support systems linked to portable molecular diagnostics kits that can disseminate disease information rapidly to a large number of farmers. Emerging research topics on P. infestans include the role of the pathogen–microbiota interaction in promotion or suppression of the disease, as well as the metabolism of P. infestans