Quantification of Field Resistance to Verticillium dahliae in Eight Russet-Skinned Potato Cultivars Using Real-Time PCR

Abstract Changes in potato production over the past 10 to 20 years, have resulted in increased emphasis being placed on breeding for resistance to Verticillium wilt, caused by Verticillium dahliae Kleb. While many russet-skinned cultivars recently have been released with reported resistance to Verticillium wilt, information is lacking on the level of pathogen colonization, and therefore, the level of true genetic resistance is not known. Eight russet-skinned cultivars were grown in field trials with low and high levels of V. dahliae in the soil, and evaluated for wilt, stem colonization, yield, and tuber vascular discoloration. A recently developed QPCR assay was validated, with strong relationships to culture plating assays over three stem sampling dates. Additionally, stem colonization levels, as determined by QPCR, were related to wilt and tuber vascular discoloration. However, total yield did not exhibit a strong relationship to any other parameter evaluated in this study. Results from these studies indicate that varying levels of true resistance are present in the russet-skinned cultivars evaluated, and that the QPCR assay can be reliable in rapidly evaluating resistance to V. dahliae under field conditions. Based on pathogen quantification using stem colonization derived from traditional plating assays and QPCR, the resistance level of several cultivars is more clearly defined and discussed. Resumen Los cambios en la producción de papa en los pasados 10 a 20 años, han resultado en un aumento en el énfasis ubicado en el mejoramiento para la resistencia al marchitamiento por Verticillium, causado por Verticillium dahliae Kleb. Mientras que muchos cultivares de piel tipo russet se han liberado recientemente con resistencia reportada al marchitamiento por Verticillium, la información carece del nivel de colonización del patógeno, y de aquí que no se conozca el nivel de resistencia genética verdadera. Se sembraron ocho cultivares con piel tipo russet en ensayos de campo con niveles bajo y alto de V. dahliae en el suelo, y evaluados para marchitez, colonización del tallo, rendimiento, y decoloración vascular del tubérculo. Se evaluó recientemente un ensayo QPCR, con relaciones fuertes a ensayos de cultivos en placas sobre tres fechas de muestreo del tallo. Adicionalmente, los niveles de colonización del tallo, como se determinaron por QPCR, se relacionaron al marchitamiento y a la decoloración vascular del tubérculo. No obstante, el rendimiento total no exhibió una relación fuerte a ningún otro parámetro evaluado en este estudio. Los resultados de estos estudios indican que están presentes diversos niveles de resistencia verdadera en las variedades de piel tipo russet evaluadas, y que el ensayo de QPCR puede ser confiable en la evaluación rápida de resistencia a V. dahliae bajo condiciones de campo. Con base en la cuantificación del patógeno mediante el uso de la colonización del tallo derivada de los ensayos tradicionales de placas y QPCR, el nivel de resistencia de varios cultivares está más claramente definido y discutido

Phytophthora nicotianae diseases worldwide: new knowledge of a long-recognised pathogen

Phytophthora nicotianae was first isolated from tobacco at the end of the 19th century. This organism is now considered as one of the most devastating oomycete plant pathogens, with a recognized host range of more than 255 species over five continents and a wide diversity of climates. The economic losses caused by P. nicotianae are difficult to estimate, because of the diversity of its hosts and ecological niches. For these reasons, this pathogen represents a continuous challenge to plant disease management programmes, which frequently rely solely on the use of chemicals. Phytophthora nicotianae is better adapted than its competitors to abiotic stresses, especially to climate warming. As a result, its importance is increasing. This review illustrates, with some examples, how P. nicotianae currently impacts plant economies worldwide, and how it may constitute more severe threats to agriculture and natural ecosystems in the context of global climate change

North Dakota Potato Wilt Survey - 1977

A potato wilt survey conducted in two parts was performed during the 1977 growing season in five counties of North Dakota. Results indicate Fusarium spp. is the major wilt pathogen of potatoes. Verticillium spp. and Erwinia carotovora var. atroseptica (blackleg organism) were also found in high percentages in wilted plants. Colletotrichum and Rhizoctonia were isolated in nearly equal proportions. A high percent of wilted plants were found to contain more than one wilt-causing organism which indicated that mixed infection occurred. The interaction of wilt organisms in multiple infections increases the complexity of the potato wilt disease and makes control much more difficult

Guidelines for Seed Potato Selection, Handling and Planting

PP-87

Ring rot of potatoes

PP-507 rev

Blackleg and soft rot of potatoes

PP-903; This circular provides information on the symptoms, cause and diseases management of blackleg and soft rot of potatoe

Genetic diversity of \u3ci\u3e‘Cadidatus\u3c/i\u3e Liberibacter solanacearum’ strains in the United States and Mexico revealed by simple sequence repeat markers

‘Candidatus Liberibacter solanacearum’ is associated with the Zebra Chip (ZC) disorder of potatoes. A panel of eight simple sequence repeat (SSR) markers was developed and used to genetically characterize ‘Ca. L. solanacearum’ strains obtained from ZC-affected potato plants in the United States and Mexico. The multilocus SSR markers in this study effectively differentiated genotypes and estimated genetic diversity of ‘Ca. L. solanacearum’ strains. Genotype assignment analyses identified two major lineages of ‘Ca. L. solanacearum’ in the North American populations while only one lineage type was identified in Mexican population. No clear genetic structure was found among haplotypes based on geographical proximity or host. The high resolution power of the SSR marker system developed in this study provides a useful tool for genotyping closely related strains and tracking sources of the pathogen. Genotype information combined with epidemiological data will advance knowledge of ZC disease and will facilitate development of effective disease management

Multiplex real-time PCR for detection, identification and quantification of ‘Candidatus Liberibacter solanacearum’ in potato plants with zebra chip

The new Liberibacter species, ‘Candidatus Liberibacter solanacearum’ (Lso) recently associated with potato/tomato psyllid-transmitted diseases in tomato and capsicum in New Zealand, was found to be consistently associated with a newly emerging potato zebra chip (ZC) disease in Texas and other southwestern states in the USA. A species-specific primer LsoF was developed for both quantitative real-time PCR (qPCR) and conventional PCR (cPCR) to detect and quantify Lso in infected samples. In multiplex qPCR, a plant cytochrome oxidase (COX)-based probe-primer set was used as a positive internal control for host plants, which could be used to reliably access the DNA extraction quality and to normalize qPCR data for accurate quantification of the bacterial populations in environment samples. Neither the qPCR nor the cPCR using the primer and/or probe sets with LsoF reacted with other Liberibacter species infecting citrus or other potato pathogens. The low detection limit of the multiplex qPCR was about 20 copies of the target 16S rDNA templates per reaction for field samples. Lso was readily detected and quantified in various tissues of ZCaffected potato plants collected from fields in Texas. A thorough but uneven colonization of Lso was revealed in various tissues of potato plants. The highest Lso populations were about 3×108 genomes/g tissue in the root, which were 3-order higher than those in the above-ground tissues of potato plants. The Lso bacterial populations were normally distributed across the ZC-affected potato plants collected from fields in Texas, with 60% of ZC-affected potato plants harboring an average Lso population from 105 to 106 genomes/g tissue, 4% of plants hosting above 107 Lso genomes/g tissue, and 8% of plants holding below 103 Lso genomes/g tissue. The rapid, sensitive, specific and reliable multiplex qPCR showed its potential to become a powerful tool for early detection and quantification of the new Liberibacter species associated with potato ZC, and will be very useful for the potato quarantine programs and seed potato certification programs to ensure the availability of clean seed potato stocks and also for epidemiological studies on the disease