Optimisation of sample size for the detection of latent infection byRalstonia solanacearum in potato seed tubers in the highlands of Peru

Abstract

SummaryA sampling strategy was evaluated in the Andean highlands of Peru to optimise the detection of Ralstonia solanacearum in seed tubers harvested from symptomless crops. A sensitive and specific serological method developed at CIP was used to detect the pathogen in latently infected tubers. Optimum sample size was evaluated for symptomless crops after analysing various numbers of composite samples and using a binomial distribution model to calcillate the detection probabilities. R. solanacearum was detected in all lots from fields with visible symptoms, so validating the detection technique. About half of the seed lots from apparently healthy fields at altitudes of up to 3,100 m were found positive for the pathogen. R. solanacearum was detected with 99% probability in samples of 350 tubers from seed lots from symptomless crops. This number of seed tubers could feasibly be processed in a seed-health test without incurring too high a cost for labour and materials.

A comprehensive comparison of assays for detection and identification of Ralstonia solanacearum race 3 biovar 2

“…Finally, the probability of detecting R. solanacearum in a crop field is limited by sample size, pathogen incidence and diagnostic methodology. For postharvest testing of potatoes, for example, the sample should be a minimum of 400 tubers or stems randomly collected from the consignment in question to provide a 0Á99 probability of detecting a 1Á5% incidence of infected units in a given population (De Boer et al 1996;Priou et al 2001).…”

Capacidad predictiva de DAS-ELISA al virus mosaico estriado de la cebada en trigo

“…The level of infection of a seed or incidence of the pathogen in the crop is key for its detection (Scott and Zummo, 1995) also determines the sample size or composite sample, as found by Priou et al (2001), that reducing the composite sample size of potato tubers are based on the level of incidence of Ralstonia solanacearum in crops. Because when comparing the 36 values showed in Table 3, obtained from the combination of the three factors, as if they were individual treatments does not make much sense, an analysis of variance was performed considering the factorial structure of the treatments, 3 factors: i) number of single samples (NMS) with 4 levels (25, 20, 15 and 10); ii) Sample size (TM) with three levels (15, 10 and 5); and iii) level of infection (NI) with three levels (15, 10 and 5).…”

“…El nivel de infección de una semilla o de incidencia del patógeno en el cultivo es clave para su detección (Scott y Zummo, 1995), además que determina el tamaño de muestra o muestra compuesta, como lo encontrado por Priou et al (2001), que la reducción del tamaño de muestra compuesta de tubérculos de papa están en función del nivel de incidencia de Ralstonia solanacearum en los cultivos.…”

“…Figure 2 shows the linear trend of the average absorbance values of MC samples according to NMS, TM and NI with only the MC10-10-5 value below the threshold line. Priou et al (2001) found that as the level of disease incidence by Ralstonia solanacearum decreases in culture, fungus detection decreases in tuber. Therefore these authors suggest to analyze large composite samples when disease levels are low in the crop.…”

“…La Figura 2 muestra la tendencia lineal de los valores promedio de absorbancia de las muestras MC de acuerdo al NMS, TM y NI con solo el valor de la MC10-10-5 por debajo de la línea del umbral. Priou et al (2001) encontraron que conforme el nivel de incidencia de la enfermedad por Ralstonia solanacearum disminuye en el cultivo, se reduce la detección del hongo en el tubérculo. Por lo anterior, estos autores sugieren analizar muestras compuestas grandes cuando los niveles de enfermedad son bajos en el cultivo.…”