Colonization of roots, stolons, tubers and stems of various potato (Solanum tuberosum) cultivars by the black‐dot fungus Colletotrichum coccodes

Abstract

In an attempt to better understand the importance of tuber-borne inoculum in black dot development, several potato cultivars were inoculated with various Colletotrichum coccodes isolates. Symptoms developed first on underground organs (starting 2 weeks after inoculation on roots, and later on stolons and tubers) of inoculated plants; stem infections developed only after 7-10 weeks, depending on the cultivar. Infection with C. coccodes resulted in a reduction in numbers of stolons and tubers in cv. Bintje, but not in the later maturing cv. Roseval. Significant isolate by cultivar interactions were detected from the analysis of root symptoms after inoculation of three potato cultivars (Bintje, Spunta and Desiree) with five C. coccodes isolates. Such an interaction was also detected for stolon/tuber symptoms at the latest scoring date (98 days after inoculation), but not at earlier dates (58, 70 and 84 days after inoculation). These results suggest that protocols based on root colonization might be used for investigating cultivar response to black dot and pathogenicity of C. coccodes isolates, and that some specificity exists in the reaction of potato genotypes to this pathogenic fungus.

Colonization of Potato Roots and Stolons by Colletotrichum coccodes from Tuberborne Inoculum

“…The assumptions of normality and equal variance for the regression model were satisfied (Kutner et al 2005). Data from Andrivon et al (1998) were similarly analyzed with regression except the number of days after planting (inoculation) was used as the independent time variable. Pearson's chi-square (χ 2 ) goodness-of-fit test was used to validate the accuracy of the visual assessment for diseased tissue.…”

“…Values for time and distance of C. coccodes expansion from an inoculated seed-piece have previously been reported but growth rates were not calculated (Andrivon et al 1998). Colonization on roots by C. coccodes of cultivars Bintje and Roseval was determined visually by Andrivon et al (1998) using cortical rot symptoms or sclerotia if present and the observations were plotted to compare disease extension between inoculated and control plants.…”

“…Colonization on roots by C. coccodes of cultivars Bintje and Roseval was determined visually by Andrivon et al (1998) using cortical rot symptoms or sclerotia if present and the observations were plotted to compare disease extension between inoculated and control plants. In that study, disease assessment data was provided at 7 days after inoculated tubers were planted and at 7 day intervals thereafter until 84 days after planting.…”

“…To calculate growth rates from this previously published data, values for time (weeks) and symptom extension from the seed piece (mm) were obtained by interpreting data points directly from the uppermost plot in Fig. 2 of Andrivon et al (1998). Growth rates were then calculated using regression analysis.…”

“…While considerable research has been conducted comparing the effects of tuber and soil inoculum sources on disease development (Andrivon et al 1998;Nitzan et al 2008), a need exists to further characterize colonization of roots and stolons by C. coccodes. Infection from a single, identifiable inoculum source, such as an infected seed-piece would allow colonization to be critically characterized as compared to multiple infections in the rhizosphere.…”