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Quantitative Response of Cucumis melo Inoculated with Root Rot Pathogens

This experiment quantified the effects of three root rot pathogens on muskmelon (Cucumis melo L., var. cantalupensis) growth traits using computerized image analysis. Plants were grown from seed in sand infested with the soilborne pathogen Monosporascus cannonballus, Acremonium cucurbitacearum, or Rhizopycnis vagum. After 28 days in the growth chamber, images of plants were analyzed to quantify their response. Compared to noninoculated muskmelons, inoculated plants had significantly increased mean root diameter (45%), decreased root length (26%, primarily in roots of <0.5 mm diameter), decreased number of root tips (27%), decreased rhizosphere volume (40%), and decreased cumulative and mean surface area of leaves (24%). Effects of M. cannonballus on muskmelon growth were significantly different compared to A. cucurbitacearum and R. vagum. Isolate effects manifested a greater magnitude of difference on muskmelon traits than those observed at the species level. Multivariate analyses of plant responses were more powerful than univariate analyses to differentiate among effects of pathogen species and pathogen isolates. Discriminant analysis were useful to identify groups of plant traits modified by each fungal species or isolate at low disease levels. Digital image analyses proved to be a useful technique in quantitative assessment of plant damage caused by soilborne root rot pathogens.