Anatomy and morphology of vitis roots in relation to pathogenesis caused by Phymatotrichum omnivorum (Shear) Duggar

Abstract

Among 4 cultivars studied, Vitis Champini Planch cv. Dogridge demonstrated the greatest plant vigor and host tolerance to Phymatotrichum root rot caused by Phymatotrichum omnivorum (Shear) Duggar. V. rotundifolia Mich x cv Noble and vinifera L. cv. Barbera appeared least vigorous and least tolerant of the pathogen. Host plant death and fungal structures found in root tissue from field and controlled inoculum studies indicated that 'Dogridge' is tolerant and not resistant as concluded in earlier research. The lack of symptom expression seen as moisture stress and stunting in 'Dogridge' and to a lesser extent in V. labruscana Bailey cv. Concord is correlated with high root regeneration potential, root growth and extensiveness. Consequently, 'Noble' with an extremely shallow root system, and the least propensity to regenerate new roots was most susceptible to Phymatotrichum root rot and was the first cultivar to express symptoms. P. omnivorum fungal structures were found in root tissue of all cultivars after the media had been inoculated with sclerotia. A modification of Cartwright's stain with paraffin embedded root tissue was the most effective stain series tried in differentiating the pathogen and host structures. Multiple periderm development and fewer openings in the periderm were correlated with pathogen tolerance. 'Dogridge' had the most suberin accumulation in phellem cell walls and 'Barbera' the least. 'Noble' periderm cell walls were highly lignified, but large intercellular spaces could allow easy pathogen spread. Numbers of raphides increased in inoculated susceptible cultivars and not in tolerant 'Dogridge' indicating a lack of disease development. Inoculation with P. omnivorum sclerotia in planted containers was not successful in accurately determining levels of susceptibility among cultivars.