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- Author or Editor: Wesley T. Watson* x
Phymatotrichopsis omnivora (Duggar) Hennebert (syn. Phymatotrichum omnivorum Duggar) is a recalcitrant soilborne pathogen that causes serious root rot problems on numerous plant species in the southwestern United States and northern Mexico. Apple trees [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf. (syn. M. domestica Borkh. non Poir.)] are highly susceptible to P. omnivora with most tree death occurring in the summer months. Studies were conducted from 1996 to 1999 to examine when and at what rate infection and colonization of roots of apple trees by P. omnivora actually occurs. In three-year-old trees growing in orchard soils in 45-gallon containers (171,457 cm3) and inoculated with sclerotia in August 1997, infection occurred in the nursery after 12 weeks. For trees inoculated with sclerotia in February 1998, infection occurred within 15 weeks. After 18 weeks, 100% of trees were infected after inoculation in August and 80% of trees were infected after the February inoculation. This information is vital to understanding the epidemiology of Phymatotrichum root rot in apple orchards.
Several techniques have been used to study root growth and pathogen movement along roots between trees, including profile walls, micro-rhizotrons, and soil cores. These assessments can be very time consuming, cost prohibitive, and ineffective when studying soilborne pathogen movement across overlapping roots between adjacent trees in an orchard. Three aboveground rhizotrons were designed and constructed to study the movement of Phymatotrichopsis omnivora (Duggar) Hennebert (syn. Phymatotrichum omnivorum Duggar) along overlapping apple roots [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf. (syn. M. domestica Borkh. non Poir.)] in simulated orchard conditions. Two experiments involved boxes using either observation windows or micro-rhizotron observation tubes between trees. A third experiment utilized 45-gallon containers (171,457 cm3) joined by innovative observation windows. The container rhizotrons reduced labor and material costs, were more effective at monitoring roots, were more convenient than field measurements, and more closely simulated orchard growing conditions. This method provides several advantages to better study and manipulate the rooting environment of orchard-grown trees.