2007 Rhizoctonia Nursery - Experiment 2R
The trial was a randomized complete-block design with five replications in one-row plots (76 cm row spacing) 4 m long at the ARS Fort Collins Research Farm, CO. The field had been summer fallowed in 2004, 2005, 2006, and planted to barley in 2003. The soil (Garrett loam, 0 to 1 % slope, pH 7.8) was deep ripped in Nov 2006, and disked, roller harrowed and leveled in May prior to bedding and planting. The field was fumigated Apr 2006 with Telone II (18 gallons/acre) for control of potentially confounding soil-borne diseases (esp. rhizomania) and insects. Seed was planted on 22 May, and furrow irrigated as needed. The first irrigation, on 6 Jun, germinated the seed. The plant population was thinned to 20-25 cm spacing by hand in late June. Inoculation with dry, ground, barley grain inoculum of Rhizoctonia solani isolate R-9 (AG-2-2) was applied to the crown of the plants on 1 Aug at a rate of 5.1 g/m row and again (due to heavy rainfall after initial inoculation) on 10 Aug at a rate of 2.4 g/m. A Gandy electrically driven applicator with Hawkins Ditchers? attached was used to apply the inoculum and place soil onto the plant crowns. Beets were harvested 3 Oct, with a single row lifter (pulled and cleaned by hand) and each root was rated for rot on a scale of 0 (no damage) to 7 (dead plant with root completely rotted). Average disease severity was determined to create a disease index (DI) for each PI. The scores were adjusted to a 1 (healthy) to 9 (dead) scale: [DI*(9/8)]+1. Analyses of variance (PROC GLM) were performed on disease indices (DI). Means of entries in the test were statistically significant (P < 0.0001). There were six screening tests in the 2007 nursery, including plant introductions, experimental breeding material, and commercially cultivated varieties. Controls were included in all tests. The disease started slowly but, by the end of September, Rhizoctonia root rot reached severe levels in most of the nursery. The average DI across the six tests in the 2007 nursery for highly resistant FC705-1, resistant FC703, and susceptible FC901/C817 controls were 1.8, 2.6, and 4.6, respectively. The DI range for all of the lines evaluated in the nursery was 6.7 to 1.3. In all of the tests in 2007, there were highly significant differences among the entries for DI. Four of the PIs had a significantly lower DI than the susceptible check, PI 552534, PI 504261, PI 552533, and PI 546420, and three of these were not significantly different from the highly resistant check. PI 546420 was significantly higher (more susceptible) than the highly resistant check. It is interesting that two of the PIs, which showed resistance to Rhizoctonia root rot, were developed by the USDA-ARS prebreeding program in Fargo, ND. PI 552533 (F1013) was developed from a Turkish accession (PI 169025) and PI 552534 (F1014) was developed from a Russian accession (PI 355959)
This has been reported in: Panella, L., A. L. Fenwick, A. L. Hill, M. McClintock, and T. Vagher. Rhizoctonia root rot resistance of Beta PIs from the USDA-ARS NPGS, 2007. Plant Disease Management Reports. (online) 2:V057. DOI:10.1094/PDMR02. The American Phytopathological Society. St. Paul, MN. 2008.