Evaluation location: Colorado, United States
Experiment 2R, 2006.
The trial was a randomized complete-block design with five replications in one-row plots (56 cm row spacing) 4 m long at the ARS Fort Collins Research Farm, CO. The field had been summer fallowed in 2004 and 2005, and planted to barley in 2003. The soil (Garrett loam, 0 to 1 % slope, pH 7.8) was deep ripped and plowed in Nov 2005, and disked, roller harrowed and landplane-leveled in Apr prior to bedding and planting. The field was fumigated with Telone II 11 Apr for control of potentially confounding soilborne diseases and insects. Seed was planted on 24 May to moisture, and furrow irrigated as needed. The plant population was thinned to 20-25 cm spacing by hand. Inoculation with dry, ground, barley grain inoculum of Rhizoctonia solani isolate R-9 (AG-2-2) was performed on 13 Jul 06 at a rate of 2.2 g/m row with inoculum applied on the crown of the plant. Immediately after inoculation, plots were cultivated (using an in-row duck-foot cultivator) to place soil onto the plant crowns. Beets were harvested 8 Sep, 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. The PIs were tested in a disease nursery that included eight additional tests, involving experimental breeding material and commercial cultivated varieties. Controls were included in all nine tests. Rhizoctonia root rot reached moderate severity levels in early Sep for the entire nursery. Average DI across all nine tests in the 2006 nursery for highly resistant FC705-1, resistant FC703, and susceptible FC901/C817 controls were 1.7, 1.8, and 3.5, respectively. The greatest and least DI for all of the lines evaluated in the nursery, including materials not in the PI tests, were 5.8 and 1.0, respectively. For the PI, DI differences among entries were significant (P < 0.001). Three PIs (#518377, #540574, and #540633) had DIs that were not significantly different from either the resistant or the highly resistant controls (#991017 or #831083, respectively). One PI (#546388) had a DI that was not significantly different from the resistant control, although it was significantly different from the highly resistant control.
This has been published in: Hanson, L. E. and L. Panella. Rhizoctonia root rot resistance of Beta PIs from the USDA-ARS NPGS, 2006. Plant Disease Management Reports. (online) 1:V023. DOI: 10.1094/PDMR01. The American Phytopathological Society. St. Paul, MN. 2007.