ARS | Publication request: Rhizoctonia Crown and Root Rot Resistance of Beta Plant Introductions from the USDA, Agricultural Research Service's National Plant Germplasm System, 2010

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 5, 2011
Publication Date: March 28, 2011
Citation: Panella, L.W., Vagher, T.O., Fenwick, A.L., Webb, K.M. 2011. Rhizoctonia Crown and Root Rot Resistance of Beta Plant Introductions from the USDA, Agricultural Research Service's National Plant Germplasm System, 2010. Plant Disease Management Reports. 5:FC067. Online publication doi:10.1094/PDMR05.

Interpretive Summary: Thirty types of wild beet from the beet collection of the USDA-ARS National Plant Germplasm System were screened for resistance to Rhizoctonia root and crown rot, at the USDA-ARS Fort Collins, CO Research Farm. The statistical design used in Rhizoctonia screening nursery in 2010 was a randomized complete-block design. The different types of wild beet were replicated five times in one-row plots. Seed was planted on May 25 to moisture, fertilized and furrow irrigated as needed. The field was thinned (10 to 12 inches between plants) and hand weeded on June 18 to 20 and again one July 3 to 4 and July 24. The nursery was inoculated with dry, ground, barley grain colonized with Rhizoctonia solani (which causes rhizoctonia root rot). Plots were cultivated afterwards to place soil onto the plant crowns and thereby increase disease severity. Beets were harvested from August 16 to 18 with a single row lifter (pulled and cleaned by hand) and each root was rated for root rot on a scale of 0 (no damage) to 7 (dead plant with root completely rotted. The scores were averaged over all beet in a plot and statistically analyzed. 2010 had a cool spring with good early season rainfall in Fort Collins, CO. The crop grew well. In July and August, daytime temperatures remained high and there was a severe infection and epidemic. There was a large separation of disease severity between the highly resistant and highly susceptible lines. Four of the PIs had an average score of 4.6, which was not significantly different from the highly resistant control. Two more PIs were rated with an average under 5.0. There were differences of resistance within these types of wild beets and some of the roots looked very clean on evaluation. There may be resistance genes in these resistant wild beets, which will be reevaluated to confirm resistance to Rhizoctonia root and crown rot. These results will be entered into the USDA-ARS, Germplasm Resources Information Network database (http://www.ars-grin.gov/npgs/index.html).

Technical Abstract: Thirty wild beet (Beta vulgaris subsp. maritima (L.) Arcang) plant introduction (PI) accessions from the Beta collection of the USDA-ARS National Plant Germplasm System were screened for resistance to Rhizoctonia root and crown rot, at the USDA-ARS Fort Collins, CO Research Farm. The Rhizoctonia screening nursery in 2010 was a randomized complete-block design with five replications in one-row plots (76 cm row spacing) 4 m long. Seed was planted on 25 May to moisture, fertilized and furrow irrigated as needed. Only pre-plant (22 May, glyphosate and clopyralid) and pre-emergence herbicides (29 May, glyphosate and clopyralid) were used this year. The field was thinned (20 - 25 cm spacing) and hand weeded 18 to 20 Jun, and hand weeded again 3 to 4 Jul and 24 Jul. Inoculation with dry, ground, barley grain colonized with Rhizoctonia solani isolate R-9 (AG-2-2 IIIB) was applied to the crown of the plants on 15 Jul at a rate of 6.9 g m-1 row. Plots were cultivated afterwards to place soil onto the plant crowns. Beets were harvested from 16 to 18 Aug, 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 per plot was determined to create a disease index (DI) for each entry. Analyses of variance (PROC ANOVA/GLM) were performed on disease indices DI, % healthy roots (classes 0 and 1 combined) and % roots in classes 0 through 3 (harvestable roots). Data in classes 0-1 and 0-3 were transformed using arcsine square root to normalize the data for analyses (AP 0-1 and AP 0-3, respectively). 2010 had a cool spring with good early season rainfall in Fort Collins, CO. The crop grew well. In Jul and Aug, daytime temperatures remained high and there was an excellent infection and severe epiphytotic. There was good separation of disease severity between the highly resistant and highly susceptible lines. Four of the PIs had a DI score of 4.6, which was not significantly different from the highly resistant control. Two more PIs were rated with a DI under 5.0. There was segregation for resistance in these accessions with some of the roots looking very clean on evaluation. There may be resistance genes in these accessions and they will be reevaluated to confirm resistance to Rhizoctonia root and crown rot. These data will be entered into the USDA-ARS, NPGS GRIN database (http://www.ars-grin.gov/npgs/index.html).