Location: Soil Management and Sugarbeet ResearchTitle: Evaluation of Beta PIs from the USDA-ARS, NPGS for Rhizoctonia crown and root rot resistance, 2022
|KUMAR, AVNEESH - Colorado State University|
Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2023
Publication Date: 3/15/2023
Citation: Dorn, K.M., Metz, N.J., Fenwick, A.L., Todd, O.E., Kumar, A., Yeater, K.M., Nielson, A.L., Floyd, B.A., Sowder, B.M. 2023. Evaluation of Beta PIs from the USDA-ARS, NPGS for Rhizoctonia crown and root rot resistance, 2022. Plant Disease Management Reports. 17. Article eV103.
Interpretive Summary: Half of all table sugar produced in the United States comes from sugar beet. The major threats to American beet sugar production continue to be fungal pathogens that decrease yield and crop quality, including the soil-borne fungus Rhizoctonia. As chemical controls for these pathogens are limited, enhanced breeding for disease resistance is critical to sustain the beet sugar industry. USDA-ARS researchers in Fort Collins, CO tapped into the National Plant Germplasm System to identify and screen a diverse panel of beet lines for resistance to Rhizoctonia. The research team identified seven lines with moderate levels of resistance to Rhizoctonia, including one crop wild relative that represents a potentially novel source of genetic resistance to this important trait. Continued genetic, genomic, and breeding efforts using the lines identified in this study will deliver useful new information for researchers studying the interaction of sugar beet with Rhizoctonia, alongside potentially new forms of Rhizoctonia resistance for commercial breeders.
Technical Abstract: Thirty-two Beta vulgaris subsp. vulgaris and Beta vulgaris subsp. maritima (L.) Arcang (Bvm) accessions from the Beta collection of the USDA-Agricultural Research Service National Plant Germplasm System (NPGS) were screened for resistance to Rhizoctonia crown and root rot (RCRR) at the Colorado State University Agricultural Research, Development, and Education Center in Fort Collins, Colorado. This field evaluation included 24 beet entries, 6 sea beet entries and two beet controls. The resistant check PI 599688 (FC709-2), and the susceptible check germplasm FC901xC817, are standard RCRR germplasm. The nursery was planted in a completely randomized design with 5 replications per entry. Each replicate was planted in one-row plots (76 cm row spacing) 3.7 m long. Plots were planted on May 19th with 2.5 cm of irrigation applied on 24 May. The field was watered by overhead sprinkler weekly (ca. 1.9 - 2.5cm, depending on precipitation) to promote uniform germination, emergence, and plot establishment. An inoculum of dry ground hulless barley grain infested with Rhizoctonia solani isolate R-9 (AG-2-2 IIIB) was applied to the crown of the plants on 11 Jul at a rate of 6.3 g m-1 of row. A Gandy® electrically driven applicator was used to apply the inoculum and the field was cultivated afterwards to place soil onto the plant crowns. Disease progression was uniform, and influenced by a severe hail storm 28 Jul with a hard rain that significantly wounded the leaf canopy while disease pressure was already well established at 17 days post inoculation (DPI). Due to the advanced stage of disease across the nursery, it was decided to rate the experiment early at 23 DPI on 3 Aug. Roots were pulled and harvested with a single row lifter, cleaned by hand, and each root was rated for RRCR 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. Per-replicate root ratings were rank transformed prior to analysis with the mixed linear models (Proc MIXED) procedure in SAS. The Dunnett’s one-tailed t-test (P = 0.05) option in the LSMEANS statement was used to compare entries to the resistant check FC709-2 and susceptible check FC901xC817, based on the rank of DI. Disease progression was excellent across the entire nursery, with high levels of disease throughout this test. The resistant check PI 599688 (FC709-2) had the lowest mean disease index (DI) rating of 2.51. A total of 7 entries were not statistically different from FC709-2, including the susceptible check FC901 x C817. Only one entry (PI 590790) was statistically different compared to the susceptible check, with the highest entry DI in the test (6.91). Among the most resistant germplasm in the test, PI 590696, PI 222234, and PI 590765, and W6 45821 possessed high proportions of roots with ratings of 2 and 3, but few to no roots with scores of 0 or 1, indicating potentially segregating minor resistance genes for RCRR. Entry W6 45821 is of particular interest, as a relatively new Bvm NPGS accession collected from Morocco, and could represent a potentially new source of RCRR resistance from a crop wild relative of sugar beet. Lines identified as potentially resistant will be retested in field and greenhouse to determine whether entries will be incorporated into the USDA-ARS RRCR resistance breeding program at Fort Collins, CO to enhance sugar beet pre-breeding germplasm. These results will be accessible to interested parties through the USDA-ARS, NPGS GRIN database http://www.ars-grin.gov.