Variability in Reaction to Root and Crown Rot Caused by Rhizoctonia Solani Among Table Beet Cultivars, Breeding Lines, and Plant Introductions in Controlled Environment Conditions

Abstract

Table beet (Beta vulgaris ssp. vulgaris) is adversely affected by the soilborne fungus, Rhizoctonia solani, which greatly decreases root quality. There are no reports of breeding efforts designed to improve resistance to this fungus in table beet. A collection of table beet PIs, cultivars, and publicly available inbreds were characterized for their response to inoculation with R. solani in three replicated greenhouse experiments conducted between 2017 and 2019. An isolate of AG 2-2 IIIB was used to inoculate 8-week old plants, and both susceptible and resistant sugar beet genotypes were used for comparison. Plants were evaluated for internal and external disease characteristics 3 and 5 weeks postinoculation. Compared with uninoculated controls, PI accessions ranged from 2% to 44% infection, whereas cultivars and inbred lines ranged from 16% to 53% and 22% to 52%, respectively. No commercial cultivar outperformed the resistant sugar beet genotype; however, several PI accessions exhibited lower mean diseased tissue percentages than the resistant sugar beet. This suggests that resistance to R. solani may exist in table beet germplasm. PI accessions exhibited greater resistance on average than did cultivars. Inbred lines exhibited the least amount of variation. Ordinal regression allowed for prediction of infection response, which may be helpful in future selection efforts. ‘Badger Flame’, Ames 22164, PI 502294, PI 169015, ‘Long Season’, ‘Red Cloud’, and ‘Albina Vereduna’ were some of the most resistant accessions in our screens. The findings from this study can be used to inform decisions for breeding for host plant resistance in table beet.

Novel QTL associated with Rhizoctonia solani Kühn resistance identified in two table beet × sugar beet F2:3 populations using a new table beet reference genome

“…Non‐inoculated controls were included in each replication. Disease evaluations were completed 3 weeks after inoculations as described by Wigg and Goldman (2020). Internal and external disease ratings for root symptoms on a scale from 0–5 were assigned to each root as follows: 0 = 0% diseased tissue, root surface clean with no visible lesions; 1 = 1%–10% diseased tissue, superficial, scattered non‐active lesions; 2 = 11%–30% of root affected; 3 = 31%–60% of root affected; 4 = 61%–99% of root blackened with rot extending into interior; and 5 = root 100% rotted and foliage dead or dying (adapted from Campbell et al., 2014; Ruppel et al., 1979).…”

“…Solo displayed mean diseased tissue percentages of 27.1% and 33.7%, respectively, compared to 6.6% in FC709-2, a highly resistant sugar beet germplasm (Wigg & Goldman, 2020). Given this lack of strong resistance, a major goal of our table beet breeding program is to incorporate disease resistance into inbred breeding lines.…”

“…There are very few available cultivars with partial resistance to R. solani including ‘Solo,’ ‘Shiraz,’ ‘Rubra,’ ‘Kestrel’ (Pethybridge et al., 2018), and ‘Pacemaker III' (Goldman, 1996; Pethybridge et al., 2018). In greenhouse screens conducted in 2018, Pacemaker III and Solo displayed mean diseased tissue percentages of 27.1% and 33.7%, respectively, compared to 6.6% in FC709‐2, a highly resistant sugar beet germplasm (Wigg & Goldman, 2020). Given this lack of strong resistance, a major goal of our table beet breeding program is to incorporate disease resistance into inbred breeding lines.…”

Screening Table Beet and Swiss Chard for Resistance to Pseudomonas syringae pathovar aptata

“…PI accessions were expected to have greater variability in response to spray inoculation with PSA than commercial cultivars as PIs commonly have a broad range of variability for agronomic traits (Wigg and Goldman, 2020). The PI accessions did have the largest range of mean AUDPC ratings in both repeats; however, the range in mean AUDPC ratings for the commercial screen of lightcolored foliage accessions was similar.…”

Mycorrhizal fungi isolated from Chilean orchids as biocontrollers of the pathogen Rhizoctonia solani

“…These fungi can attack crops and nurseries producing rot, dampingoff, and blight, among other diseases (Lamichhane et al 2017, Landis 1989. Rhizoctonia solani Kühn is a cosmopolitan phytopathogenic fungus that affects several economically important crops (Ma et al 2013, Sneh et al 1991, Wigg & Goldman 2020. Its control has been largely based in the use of agrochemicals, with the consequent detrimental effect on human health and the environment (Gunnell et al 2007, Mir-Tutusaus et al 2014, Park et al 2020.…”