Improving Evaluation of Potato Resistance to Rhizoctonia solani infection by Optimizing Inoculum Method Combined with Toxin-based Assay

Abstract

Background: Rhizoctonia solani causes stem canker and significantly impacts the production of potato. Conventional assay to evaluate potato resistance using R. solani inoculum is time consuming. To establish an effective and fast assay, 20 potato germplasms were examined using both R. solani inoculum and R. solani-derived toxin (RS toxin). Results: In field trials of 2009 and 2010, wheat-bran-based inoculum of R. solani was incorporated at either 0, 2, 3, 4 or 5 g per seed piece in the soil followed by sowing potato seed pieces in the furrow. Stem canker was evaluated in the growing season. Inoculum of wheat-bran-based 2, 3, or 4 g could well distinguish resistance of potato germplasms. For a quick assay of resistance screening, a toxin-based method was established by treating potato seedlings with the toxin of R. solani (RS toxin). RS toxin was prepared by heating R. solani culture. Potato seedlings were obtained through tissue culture and grown in Murashige and Skoog medium. Seedlings at the stage of 12 cm in height were transferred into agar medium amended with RS toxin and incubated for eight days. The inhibition caused by RS toxin was positively correlated with toxin concentration. By evaluating various potato cultivars that have different sensitivities to toxin, the inhibition of potato stems sections and seedlings was from 33% to 100% and from 32% to 148%, respectively. Results of toxin-based evaluation were highly correlated with the field data using pathogen inoculum (r = 0.731, P < 0.01). Conclusions: Inoculation with wheat bran-mediated R. solani of 2, 3 or 4 g per seed piece was an effective method for the evaluation of potato resistance in field trials. The toxin-based assay could improve efficiency and speed of disease resistance evaluation of potato germplasms. Both assays showed that none of the 20 potato materials was completely resistant to R. solani. However, cultivar ‘Desiree’ had the lowest level of disease, whereas ‘Atlantic’, ‘Favorita’, and ‘Shepody’ showed the high susceptibility.

Metabolomic analysis of sheath blight disease of rice (Oryza sativa L.) induced by Rhizoctonia solani phytotoxin

“…The toxin was employed to screen rice germplasms in a detached leaf assay instead of the conventional inoculum‐based assay (Shaofeng et al, 2017). The significance of the phytotoxin in evaluating germplasm lines for R. solani resistance has also been established in potatoes in 2‐year field trials (Zhang et al, 2021). The results generated a very strong statistical correlation ( r = 0.731, p < 0.01) with the pathogen inoculum (Zhang et al, 2021).…”

“…The significance of the phytotoxin in evaluating germplasm lines for R. solani resistance has also been established in potatoes in 2‐year field trials (Zhang et al, 2021). The results generated a very strong statistical correlation ( r = 0.731, p < 0.01) with the pathogen inoculum (Zhang et al, 2021).…”

Identification of a new phytotoxic compound from culture filtrates of an aggressive Rhizoctonia solani AG 1A isolate inducing sheath blight of rice

“…The significance of the phytotoxin in ShB development was further demonstrated by inactivating its phytotoxicity [20,22,25] or by employing it in screening rice germplasms for ShB resistance [26]. The significance of the phytotoxin in evaluating germplasm lines for R. solani resistance has also been established in potatoes in 2-year field trials [27]. Though the phytotoxin associated with ShB was characterized to be a carbohydrate [19,28], multiple phytotoxins have been identified in other R. solani AG groups.…”