Development of an Efficient Bioassay Method to Evaluate Resistance of Chili Pepper Cultivars to Ralstonia solanacearum

Abstract

Bacterial wilt caused by Ralstonia solanacearum is an important disease in cultivation of chili pepper, causing plant death and significant yield losses. Cultivation of disease-resistant varieties is the most suitable measure to control bacterial wilt of chili pepper. To establish an efficient screening method for resistant chili pepper to R. solanacearum, six resistant or susceptible cultivars to the R. solanacearum were selected and the development of bacterial wilt on the cultivars according to several conditions was investigated. Drenching bacterial suspension into the cut roots using a scalpel was more simple and effective to distinguish resistant and susceptible cultivars than inoculation methods of root-dipping or soil-drenching without wounding. A resistant pepper, 'MC4' to R. solanacearum showed high resistance under the developed conditions which were 21-to 28-day-old pepper inoculated with 1×10 8 cfu/ml of bacterial suspension. On the other hands, the susceptible cultivars represented high disease severity under the conditions. These results indicated that we developed an efficient method to evaluate resistance of chili pepper cultivars against bacterial wilt. In addition, we successfully evaluated resistance degree of 140 commercial chili pepper cultivars to R. solanacearum using the developed method.

Leaf-to-whole plant spread bioassay for pepper andRalstonia solanacearuminteraction determines inheritance of resistance to bacterial wilt for further breeding

“…The 'Gangryeokjosenggeon' (R), 'Meotjinsanai' (MR), 'PR-Daedeulbo' (S), and 'Supermanidda' (S) have the same traits in either inoculation method (Table 1). However, the traits of the root-drenching method in 'PR-Cheongyang', 'Ilsongjung', 'Muhanjilju', and PR-'Jangwongeubje' were MR or S phenotypes [15], but in this study represented all R phenotypes. 'Muhanjilju' and 'Meotjinsanai' also displayed previously different traits with S, MR, and R on infection methods and/or R. solanacearum strains [16], whereas we observed R and MR uniformly in each cultivar, respectively (Table 1 and Fig.…”

“…1C). Collectively, these data indicated that 'MC4' also has a suitable resistance to leaf wilting disease by R. solaneacerum alongside BW disease through root infection [15].…”

“…We also calculated the area under the disease progress curve (AUDPC) and relative (r) AUDPC (%) based on DSI scores at 7, 10, and 15 dai. Not only the DSI for wilting evaluation, but also the rAUDPC (%) value was able to distinguish between 0-30 % R, 30-40% MR, and 40-100% as S 15 dai [15]. The AUDPC and rAUDPC (%) were distributed as 3.5 and 8.9% in 'MC4', and 'Subicho' was 38.5 and 100%, displaying significant results as controls.…”

“…Most studies on resistance to R. solanacearum in plants have used two screening methods of R. solanacearum, such as root cut (soil)-drench and root-dipping inoculation [15][16][17][18]. However, both methods are difficult to determine the resistance degree according to the size of artificially root wounds lead to the standard deviation is large due to low uniformity after inoculation [17].…”

“…Recently, a major QTL named qRRs-10.1 in chromosome was revealed as a resistance pepper line C. annuum 'BVRC1' [28]. Among them, C. annuum 'MC4' is a well-known accession with a strong level of resistance to various R. solanacearum strains [15,22,29,30]. However, despite reports of C. annuum 'MC4' resistance to BW, genetic inheritance analysis of BW resistance in C. annuum 'MC4' has not been determined yet because of pathogen strains complexity and a lack of an efficient bioassay of R. solanacearum in peppers.…”