Kyoto-Manganji No. 1 pepper (Capsicum annuum) cultivar as a standard for partial resistance to bacterial wilt disease

Bacterial wilt (BW) caused by the soil-borne bacterium Ralstonia solanacearum E. F. Smith (species complex) is one of the most serious diseases of peppers in tropical and subtropical regions and in warm temperate regions such as Japan. The pepper cultivar, Kyoto-Manganji No. 1 (MDH) (Capsicum annuum L.), is a double haploid and was bred from a landrace in Kyoto Prefecture, Japan. Although it has been reported that MDH is resistant to BW, virulent BW strains such as KP9547 have recently affected the production of MDH. Therefore, we evaluated the resistance of MDH to BW based on three separate inoculation experiments using challenges with 42 virulent BW strains from various regions of Japan. Thirty-five strains were virulent to California Wonder (CW), a sensitive cultivar and 26 strains were virulent to MDH, a resistant cultivar. Seven strains from potato and tobacco plants were not virulent on pepper. The average disease indices of the three experiments were significantly lower for MDH than for CW. Therefore, MDH is considered to display a partial resistance. This is the first report of BW resistance test in a partially resistant pepper cultivar using various strains of Ralstonia solanacearum, which cover all the categories of races (1, 3 and 4), biovars (N2, 3 and 4) and phylotypes (Iand IV) reported in Japan. Therefore, MDH may be useful as a standard for partial resistance to BW to evaluate the resistance of Capsicum germplasm and virulence of R. solanacearum strains.