Characterization of three soybean landraces resistant to Asian soybean rust disease

Abstract

Phakopsora pachyrhizi is an obligatory biotrophic fungus that causes Asian soybean rust (ASR) disease. ASR control primarily involves chemical control and the use of resistant soybean cultivars carrying an Rpp (resistance to P. pachyrhizi) gene. This study aimed to characterize the ASR resistance of three soybean Asian landraces. By screening the world core collection (WC) of soybean, which consists of 80 varieties, three landraces were identified in Southeast Asia as resistant to ASR. Genetic mapping using the F2 population derived from a cross with an ASR-susceptible variety, BRS 184, indicated that KS 1034 (WC2) has ASR resistance conferred by a single dominant resistance gene, mapped on chromosome 18, in the same region where Rpp1 was mapped previously. The BRS 184 × WC61 (COL/THAI/1986/THAI-80) F2 population, on the other hand, showed an ASR resistance locus mapped by quantitative trait locus analysis on chromosome 6, in the region where the resistance conferred by PI 416764 Rpp3 resides, with a logarithm of the odds score peak at the same position as the marker, Satt079, while the BRS 184 × WC51 (HM 39) population showed the resistance to ASR allocated between Satt079 and Sat_263 markers, also in the region where Rpp3 was mapped previously. Both WC51 and WC61 have the same infection profile as FT-2 and PI 462312 when tested against the same ASR isolate panel. These three WCs can be used in MAS programs for introgression of Rpp1 and Rpp3 and the development of ASR-resistant cultivars in the breeding program.

Confirmation of Rpp Genes Conferring Resistance to Asian Soybean Rust and Mapping of Rpp1 Allele from PI 594723

“…The PI 594723 presented strong resistance, while the PI 200492 was classi ed as being weakly resistant (RB3 lesion type). Aoyagi et al (2020) observed susceptibility of PI 200492 against Brazilian ASR. Therefore, the PI 587880A showed less sporulation to ASR isolates, corroborating the present study results.…”

“…Therefore, the PI 587880A showed less sporulation to ASR isolates, corroborating the present study results. Aoyagi et al (2020) reported clear differences in the ASR reactions from genotypes carrying Rpp1 and Rpp1-b, and also among sources of Rpp1 such as PI 587886, Himeshirazu, and PI 200492, showing infection reactions of susceptibility, high resistance, and immunity respectively to the same isolate. Hossain et al (2015) and Akamatsu et al (2017) corroborate these differences in reactions to different isolates between accessions with the Rpp1 locus and genotypes with Rpp1-b.…”

“…The trials were conducted in eld conditions, where the combination of different ASR isolates, natural infection and weather conditions could promote high inoculum pressure. In addition, the ASR isolates presented in Brazil are considered more virulent than ones found in Japan, Argentina, and Paraguay (Yamanaka et al 2010;Aoyagi et al 2020).…”

“…The F 2 population showed a distorted segregation ratio that did not t a ratio of 3:1 (Table 3). Aoyagi et al (2020) and Akamatsu et al (2017) reported the susceptibility of PI 200492 to ASR isolates from Brazil. c There were no LOD peaks above the threshold to population F 2 .…”

“…In general, the Brazilian ASR isolates are known as the most aggressive. The Rpp1 (PI 200492) is highly resistant to Japanese and Mexican ASR isolates, but a lack of resistance has been reported to Brazilian ASR isolates (Aoyagi et al 2020;Akamatsu et al 2017;Hossain et al 2015). In contrast, the Rpp1-b (PI 587880A, PI 594538A) is resistant to most Brazilian ASR isolates (Ray et al 2009;Yamanaka et al 2016;Akamatsu et al 2017), highlighting a clear allelic difference between Rpp1 and Rpp1-b.…”