Characterization of genes <Emphasis Type="Italic">Rpp2</Emphasis>, <Emphasis Type="Italic">Rpp4</Emphasis>, and <Emphasis Type="Italic">Rpp5</Emphasis> for resistance to soybean rust |
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| Authors: | Noelle Giacomini Lemos Alessandro de Lucca e Braccini Ricardo Vilela Abdelnoor Maria Cristina Neves de Oliveira Kazuhiro Suenaga Naoki Yamanaka |
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| Institution: | (1) Japan International Research Center for Agricultural Sciences (JIRCAS), 1-1, Ohwashi, Tsukuba Ibaraki, 305-8686, Japan;(2) State University of Maringa, Colombo Avenue 5790, Maringa, PR, 87020-900, Brazil;(3) Brazilian Agricultural Research Corporation, National Soybean Research Center (Embrapa Soja), Caixa Postal 231, Londrina, PR, 86001-970, Brazil; |
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| Abstract: | Asian rust, caused by the fungus Phakopsora pachyrhizi, is the most severe disease currently threatening soybean crops in Brazil. The development of resistant cultivars is a top
priority. Genetic characterization of resistance genes is important for estimating the improvement when these genes are introduced
into soybean plants and for planning breeding strategies against this disease. Here, we infected an F2 population of 140 plants derived from a cross between ‘An-76’, a line carrying two resistance genes (Rpp2 and Rpp4), and ‘Kinoshita’, a cultivar carrying Rpp5, with a Brazilian rust population. We scored six characters of rust resistance (lesion color LC], frequency of lesions having
uredinia %LU], number of uredinia per lesion NoU], frequency of open uredinia %OU], sporulation level SL], and incubation
period IP]) to identify the genetic contributions of the three genes to these characters. Furthermore, we selected genotypes
carrying these three loci in homozygosis by marker-assisted selection and evaluated their genetic effect in comparison with
their ancestors, An-76, PI230970, PI459025, Kinoshita and BRS184. All three genes contributed to the phenotypes of these characters
in F2 population and when pyramided, they significantly contributed to increase the resistance in comparison to their ancestors.
Rpp2, previously reported as being defeated by the same rust population, showed a large contribution to resistance, and its resistance
allele seemed to be recessive. Rpp5 had the largest contribution among the three genes, especially to SL and NoU. Only Rpp5 showed a significant contribution to LC. No QTLs for IP were detected in the regions of the three genes. We consider that
these genes could contribute differently to resistance to soybean rust, and that genetic background plays an important role
in Rpp2 activity. All three loci together worked additively to increase resistance when they were pyramided in a single genotype
indicating that the pyramiding strategy is one good breeding strategy to increase soybean rust resistance. |
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