Abstract
The present study aimed at pyramiding ASR-resistance genes through microsatellite (SSR) marker-assisted selection (MAS) and demonstrating the pyramiding steps. To obtain the first generation of gene pyramiding, crosses were made between introduced plants (PI’s), which have the genes Rpp1 , Rpp2 , Rpp3 , Rpp4 , and Rpp5 . F 1 plants from the initial crosses were intercrossed to obtain plants with the four resistance genes (second pyramiding generation). Plants selected from this second generation were again intercrossed (third pyramiding generation) to increase the number of pyramided genes. For MAS, we used informative SSR markers in each cross. SSR markers were considered informative when the source resistance allele containing the target gene could be followed in the progeny, even in crosses between hybrids that both contained the same allele. Markers published in the ASR genetic mapping studies and in the consensus map of the soybean were used. We obtained plants containing from 2 to 4 genes pyramided per plant. These plants can be used as a source of multiple resistance in breeding programmes for obtaining soybean varieties with more durable resistance to ASR.
Highlights
The soybean [Glycine max (L.) Merrill] is the most important oilseed for the Brazilian economy, ranking the country as the second largest producer worldwide with a planted area of 33.2 million hectares and production approximately 100.90 million tons in the 2015-2016 harvest year (Conab, 2016)
A limiting factor for increasing the Brazilian soybean production chain and for improving the international economic position stems from drawbacks faced by farmers with disease occurrence (Arias et al, 2010), such as Asian soybean rust (ASR), in which the aetiological agent is the fungus Phakopsora pachyrhizi Sydow & Sydow, due to the high cost of its control and the sharp reduction productivity in the absence of the proper management of crops
The present study aimed to demonstrate the steps of pyramiding ASR resistance genes using marker-assisted selection (MAS) and to obtain plants containing more than one resistance gene to the disease
Summary
The soybean [Glycine max (L.) Merrill] is the most important oilseed for the Brazilian economy, ranking the country as the second largest producer worldwide with a planted area of 33.2 million hectares and production approximately 100.90 million tons in the 2015-2016 harvest year (Conab, 2016). A limiting factor for increasing the Brazilian soybean production chain and for improving the international economic position stems from drawbacks faced by farmers with disease occurrence (Arias et al, 2010), such as Asian soybean rust (ASR), in which the aetiological agent is the fungus Phakopsora pachyrhizi Sydow & Sydow, due to the high cost of its control and the sharp reduction productivity in the absence of the proper management of crops. Hittalmani, Parco, Mew, Zeigler, and Huang (2000) observed an increased resistance to the fungus Magnaporthe grisea, which causes rice blast disease after pyramiding three genes into a single genotype, with the aid of RFLP and PCR-based markers. Research on gene pyramiding usually presents the final results obtained, without showing the pyramiding steps In this manner, the present study aimed to demonstrate the steps of pyramiding ASR resistance genes using MAS and to obtain plants containing more than one resistance gene to the disease
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