|ZHANG, SHICHEN - Michigan State University|
|WEN, ZHIXIN - Michigan State University|
|DIFONZO - Michigan State University|
|WANG, DECHUN - Michigan State University|
Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2018
Publication Date: 2/22/2018
Citation: Zhang, S., Wen, Z., Difonzo, Song, Q., Wang, D. 2018. Pyramiding different aphid-resistance genes in elite soybean germplasm to combat dynamic aphid populations. Molecular Breeding. 38(3)29. https://doi.org/10.1007/s11032-018-0790-5.
Interpretive Summary: Soybean is one of the most important crops in North America because of its multiple uses as an animal feed, cooking oil, biofuel, and human protein source. However, soybean production in North America has been threatened by the soybean aphid, invasive species native to Asia. Soybean aphid has aggressively dispersed to all major soybean producing areas in the U.S. and Canada since its discovery in southern Wisconsin in 2000. The direct aphid stylet-feeding on plant sap can cause up to 40% soybean yield loss. Transmissions of plant viruses by soybean aphids lead to further yield loss in soybean production. Currently, insecticides are wildly used to manage soybean aphids. However, this method increases production cost, the risk of environmental contamination and the mortality of beneficial insects. A friendly way to manage soybean aphids is to utilize the native host-plant resistance present in soybean germplasm. Despite 30 soybean germplasm resistant to aphids have been identified, most contain only one of the 6 resistance genes discovered so far. The biggest problem of cultivars with a single resistance gene is the loss of resistance because of variation of virulent biotypes. Therefore, integrating cultivars with multiple resistance genes, particularly with different modes of action, is important to achieve a broad and durable resistance. With the assistance of molecular markers closely linked to the resistance genes, we pyramided different aphid-resistance genes to elite soybean germplasm and developed 11 improved soybean lines with different combinations of aphid-resistance genes. Assessment of their effectiveness against aphids showed that lines with multiple resistance genes provide much broader and more durable resistance to diverse and dynamic aphid populations than lines with one or two resistance genes. These lines are valuable resources for soybean breeders to develop cultivars to combat aphids in the U.S.
Technical Abstract: The soybean aphid, an invasive species, has posed a significant threat to soybean production in North America since 2001. Use of resistant cultivars is an effective tactic to protect soybean yield. However, the variability and dynamics of aphid populations could limit the effectiveness of host-resistance gene(s). Gene pyramiding is a promising way to sustain host-plant resistance. The objectives of this study were to determine the prevalent aphid biotypes in Michigan, and to assess the effectiveness of different combinations of aphid-resistance genes. A total of eleven soybean genotypes with known resistance gene(s) were used as indicator lines. Based on their responses, Biotype 3 was a major component of Michigan aphid populations during 2015 - 2016. The different performance of Rag-'Jackson' and Rag1-'Dowling' along with the breakdown of resistance in plant introductions (PIs) 567301B and 567324 may be explained by Biotype 3 or an unknown virulent biotype establishing in Michigan. With the assistance of flanking markers, twelve advanced breeding lines carrying different aphid-resistance gene(s) were developed and evaluated for effectiveness in five trials across 2015 to 2017. Lines with rag1c, Rag3d, Rag6, Rag3c+Rag6, rag1b+rag3, rag1c+rag4, rag1c+rag3+rag4, rag1c+Rag2+rag3+rag4 and rag1b+rag1c+rag3+rag4 demonstrated strong and consistent resistance. Due to the variability of virulent aphid. populations, different combinations of Rag genes may perform differently across geographies. However, advanced breeding lines pyramided with three or four Rag genes likely will provide broader and more durable resistance to diverse and dynamic aphid populations.