Resistance to Asian soybean rust and yield of new soybean cultivars, JFNC 1 and JFNC 2, harboring three resistance genes

Asian soybean rust (ASR) caused by Phakopsora pachyrhizi is one of the most devastating diseases affecting soybean production. Recently, two new soybean cultivars, JFNC 1 and JFNC 2, harboring three ASR-resistance genes, Rpp2, Rpp4, and Rpp5, developed by line breeding and marker-assisted selection have been released in Paraguay. Furthermore, the cultivars JNFC 1 and JNFC 2 were evaluated by comparing them with their recurrent parents Aurora and YG 203, respectively, for disease severity and yield in the plots sprayed and unsprayed with fungicides during 2017/2018 and 2018/2019 in Paraguay. Disease parameters including infection index, number of uredinia per lesion, frequencies of lesions with uredinia, and sporulation level caused by ASR infection were also compared between the resistant cultivars and the recurrent parents in the laboratory. Disease severity was low in JFNC 1 and JFNC 2, irrespective of fungicide treatment; however, the disease severity in Aurora and YG 203 decreased considerably in plots sprayed with fungicides than those in the unsprayed plots. JFNC 1 and JFNC 2 were highly resistant to all disease parameters than Aurora and YG 203. Yield loss in unsprayed plots was in the range of 10-23% and 37-49% for JFNC 1 and Aurora, respectively, while it was 9-12% and 16-20% for JFNC 2 and YG 203, respectively. Yield loss in unsprayed plots was lower in JFNC 1 than that in Aurora. YG 203 may exhibit tolerance, considering its high disease severity and minimal yield loss in the unsprayed plots. JFNC 1 and JFNC 2 resisted ASR as observed from the values of the disease parameters. These results indicate that JFNC 1 and JFNC 2 were more resistant to ASR than their recurrent parents. Therefore, pyramiding the three Rpp genes into susceptible cultivars contributes to enhanced ASR resistance.

Automated summary

Two new soybean cultivars with resistance to Asian soybean rust (ASR) were developed in Paraguay and found to have better disease resistance and yield compared to traditional cultivars.