Heritable, de novo resistance to leaf rust and other novel traits in selfed descendants of wheat responding to inoculation with wheat streak mosaic virus.

Dallas L Seifers,Steve Haber,Terry J Martin,Brent D Mccallum

doi:10.1371/journal.pone.0086307

Abstract

Stable resistance to infection with Wheat streak mosaic virus (WSMV) can be evolved de novo in selfing bread wheat lines subjected to cycles of WSMV inoculation and selection of best-performing plants or tillers. To learn whether this phenomenon might be applied to evolve resistance de novo to pathogens unrelated to WSMV, we examined the responses to leaf rust of succeeding generations of the rust- and WSMV-susceptible cultivar ‘Lakin’ following WSMV inoculation and derived rust-resistant sublines. After three cycles of the iterative protocol five plants, in contrast to all others, expressed resistance to leaf and stripe rust. A subset of descendant sublines of one of these, ‘R1’, heritably and uniformly expressed the new trait of resistance to leaf rust. Such sublines, into which no genes from a known source of resistance had been introgressed, conferred resistance to progeny of crosses with susceptible parents. The F1 populations produced from crosses between, respectively, susceptible and resistant ‘Lakin’ sublines 4-3-3 and 4-12-3 were not all uniform in their response to seedling inoculation with race TDBG. In seedling tests against TDBG and MKPS races the F2s from F1 populations that were uniformly resistant had 3∶1 ratios of resistant to susceptible individuals but the F2s from susceptible F1 progenitors were uniformly susceptible. True-breeding lines derived from resistant individuals in F2 populations were resistant to natural stripe and leaf rust inoculum in the field, while the ‘Lakin’ progenitor was susceptible. The next generation of six of the ‘Lakin’-derived lines exhibited moderate to strong de novo resistance to stem rust races TPMK, QFCS and RKQQ in seedling tests while the ‘Lakin’ progenitor was susceptible. These apparently epigenetic effects in response to virus infection may help researchers fashion a new tool that expands the range of genetic resources already available in adapted germplasm.

Highlights

When a virus systemically infects a plant, it can induce changes in many of the traits expressed by the host during the interval between inoculation and senescence
In a specific instance arising from our efforts to identify new sources of resistance to Wheat streak mosaic virus (WSMV), we discovered genetic resistance to WSMV infection in a single accession of CO960293, an elite winter wheat line with a pedigree of WSMV-susceptible parents [9]
We show that other traits are induced de novo, including resistance to stem rust caused by specific races of Puccinia graminis and a necrosis factor not previously reported in wheat

Summary

Introduction

When a virus systemically infects a plant, it can induce changes in many of the traits expressed by the host during the interval between inoculation and senescence. Sets of 15 to 20 seeds of each of the 55 sublines, descended from ‘R1’, along with the susceptible control ‘Lakin’ were planted into 21631- cm soil-filled metal flats to test for seedling resistance to leaf- and stripe rust.

Results

Conclusion