Submitted to: National Allium Research Conference
Publication Type: Abstract Only
Publication Acceptance Date: September 22, 2012
Publication Date: November 29, 2012
Citation: Havey, M.J., Cramer, C.S., Pappu, H., Schwartz, H., Chan, A., Town, C. 2012. Ensuring US onion sustainability: Breeding and genomics to control thrips and iris yellow spot virus [abstract]. National Allium Research Conference. Paper No. O-21.
This five-year project was initiated in the fall of 2008 and has three main goals: evaluate onion germplasms for reduced damage by thrips and/or Iris yellow spot virus (IYSV); elucidate the diversity among IYSV isolates and develop efficient inoculation protocols; and produce a detailed molecular map of onion for eventual tagging of pest resistances. Diverse sources of onion germplasms have been evaluated in field trials over six environments (at least three each in New Mexico and Colorado) using natural pressures by thrips and/or IYSV. Vigorous, well-adapted germplasms tended to perform better and selections were made from USDA plant introductions 172702, 172703, 239633, 258956, 264320, 343049, 546140, 546188, and 546192. The full length N-gene of IYSV was cloned and sequenced and diversity analyses revealed evidence for genetic divergence and evolution in the IYSV N-gene sequences between 2003 and 2011. Although mechanical transmission of IYSV was achieved, frequencies at approximately 20% are too low to be used in large-scale screenings of onion germplasms. Transcriptome sequencing of onion was undertaken to identify single nucleotide polymorphisms (SNPs) for genetic mapping and yielded over 1 billion bases of expressed sequence. Over 1,200 SNPs between two parental lines (OH1 and 5225) were randomly chosen for mapping using gynogenic haploids extracted from hybrids from a cross of OH1 by 5225. Linkage groups from approximately 500 segregating SNPs were assigned to chromosomes using previously developed families.