The use of SNP hybridisation arrays and cytogenetics to characterise deletions of chromosome 4B in hexaploid wheat (Triticum aestivum L.).

KEY MESSAGE: Many deletions of the wheat Della ( Rht - B1 ) gene and its flanking regions were isolated in a simple phenotypic screen, and characterised by modified analysis of SNP hybridisation data and cytogenetics. In a dwarf wheat suppressor screen, many tall 'revertants' were isolated following mutagenesis of a severely dwarfed (Rht-B1c) hexaploid wheat. About 150 lines were identified as putative deletions of Rht-B1c, based on the PCR analysis. Southern blot hybridisation established that most of them lacked the Rht-B1 gene, but retained the homoeologues Rht-A1 and Rht-D1. PCR assays were developed for orthologues of two genes that flank Rht-1/Della in the genomes of the model species Brachypodium and rice. Deletion of the B-genome-specific homoeologues of these two genes was confirmed in the Rht-B1 deletion lines, indicating loss of more than a single gene. SNP chip hybridisation analysis established the extents of deletion in these lines. Based on the synteny with Brachypodium chromosomes 1 and 4 g, and rice chromosomes 3g and 11g, notional deletion maps were established. The deletions ranged from interstitial deletions of 4BS through to loss of all 4BS markers. There were also instances, where all 4BS and 4BL markers were lost, and these lines had poor fertility and narrow stems and leaves. Cytogenetic studies on selected lines confirmed the loss of portions of 4BS in lines that lacked most or all 4BS markers. They also confirmed that lines lacking both 4BS and 4BL markers were nullisomics for 4B. These nested deletion lines share a common genetic background and will have applications in assigning markers to regions of 4BS as well as to 4BL. The potential for this type of analysis in other regions of the wheat genome is discussed.

Genetic variation for leaf carbon isotope discrimination and its association with transpiration efficiency in canola (Brassica napus).

Drought is a major constraint to canola production around the world. There is potential for improving crop performance in dry environments by selecting for transpiration efficiency (TE). In this work we investigated TE by studying its genetic association with carbon isotope discrimination (Δ) and other traits, e.g. specific leaf weight (SLW) and leaf chlorophyll content (SPAD). Among the 106 canola genotypes - including open-pollinated, hybrid, inbred types and cytoplasmic variants - tested in the field and glasshouse there was significant genotypic variation for TE, Δ, plant total dry weight, SLW and SPAD. Strong negative correlations were observed between TE and Δ (-0.52 to -0.76). Negative correlations between Δ and SLW or SPAD (-0.43 to -0.78) and smaller but significant positive correlations between TE and SLW or SPAD (0.23 to 0.30) suggested that photosynthetic capacity was, in part, underpinning the variation in TE. A cytoplasmic contribution to genetic variation in TE or Δ in canola was also observed with Triazine tolerant types having low TE and high Δ. This study showed that Δ has great potential for selecting canola germplasm with improved TE.