Location of a Triticum speltoides chromosome segment conferring resistance to leaf rust in Triticum aestivum

A leaf rust resistant line, 2-9-2, was selected in the fourth backcross generation to Triticum aestivum of an interspecific hybrid, T. aestivum × Triticum speltoides. The resistance segregated independently of T. speltoides leaf rust resistance gene Lr28, previously shown to be incorporated into wheat chromosome 1B in two other transfer lines. Monosomic and telosomic analyses showed that the gene in line 2-9-2, Lr36, was incorporated into the short arm of chromosome 6B. C-banding analysis showed that the homoeologous crossing-over occurred distally to an interstitial C-band in the satellite and linkage analysis showed Lr36 to be tightly linked to the telomeric C-band.Key words: C-banding, physical mapping, linkage, wheat, chromosome 6B, introgression.

AGRONOMIC AND QUALITY CHARACTERISTICS OF WHEAT LINES WITH LEAF RUST RESISTANCE DERIVED FROM TRITICUM SPELTOIDES

Eleven lines of wheat (Triticum aestivum L.) carrying resistance to leaf rust (Puccinia recondita Rob. ex. Desm.) derived from five accessions of Triticum speltoides Tausch were grown in yield tests in 1977 and 1979. The grain was tested for quality characteristics in both years. Although the lines had been backcrossed four or five times to either Manitou or Neepawa, only four of the eleven showed any real promise of equalling their recurrent parent in agronomic and quality characteristics. Lines derived from the same accession of T. speltoides were surprisingly variable. The generally deleterious effects of the transferred chromatin are due either to genes linked to the genes for leaf rust resistance plus incomplete compensation by the speltoides chromosome segment for the aestivum segment it replaced, or to the effects of additional translocations that were not eliminated during backcrossing. A second cycle of homoeologous recombination is proposed as a way to eliminate some of the deleterious genes.

GENETIC VARIABILITY IN AEGILOPS SPELTOIDES AFFECTING HOMOEOLOGOUS PAIRING IN WHEAT

Three Chinese Spring ditelocentric lines and four Agropyron telocentric addition lines were crossed with a single population of Aegilops speltoides. Chromosome pairing was studied in the hybrid plants. The mean chiasma frequencies per cell in different hybrid plants indicate the existence of three different genotypes in the population of Ae. speltoides each differing significantly in ability to suppress the diploidizing mechanism in polyploid wheat. Plants at the three levels of pairing showed means of 6.4, 10.4 and 15.0 chiasmata per cell, respectively.Agropyron telocentric chromosomes did not pair with their wheat homoeolgues at the lowest pairing level. At intermediate and high pairing levels they did pair with wheat chromosomes. The increase in pairing of Agropyron telocentrics paralleled the increase in chiasma frequency per cell.The action of genes controlling homoeologous synapsis is discussed and it is suggested that pairing affinity between chromosomes may result from the interaction between two factors: homology in nucleotide sequences at specific sites in chromosomes, and degree of activation of these sequences.