Chromosome 7D of the wheat line VPMl derived from a cross oi Aegilops ventricosa with wheat confers resistance to the facultative fungal parasite Pseudocercosporella herpotnehoides. To determine the number of genes responsible for this resistance, homozygous recombinant hnes were developed from an F| between the wheat variety 'Hobbit sib' and a substitution line carrymg chromosome 7D of VPMl in a 'Hobbit sib' background.Resistance to Pseudocercosporella herpotnehoides IS shown to be determmed by a single gene located di.stally on tbe long arm of chromosome 7D. EpDlb, a unique alleie of a gene encoding the readily detectable isoenzyme -endopeptidase, maps without recombination to Pchl suggesting for two separate genes a ma.ximum recombination value of 0.03 (P 0.05). Resistance to Pherpotriehoides could alternatively be a product of Ep-Dlh.Pchl is also mapped against a gene for adult plant resistance to brown rust {Pucania recondita), to Rc3 which confers coleoptiie colour, and to a-Amv-D2, an isQzyme that encodes a-atnylase production.

Grain size in wheat is the most stable yield component and has a favorable effect on flour yield. To identify the chromosomes associated with the large grains of line G603-86, (grain weight over 60 mg and grain length of about 9 mm), F3 lines, extracted from F2 populations obtained from Fl monosomics of crosses between G603-86 (P1) and the monosomic set of Favorit (P2) were tested in the field. ANOVA showed significant differences among parents for grain weight and grain length, but not for grain width or the factor expressing the difference in grain form and density. Homoeologous groups had significant effects on grain weight and on all components of grain weight, while genomes were not significantly different for any of these characters. Grain weight was significantly increased by chromosomes 6D and 4A of G603-86. Grain length was significantly increased by chromosomes 4A, 4B, 2B, 3A and 1B, grain width by chromosomes 1A and 1B, and the factor form-density by chromosomes 6D and 6A. The high grain size in G603-86 results from the effects of genes located on many chromosomes which affect grain dimensions, form and density.

A novel photoperiod response gene, designated Ppd-B2, was mapped to wheat chromosome arm 7BS, using a set of lines carrying various segments of 7BS from the early flowering breeding line 'F26-70 7B' in a background of the variety 'Favorit'. The gene was 4.4 cM distal of the microsatellite locus Xgwm0537 and 20.7 cM proximal to Xgwm0255. In contrast to the well-characterized Ppd-1 genes, which require short days for expression, Ppd-B2 was detected when plants were exposed to a long photoperiod. The accelerated flowering produced by Ppd-B2 was correlated with increased grain protein content.

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