Efficiency of Pc genes of resistance to prevalent pathotypes of Puccinia coronata avenae

This paper deals with efficiency of some Pc genes of resistance to pre valent pathotypes of crown rust causer in oat. It was found that in seedlings stage the most efficient were genes Pc 68 and Pc 39 (100%). Satisfying degree of efficiency demonstrated genes Pc 38 and Pc 55 (87,5%). Majority of genes expressed partial resistance. Efficiency of Pc genes of resistance to prevalent pathotypes of pathogen in both years of investigation was satisfying and it was 61,45%.

Inheritance of resistance to Puccinia coronata avenae and P. graminis avenae in an accession of Avena sterilis from Spain

Accessions of wild Avena spp. obtained from the Iberian Peninsula were screened for resistance to oat crown and oat stem rust. Of a number of accessions which showed resistance, A. sterilis accession IB3056 was selected for further genetic analysis because it had combined resistance to both crown and stem rusts and as a hexaploid was readily hybridizable with A. sativa. IB3056 was crossed and backcrossed with the susceptible cultivar 'Makuru' and progeny were analyzed for segregation to a range of rust races. A single dominant gene conferred resistance to crown rust. The resistance was highly effective against all isolates of Puccinia coronata avenae tested. The crown rust resistance of IB3056 was due either to gene Pc68 or was very closely linked or allelic to Pc68. Seedling plants of the IB3056 parent were susceptible to all isolates of P. graminis avenae tested, but in the adult plant stage they were resistant. All IB3056/2* Makuru progeny also were susceptible to stem rust as seedlings, but BC1F2 adult plants segregated for resistance in ratios indicating a single dominant gene, designated Pg17.Key words: oat crown rust, oat stem rust, adult plant resistance, seedling resistance

Ultrastructure of haustorium development in Puccinia coronata avenae. I. Cytochemistry and electron probe X-ray analysis of the haustorial neck ring

The structure and composition of the haustorial neck ring in Puccinia coronata avenae was determined by histochemical methods and by electron-probe X-ray analysis (EDX). In mature haustoria, the neck ring structure was composed of two cylindrical bands. A broad band, nearer to the haustorial mother cell, was designated as the α (alpha) band and a narrower band, nearer to the haustorial body, the β (beta) band. The chemical composition of the two bands was different. The results of EDX analysis showed silicon as the major element present in the α band, and iron and phosphorus (possibly in the form of ferric pyrophosphate), the major elements of the β band. Digestion with protease or treatment with the organic solvents chloroform–methanol, ether–ethanol, or acetone failed to extract either band, indicating the presence of little, if any, protein or lipid materials.

Ultrastructure of spermatium ontogeny in Puccinia coronata avenae

Spermatium formation in Puccinia coronata avenae was concluded to be annellidic but with some phialidic analogies. The spermatiophore wall consisted of a prominent outer layer and a very thin inner layer. During formation of the first spermatium initial, the apical end of the spermatiophore became somewhat swollen and a septum was then formed centripetally at the base of the swelling to delimit the primary spermatium. The wall layers of the first spermatium were derived from the wall layers of the spermatiophore. The mature septum consisted of two bilayered walls separated by a clear septal lamella. The upper septal wall formed the basal wall portion of the preceding spermatium and the lower septal wall became the distal wall portion of the succeeding spermatium. The layers of each septal wall were confluent with the inner and outer periclinal wall layers of the developing spermatia. After spermatium secession, the broken outer wall layer left remnants as a basal frill on the spermatium and an annular scar on the spermatiophore. Each succeeding spermatium formed at a near-fixed locus on the spermatiophore. Although the formation of succeeding spermatia appeared superficially to be phialidic, examination of wall relationships indicated that the formation of each successive spermatium recapitulated the holoblastic first spermatium.As the spermatia matured, the outer wall layer, including the basal frill, gradually dissipated. The thickness of the spermatium wall was maintained by expansion of the inner layer. In mature spermatia, the inner layer comprised the bulk of the wall, and the outer layer was left as a thin tenuous band surrounding the spermatium.