Transfer of genetic resistance to the Russian wheat aphid from rye to wheat

Horn, Marizanne (1997-03)

Thesis (MSc.) -- Stellenbosch University, 1997.

Thesis

ENGLISH ABSTRACT: An octoploid triticale was derived from the F1 of a Russian wheat aphid resistant rye, 'Turkey 77', and 'Chinese Spring' wheat. The alloploid was crossed (a) to common wheat, and (b) to the 'Imperial' rye to 'Chinese Spring' disomic addition lines. F2 progeny from these crosses were tested for Russian wheat aphid resistance and C-banded. Resistance was found to be associated with chromosome arm 1RS of the 'Turkey 77' rye genome. This initial work was done by MARAIS (1991) who made a RWA resistant, monotelosomic 1RS ('Turkey 77') addition plant available for the study. The F3 progeny of this monotelosomic addition plant was used to confirm the RWA resistance on chromosome 1RS. The monotelosomic addition plant was then crossed with the wheat cultivar 'Gamtoos', which has the 1BL.1 RS 'Veery' translocation. Unlike the 1RS segment in 'Gamtoos', the 'Turkey 77'- derived 1RS telosome did not express the rust resistance genes 5r31 and Lr26 which could then be used as markers. From the F1 a monotelosomic 1RS addition plant that was also heterozygous for the 1BL.1 RS translocation, was selected and testcrossed with an aphid susceptible common wheat, 'Inia 66'. Meiotic pairing between the .rye arms resulted in the recovery of five euploid, Russian wheat aphid resistant plants out of a progeny of 99 euploids. One recombinant also retained 5r31 and Lr26 and was allowed to self pollinate. With the aid of SOS-PAGE profiles, Russian wheat aphid resistant 1BL.1 RS translocation homozygotes were identified and it was possible to confirm that the Russian wheat aphid resistance gene was in fact transferred to the 1BL.1RS ('Veery') translocation. Two attempts were made to map the Russiar, wheat aphid locus or loci. (1) Telosomic mapping was attempted. For this purpose a plant with 2n = 40 + 1BL.1 RS + 1RS was obtained, and testcrossed with a Russian wheat aphid susceptible wheat. (2) A disomic, recombined 1BL.1 RS translocation line with Russian wheat aphid resistance but lacking the Lr26 and Sr31 alleles was crossed with 'Gamtoos' and the F1 testcrossed. The testcross in both strategies were done with 'Chinese Spring'. In the first experiment the Sr31 locus was located 10.42 map units from the Lr26 locus. The rust resistance data implied that the genetic distance estimates may be unreliable and therefore the laborious Russian wheat aphid resistance tests were not done. In the second experiment a Russian wheat aphid resistance gene was located 14.5 map units from the Lr26 locus. In the latter cross nonmendel ian segregation of the Russian wheat aphid resistance evidently occurred which implied that the estimated map distance may be inaccurate. It was also not possible to determine the number of genes involved from the data.

AFRIKAANSE OPSOMMING: 'n Oktaplo"lede triticale is gemaak vanaf die F1 van 'n kruising tussen 'n Russiese koringluis-weerstandbiedende rog, 'Turkey 77', en die koringkultivar 'Chinese Spring'. Die alloplo"led is gekruis met gewone broodkoring en met 'Imperial' rog/'Chinese Spring' disomiese addissielyne. Die F2 nageslag vanaf hierdie kruisings is getoets vir Russiese koringluisweerstandbiedendheid en C-bande is ook gedoen. Weerstand is gevind wat geassosieer is met die 1RS chromosoomarm van 'Turkey 77'. Hierdie oorspronklike werk is deur MARAIS (1991) gedoen en uit sy materiaal is 'n monotelosomiese 1RS ('Turkey 77') addissieplant beskikbaar gestel vir die huidige studie. Die F3 nageslag van hierdie monotelosomiese addissieplant is gebruik om die weerstand teen die Russiese koringluis op chromosoom 1RS te bevestig. Die monotelosomiese addissieplant is ook gekruis met die koringkultivar 'Gamtoos' wat die 1BL.1 RS-translokasie dra. Hoewel die 1RS segment van 'Gamtoos' die roesweerstandsgene, Sr31 en Lr26 uitdruk, is dit nie die geval met die 'Turkey 77' 1RS telosoom nie. Hierdie gene kon dus as merkergene gebruik word. Vanuit die F1 is 'n monotelosomiese 1RS addissieplant geselekteer wat ook heterosigoties was vir die 1BL.1 RStranslokasie. Hierdie plant is getoetskruis met 'n luisvatbare gewone broodkoring, 'Inia 66'. Meiotiese paring tussen die rogarms het daartoe gelei dat vyf euplo"lede Russiese koringluis-weerstandbiedende nageslag uit 99 euplo"lede nageslag geselekteer kon word. Een rekombinant het ook Sr31 en Lr26 behou en is toegelaat om self te bestuif. Met behulp van SDSPAGE profiele is Russiese koringluis-weerstandbiedende 1BL.1 RStranslokasie homosigote ge"ldentifiseer en kon bevestig word dat die weerstandsgeen vir die Russiese koringluis oorgedra is na die 1BL.1 RS ('Veery') -translokasie. Twee strategies is gevolg om die Russiese koringluislokus of -loci te karteer: (1) 'n Telosomiese analise is gedoen. 'n Plant met 2n = 40 + 1BL.1 RS + 1RS is verkry en met 'n luisvatbare koring bestuif. (2) 'n Gerekombineerde, disomiese plant met Russiese koringluis-weerstandbiedendheid maar sonder die Lr26 en Sr31 allele is gekruis met 'Gamtoos' en die F1 getoetskruis. Die toetskruisouer in beide die strategiee was 'Chinese Spring'. In die eerste eksperiment is die Sr31-lokus 10.42 kaarteenhede vanaf die Lr26-lokus gelokaliseer. Die raesdata het ge"impliseer dat onbetraubare genetiese kaarteenhede geskat sou word en daarom is die omslagtige Russiese koringluis weerstandsbepalings nie gedoen nie. In die tweede eksperiment is die Russiese koringluis-weerstandsgeen op 14.5 kaarteenhede vanaf die Lr26-lokus gelokaliseer. Nie-Mendeliese segregasie van die Russiese koringluis-weerstand in hierdie karteringseksperiment het ge'impliseer dat die berekende kaartafstand onakkuraat mag wees. Dit was ook nie moontlik om op grand van die data die aantal gene betrakke af te lei nie.

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