Characterization of Yr15 resistance to stripe rust of wheat

Abstract

English: Stripe (yellow) rust, caused by Puccinia striiformis Westend f. sp. tritici, is a major disease of bread wheat, Triticum aestivum L., in South Africa. The objective of this study was to evaluate the Yr15 gene as a potential resistance source for breeding purposes. Histological evidence was provided that Yr15 conditions a hypersensitive reaction typical of non-durable resistance. Fluorescence, phase contrast and scanning electron microscopy complemented each other and may be used to quantify various aspects of resistance expression in the wheat stripe rust pathosystem. The frequency of stomatal penetration was extremely low and no meaningful differences in early infection structures were observed between the resistant Yr15 and susceptible Avocet 'S' lines. Papillae were not involved in the resistance response to pathotype 6E16. In studies of defense-related proteins, an induction of β- 1,3-glucanase activity in both resistant and susceptible wheat genotypes was detected within 96 h post-inoculation (hpi). This induction, however, was constitutive and did not depend on the infection process. Likewise, no changes in chitinase activity were observed between resistant and susceptible plants. A pronounced increase of peroxidase activity between 0 and 168 hpi, in both infected and uninfected resistant and susceptible plants was observed, suggesting a constitutive expression of this enzyme. Using AFLP (Amplified Fragment Length Polymorphism) technology to detect possible molecular markers for Yr15, two primer combinations yielded polymorph isms between the bulked susceptible and resistant SST55 x Yr15/6*AvS F2 DNA, as well as between the susceptible and resistant parents. Fragment sizes ranged from 50 to 420 bp. Of these, one 95 bp fragment identified using primers MseCAA + Eco-ACA and one 205 bp fragment identified using primers MseCAA + Eco-AAC were detected in the resistant parent and the resistant F2 group. This indicates that these fragments are closely associated with Yr15 making them ideal candidates for further investigation.

Afrikaans: Streep (geel) -roes, veroorsaak deur Puccinia striiformis Westend f. sp. tritici, is In belangrike siekte van broodkoring, Triticum aestivum L., in Suid-Afrika. Die doelwit van hierdie studie was om die Yr15 geen as In potensiële weerstandsbron te evalueer vir verdere aanwending in telingsprogramme. Histologiese bewyse is gelewer dat Yr15 In hipersensitiewe reaksie tipies van nie-volhoubare weerstand bemiddel. Fluoressensie, fasekontras en skandeer-elektron-mikroskopie het mekaar gekomplementeer en kan gebruik word om sekere aspekte van weerstanduitdrukking in die koringstreeproes-patosisteem te kwantifiseer. Die frekwensie van stomata le penetrasie was laag en geen beduidende verskille in vroeë-infeksiestrukture kon tussen die bestande Yr15 en vatbare Avocet'S' lyne waargeneem word nie. Papillae was nie betrokke by die weerstandsreaksie teen patotipe 6E16 nie. In studies van proteïne wat met verdedigingsmeganismes geassosieer word, is In induksie in β1 ,3-glukanase-aktiwiteit in beide bestande en vatbare lyne, binne 96 h na inokulasie waargeneem. Hierdie induksie was konstitutief en is nie beïnvloed deur die infeksieproses nie. Soortgelyk het geen verskille in chitinase-aktiwiteit tussen bestande en vatbare lyne voorgekom nie. In Toename in konstitutiewe peroksidaseaktiwiteit tussen 0 en 168 h na inokulasie is waargeneem by geïnfekteerde en kontrole bestande en vatbare plante. In die toepassing van AFLP ("Amplified Fragment Length Polymorphism") tegnologie om moontlike molekulêre merkers vir Yr15 te vind, het twee priemstuk-kombinasies polimorfismes tussen SST55 x Yr15/6*AvS F2 DNA, onderskeidelik saamgevoeg vir bestande en vatbare segregate, aangedui. Fragmentgroottes het gewissel tussen 50 en 420 bp. Een 95 bp fragment, soos geïdentifiseer deur die priemstukke MseCAA + Eeo-ACA en een 205 bp fragment, soos geïdentifiseer deur die priemstukke MseCAA + Eeo-AAC het in beide die bestande ouer en die bestande F2 groep voorgekom. Hierdie fragmente is dus nou geassosieer met Yr15 en is ideale kandidate vir verdere ondersoek.