The influence of environment on the expression of Russian wheat aphid; Diuraphis noxia (Kurdjumov) resistance

Abstract

English: The purpose of this study was to investigate the effect of variations in climatic factors such as vernalization periods, minimum- and maximum temperatures and rainfall on the expression of host plant resistance to RWASA1 (original biotype) and RWASA2 (newly identified biotype) in the eastern Free State of South Africa between 2003 and 2006. Climatic records indicate above-average temperatures and reduced rainfall occurred in the Eastern Free State in 2003 to 2005 probably contributing to widespread RWA damage on dryland wheat crops. Greenhouse experiments confirmed that vernalization did not alter RWA plant resistance ranking of wheat entries. However, infestation did produce significant damage by RWASA2 on Elands, Gariep and Limpopo but not on CItr 2401 (containing Dn-4 and another unidentified Dn-gene) and Halt (Dn-4). Resistance rating to RWASA1 of Halt, Komati and Matlabas in greenhouse tests at 18°C/12°C, 22°C/16°C and 26°C/22°C shifted to less resistant- or susceptible categories and changed the ranking of SST 966 as temperature increased. Also, RWASA2 ratings at increased temperature shifted Halt to a more resistant category and changed rankings of Komati and SST 399. Komati, Matlabas, SST 966 or SST 399 did not express any host plant resistance to RWASA2 through leaf area or leaf roll and chlorosis supporting the susceptible ratings that were given to the same varieties in the visual screening test. Seeddressing in AMMI results for 2003 to 2006 were able to increase yields under higheryielding conditions in seasons when moisture- and heat stress occured and the yield performance of cultivars was stabilized irrespective of whether they contained genetic resistance to RWA. Identifying new RWA resistance donors provide an excellent opportunity to exploit novel germplasm with potential new genetic variance for RWA resistance, as well as other beneficial traits such as drought-tolerance. Three germplasm pools were evaluated for this purpose. Twenty-one entries from the Stillwater, Oklahoma/SGI RWA resistance pool expressed resistance against RWASA2 in the seedling test and where generally well adapted to local conditions. Seedling evaluation of the CIMMYT pool revealed twenty entries with acceptable resistance to RWASA2 though field adaptability particularly to biotic stress was occasionally lacking. Twenty entries from the Iranian pool were resistant to RWASA2 though unadapted for resistance to stripe rust; Puccinia striiformis Westend f.sp tritici Eriks., occurring in the Eastern Free State.

Afrikaans: Die doel van hierdie studie was om die invloed van variasie in vernalisasie, minimumen maksimum temperature en reënval op uitdrukking van gasheerplant weerstand teen RWASA1 (oorspronklike biotipe) en RWASA2 (nuut geidentifiseerde biotipe); Diuraphis noxia (Kurdjumov) in die Oos Vrystaat tussen 2003 en 2006 te bepaal. Klimaatsrekords dui aan dat bogemiddelde temperature en laer reënval in die Oos Vrystaat in 2004 en 2005 voorgekom het en waarskynlik bygedra het tot die algemene voorkoms van RKL skade in droëlandkoring. Glashuisproewe bevestig dat ongevernaliseerde- of gevernaliseerde plante nie die RKL weerstandsrangorde verander nie maar RWASA2 wel hoë skadelikheid op Elands, Gariep en Limpopo maar nie CItr 2401 (bevat Dn-4 en ‘n ander ongeidentifiseerde Dn-geen) veroorsaak. Weerstandwaardebepaling van Halt, Komati en Matlabas teen RWASA1 in glashuisevaluasies by 18°C/12°C, 22°C/16°C en 26°C/22°C verskuif na matige weerstand of vatbare kategorieë en verander die rangorde van SST 966 tydens temperatuur verhoging terwyl weerstandsbepaling van Halt teenoor RWASA2 by hoër temperatuur na ‘n meer weerstandbiedende kategorie verskuif en die rangorde van Komati en SST 399 verander. Geen gasheerweerstand uitgedruk in blaaroppervlak, blaarrol en chlorose teenoor RWASA2 kom voor by Komati, Matlabas, SST 966 en SST 399 nie en bevestig vatbaarheid van hierdie kultivars in die visuele evaluasies. AMMI resultate vir 2003 tot 2006 toon dat saadbehandeling opbrengs verhoog onder hoë-opbrengs omstandighede in seisoene waarin vog- en hitte stremming voorkom en koringopbrengs van kultivars stabiliseer ten spyte daarvan of die kultivars RKL weerstand bevat of nie. Identifikasie van nuwe RKL weerstandsbronne bied ‘n uitstekende geleentheid vir die ontginning van nuwe kiemplasma met potensiële nuwe genetiese variasie vir RKL weerstand maar ook ander belangrike eienskappe soos droogteweerstand en drie kiemplasmapoele is vir hierdie doel geevalueer. Een-en-twintig inskrywings uit die Oklahoma/ARC-SGI poel het saailingweerstand teenoor RWASA2 getoon en is algemeen goed aangepas vir plaaslike toestande. Saailingevaluasie van die CIMMYT poel het twintig inskrywings geidentifiseer met weerstand teenoor RWASA2 alhoewel aanpassing van hierdie inskrywings teenoor veral biotiese stremming wisselvallig is. Twintig inskrywings uit die Iranese poel toon weerstand teenoor RWASA2 maar is veral gevoelig vir streeproesinfestasie deur Puccinia striiformis f.sp tritici wat huidiglik in die Oos- Vrystaat voorkom.