Abstract
Wheat stem rust caused by Puccinia graminis f. sp. tritici is a disease that causes complete annihilation of wheat crops over wide areas during epidemic years. The highland of Ethiopia is considered as a hot spot area for the development of stem rust complex. Hence, this study was carried out to detect the virulence diversity of P. graminis f. sp. tritici in Southern Tigray. The findings of this paper were based on race analysis through inoculation of stem rust populations, isolation and multiplication of single-pustule of the pathogen and race determination by inoculating on stem rust differential hosts. The phenotypic characterization of P. graminis f. sp. tritici resulted in identification of 20 races from 32 isolates, which included the most prevalent races TTSNK, RRJJC and HRJJC with a frequency of 9.4% each and the most virulent races TTKSK and TTSSK each making 85% of Sr genes ineffective. Three important races (TTSSK, TTSNK and RRTTF) are new to the study area and the country (Ethiopia) as a whole putting a significant wheat proportion at risk. Among 20 wheat stem rust differential hosts, four were found effective for 75% and more of the races identified. Differential host carrying Sr24 was effective to all, while gene SrTmp was effective to 90% of the races followed by Sr17 and Sr31 each effective for 75%. In contrast, differential hosts carrying SrMcN, Sr9b, Sr9g and Sr10 were ineffective to 96.9, 93.8, 87.5 and 81.2% of the isolates tested, respectively. Thus, use of effective Sr genes such as Sr24 and SrTmp in single cultivar through gene pyramiding has paramount importance as the additive effects of several genes gives the cultivar a wider base stem rust resistance along with periodic race survey.
Highlights
Wheat (Triticum spp) is among the most important crops grown in Ethiopia
Over 30 fungal wheat diseases have been identified in Ethiopia, stem rust caused by P. graminis f. sp. tritici is one of the major production constraints in most wheat growing areas of the country, causing yield losses of up to 100% at times of epidemics (Belayneh and Emebet, 2005)
Using the international system of nomenclature for P. graminis f. sp. tritici (Roelfs and Martens, 1988; Jin et al, 2008), 20 races were identified based on their reaction on 20 differential hosts
Summary
It is among the cereal crops that contribute significantly to food security in the country Wheat ranks second both in terms of volume of production and productivity after maize with the total volume of production of 2.54 million tons at the national level and it ranks third in terms of area coverage with the total area of 1.5 million ha after maize and tef (CSA, 2009). It is produced largely in the South, Central, Northwest and the remaining small amount is produced in the rest of the North and South regions of the country (MoARD, 2009). Stem rust received even more attention when the popular bread wheat cultivars Enkoy and Kubsa became susceptible in 1992/93 & 1994, respectively (Temesgen et al, 1996)
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