Abstract
Stem rust caused by Puccinia graminis Pers.f.sp.<i>tritici</i> Eriks.and E.Henn.(Pgt) is one of the most destructive diseases of wheat which causing considerable yield losses in wheat growing areas worldwide. It has become a renewed threat to global wheat production after the emergence and spread of race TTKSK (also known as Ug99) and related races from Africa. Races of the pathogen in the “Ug99 lineages” are of international concern due to their virulence for widely used stem rust resistance genes and their spread throughout Africa. Disease resistant cultivars provide one of the best means for controlling stem rust. Bale zone, located on the Southeast part of Ethiopia, is one of the main wheat growing regions, playing a pivotal role in the wheat stem rust epidemic in Ethiopia. This study investigated levels of resistance in key wheat cultivars (lines) grown in Bale zone using seedling resistance evaluation and marker aided selection. Twenty wheat cultivars were evaluated for their response to stem rust infection at seedling stage under green house condition. Wheat cultivars were challenged with four stem rust races <i>viz</i> TTKSK, TRTTF, TTTTF and JRQCQ. A high level of phenotypic variation was observed in response to these races in the test entries, allowing for selection in these germplasm as a pre-breeding work. Out of the tested cultivars, three wheat cultivars exhibited low infection types (0–2) response to all the four races and hence selected as a source of resistance to stem rust. In addition, the existence of <i>Sr2, Sr22, Sr24, Sr25, Sr26, Sr35</i> and Sr36 genes in wheat cultivars were assessed using specific DNA markers. Using molecular markers, resistance gene Sr2 was identified in 2 cultivars and <i>Sr24</i> in five cultivars. However, no <i>Sr25, Sr26, Sr35</i> and <i>Sr36</i> were identified in any cultivars tested using DNA markers. The results of both seedling evaluation and marker based resistance gene identification will enable to breed wheat varieties with durable resistance to stem rust disease.
Highlights
The Infection Types (ITs) frequency distribution presented in Figure1depicts a variability in reaction among the test cultivars for all four races used in this study with the majority of the cultivars showing resistance reaction with score of 2.Only few cultivars showed a susceptible reaction with score of 3 (Figure1).The results of test of the wheat cultivars to four races showed that, the tested entries differ in their resistance to disease
Seedling resistance toTTKSK (Ug99), TRTTF, JRCQC was observed in 16 (80%), 19 (95%),16 (80%), and 18 (90%) cultivars, respectively (Table 6).The ranking values of the four races based on their frequencies of avirulence/virulence interactions considering wheat cultivars collection as a whole
The current results revealed that the majority of the wheat cultivars showed infection type score of 2 and 22+, the durum wheat cultivars
Summary
Due to the imminent risk in Ethiopian wheat production posed by Ug99 and other variants of stem rust races, analysis of resistance against stem rust and delineation of the resistance genes in the cultivars (lines) locally grown are of great significance in evaluation of the risk It raises the possibility of development of new rust-resistant sources. There is limited information on the presence/absence of major stem rust resistance genes by reported linked or diagnostic molecular markers in Ethiopian-adapted wheat cultivars those dominantly grown in Bale zone. Major wheat cultivars that are growing in Bale zone were evaluated for resistance to stem rust races such as TTKSK, TRTTF, TTTTF and JRCQC under the controlled conditions of a green house at seedling stage. This study was carried out with the aim of evaluating wheat cultivars to help the breeder in identifying the best parents to be used in the breeding program in fight against stem rust by employing both seedling resistance evaluation results and marker based profiling of wheat cultivars
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