Crop Protection

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    PHENOTYPIC AND GENOTYPIC CHARACTERIZATION OF THE WHEAT STEM RUST PATHOGEN (Puccinia graminis f.sp. tritici) AND VARIETIES’ REACTION TO MAJOR STEM RUST RACES IN ETHIOPIA
    (Hawassa University College of Agriculture, 2019) TSEGA’AB TESFAYE WANORE
    Stem rust caused by Puccinia graminis f.sp. tritici (Pgt) is one of the most important diseases of wheat (Triticum aestivum) across the globe. Because of the sudden changes in stem rust race patterns, commercial varieties are becoming vulnerable globally at large and particularly in Ethiopia. The objectives of this study were to i) assess the distribution of wheat stem rust across selected major wheat producing regions of Ethiopia, ii) study population diversity of pgt races and iii) identify physiological race and the reaction of wheat genotypes to major races of the pathogen. For this purpose, a total of 464 wheat fields were surveyed in eight zones and 37 wheat producing districts of Amhara and Oromia regional states of Ethiopia. Besides, 60 disease samples were collected for race analyses using 20 differentials in a greenhouse trial and molecular diversity of the pathogen was studied using custom PgtSNP 3.0K chip. The reaction of 75 wheat genotypes and 1 universal susceptible check to major races of the pathogen was also evaluated in the greenhouse. Stem rust prevalence in the surveyed areas ranged from 0 to 100%, while disease incidences and severity varied between 0 and 25% and 0 and 11.5%, respectively. Greenhouse trials involving 20 differential cultivars resulted in the identification of three Pgt races (TKTTF, TTKSK and TTRTF) among the collected stem rust samples. Of these, TTRTF has not been previously reported in Ethiopia and hence, this is the first report of TTRTF in Ethiopia. Race TKTTF, also known as “Digalu race”, was the most frequent (75% frequency) of all the races of Pgt. The remaining two races TTKSK (Ug-99) and TTRTF were detected with frequencies of 4.16 and 22.91%, respectively. Eighty five percent of the stem rust resistance genes (Sr5, Sr21, Sr9e, Sr7b, Sr6 Sr8a, Sr9g, Sr9b, Sr17, Sr9a, Sr9d, Sr10, Sr38 and McN) were ineffective to all the races detected and 30% of the resistance genes were found to be effective to one or more of the races identified. However, in the present study only the differential host carrying Sr24 was effective to all the races identified in the study areas. The presence of the three Pgt races was also confirmed by molecular study, which categorized the isolates into three clades as I, IVB and IIIB for TTKSK, TKTTF and TTRTF, respectively. The resistance screening trial revelaed that five durum wheat genotypes namely Bichena, Tob-6, Assasa, Kokate and DW/NVT-LMA and six bread wheat genotypes namely, Sulla, Hidase, Wane, 36ESWY, ETBW 8459 and 36ESWYT were resistant against all the races at the seedling stage. These resistant genotypes can be used in wheat improvement programs after being checked under field condition for their adult stage resistance.