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Abstract

MOLECULAR, MORPHOLOGICAL AND HOST-PATHOGEN HISTOCOMPATIBILITY STUDIES OF WHEAT YELLOW RUST Muazam ul Islam and Waqas Ahmad Institute of Biotechnology and Genetic Engineering The University of Agriculture, Peshawar Khyber Pakhtunkhwa-Pakistan September, 2024 ABSTRACT Wheat (Triticum aestivum L.) positions as the second most important cereal crop after rice, being the prime dietary source for a large portion of the global population. Wheat yellow rust (YR) disease is a major threat to the production worldwide. This study aimed to understand the host (wheat) interaction dynamics with the YR pathogen Puccinia striiformis through field screening, microscopic host pathogen histocompatibility, and YR resistance gene associated SSR (Simple Sequence Repeat) molecular marker studies. Total fifteen diverse wheat genotypes i.e., Pirsabak-13, Faisalabad-08, AAS-2002, Pirsabak-08,Atta Habib, GA-2002, Fronkolin, TD-1, 2KD-1, Line 2566, Line 2523, Line 2527, Line 2522, Pirsabak-85, and Pirsabak-04 were used in two locations triplicate field trial with the aim to assess the YR coefficient of infection (CI) and host response as relative resistance index (RRI). After analysis, five genotypes i.e., PS-13 (7.2), Frankolin (7.2), Line-2566 (7.6), Line-YR5 (8.8) and Line YR10 (9) were found to exhibit the most desirable response with locations average RRI values in range from 7 to 9. Whereas, Faisalabad-08, Pirsabak-08, Atta Habib, and Pirsabak-85 were found to exhibit below par resistance response with RRI values falling under than 5. Based on field assessment of the YR disease response for the tested wheat genotypes, three genotypes each from the resistant (Line 2566, Line-Yr5, and Line-Yr10), moderately resistant (PS-13, GA-2002 and Fronkolin), Moderately susceptible (FS-08, PS-08, and Atta-Habib), and susceptible (TD-1, PS-85, and Morocco) were used for microscopic histocompatibility studies. Microscopic studies confirmed the consistent presence of active uridinospore, with ruptured pustules among the susceptible genotypic specimen, whereas no pustules (resistant) or limited pustules, tightly packed with inactive spores and clear presence of chlorosis and necrosis (moderately resistant). This study also undertook molecular characterization studies of all the wheat genotypes using YR resistance genes (Yr5, Yr10, Yr15, YrSP, Yr29, and Yr30) associated SSR markers. Among the resistant genotypes two alleles i.e., Yr5_C and Yr30_B demonstrated strong association. Among the moderately resistant genotypes, alleles Yr5_E, Yr5_F, and YrSP_A showed strong association. On the other hand, alleles Yr10_A and Yr30_C were strongly implicated in the moderately susceptible genotypic bulk. Finally, among the susceptible genotypic bulk alleles Yr5_G, YrSP_B, and Yr29_A were most prevalent. In summary, Yr5 was found to be most dynamic among all with five of its associated alleles being implicated in one of the four resistance bulks. This study has shed further light on the current understanding of the dynamics of YR pathogen and host interaction in the backdrop of morphological, microscopic and molecular approaches. This study further recommends to extend the knowledge base acquired through the current study for use in marker assisted selection and screening of the wheat germplasm to develop new YR resistant cultivars.

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