Abstract
Tan spot caused by Pyrenophora tritici-repentis (Ptr) is an important disease of wheat in many wheat producing areas of the world. A genome wide association study (GWAS) was conducted using 11,401 SNP markers of the Illumina Infinium 15K Bead Chip with whole genome coverage to identify genomic regions associated with resistance to tan spot in a diverse panel of 184 wheat genotypes originating from South Asia and CIMMYT. The GWAS panel was phenotyped for seedling resistance to tan spot with Ptr race 1 in two greenhouse experiments. Besides CIMMYT germplasm, several lines from South Asia (India, Bangladesh and Nepal) showed good degree of resistance to tan spot. Association mapping was conducted separately for individual experiments and for pooled data using mixed linear model (MLM) and Fixed and random model Circulating Probability Unification (FarmCPU) model; no significant MTAs were recorded through the MLM model, whereas FarmCPU model reported nine significant MTAs located on chromosomes 1B, 2A, 2B, 3B, 4A, 5A, 5B, 6A, and 7D. The long arms of chromosomes 5A and 5B were consistent across both environments, in which the Vrn-A1 locus was found in identified region of chromosome 5A, and MTA at IACX9261 on 5BL appears to represent the resistance gene tsn 1. MTAs observed on chromosomes 1B, 2A, 2B, 3B, 4A, 6A, and 7D have not been reported previously and are likely novel.
Highlights
Wheat is a widely grown cereal crop around the world, and it is considered as staple source of nutrition for nearly 40% of the world’s population and supplies 20% of dietary protein and food calories (Giraldo et al, 2019)
184 diverse spring wheat genotypes were screened for seedling tan spot resistance in a greenhouse for the identification of significant Marker-trait association (MTA)
Field screening of large number of genotypes for tan spot is considered challenging due to the often-natural incidence of other foliar diseases that mimic tan spot symptoms; in addition, limitation of required light and humidity for inoculum growth in field condition precludes pathogen growth (Singh et al, 2009)
Summary
Wheat is a widely grown cereal crop around the world, and it is considered as staple source of nutrition for nearly 40% of the world’s population and supplies 20% of dietary protein and food calories (Giraldo et al, 2019). A major disease of wheat is tan spot (synonym yellow spot or yellow leaf spot) which occurs in both temperate and warmer wheat growing areas in the world (Duveiller et al, 1998). This disease is caused by the necrotrophic fungal pathogen Pyrenophora tritici-repentis (Died.) Dreches [anamorph Dreschslera triticirepentis (Died.) Shoemaker]. Tan spot pathogen infects the whole plant but is generally most prominent on leaves followed by stem and head tissues This infection leads to reduction in photosynthetic area and eventually leads to yield reduction and quality deterioration. In recent years this necrotrophic disease is causing increased wheat yield losses globally, which is associated with reduced tillage practices as necrotrophic pathogens overwinters in wheat stubble (Cotuna et al, 2015)
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