Bilateral BBSRC-Embrapa: Uncovering the genetic and functional basis of the unique leaf rust resistance in the Brazilian wheat variety Toropi

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The global demand for wheat is increasing, but so is the distribution and aggressiveness of the pathogens that seriously impact on wheat productivity. The Food Agricultural Organisation (FAO) estimates that wheat production must increase by 60% by 2050 to meet the demand from the growing human population. The fungal pathogens responsible for rust of wheat are a major constraint to achieving this increase in production and in recent years we have seen numerous epidemics due to the breakdown of rust race-specific resistance (R-) genes. There are three rust pathogens of wheat, stripe (yellow-Puccinia striiformis), leaf (brown-P. triticina) and stem (black-P. graminis) rust. In the UK stripe rust is the most prevalent, occurring every year. Leaf rust has been confined to warmer regions, being prominent in the south-west of England. However, in recent years the UK Cereal Pathogen Virulence Survey has detected leaf rust on wheat as far north as the border with Scotland. This is considered to be as a result of milder winters increasing the ability of the pathogen to overwinter, and warmer springs allowing leaf rust to take hold in regions of the UK where previously it has not been considered a problem.In Brazil leaf rust is the major problem. Many sources of leaf rust resistance used in wheat varieties have proven to be race-specific, with virulence rapidly arising in the P. triticina population, overcoming the resistance after only a few years of deployment in new wheat varieties. However, a small number of slow-rusting, adult plant resistance (APR) genes effective against leaf rust have been reported. These include Lr34, Lr46, Lr67 and Lr68. These leaf rust APR genes have proven effective over long periods of time, large acreages and under high disease pressure. Some of these durable, leaf rust APR genes have now been cloned, confirming, as suspected, that they do not function in the same way at race-specific, leaf rust R-genes. The old Brazilian cv. Toropi contains a unique, durable source of leaf rust APR. Preliminary studies have identified two genes in Toropi which account for 71% of the resistance. However these two genes are poorly defined and we know very little about their mode of action, e.g. at what plant growth stages the leaf rust APR becomes effective and whether environmental factors such as temperature can effect the action of these resistance genesIn this study we will improve the genetic resolution of each gene by generating a high-density genetic map of Toropi using state-of-the-art DNA marker systems, and wheat genomic resources. We will develop wheat genetic materials that will enable us to unravel the mode of action of each gene, and marker tools that will enable each leaf rust APR gene to be identified and followed during the process of breeding new improved wheat varieties. We also aim to incorporate these Toropi resistance genes into elite Brazilian wheat varieties, using the marker tools we develop, thereby providing the Brazilian wheat breeder with materials they can enter directly into their wheat breeding programs.To help understand the mode of action and biology underlying these leaf rust APR genes we will study the development of the leaf rust fungal pathogen in wheat at the microscopic level, infecting wheat plants at different stages of it growth and when grown at different temperatures.This project also focusses on the training of young Brazilian researchers, and on broadening the international collaborative research network of the Brazilian team.