Races Identification of Wheat Rusts in Syria during the 2019 Growing Season

Kharouf, Sh., Sh. Hamzeh and M.F. Azmeh. 2021. Races Identification of Wheat Rusts in Syria during the 2019 Growing Season. Arab Journal of Plant Protection, 39(1): 1-13. Wheat rust diseases, caused by Puccinia striiformis f. sp. tritici (stripe or yellow rust), P. triticina f. sp. tritici (leaf or brown rust) and P. graminis f. sp. tritici (stem or black rust) are important factors affecting both durum and bread wheat production in Syria. Considerable losses were caused by these diseases, especially stripe rust, estimated at more than one million metric tons, in the 2010 season, out of 5 million anticipated production. Therefore, it is essential to monitor and follow the movement of these three rust physiological races. In the 2019 growing season, 165 wheat fields were surveyed, and 312 samples were collected and characterized. Ten races of stripe rust were identified in ten locations, of which, four represent new record in Syria, namely the races 16E154, 69E150, 264E46 and 258E64. In addition, four races of leaf rust were identified in four locations, one of which (BKLP) is a new record in Syria. In addition, three previously recorded stem rust races were identified from three different locations. It should be mentioned that the newly recorded races of stripe rust are able to overcome resistance genes Yr1 and Yr5, on which the resistance of durum wheat cultivars such as "Cham3" depended, with a disease severity of 40S recorded in the same locations. It is also worth noting that the stripe rust race 462E128 (warrior) was not detected in the isolates studied. Likewise, the stem rust race Ug99 was also not identified, and because of the aggressiveness of this race, continuous inspection through field surveys accompanied with pathogenicity tests is essential during the coming seasons. Keywords: Stripe (yellow) rust, Leaf (brown) rust, stem (black) rust, race identification, wheat, Syria

Wheat rust epidemics damage Ethiopian wheat production: A decade of field disease surveillance reveals national-scale trends in past outbreaks

Wheat rusts are the key biological constraint to wheat production in Ethiopia—one of Africa’s largest wheat producing countries. The fungal diseases cause economic losses and threaten livelihoods of smallholder farmers. While it is known that wheat rust epidemics have occurred in Ethiopia, to date no systematic long-term analysis of past outbreaks has been available. We present results from one of the most comprehensive surveillance campaigns of wheat rusts in Africa. More than 13,000 fields have been surveyed during the last 13 years. Using a combination of spatial data-analysis and visualization, statistical tools, and empirical modelling, we identify trends in the distribution of wheat stem rust (Sr), stripe rust (Yr) and leaf rust (Lr). Results show very high infection levels (mean incidence for Yr: 44%; Sr: 34%; Lr: 18%). These recurrent rust outbreaks lead to substantial economic losses, which we estimate to be of the order of 10s of millions of US-D annually. On the widely adopted wheat variety, Digalu, there is a marked increase in disease prevalence following the incursion of new rust races into Ethiopia, which indicates a pronounced boom-and-bust cycle of major gene resistance. Using spatial analyses, we identify hotspots of disease risk for all three rusts, show a linear correlation between altitude and disease prevalence, and find a pronounced north-south trend in stem rust prevalence. Temporal analyses show a sigmoidal increase in disease levels during the wheat season and strong inter-annual variations. While a simple logistic curve performs satisfactorily in predicting stem rust in some years, it cannot account for the complex outbreak patterns in other years and fails to predict the occurrence of stripe and leaf rust. The empirical insights into wheat rust epidemiology in Ethiopia presented here provide a basis for improving future surveillance and to inform the development of mechanistic models to predict disease spread.

Screening of wheat (Triticum aestivum L.) genotypes for rust-resistance and assessment on prevalence and distribution of the rust diseases in wheat production fields

Evaluation of 45 wheat genotypes was performed to quantify genetic responses to inoculation of rust pathogens in aqueous suspension at the early vegetative stage. The study was conducted in field conditions at Plant Pathology Division, Nepal Agricultural Research Council, Lalitpur, Nepal in winter, 2013. Results showed large variations of rust resistance on wheat genotypes. Thirty-six genotypes were susceptible to yellow rust (YR), 18 had high severity, 7 had moderate severity, 6 had low severity, 5 had trace reactions, while 9 were rust-resistant. Old varieties (Lerma-52, Kalayansona, RR-21, NL-30, HD-1982, UP-262, Lumbini, Vinayak, Vaskar, Nepal-297, Nepal-251, BL-1135, Annapurna-4, Achyut, Rohini, and BL-1473) had high severities of YR, but relatively recent cultivars had medium severities. YR was severe (100S) in genotypes HD-1982, Vaskar, Vijay, and Rohini followed by RR-21, NL-30, UP-262, Nepal-297, BL-1135, and Annapurna-4 (90S). The pipeline cultivars: Aditya, NL-971, BL-3503, BL-3623, NL-1008, NL-1064, Becard#1, and Chyakhura-1 had trace to moderate reactions of YR with low severity indices. But varieties Vijay and NL-1055 showed high severity of YR (100S and 80S, respectively). Overall, leaf rust (LR) was minor while stem rust (SR) developed in traces on a single genotype (Annapurna-1). A survey of wheat rusts across 66 production fields revealed the prevalence of YR and LR at high levels, but none on SR. The occurrence of LR was higher than YR; 48.48% vs 36.36% of assessed fields, respectively. YR was a primary concern of rust diseases with most fields under high severity (62.5%) and incidence (54.16%) levels. LR had low incidence and moderate severity levels. A considerable gap exists between an extension of such research outcomes and the producers, who demonstrated little know-how on wheat rusts and varieties. These results may support and enhance varietal selection, breeding programs, and effective management and control strategies against wheat rust diseases.

AN OVERVIEW OF COMPARISON BETWEEN WHEAT RUSTS MYCOFLORA IN INDIA WITH GLOBAL SCENARIO

Wheat rusts are the oldest plant disease known to human and caused by Puccinia species. Puccinia species are the main constraints in wheat production wherever wheat is grown. Early literatures mention these devastating diseases and their ability to destroy entire wheat crops. These wheat rust pathogens are highly transmissible through air current in both cases, primary and secondary infections. Primary infection occur through alternate host developing spore (Aeciospores) and secondary infection caused by wheat (primary host) developing spore (Uredospores). Secondary infection results epidemics, several time as globally occurrence. Ecologically, the persistence of rusts as a significant disease in wheat can be attributed to specific characteristics of the rust mycoflora. Their ability to spread aerially over the large distance, production of urediospores in enormous number and evolving new pathotypes, makes the management of wheat rusts a very daunting task. These characteristics include a capacity to produce a large number of spores which can be wind disseminated over long distances and infect wheat under favorable environmental conditions and the ability to change genetically, thereby producing new races with increased aggressiveness on resistant wheat cultivars. KEY WORDS: Wheat Rust, Puccinia, Rust Mycoflora, Stem Rust, Leaf Rust, Stripe Rust

Status of Wheat Rust Research and Progress in Rust Management-Indian Context

The rusts of wheat, caused by three species of Puccinia, are very devastating diseases and are major biotic constraints in efforts to sustain wheat production worldwide. Their capacity to spread aerially over long distances, rapid production of infectious uredospores, and abilities to evolve new pathotypes, makes the management of wheat pathogens a very challenging task. The development and deployment of resistant wheat varieties has proven to be the most economic, effective and efficient means of managing rust diseases. Rust resistance used in wheat improvement has included sources from the primary gene pool as well as from species distantly related to wheat. The 1BL/1RS translocation from cereal rye was used widely in wheat breeding, and for some time provided resistance to the wheat leaf rust, stripe rust, and stem rust pathogens conferred by genes Lr26, Yr9, and Sr31, respectively. However, the emergence of virulence for all three genes, and stripe rust resistance gene Yr27, has posed major threats to the cultivation of wheat globally. To overcome this threat, efforts are going on worldwide to monitor rust diseases, identify rust pathotypes, and to evaluate wheat germplasm for rust resistance. Anticipatory breeding and the responsible deployment of rust resistant cultivars have proven to be effective strategies to manage wheat rusts. Efforts are still however being made to decipher the recurrence of wheat rusts, their epidemiologies, and new genomic approaches are being used to break the yield barriers and manage biotic stresses such as the rusts. Efficient monitoring of pathotypes of Puccinia species on wheat, identification of resistance sources, pre-emptive breeding, and strategic deployment of rust resistant wheat cultivars have been the key factors to effective management of wheat rusts in India. The success in containing wheat rusts in India can be gauged by the fact that we had no wheat rust epiphytotic for nearly last five decades. This publication provides a comprehensive overview of the wheat rust research conducted in India.