Publisher Summary This chapter provides an overview of distribution, importance, and control of wheat leaf rust. Wheat leaf rust, caused by Puccinia recondite, usually does not cause spectacular damage; however, on a worldwide basis, it causes more damage than other wheat rusts. The leaf rust organism can be grown in axenic culture, although growth is limited. Therefore, although availability of nutrients in the host influences the rate and amount of rust development, specific nutrients are not likely to be responsible for the specificity shown in gene-for-gene interactions. Wheat leaf rust occurs wherever wheat is grown, and it is the commonest, most widely distributed of all cereal rusts. The chapter describes the mechanisms that most likely contribute to the evolution of leaf rust races—asexual recombination, alternate hosts, and mutation. Avirulence in leaf rust is usually dominant; a recessive mutation to virulence at one allele of any locus can, therefore, only be detected by selfing cultures on the aecial host. Thus, when a part of a rust population is heterozygous for virulence at a particular locus, a mutation occurring at the other allele would result in a virulent strain in the rust population.

Wheat Leaf Rust

Ni is the most recent candidate to be added to the list of 13 essential mineral elements for higher plants although failure to complete the life cycle in the absence of Ni has only been demonstrated in a few plant species. Ni is considered an essential element primarily because of its function as an irreplaceable component of urease which is responsible for the hydrolysis of urea N, and which seems to be the only proven nutritional function of Ni in higher plants. For production of full urease activity and growth on urea N a critical deficiency level of around 100 μg kg—1 DW seems appropriate, while plants depending on mineral N may have a lower Ni requirement. Ni has also other effects on plant growth, of which the phytosanitary action is possibly most significant in the field. The incorporation of Ni into urease apoprotein requires the active participation of several accessory proteins, and mutations in genes coding the accessory proteins as well as the urease apoprotein have been exploited to characterise aspects of urease activation. The mobility of Ni within the plant, as compared to other heavy metals, is usually high, although little is known of the uptake mechanisms and the form of transported Ni under Ni-deprived conditions. This as well as other effects of Ni that cannot be related to its structural component of urease, remain to be elucidated.



Die Bedeutung von Nickel fur das Wachstum und den Stoffwechsel von Pflanzen



Ni ist der jungste Kandidat fur die Liste der bisher 13 essentiellen mineralischen Nahrelemente hoherer Pflanzen, obwohl der Beweis fur seine Notwendigkeit zur Vollendung des Lebenszyklus einer Pflanze erst bei wenigen Arten gelang. Die Essentialitat von Ni begrundet sich insbesondere auf dessen Funktion als unersetzlicher Bestandteil des Enzyms Urease, welches die Hydrolyse von Harnstoff katalysiert. Dies ist die bislang einzige nachgewiesene Funktion von Ni in der hoheren Pflanze. Hinsichtlich des Wachstums harnstoffernahrter Pflanzen und der Ureaseaktivitat konnte ein kritischer Gehalt von etwa 100 μg kg—1 TM abgeleitet werden, wahrend Pflanzen, die mineralischen N erhalten, einen wesentlich geringeren Ni-Bedarf haben. Ni hat noch weitere Effekte auf das Pflanzenwachstum, von denen die phytosanitaren Wirkungen unter Feldbedingungen sicherlich die wichtigsten sind. Der Einbau von Ni in die Ureaseapoproteine erfordert die aktive Beteiligung mehrerer akzessorischer Proteine und Mutationen der Gene, die diese akzessorischen Proteine und die Ureasestrukturgene kodieren, wurden erfolgreich zur Aufklarung zahlreicher Aspekte der Ureaseaktivierung eingesetzt. Die innerpflanzliche Mobilitat von Ni ist, verglichen mit anderen Schwermetallen, normalerweise relativ hoch, doch liegen nur wenige Informationen uber die Ni-Aufnahme und transportierten Ni-Spezies bei niedrigem Ni-Angebot vor. Diese und andere Aspekte der Ni-Ernahrung, die nicht auf dessen strukturelle Bedeutung in der Urease zuruckgefuhrt werden konnen, harren ihrer Untersuchung.

Significance of nickel for plant growth and metabolism

Wheat leaf rust, caused by Puccinia triticina Eriks., is of worldwide concern for wheat producers. The disease has been an annual problem for Canadian wheat producers since the early days of wheat cultivation in the 1800s, and research focused on combating this disease began in the early 1900s. Significant progress was made towards understanding the epidemiology of wheat leaf rust and developing genetic resistance in many countries worldwide. This review paper focuses exclusively on the research and development done in whole, or in part, in Canada. An integrated approach to controlling wheat leaf rust consisted of research in the following areas: the early research on wheat leaf rust in Canada, breeding and commercialization of high quality rust resistant wheat cultivars, discovery and genetic analysis of leaf rust resistance genes, the population biology and genetics of the P. triticina/wheat interaction. This review summarizes the research in each of these areas and the connections between the d...

A review of wheat leaf rust research and the development of resistant cultivars in Canada

The importance of seed Ni reserves for plant growth and N metabolism is poorly understood This study investigated the effects of both seed Ni and externally supplied Ni on the impact of foliarly-applied urea and N-nutritional status of soybean Soybean seeds were produced by growing plants in nutrient solutions containing different Ni levels, and their urease activities were measured Plants were then grown from these seeds with or without external Ni After treating half of the plants with foliar urea, the urea damage symptoms, elongation rates and chlorophyll concentrations were followed over one week Biomass and mineral concentrations of different plant parts were determined Nickel supply at increasing rates improved seed yield by up to 25 % Seeds with Ni concentrations varying between 004–832 mgkg−1 were obtained Depending on the Ni concentration, the seed urease activities differed up to 100-fold Leaf damage due to foliar urea spray was significantly alleviated by higher seed Ni as well as external Ni supply Higher Ni also promoted shoot elongation and improved chlorophyll concentrations Nickel was 10-times more concentrated in the youngest part than in older leaves In the absence of foliar urea, Ni enhanced the N concentration of the growing part of the shoot by up to 30 % A better utilization of foliarly-applied urea-N is achieved in soybean when adequate Ni is supplied to plants by seed reserves and/or externally High seed Ni levels are also required for preventing foliar urea damage and improving N remobilization

Nickel-enriched seed and externally supplied nickel improve growth and alleviate foliar urea damage in soybean

Nearly a decade has elapsed since Dickson (19) reviewed the subject of chemical control of cereal rusts. He concluded that available chemicals do not appear to be an economical means of control of rust. He also noted that basic research is a prerequisite to the development of effective chemi­ cal control. The tempo of basic research on the cereal rusts has increased since his review. The most notable accomplishment of the past decade has been the cultivation in vitro of Australian isolates of the wheat stem rust fungus (99, 100) and the confirmation thereof (15). The progress of physio­ logical and biochemical studies of rust uredospores and infections were recently reviewed by Staples & Wynn (89) and Shaw (80, 81). Progress in the development of chemical control has resulted from empiri­ cal searches for effective chemicals and from applied studies to evaluate the performance of these chemicals in the field. Economically feasible control of rust often was achieved with some chemicals by properly timing applica­ tions to the stage of development of rust and host. Knowledge of the epi­ demiology of the cereal rusts has improved, partly as a result of the mathe­ matical concepts formulated by Van der Plank (92), and partly by new approaches to field observations. The present review examines the rela­ tionships between factors governing the development of rust epidemics and the mode of action of various chemicals that affect chemical control of cereal rusts, with emphasis on stem rust of wheat caused by Puccinia graminis Pers. £. sp. tritici Eriks. and E. Henn.

Chemical Control of the Cereal Rusts

Introduction 486 Inorganic Sulfur Compounds 488 Organic Sulfur Compounds 489 Copper Compounds 490 Mercury Compounds 490 Boron, Selenium, Fluorine, Iron, Lithium, Manganese, Nickel 491 Phenolic Compounds 491 Quinones 492 Heterocyclic Nitrogen Compounds 492 Oxines or 8-Quinolinols and Derivatives 492 Other Organic Compounds 4........9....3 ....... 493 Antibiotics and Derivatives 493 Herbicides and Plant Growth Regulators .... 494 Chemical Composition and Metabolism ......... 494 Basic Research A Prerequisite to Chemical Control of Rusts 500 Literature Cited 50.... 2 ........ 502

J. G. Dickson

Papers

Chemical control of cereal rusts