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Rhynchosporium Secalis (Oud.) Davis and Barley Leaf Scald in South Australia

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Rhynchosporium Secalis (Oud.) Davis and Barley Leaf Scald in South Australia *^'lii i;['tìrulrr LIßI{ÅIìY Rlrynchosporíum secølis (Oud.) Davis and Barleyl-eaf Scafd in SouthAustralia J.^4. Davidson Depar"lrnent of Plant Science Thesis submitted for Master of Agricultural Science, University of Adelaide, MaY, L992 Pæp AIMS I LITERATIIRE REVIEW 1ll CHAPTER 1: SURVEY OF THE PATHOGENICITY RANGE OF RITVNCHOSPORIUM SECALIS, THE CAUSAI PATHOGEN OF BARLEY LEAF SCALD, IN SOUTH AUSTRALIA. INTRODUCTION 2 GENERAI MATERIALS 2 A. MOBILE NURSERIES Materials and Methods 4 Results 6 B. GLASSHOUSE TESTING Materials and Methods 16 Results 18 C. DISCUSSION % CHAPTER 2: MEASUREMENT OF RESISTANCE TO RHYNCHOSPORIUM SECALIS IN BARLEY, IN THE FIELD AND THE GLASSHOUSE. INTRODUCTION 38 A. FIELD SCREENING Materials and Methods 39 Results 42 B. GLASSHOUSE SCREENING Materials and Methods 46 l) CoupARrsoN oF SpRAy INocur,¿.uoN AND SINGLE DROPLET INOCULATION (i) Spray Inoculation Materials and Methods 47 Results ß (ii) Single Droplet Inoculation Materials and Methods 53 Results 53 Discussion 57 B) MEASUREMENT OF DISEASE COMPONENTS (i) Comparison of four Rhynchosporiurn secalis pathotypes 1 Materials and Methods 58 {,t Results 60 (ii) Effect of inoculum concentration Materials and Methods 72 Results 73 (iii) Measurement of disease components on sixteen barley lines Materials and Methods 80 Results 81 C. DISCUSSION m I CHAPTER 8: YIELD LOSSES IN BARLEY ASSOCIATED WITH LEAF SCALD 4 ,t,l it INTRODUCTION gI, Materials and Methods 95 Results 103 i L DISCUSSION TN 'tj 'l i CHAPTER 4: GENERAL DISCUSSION 7ß I APPEÎ{DICES II ji ,l 't itl i'l "l BIBLIOGRAPITY XXVII ll f,,{ ,] l ! I : I I fl Abstract Title: Rhynchosporium secalis (Oud.) Davis and Barley Leaf Scald in South Australia. by J.A. Davidson Mobile nurseries were used to identify races of ,R. secalís in the field. Results were influenced by environmental and genetic effects. Isolate race testing in the glasshouse produced inconsistent and extremely variable results. Cultivar infection rates in mobile nurseries and glasshouse tests \Mere comparable when'races' \üere disregarded. Measurement of disease symptoms (incubation period, spore production, infection rate) in the glasshouse produced inconsistent results. The isolate used affected all factors measured, while barley genotype only influenced the cultivar infection rate. Other factors affecting results rwere the inoculum concentration, culture viability, culture age and variable glasshouse conditions. Correlations between the glasshouse cultivar infection rate and cultivar freld disease levels (VoLeaf Area Diseased (7ioLAD)) varied from nonsignifrcant to highly significant. The highest correlations occurred when glasshouse infection rates were compared to the ToLAD recorded from midseason to late in the growing season. Best results occurred if 'races' were disregarded. Measurement of disease in freld trials resulted in a continuum of disease levels from 0 VoLAD to 100 VoLAD, rather than discrete groupings of resistant and susceptible types. Yield loss occurred as the result of disease at any stage of the growing season and all yield parameters may be affected. Field VoLAD and freld infection rates were well correlated, especially at midseason. It was concluded that races should be disregarded in the study of R.secalís. While major genes are defïnitely involved in the inheritance of scald resistance, the suspected presence of modifi.ers affects the expression of the disease, and this is further influenced by environmental factors. This thesis contains no material which has been accepted for the award of any other degree or diploma in any University, and. that, to the best of my knowledge and belief, the thesis contains no material previously published or written by another person, except where due reference is made in the text of the thesis. I consent to the thesis being made available for photocopy and loan if accepted for the award of the thesis. Acknowledgements Funding for this project was made available by the Barley Industry Research Council and was administered by the South Australian Department of Agriculture. Dr. A. Mayfield and Dr. A. Dube from the Department of Agriculture acted in a supervisory capacity. Special thanks to Dr. D. Sparrow, from the Department of Plant Science, Waite Agricultural Research Institute for his patience and understanding, as well as supervision. The Barley Breeding Unit, at the Waite Institute, headed by Dr. D. Sparrow, assisted with handling of field trials and made breeding material available for this project. AIM S This study was designed to produce more information about the fungal pathogen Rhynchosporium secalis and the effect of the disease it causes, barley leaf scald, upon the barley crop in South Australia. Information from this study should aid in resistance breeding efforts against this pathogen. Four aims were set out in this study. 1. The identification of races or pathotypes in the naturally occurring population of R.secalts in southern Australia. 2. To test the ability of known resistance genes to suppress disease development in the field when presented with a wide raîge of R.secalis pathotypes collected in southern Australia. 3. To develop glasshouse screening tests that would reflect the same order of resistance or susceptibility of barley lines as was seen in the field. 4. To identify how scald disease damages barley crops in South Australia, and the level of disease that is tolerable ie. does not result in a yield reduction. This would aid in the selection of partially resistant barley lines. Âtgl^uu flun'tvusüT iii hrfu.oduction Barley leaf scald is a leaf disease of barley which has been reported in many parts of the world. Several common names in use are leaf blight, leaf blotch, leaf spot and leaf scald. Designation of the disease as leaf scald \Mas supported by North American workers who claimed that it was distinctive and would not be confused with other cereal diseases (Caldwell, 1937). The disease began to increase in signifìcance in different countries from the 1940's to '60's (Reed, L957, Skoropad, 1960, Connold, 1963, Campbell, !964, Doling, 7964, Hansen and Magnus, L968, Ktg, 1972), probably due to increased barley production. This in turn lead to earlier seeding and shortening of crop rotations, and the use of winter crops. Such measures provided a year round host for the fungus. Other factors probably contributing to the increased incidence of leaf scald were the use of combine harvesters which scattered straw and the release of mildew resistant but scald susceptible varieties (Skoropad, 1960, Doling, \964, Jenkins and Jemmett,t967, Ktg, 7972). The causal organism of leaf scald is the fungus Rhynchosporium secalis (Oud.) Davis. Its earliest recorded occurrence \üas in 1894 in Germany when Frank examined herbarium specimens of barley that revealed the presence of leaf scald (Caldwell, 1937). It was originally isolated from rye and described, in 1897, by Oudemans who named it Marsonia seca,Iis, later changed to Marssonino, secalis. Its genus was later transferred to Rhynchosporium because of its beaked shaped spores, and given the specifïc name graminicolø Heinsen. Finally Davis in the United States named it Rhynchosporium secøIis (Oud.) Davis, in accordance with the International Rules of Nomenclature (Brooks, 1928). iv The fungus can attack any part of the barley leaf, from seedling to senescence (Skoropad, 1960), producing blotches of irregular shape. To a lesser degree the sheath is also attacked (Caldwell, 1937). The auricles are commonly attacked, possibly due to water being held in this region (Brooks, 7928, Smith, 1937 , Gilmour, 1967). The blotches frrst appear as blue-green water-soaked areas and then produce dark-brown edges with lighter centres. These lesions can coalesce and destroy the entire leaf (Brooks, 1928, Caldwell, 7937, Smith, 7937, Gilmour, 7967, Ozoe,1956). Successive enlargements of lesions may occur giving a zottate appearance (Caldwell, 1937). Occasionally elongated lesions appear which resemble those of barley leaf stripe (Helminthosporium gramineum) brú leaf scald lesions can be distinguished from these by their dark margins (Smith, 1937). Awns and grain (Iemma and palea) may also be infected (Ozoe, 1956, Skoropad, 1960, Gilmour, 1967). Studies on the development of leaf scald on field sown plants have shown that the distal parts of the seedling leaves are liable to infection, while in older plants the middle or basal parts are more commonly affected (Janakiram, 1980). Serious upper canopy leaf damage arises from the transfer of secondary inoculum from the first infected leaves, prior to stem elongation. About two weeks before anthesis there is an explosion of symptoms through the leaf canopy which may result in the defoliation of susceptible types (Janakiram, 1980). V Inoculum (i) Host Debris The disease can initially appear in crops due to infection from barley refuse (Caldwetl,t937, Ozoe, 1956, Reed, L957, Doling, 1964, Ayesu-Offei and Carter, 1970, Polley, 1971). The fungus survives between seasons as dormant mycelium in plant debris and sporulates under the right conditions of moisture, temperature and light (Caldwell, L937, Skoropad, 1960). The activity of the stroma within the debris is confrned to sporulation. Saprophytic growth within or beyond lesions on dead leaves is not detectable. Seedlings may be infected as they emerge and touch the debris or by splashing of spores, via raindrops (Reed, 1957). Scald lesions appear in about 12 days following the frrst rain after the emergence of seedlings (Skoropad, 1960). Skoropad
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