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RESISTANCE of WHEAT to SEPTORIA NODORUM BERK. by Elizabeth Anne Baker B.Sc.(Lond.) a Thesis Submitted in Part Fulfilment Of

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RESISTANCE of WHEAT to SEPTORIA NODORUM BERK. by Elizabeth Anne Baker B.Sc.(Lond.) a Thesis Submitted in Part Fulfilment Of RESISTANCE OF WHEAT TO SEPTORIA NODORUM BERK. By Elizabeth Anne Baker B.Sc.(Lond.) A thesis submitted in part fulfilment of the requirements for the degree of Doctor of Philosophy of the University of London Department of Botany and Plant Technology, Imperial College of Science and Technology, Silwood Park Field Station, Ascot, Berkshire. October 1975 ABSTRACT In laboratory tests on detached leaves wheat cultivars infected by S. nodorum showed continuous variation in symptoms through different degrees of necrosis, chlorosis and lesion extent. There was a dis- appearance of surface wax under the hyphae and appressoria. Although surface growth was similar in resistant and susceptible cultivars, colonisation within the leaf, in the former case, was less and restricted to the area beneath the infection droplet. No structural barriers were observed and staining reactions for lignin were negative. The exact relationship of the hyphae to the host cells could not be ascertained. At low inoculum concentrations lesion development was delayed, and in the resistant cultivar lesions often failed to develop at all. The intensity of the browning/necrotic reaction was partly suppressed in the dark and coalescence of lesions in the susceptible cultivar was prevented at 25°C. Liquid cultures of S. nodorum failed to yield any phytotoxic principles. In the field inoculations at later growth stages resulted in higher overall % infection compared to the earlier inoculations. On resistant plants fewer lesions developed and less of these spread than on the susceptible ones. High yielding cultivars had a lower % infection and lower infection rate on.the flag leaf and ear compared to the lower yielding cultivars, although in the former case a high % infection of Lile - lower leaves resulted in an apparently higher total % infection. Levels of the antifungal benzoxazolinone derivatives were shown to decrease with age; these substances could not be detected in plants over 2-3 weeks old. Other compounds, which remain to be identified, but which were active against S. nodorum, were extracted from plants at all growth stages. There were no qualitative differences between resistant and susceptible cultivars, but generally speaking the extracts from the resistant cultivar were more active. Infected tissue extracts were usually more inhibitory to S. nodorum than the extracts from healthy control material. CONTENTS Page ABSTRACT 2 INTRODUCTION AND LITERATURE REVIEW 8 MATERIALS AND METHODS 116 A. Fungi 16 B. Culture media 16 C. Plant material 18 D. Inoculation procedure , 20 E. Observation of leaf surfacqs 22 F. Preparation of material for light microscopy 22 G. Preparation of material for stereoscan 24 electron microscopy H. Extraction of plant material 25 J. Separation and purification techniques 25 K. Location and estimation of substances 27 L. Field experiments 31 M. Statistical analyses 33 EXPERIMENTAL RESULTS SECTION 1: Varietal reactions on detached leaves and 36 factors affecting their development Varietal reactions, 37 Macroscopic and microscopic development 41 of the resistant and susceptible reactions Effect of centrifugation of spores on 56 subsequent lesion development Effect of spore concentration on lesion 59 development Effect of light and temperature on 62 lesion development Investigation of the possible toxic 65 effect of S.nodorum DISCUSSION 72 SECTION 2: Development of S.nodorum infection on 77 winter and spring wheat in the field Field experiment 1A: The effects and 78 possible interactions of inoculation date, variety and leaves on development of S.nodorum infection on winter wheat. Development of S.nodorum infection 81 Analysis of variance (whole plants) 88 Meteorological conditions 1974 90 Microclimate of the crop canopy 93 Differences between parts of plant 98 Analysis of variance (parts of plant) I00 Apparent infection rates 104 Summary of infection data 108 Field experiment 18: A detailed study II0 of infection in naturally infected and artificially inoculated plants of winter wheat. Increase of lesion number and %infection 112 for flag and second leaves of winter wheat Meteorological conditions 1975 120 Statistical analysis 123 Summary 125 DISCUSSION 127 Field experiment 2A: The effects and 132 . possible interactions of inoculation date, variety and leaves on development of S.nodorum infection on spring wheat Development of S.nodorum infection 134 Analysis of variance (whole plants) 140 Meteorological conditions 142 Differences between parts of plant 143 Apparent infection rates 145 Summary of infection data 148 Field experiment 28: A detailed study of 150 infection in naturally infected and artificially inoculated plants of spring wheat Increase of lesion number and %infection 151 for flag and second leaves and ears of spring wheat Meteorological conditions 161 Statistical analysis 162 Summary 164 DISCUSSION 166 SECTION 3: Studies on pre- and post-formed antifungal 169 compounds in winter wheat resistant and susceptible to S.nodorum I.The presence of pre- and post-formed 170 inhibitors of S.nodorum in crude and partially purified extracts of wheat tissues of varying ages 1.Healthy week old seedlings 170 2.Healthy and inoculated 30 day old glass- 172 house grown plants 3.Healthy and inoculated 7 week old glass- 177 house grown plants 4.Healthy and inoculated and naturally 183 infected 6 month old field grown plants Summary 188 II.Chromatographic separation and assay of 191 pre- and post-formed antifungal compounds in winter wheat of varying ages 1.Preformed inhibitors present in healthy 192 intact wheat plants '2.Potential antifungal compounds in healthy 195 intact wheat plants 3.Antifungal compounds in artificially 202 inoculated wheat 4.Antifungal compounds at various growth 219 stages in healthy and naturally infected field grown winter wheat Summary 21,5 III. The disappearance of the benzoxazinone 219 compounds in winter wheat resistant and susceptible to S.nodorum A.1.Glasshouse grown plants 219 2.Cooled cabinet grown plants 220 3.Field grown plants 220 B.1.Assessment of ferric chloride reaction 221 by optical density 2.Assessment of benzoxazinones by UV spectra 223 C. The levels of benzoxazinones in healthy 223 wheat plants DISCUSSION 228 FINAL DISCUSSION 232 BIBLIOGRAPHY 235 ACKNOWLEDGEMENTS 242 APPENDICES 243 1A. Weekly mean % S.nodorum infection, winter wheat 1974 244 18. Detailed study of infection, winter wheat 1975 263 Summary of data for 1974 270 Summary of data for 1975 271 2A. Weekly mean % S.nodorum infection, spring wheat 1974 2721 28. Detailed study of infection, spring wheat 1974 293 3. Spore droplet bioassays 330 INTRODUCTION AND LITERATURE REVIEW "Septoria - the lurking threat to wheat yields" This headline appeared in Farmers Weekly in 1973, and although Septoria disease of wheat has been recognised in England since 1845 (Berkeley) only recently has the extent of yield loss been appreciated. A three year (1970-1972) study by the Agricultural Development and Advisory Service, covering 500 acres on 300 farms showed that Septoria spp. caused worst diseases of wheat and were far more serious nationally than mildew or yellow rust. Yield reductions of up to 65% have been recorded (Jenkins and Morgan, 1969; BrOnnimann, Sally and Sharp, 1972). Also, since grain quality is adversely affected and quality requirements for selling wheat for denaturing are strict, the importance of the disease should not be underestimated. Septoria disease is important in the wheat growing areas of over 50 countries (CMI Plant Disease Distribution Map No. 397). Why has Septoria suddenly become so important? Disease build-up has resulted from a succession of mild winters and cool damp summers, combined with an increasing wheat acreage, particularly of the more susceptible dwarf cultivars (Scott, 1973). Emphasis on non-ploughing techniques which result in less efficient stubble cultivations is another factor. The two most prevalent species are Leptosphaeria (Septoria) nodorum Berk., and Septoria tritici Rob. ex Desm. The common names are leaf and glume blotch, and leaf spot respectively. Both species are specialised facultative parasites, which infect Triticum spp. to a high degree but can be made to weakly infect a number of other cereals and grasses (Weber, 1922; Schmiedeknecht, 1967; Dereveyankin, 1969; Shearer and Zadoks, 1972). So far no_physiological races are known, only differences in mycelial growth behaviour and sporulation ability (BrOnnimann, 1968a; Scharen and Krupinsky, 1970a). The symptoms of Septoria diseases are difficult to distinguish and identify, particularly in the early stages of infection when aporulating bodies are absent, and can be confused with natural senescence. The species Septoria nodorum has been used in this research. It can attack all aerial parts of the plant, although appreciable effects on yield -. only occur when the flag leaf and ear become heavily infected (BrOnnimann, 1968a). Penetration is by pycnidiospores, directly through the cuticle, after which=hyphae enlarge slightly and-grow intercellularly before entering the cells (Weber, 1922). However the exact relationship of the fungal hyphae with host cell walls remains to be determined, since it has proved impossible to stain hyphae satisfactorily within the leaf (Morgan, 1974). Lesions on the leaves occur most usually near the tip in natural infections, and appear as linear light brown spots with a yellow margin. In susceptible cultivars the lesions spread and coalesce, but they remain limited necrotic flecks in non-compatible reactions. On the
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