Sis 74 / 



CONTENTS 



AGRIC. Pa _ 



UBRARY 



Introduction and historical review ........................................ 3 



Problem ............................................................... 4 



Methods ............................... ................................ 5 



Source of pathogene .................................................. 5 



Selection of host varieties ............................................. 6 



Check plants ............................... ......................... 6 



Specific identity of the pathogene ..................................... 7 



Temperature relations .................................................... J 6 



Growth of fungus on potato dextrose agar ............................ 16 



Spore germination .................................................. 18 



Effect of hydrogen-ion concentration and temperature on spore germination 21 



Infection ........................................................... 2 5 



Influence of type of soil .................................................. 27 



Influence of soil moisture ......... ....................................... 3 1 



Influence of soil fertility ................................ . ................ 39 



Comparison of several root-rot causing organisms ......................... 4 



Summery and conclusions ................................................ 44 



Literature cited ......................................................... 47 



ILLUSTRATIONS 



Fig. i. Types of curves obtained from measuring length of snores of 



Helminthosporium sativum produced on potato dextrose ........... n 



Fig. 2. Length of spores produced on potato dextrose agar at various 



temperatures .................................................. 15 



Fig. 3. Length of spores produced on different substrata at 24 C ............ 16 



Fig. 4. Growth of H. sativum on potato dextrose agar in Petri dishes ....... 17 



Fig. 5. Daily rate of growth of H. sativum on potato dextrose agar in Petri 



dishes ........................................................ 18 



Fig. 6. Percentage germination of spores in phosphoric acid-potassium 



hydroxide solutions of various hydrogen-ion concentrations ....... 23 



Fig. 7. Percentage germination of spores in Czapek's solution minus the 



sugar at various hydrogen-ion concentrations ..................... 24 



Plate I. Helminthosporium sativum P.K.B. grown on potato dextrose agar 



at different temperatures ........ ' ............................... 49 



Plate II. Helminthosporium sativum P.K.B. grown on potato dextrose agar 



at different temperatures ....................................... 50 



Plate III. Marquis wheat showing effect of Helminthosporium root-rot in 



different soils ................................................. 51 



Plate IV. Lion barley plants, 3 weeks old, growing on soils inoculated with 



various organisms ............................................. 52 



Plate V. Lion barley plants 3 weeks old showing effect of soil organisms 



on development of root systems ................................. 53 



Plate VI. Lion barley pl?nts, 3^ weeks old, showing effect of root infection 



by H. sativum P.K.B .................................... ........ 54 



