The effect of pH value on the toxicity of culture filtrates ofHelminthosporium Sativum and on its possible correlation to extracellular nitrogen accumulation
Helminthosporium sativum P.K. & B. was grown on modified Fries No. 3 medium buffered at pH 4.7, 5.5, 6.7, and 7.8. The nitrogen content of the culture filtrate, mycelial growth and the toxicity of the filtrate (as measured by its wilt inducing capacity to lupin seedlings) were traced over 24 days. The correlation between nitrogen accumulation and the toxicity of the filtrates was clear in case of media originally buffered at 4.7, 5.5 and 7.8. On the other hand, there was no correlation between growth of the mycelial mats and toxin production. The toxicity of the filtrate was attributed to two substances at least, one of unknown composition produced during the accelerated growth phase, while the other is nitrogenous and produced during the decline growth phase i.e. autolytic in nature. Acidity of the medium favoured toxin production during the first two weeks of incubation. The toxicity of the filtrate remained stable within a wide range of pH between pH 3–9.4.
The pathogenicity of six strains of Helminthosporium sativum to three cereals with special reference to barley
The pathogenicity of 6 strains ofHelminthosporium sativum P.K. & B. isolated from either oats, wheat or barley was studied. Oats was resistant to all strains followed by wheat while barley was susceptible. Barley variety Balder was the most resistant while Piroline was the most susceptible. Susceptibility of Piroline was manifested by higher percentage infection, bigger necrotic areas and wilting of the infected leaf. Toxic filtrates of the different strains could reproduce necrosis, wilting or chlorosis on cut leaves. Response of Balder and Piroline was similar in the filtrates of three strains, while in those of the other three Balder was more resistant. Formation of at least 2 toxic substances in the host tissues, one responsible for wilting and the other for necrosis, was suggested. No correlation was found between the dimensions of the spore or the number of its constituent cells and the virulence of the strain.
GROWTH AND METABOLISM OF ASPERGILLUS NIDULANS EIDAM IN SURFACE CULTURE
Aspergillus nidulans was grown on glucose, fructose, sucrose, or maltose in a high-sugar medium favorable for fat formation. Glucose was more readily metabolized than the other sugars, giving a heavy felt with the highest fat content in a shorter time. Sucrose was inverted before absorption and was more conducive to growth than to fat formation. Maltose was probably absorbed after hydrolysis. It gave a heavy felt and a high fat yield but after a longer period of incubation than with glucose. Maltose metabolism was marked by lower nitrogen utilization. Hence, the maltose-fed mycelial felts had the highest carbohydrate content and the lowest protein content.Growth proceeded as long as there was available sugar in the culture medium. Extracellular nitrogenous compounds appeared in the culture media before the complete exhaustion of the sugar in some cases, providing evidence that this process is not purely autolytic in nature. The early growth phase on the different sugars was characterized by low-fat, high-...