The Relation of Temperature to the Development of Disease in Plants

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Abstract
The discussion is directed towards (a) the influence of temp. upon the development of a definite group of diseases, (b) the application of this to selection for disease resistance, and (c) the nature of the resistance to disease in these special instances. Seedling blights of wheat and maize caused by Gibberella saubinetti are greatly influenced by temp. Wheat seedlings blight in a warm soil, but not in a cold soil; conversely, maize seedlings blight in a cold soil, but escape blight in a warm soil. Cortical invasion and decay was found to be due to an unbalanced metabolism within the seedling during early germination, as a result of which the cell walls of the protective tissues were composed of pectin-like substances instead of cellulose reinforced with lignin in wheat, or suberin in maize. The walls, therefore, were readily hydrolyzed, which resulted in an invasion by the parasite. Selection for resistance in segregating inbred lines of maize grown in cold soils infested with the parasite offered a means for securing resistant lines of maize which grew well at low temp. A further analysis of these lines in contrast with susceptible lines of maize revealed that the "inheritable resistance" is similar in nature to the "induced resistance" brought on by high soil temp. Resistance apparently is brought about by an intensification and stabilization of factors controlling a balanced seedling metabolism. As a result, cellulose walls reinforced with suberin occur which are unsuited to the nutritive requirements of the parasite through a wide range of unfavorable environmental conditions.

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