Techniques of Controlled-Condition Experiments

Abstract

When cultivation of specific crops was expanded beyond their traditional habitats, diseases, previously thought to be confined to specific environments, were found to appear also in the new, apparently adverse habitats. This phenomenon usually results from intensive cropping techniques which render originally adverse habitats more favourable to disease development. However, experiments under controlled conditions (CC) showed that some pathogens possessed hitherto unknown potentials that helped them to thrive under the new conditions. For instance, CC tests demonstrated that development of Phytophthora infestans is facilitated by dryness at a specific stage of its life cycle (Rotem and Cohen 1974). Other CC tests revealed that some pathogens which had been known to require prolonged wettings for infection succeeded in semi-arid habitats due to their ability to use several short wettings interrupted by dry intervals (Bashi and Rotem 1974). Only CC tests supply data on temperature and wetting requirements in discrete phases of the pathogen’s life cycle. Data from CC experiments assist simulation and forecasting programs and rationalize approaches to chemical and cultural control. Such contributions of CC experiments are well known und their merits need no further elucidation. Therefore, instead of repeating the advantages of studies in CC, we stress in this chapter the shortcomings encountered in such studies.