This paper originates from an address at the 8th International Symposium on Nitrogen Fixation with Non-Legumes, Sydney, NSW, December 2000 Azospirilla are free-living rhizobacteria that are able to promote plant growth and increase yields in many crops of agronomic importance. It is assumed that the bacteria affect plant growth mainly by the production of plant growth promoting substances, which leads to an improvement in root development and an increase in the rate of water and mineral uptake. In the present review, we discuss the physiological responses of the plant roots to inoculation with Azospirillum, and report on field and greenhouse experiments carried out with these bacteria during 1994–2001 in Belgium, Uruguay, Mexico and Israel.

Various aspects of the integration of genotype resistance and chemical control of Ascochyta blight (caused by Didymella rabiei) in chickpea were examined in field experiments from 1993 to 1999 and in greenhouse experiments. Four commercially available chickpea cultivars representing a range of resistance to D. rabiei were used. The efficacy of chemical control in a highly susceptible cultivar was significantly (P < 0.01) related to the conduciveness of the environment to the pathogen. Adequate disease suppression (>80% control) was achieved when weather supported mild epidemics, but insufficient control (<20%) was achieved when weather supported severe epidemics. The contribution of genotype resistance to disease suppression in a moderately susceptible cultivar varied from <10% when weather supported severe epidemics to approximately 60% when weather supported mild epidemics. Spraying a moderately resistant cultivar resulted in 95% control when weather supported mild epidemics, but only 65% control was achieved when weather supported severe epidemics. The existing level of resistance in a moderately resistant cultivar resulted in 70% control when weather supported severe epidemics; fungicides improved control efficacy significantly to >95%. Under mild epidemics, moderate resistance alone provided >95% control. The level of genotype resistance available in a highly resistant cultivar was sufficient to suppress the disease under all weather conditions, even without application of fungicides. The possibility of relying on postinfection rather than prophylactic application of fungicides was tested in the greenhouse and in four field experiments. Activity of the systemic fungicide tebuconazole was detected when the fungicide was applied up to 3 days postinfection, and application of tebuconazole or difenoconazole in the field as a postinfection treatment (i.e., after rain or overhead irrigation) suppressed the disease as effectively as preventive applications and required fewer sprays. In two experiments, the interaction between genotype resistance and chemical control at various amounts of irrigation applied via overhead sprinklers (as a simulation of rain) was tested. The results show that both the level of genotype resistance and the quantity of water should be taken into account in deciding whether to apply a postinfection spray.

The significance of preventing primary infections resulting from the teleomorph stage of Didymella rabiei was tested in field experiments in 1998 and 2000. Control efficacy was greater and yield and its components were higher in plots where the fungicide difenoconazole had been sprayed in time to protect the plants from infections resulting from airborne ascospores than in plots where sprays were not applied on time. Forty empirical models reflecting the influence of temperature and interrupted wetness on initial maturation of D. rabiei pseudothecia were developed and verified by using data recorded in chickpea fields in 1998. Seven of the models then were validated with data recorded in 1999 and 2000. The following model provided the best predictions: starting at the beginning of the rainy season (October to December), the predictor of the model was assigned one severity value unit when there was a rain event (1 day or more) with ≥10 mm of rain and an average daily temperature (during the rainy days) of ≤15°C. According to the model, pseudothecia mature after accumulation of six severity values and ascospores will be discharged during the following rain.

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