Development of methods to monitor and control Aphanomyces root rot and black root rot of beans
Aphanomyces root rot (ARR) is a soil borne fungal disease causing browning of roots and stems of green beans and in severe cases causing death of plants, often in combination with other pathogens. The fungus causing the disease is favoured by wet conditions and can build up rapidly in soil from low levels. Blocks with infected soil must remain free of beans for up to ten years to reduce the levels of the fungus. In soil surveys a number of bean farms were found to have the fungus, and therefore the potential of causing disease beans. Using a soil bioassay before planting can give a guide to the level of the disease in blocks that are to be planted. A DNA test for the organism developed in the project will also assist in the identification of soils with the fungus. A number of rotational crops were assessed for their potential to reduce ARR and some disease reduction was identified as well as enhancing bean growth. Other management tools for reducing ARR include improving drainage by planting on beds or hills and carefully monitoring irrigation. In variety screening trials, bean varieties showed no reduction in disease levels but some were stronger plants and able to reduce the affects of the disease. The fungus affecting beans was not shown to infect peas. Black root rot (BRR), causing blackening of stems and roots, is another soil borne fungus identified on bean farms. The fungus was found more in bean farms on Tasmania and Victoria, than in New South Wales. The fungus has a wide host range and appears to infect beans in cooler conditions. Varieties with better tolerance to the disease were identified and screening for resistance to the disease should be ongoing. Some bacterial based soil drenches improved bean plant establishment and vigour but did not reduce ARR or BRR. In trials a soil drench of a commonly used fungicide was found to assist in the control of ARR as well as Ashy stem blight, another soil borne fungal disease of beans. The project has identified diseases of beans, the specific symptoms of each of them, their occurrence in different growing regions, and methods to reduce disease.