Fungi associated with root rot of irrigated safflower in the Namoi Valley, New South Wales

Abstract

Root rot is an important disease of irrigated safflower in the Namoi Valley. Affected Plants wilt, become chlorotic and often die, especially when the crop is young. Below ground the wilted plants exhibit severe pruning of the lateral roots and the tap root itself may be rotted in extreme cases. Extensive culturing of the lateral roots of diseased plants in the field and from plants growing in naturally infested field soil in a growth cabinet yielded 1757 isolates of fungi, comprising 10 genera and some sterile species However, the preponderance of Pythium ultimam and P. debaryanum among isolates from diseased roots and the pathogenicity of these to safflower suggests that they are the primary cause of the disease in the field None of the other fungi was shown to be capable of inducing root rot in seedling plants. We suggest that extensive physical damage caused to plant roots by the movement of the self-mulching soils of the Namoi Valley predisposes the roots to infection by unspecialized parasites such as P. ultimum and P. debaryantlm