This disease was previously known as ‘Lupin Sudden Death’. The causal organism has since been identified as Phytophthora spp., hence the change in name to phytophthora Root Rot. This disease has been seen sporadically in lupin crops in southern New South Wales and parts of Victoria for several years, especially in crops that have been waterlogged.
The disease causes sudden wilting and death of lupin plants within days during pod filling. Leaves suddenly turn yellow and drop, often within a 24 hour period. A dark sunken lesion may extend from the base and often up one side of the stem.
Infected plants are found to have a rotted taproot when pulled out of the ground. The taproot is woody in appearance with little if any outer tissue remaining and with few, if any, lateral roots, (Figure 9.7).
The pattern of distribution within a crop can vary from single scattered plants to large areas of crop often in low lying areas. Plants fail to fill pods or produce small seed.
Figure 9.7 Lupin plants with typical rotted root system, and lower stem lesions
The fungus survives in the soil and becomes established when a new crop is sown. To date it is not known what other hosts carry this fungal pathogen between lupin crops. However, there appears to be several essential prerequisites for this disease to develop. Soil temperatures must be above 15°C for symptoms to appear. This explains why symptoms in the field do not appear until early spring as soil temperatures rise. A period of waterlogging also appears to be required for root infection to occur. Experiments have shown that narrow leafed lupins survive flooding for at least 8 days in the absence of phytophthora, but die within a short period when the pathogen is present.
To date more work is required to determine the exact cycle of this disease. The species of the pathogen is still yet to be determined and may even be a new, previously unknown species.
At this early stage it is difficult to recommend management strategies. However, the most effective practice that can be recommended would be to avoid paddocks that are prone to water logging or are known to have a hardpan problem that could result in the formation of perched water tables.
PHOMOPSIS STEM AND POD BLIGHT OF LUPINS
ANTHRACNOSE OF LUPINS