This disease is caused by the oomycete Phytophthora medicaginis. In northern New South Wales this disease is a serious constraint to production but is rarely seen in southern Australia. At present phytophthora root rot is often the most serious disease of chickpeas grown in northern Australia and as a consequence it poses a potential threat to chickpea production in wetter regions.
The disease is usually observed late in the season but may also affect young plants. Badly affected seedlings suddenly wither and die with no obvious disease symptoms.
Infected plants are often stunted with obvious yellowing and drying of the foliage. They have few lateral roots and the lower portion of the tap root is often decayed. The remaining tap root is usually discoloured dark brown to black, (Figure 5.13). Sometimes the discolouration can extend to the base of the plant. The advancing margins of the lesions may also have a reddish-brown discolouration.
Figure 5.13 Healthy chickpea plant (far left), compared to phytophthora infected plants. Note lack of lateral roots and discoloured root tissue
The fungus survives in soil, plant debris and on other hosts, in particular lucerne.
The disease has been most severe in fields where previous lucerne stands have been affected by phytophthora root rot. In wet soils, spores of the fungus are released and attack the developing roots of susceptible plants. If soils remain wet the disease rapidly spreads to other plants, (Figure 5.14).
Figure 5.14 Disease cycle of Phytophthora root rot of chickpeas. Illustration by Kylie Fowler
PHOMA STEM ROT OF CHICKPEAS
BOTRYTIS GREY MOULD OF CHICKPEAS