Tropical Grain Legumes Bulletin, (1978), 11, 24-5
by R. Sheldrake, A. Narayanan, J Kannaiyan
The symptoms of the pigeonpea wilt (causal fungus: Pusarium udum) generally appear during the reproductive phase, particularly while pod-filling is taking place (Mundkur, 1935).
In an off-season crop planted in December 1974 we observed that while there was a high incidence of wilt during the pod-filling phase of untreated plants, almost all the plants where pod development had been prevented by the removal of flowers remained healthy.
Conversely, we found that the incidence of the disease increased when the plants were defoliated during the reproductive phase. In an experiment carried out on medium- duration cultivars grown during the normal season (planted in June 1975) leaves were removed at the time flowering began, and subsequent defoliations were made as new leaves were produced. Different degrees of defoliation were employed: 33% (one leaf out of three removed), 50% (alternate leaves removed), 67% (two leaves out of three removed), 75% (three leaves out of four) and 100% (all leaves removed). We found that, in general, the incidence of the wilt increased with the severity of defoliation.
A second experiment was carried out on medium-duration plants (56 lines in the breeders' plots) which had been ratooned at the time of the harvest of the first flush of pods. These plants regenerated new branches and entered into a second reproductive phase, during which (on March 1 1976) one row of plants of each line was completely defoliated and another row was left as a control. Two months later the plants were scored for wilt. Of the controls, 16 out of 380 plants (4%) had wilted whereas 174 out of 360 defoliated plants (48%) had wilted.
Defoliation of plants in the ICRISAT patholigists' wilt-sick plot has also been found to lead to an increase in the incidence of the wilt disease.