RA 00110.pdf - OAR@ICRISAT

Stunt and Counter-Stunt Symptoms in Pearl Millet Downy Mildew
(Symptomes de rabougrissement et de retablissement ulterieur dus au mildiou du mil)
S.L. Ball
Plant Pathologist, Department of Agriculture, University of Reading, Earley Gate, P.O. Box 236, Reading
RG6 2AT, Berks, UK
Stunting is a form of symptom expression exhibited by particular cultivars of pearl millet in response to
infection by Sclerospora graminicola. Such cultivars are susceptible to infection by the fungus, but do not
permit fungal sporulation and therefore limit disease spread, which gives the crop a considerable advantage
over cultivars which allow normal sporulation. Previous evidence showed that stunting was a feature of host
genotype, was unaffected by the pathogen genotypes, and was potentially a durable character. However, field
reports from India suggest that the stunt character is breaking down. Experiments were conducted to
investigate possible explanations for this phenomenon. When a pathogen collection from Zambia was
included in tests on a stunt host, hybrid BJ 104, the proportion of stunted plants was repeatedly lower than
with other pathogen collections. Consequently there could be elements in the pathogen genotype able to
overcome the stunt reaction. Conversely, the incidence of stunting differed between seed stocks of BJ 104
collected from different multiplication sites. Occasionally it was also noted that plants that stunted early may
recover. Epifluorescence microscopy was used to compare diseased tissue. Mycelium in stunted plants were
deformed and restricted. Treatment with the fungicide metalaxyl produced similar effects on the fungus and
treated plants recovered from the disease. The possibility that effects of stunting and metalaxyl on the fungus
may be related is discussed.
Studies on Pearl Millet Rust
(Etudes sur la rouille du mil)
K.B. Sharma
Agricultural Research Station, Durgapura, Jaipur, Rajasthan, India
and
V.N. Pathak
Department of Plant Pathology, College of Agriculture, Sukhadia University, Udaipur, Rajasthan 313 001,
India
Detailed studies were undertaken on five single-spore cultures of Puccinia substriata var. indica, incitant of
pearl millet rust in Rajasthan. Preinoculation exposure of the host to high humidity did not influence infection
and disease development while postinoculation exposure was found necessary. Incubation period decreased
with increasing duration of exposure to high humidity. Maximum disease levels occurred at 22°C. Light was
essential for the disease development. The incubation period increased with a decrease in light intensity. The
urediniospores survived for 40 weeks in glass vials at 5-8°C, 5 weeks under open field conditions, and 6 weeks
under tree shade. When buried in the soil they did not survive for more than 3 weeks. Teliospores remained
viable for 9 mo at room temperature, 8 mo under tree shade, and 7 mo under open field conditions. In
inoculation tests, Pennisetum americanum and Solatium melongena were found susceptible to the rust
pathogen.
Loss in grain yield was directly correlated with an increase in the coefficient of disease index (CODEX). A
fungicide, Baycor, caused 100% inhibition of urediniospores at 100 g ml -1 in vitro and provided maximum
disease control (94.5%) under field conditions.
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