RA 00015.pdf - OAR@ICRISAT

are numerous, only a few develop into mature
pods and the kernel size is considerably smaller.
Typical symptoms were observed in 3 to 4 weeks
on healthy plants grafted with diseased scions.
Using the buffer and antioxidant described earlier,
mechanical transmission was made to several
host plants. Chenopodium quinoa showed
chlorotic local lesions and the infection became
systemic. On soya (Glycine max cv. Bragg),
systemic mosaic mottling occurred. When
mechanically transmitted to groundnuts, the
vein-banding symptom was produced but no
axillary shoot proliferation, stunting, profuse
flowering, or peg formation occurred and the
subsequently formed leaflets were chlorotic and
malformed. Mechanical transmission from C.
quinoa and G. max back to groundnuts also
produced these atypical symptoms. Small quantities
of seed from infected seed remained healthy
when germinated. The results at present indicate
Figure 48. A rust-resistant groundnut cultivar
growing at ICRISA T Center.
that more than one agent may be involved in this
disease. One component is a sap-transmissible
virus. The profuse flowering, pegging, and axillary
shoot formation are similar to symptoms
produced by mycoplasma or Rickettsia-like
organisms.
Priority has been given to the two most
important worldwide foliage fungi of
groundnuts - rust (Puccinia arachidis) and leafspots
(Cercospora arachidicola and Cercosporidiumpersonatum).
Rust has spread at an alarming
rate over the last few years to all the major
groundnut-producing areas. However, little is
known about its biology, the presence or absence
of physiological races, or its methods of survival.
Infected leaf debris collected in rainy season 1976
and exposed to natural weather conditions was
assessed at weekly intervals for viability of the
uredospores. At the time of collection, germination
was in the region of 70 percent, after one
week this had fallen to 30 percent and in a further
week to 1 percent; after that, uredospores did not
germinate. In the 1976-1977 postrainy season,
the results were similar. Only the uredial stage of
the fungus was found, despite intensive searches
for the telial stage which has been recorded in
South America. None of the 37 weed plants and
11 cultivated plants inoculated with rust produced
symptoms.
To assist the breeding program, a reliable
screening technique for detecting rust resistance
is urgently required. Plants 30 days old were
inoculated with uredospore suspensions and
kept at 100 percent relative humidity at 25 to
30°C for 48 hours before being transferred to
ambient conditions. Abundant uredosori were
produced in 8 to 10 days. This technique will be
standardized to provide a high inoculum source
for field testing populations produced by the
breeders in their rust-resistance breeding
program.
A detached-leaf technique for detecting sources
of resistance is also being investigated. This
technique will have the advantage of testing, with
a known intensity of inoculum under controlled
conditions, large amounts of material in a small
area. During some initial tests, leaves which were
detached 5 days after unfolding were found to be
the most suitable. After detachment, the petioles
were placed in various culture solutions with or
without additives. The most suitable media for
keeping the leaves in good condition were found
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