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to be either Hoagland or Shrive and Robbins<br />
solutions with added kinetin at 20 ppm or<br />
benzimidazole at 20 to 60 ppm. The detached<br />
leaves were sprayed with uredospore suspensions<br />
and incubated under 100 percent relative humidity<br />
and temperatures of 25 to 30°C for 2 days.<br />
The leaves were then maintained at 70 to 80<br />
percent relative humidity and cool temperatures.<br />
Sori began to develop 8 days after inoculation;<br />
they soon darkened and enlarged before rupturing<br />
and releasing masses of uredospores. Comparisons<br />
of the detached-leaf technique with<br />
whole-plant inoculation show that disease development<br />
is similar in either case.<br />
The leafspot fungi cause worldwide reductions<br />
in groundnut yields each year. In India and parts<br />
of Africa, C. personatum is the dominant species;<br />
in USA and other parts of Africa, C. arachidicola<br />
is more important. We need to develop reliable<br />
screening techniques to assist breeders in their<br />
selection of resistant segregates. Although it has<br />
been reported that both fungi can be cultured on<br />
artificial media to produce conidiospores, spore<br />
production on the recommended media was not<br />
sufficient for our purposes. Other media, which<br />
had been recommended for different species of<br />
Cercospora, were tried but success was limited.<br />
Recently we have gained much more satisfactory<br />
results with malt agar supplemented with inocitol<br />
and thiamine hydrochloride; further investigations<br />
are being carried out with this<br />
medium. Conidial suspensions from infected<br />
leaves have given lesions on young plants in 13<br />
days after an initial 72 hours of incubation at<br />
high humidities followed by transfer of the plants<br />
to ambient conditions.<br />
Cultures of Aspergillus flavus are being isolated<br />
and maintained for use when the breeding<br />
program for resistance to this important fungus<br />
gets under way in the near future.<br />
Two disease surveys were carried out in<br />
Andhra Pradesh. At most sites leafspots and<br />
rusts were the major pathogens. Other important<br />
fungi included Aspergillus flavus, A. niger, Leptosphaerulina<br />
arachidicola, Sclerotium rolfsii,<br />
Rhizoctonia bataticola, and Fusarium spp. At<br />
ICRISAT Center Rhizopus spp. was causing seed<br />
rots in stored kernels as well as in the field, and a<br />
Pythium sp. caused seedling damage in the<br />
screenhouse. Cultures of many of these fungi are<br />
being maintained for further study.<br />
M i c r o b i o l o g y<br />
Unlike many grain legumes, groundnuts continue<br />
to form numerous active nodules well into<br />
the grain maturity stage. In rainy season 1976<br />
cultivar Kadiri 71-1 had formed an average of 70<br />
nodules/plant 28 days from sowing, with approximately<br />
half of them on the primary root. By 90<br />
days there were 125 nodules per plant and this<br />
increased to 190 per plant by 111 days. Although<br />
the first-formed nodules senesced by 70 days,<br />
nitrogenase activity as measured by acetylene<br />
reduction assay continued until just before<br />
harvest.<br />
Nodulation and nitrogen fixation was apparently<br />
little affected by seed treatment with<br />
ethephon, or by application of herbicides and<br />
fungicides.<br />
A significant diurnal periodicity in nitrogenase<br />
activity was noted in cv Kadiri 71-1 when<br />
examined 81 days after sowing in postrainy<br />
season 1976-1977. Activity increased rapidly<br />
until 1400 hrs and then declined until dawn (Fig<br />
49). After-dawn activity again increased<br />
rapidly, suggesting a close link between nitrogenase<br />
activity and photosynthesis. The rapid<br />
decline after 1400 hrs may be related to the cloud<br />
cover which developed by 1430 or to reduced<br />
photosynthetic activity because of previous stomatal<br />
closure. This periodicity means that for<br />
valid comparisons of nitrogenase activities under<br />
different treatments, the assays would need to be<br />
done on the same day and at the same time of<br />
day.<br />
In the postrainy season the effect of drought<br />
stress on nodulation and growth of cv Kadiri<br />
71-1 was determined by withholding every alternate<br />
irrigation to some plots. Nitrogenase activity<br />
per plant reached a maximum at 54 days<br />
after sowing, just before the first stress was<br />
applied. By 66 days, activity had declined to 54<br />
µ moles C 2<br />
H 4<br />
/plant per hour for control plants<br />
irrigated 8 days previously and to 16 µ<br />
moles/plant per hour for plants stressed for 20<br />
125
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