| dc.description.abstract | The southern leaf blight of maize caused by
Helminthosporium maydis is a serious disease that
has recently been introduced into Kenya. The
disease is causing concern in many maize growing
areas of the world. Investigations were carried out
on this disease and these included studies of disease
incidence, severity, symptoms, characteristics of
the pathogen, factors affecting colony growch 2nd
conidial germination, screening 7 maize hybrids
aud zco POSl te for resistance and host ranqe . Where
the disease was observed to occur incidence was
below 5~ dnd there was only slight to light
infection possibly because of drought at the L~me
the disease survey was carried out. Symptoms were
observed to form only on leaves and consisted of
greyish-ta or straightcoloured lesions showing u
zonate pattern and measuring 0.5 x 0.5 to 3 x 10 ~m.
Colonies of the fungus formed chlamydospores ':'.11
contaminated cultures along zones of anti-biotic
activity between the fungus and bacteria. The
conidla were curved, fusiform and pale to somewbat
dark golden brown in colour. They measured 27 to
103 x 7 to 20]..[l1 and the nurrber of septa ranged from
3 to 10. Optimum conditions for conidial germination
(xiv)
were when relative humidity was between 90 and 100%
o and when the temperature was 30 C. Conidial
germination was bipolar. Germ tubes were produced
within 6 hours of the inoculation of maize leaves
and most appressoria formed between 6 and 18 hours
after inoculation near stomata which seemed to aid
penetration of the leaves by the pathogen. Fungal
colony growth rate was highest when temperature was
o
30 C at pH 6. Attempts to obtain the perfect stage
of the fungal pathogen (Cochliobolus heterostrophus)
were unsuccessful. Katumani Composite maize was
highly susceptible to the disease in the field.
Hybrids 511, 512, 612 and 622 were only moderately
susceptible while hybrids 614C, 613C and 632 were
somewhat resistant to attack by southern leaf
blight. In the host range study only one host plant
species, Rottboellia exaltata, showed infection
which was only slight, out of 13 grass and 1 sedge
species . • All three isolates of the fungus were
similar in behaviour in all the aspects of the
disease studied and w~re probably all r~ce 0 of the
pathogen since they infected only leaves. | en |
