dc.contributor.author | King'iri, AN | |
dc.date.accessioned | 2013-05-11T08:14:27Z | |
dc.date.available | 2013-05-11T08:14:27Z | |
dc.date.issued | 1993 | |
dc.identifier.citation | King'iri, A N(1993). Etiology and control of purple blotch in onions (Alliunl Cepa l) caused by Alternaria Porrl | en |
dc.identifier.uri | http://erepository.uonbi.ac.ke:8080/xmlui/handle/123456789/21744 | |
dc.description | Msc- Thesis | en |
dc.description.abstract | Investigations on J\lternaria porri pathogen with respect to
the effects of culture media. temperatures and light regimes on
growth and sporulation commenced after collection of the
isolates from Kabet e field station. University of Nairobi. Njabini
Farmer's Training Station (South Kinangop) and Kenya
Agricultural Research Institute (KARl) experimental station at
Oljorok (Nyandarua district).
Onion seeds obtained from different locations were assessed
for infection levels of the seed borne Alternaria porri and the
incidence of the infection on seed germination and losses. Seed
drcssrnu chemicals (Thiram and Captan) and foliar fungicides
(dithane M45. c1aconil 2787. ridomil MZ and kocide 101) were
tested for control or the disease.
A. porti was found to grow well in most media rich in
nutrients although best growth occured in host decoction agar.
Generally growth of the pa thogen was not affected by light. while
temperature did. with best growth occuring at 240C. During
growth. characteristic violacious pigmentation was evident. The
pathogen could not sporulate easily in artificlal conditions.
Nevertheless. the host decoctions (onion decoctions) favoured
the best growth and sporulation. The pathogen required low
temperatures (below 270C) for maximum sporulation. Light was
also essential during coniclial formation at the incubation period
of 10 to 16 days with maximum conidial production occuring at
the 13th day.
During seed health testing. the level of seed infection was
influenced by the variety. location from where the seeds were
grown or obtained and also by the testing (incubation) method
used. Bombay Red recorded the highest percentage infection
while I\:ON 3 the least infection irrespective of the location.
Seeds obtained from KalJete and Marigat locations had high
levels of infection compared to seeds from Njabini location
which had low infection level. Both freezing and agar plate
methods proved to be suitable incubation procedures favouring
sporulation and easier identification of fungus in seeds
respectively.
Seeds from Njabtnl location recorded the highest germination
percentage compared to the other locations. Exotic cultivars
compared to local checks were superior in glasshouse
germination and emergence although the difference with local
check Red Creole was small. Kabete and Martga t locations
produced seeds which gave the lowest percentage glass house
germination and emergence.
Thrrarn proved to be better than cap tan in reduction of the
seedborne inoculum. although both were effective and improved
yields considerably.
Dithane M45 and daconil 2787 effectively controlled onion
purple blotch while kocide 101 and ridomil MZ proved to be
less effective.
In conclusion, A. POTTi pathogen should be cultured on onion
decoction agar at 180C to 240C under 12h. light/12h dark for
10 - 13 days.
Seed dressing prior to planting with th iram or captan and
subsequent foliar spraying with clithane M45 or daconil 2787 at
the same rate of 50 g/20 litres at weekly intervals would greatly
improve the bulb yield. | en |
dc.description.sponsorship | University of Nairobi | en |
dc.language.iso | en | en |
dc.subject | Etiology | en |
dc.subject | Purple Blotch | en |
dc.subject | Onions(Alliunl cepa L) | en |
dc.subject | Alternaria Porri | en |
dc.title | Etiology and control of purple blotch in onions (Alliunl Cepa l) caused by Alternaria Porrl | en |
dc.type | Thesis | en |
local.publisher | Department of Plant Science and Crop Protection, University of Nairobi | en |