| dc.description.abstract | This study was carried out to establish
whether some locally available materials in Kenya can
be used as substitutes for peat in legume inoculant
production during the period 1977 to 1980. The
materials investigated consisted mainly of agricultural
residues. These were filtermud, bagasse, sawdust,
coffee husks, coir dust, charcoal dust, forest soil,
diatomite, sisal waste, maize cobs, alfalfa and wheat
straw as well as wood ash. Among these materials,
filtermud, sawdust, bagasse, coirdust and coffee husks
were found most promising in terms of availability,
organic matter content and water-holding capacity.
Further investigations using the five materials
listed above showed that filtermud was superior to the
other four. The survival rate for Rhizobium phaseoli,
in filtermud as determined by the plate count method,
was comparable to that in peat, the acclaimed overall
best carrier for rhizobia. Filtermud had an initial
viable rhizobia count of 1 X 108 /g dry weight
inoculant which declined to 1 X 107 /g dry weight
inoculant after storage for six months at 26°C. The
quality of the filtermud inoculant was high and
consistent over a storage period of four months at
26°C. The inoculant maintained a viable count in the
range of 108 to 109 rhizobia /g dry weight inoculant
.
throughout the peL'iod. The surviving rhizobia
effectively nodulated legume seedlings as indicated by
the plant infection test.
Storage of inoculants at 40°C was found to be
detrimental to the survival of R. phaseoli. Viable
rhizobia count in a filtermud-based inoculant declined
from 1.5 X 109 to 0.4 X 109 rhizobia/g dry weight
inoculant within 24 hrs. This represented a loss of 73%
in rhizobia viability. Within one week of storage at
40°C, the inoculant lost 90% of the initial rhizobia
count. Storage of inoculants at temperatures between
4°C and 26°C greatly improved rhizobia survival and
mul tiplication. The rhizobia count increased three-fold
within the first week when the filtermud inoculant was
stored at between 20° and 26°C. Storage of the
inoculant at a lower temperature (4°C) slowed down
rhizobia multiplication and only a 50% increase over
the initial rhizobia population during the same period
was recorded. A count of 1.0 X 109 rhizobia/g dry
weight inoculant was maintained over a period of one
month when the inoculants were stored at 26°C. This
compared favourably with the peat inoculant. Storage of
peat inoculant at 40°C for 24 hours showed a 55% loss
in viability. After one week at the same temperature,
the inoculant lost 97% of the initial viable rhizobia
count. When the inoculant was stored below 26°C, the
rhizobia numbers increased three-fold over the first
week.
Several stickers were tested for their
suitability during. seed inoculation. Use of water,
sucrose (10% w:v) and gum-arabic (40% w:v) as stickers
resulted in an inoculum load greater than 10 X 103
rhizobia/seed. When Fowler's syrup, molasses and yeast
extract mannitol (YEM) broth were used as stickers, a
lower inoculum load of 10 X 102 rhizobia/seed was
obtained. Seeds inoculated using gum-arabic as the
sticker and then stored at either 4°C or 25°C for a
period of four weeks recorded the highest survival of
rhizobia as compared to the rest of the inoculant
stickers. Rhizobia population on seeds inoculated using
gum-arabic declined from 10.5 X 103 to 1.1 X 103 /seed
over a period of one month at 4°C. Storage of
inoculated seeds at 25°C showed a sharp decline from
10.5 X 103 to 3.3 X 101 rhizobia/seed within the same
period.
Sucrose was not as effective as gum-arabic in
supporting rhizobia survival on seed. Inoculated seeds
stored at 4°C lost more than 50% of the initial viable
count within one week. Thus, viable rhizobia count
declined from 9.5 X 103 to 9.2 X 102 rhizobia/seed
within the same period. After one month, only 435 and
8 rhizobia/ seed survived at 4°C and 25°C, respectively.
Use of Fowler's syrup and molasses resulted in very
poor survival of rhizobia on seeds. Rhizobia numbers
declined from 2-3 X 103 to 6-7 X 102 within one month
when seeds were stored at 4°C. When similarly
inoculated seeds were stored at 25°C no rhizobia were
recovered after one month.
YEM oroth was not suitable as a sticker. It
resulted in a low inoculum load (2. 7 X
rhizobia/seed) and poorly supported survival of the
rhizobia. When inoculated seeds were stored at 4°C, the
inoculum load declined to 28 rhizobia/seed within one
month. All rhizobia on seeds were lost within two weeks
at 25°C. Using water as the sticker resulted in a high
initial rhizobia count (10 X 103
) but afforded poor
protection for rhizobia on seeds. The numbers of
surviving rhizobia declined to 2.8 X 101 per seed when
stored at 4°C for one month. When the seeds were stored
at 25°C, only 3 rhizobia /seed could be detected after
one month. The gum-arabic-CaC03 pellet supported the
highest number of rhizobia, surpassing all other
treatments. This was true of inoculated seeds stored at
either 4°C or 25°C. Pelleted seeds had a rhizobia count
of 3.7 X 103/seed after storage at 4°C for one month
while those stored at 25°C had 90 rhizobia per seed
after the same period.
Inoculation of seeds prior to planting resulted
in well nodulated seedlings when seeds were inoculated
using either gum-arabic or gum-arabic lime pellet. Good
nodulation was observed even when such seeds were
stored at temperatures between 4° and 25°C for upto
four weeks. Seeds inoculated using sucrose and water
and stored at 4°C supported the survival of more than
300 rhizobia/seed upto the fourth and third weeks,
respectively. When inoculated seeds were stored at 25°C
for more than two weeks in the case of sucrose treated
seeds and one week for water treated seeds, they
produced poorly nodulated plants.
All plants grown from inoculated seeds appeared
greener, had higher nodule weight and higher shoot dry
weight than the uninoculated control plants. Storage of
inoculated seeds at 25°C or above for more than one
week was detrimental to
multiplication. | en |
