Mushroom cultivation in Kenya began in 1970s with Agaricus bisporus as
the first commercially cultivated species. Different species of Pleurotus,
Auricularia and Lentinula edodes are also being grown today but
at a comparable low rate. These species except for Pleurotus are dependent
on spawn importation. Kenya being a tropical country is rich with mycodiversity
which are still in the wild and remain unharnessed for their nutraceutical value
Wild mushrooms have been a delicacy in Kenya for many years and are meat substitute
especially for the rural population. The uncontrolled harvesting of mushrooms
throughout the year and destruction of forest habitat to create land for settlement,
agriculture and firewood has resulted into loss of germplasm of these fungi
(Palapala et al., 2006). Apart from providing
food, cultivation of mushrooms is a method of conservation (Onyango
et al., 2011a). There is a need to develop cultivation techniques
for indigenous mushrooms for adaptation by local farmers.
During the routine survey to collect Pleurotus mushrooms useful for
cultivation, strain improvement and systematic breeding programme by Kenya Industrial
Research and Development Institute staff in Kenyas Kakamega forest, an
interesting wild species of Pleurotus citrinopileatus was found growing
on dead logs and branches of indigenous trees namely Antiaris toxicaria (Pers.)
Lesch. (Moraceae), Polyscias fulva (Hiern) Harms (Araliaceae), Ficus
thonningii Bl. (Moraceae) (Musieba et al., 2011).
In order to produce and conserve the germplasm of this native mushroom, several
substrates were tested for their efficiency in cultivation this mushroom.
MATERIALS AND METHODS
The study was conducted at the Mushroom Pilot Plant facility of the Kenya Industrial Research and Development Institute (KIRDI) between October and December, 2011. Pleurotus citrinopileatus previously collected from Buyangu forest reserve within the Kakamega forest and phonetically characterized by the author of this manuscript and maintained as pure culture at mushrooms culture bank at KIRDI was used for this study. During this study, all stock mushroom cultures were maintained on Potato Dextrose Agar (PDA) medium for one month at 5°C in a refrigerator. Subcultures were made routinely monthly. Pure cultures were kept on slants and plates at 25°C for 10 days.
Spawn preparation: Procedure by Isikhuemhen et
al. (2000) was followed with slight modification for preparation of
mushroom spawn. Briefly, spawn of the P. citrinopileatus was prepared
with intact wheat grains which were bought from Nyamakima market, Nairobi, Kenya.
One kilogram of wheat grains were washed thoroughly and boiled in 2 L of water
until semi soft. The grains were left for 10 min in hot water to allow moisture
absorption. Water was drained and the grains spread on a mesh to cool. The grains
were mixed with 1% (w/w) CaCO3 to adjust the pH and 100 g of the
wet grains put in 500 mL conical flasks. The mouth of the conical flasks were
tightly plugged with cotton wool and covered with aluminium foil. All prepared
flasks were transferred to the autoclave and sterilized at 121°C for 20
min. The flasks were allowed to cool down before aseptically inoculating them
with ten 1 cm2 pieces of mycelia taken from 10 day old cultures of
P. citrinopileatus. This was done in a laminar flow. The inoculated grains
were incubated in a dark room at 25±2°C until the mycelia fully colonized
Substrate preparation: Plastic bag technology was used in this experiment
with treatments replicated 9 times and arranged in a completely randomized design.
Seven substrates namely bean straw (Phaseolus vulgaris), sawdust African
mahogany (Khaya anthotheca), rice straw (Oryza sativa), maize
cobs (Zea mays), wheat straw (Triticum aestivum), sugarcane bagasse
(Saccharum officinarum) and banana leaves (Musa sp.) were tested.
All the substrates were compared to wheat straw because it the most commonly
employed substrate for Pleurotus cultivation (Philippoussis
et al., 2003).
The substrates were collected from a rural farm in Kangundo, Kenya and a local jaggery in Industrial area, Nairobi, air dried and chopped into pieces of 4-5 cm long using a motorized chaff cutter. The chopped substrates were wetted separately on cemented floor and allowed to drain overnight. One kilogram of the substrate was then packed into heat resistant polythene bags with a diameter of 12 cm and a length of 18 cm. The bags were closed with a twist-tie and a piece of cotton wool plugged at the neck to allow for gaseous exchange and pasteurized at 70°C for 2 h. After cooling, they were spawned individually at the rate of 5% under a laminar air flow, labeled and incubated in the dark at 25±2°C for 8-21 days to allow complete spawn run. The bags were transferred onto horizontal wooden racks in a humid mushroom growing room with a 12 h light/ 12 h dark photoperiod at 23±2°C to induce basidiome formation. The cotton plugs were removed and the bags slit at the sides using a sharp blade. The production rooms were watered twice a day to increase humidity and induce fruit body formation. The temperature and relative humidity readings of the production blocks were recorded daily. After each flush mushrooms were harvested and the production blocks watered again to promote development of another flush. Harvesting was done by hand and weighing done immediately. Date of each harvest was recorded. Total number of flushes or breaks produced per bag was also noted. The distribution of yield per flush was tabulated to observe changes in the yield over the course of multiple flushes.
The number of days from inoculation to total colonization of the substrates, first primordial formation and first flush were recorded. Mushroom yields were also weighed. Duration of time from inoculation to final harvest was also recorded.
The biological efficiency (ratio of fresh mushrooms produced/substrate dry
weight, expressed in percentages) was calculated using the formula outlined
by Onyango et al. (2011b). Total wet weight of
the mushroom was recorded during the four flushes. Yield (fresh weight of harvested
mushrooms/substrate fresh weight, expressed in percentages) was also recorded.
Also considered was the production period and number of crops. Bioconversion
was determined by substrate dry weight loss after mushrooms harvest.
All the experimental units were discarded after 62 days. Data obtained were
analyzed statistically by Minitab Release 14 statistical software (Minitab Inc,
Pennyslania, USA). An Analysis of Variance (One way ANOVA) and Tukey test were
used to indicate the significant differences between the mean values (p<0.05).
The mean yield of P. citrinopileatus on different agricultural wastes and their biological efficiency are given in Table 1 and 2. After four flushes, yields of mushroom from bean straw were markedly higher than all the substrates (Table 1). No harvestable produce was recorded from saw dust.
Though all substrate recorded successful mycelia colonization and fruiting, bean straw presented the shortest period of colonization (8 days) and the highest biological efficiency of 148%. Rice straw followed with an efficiency of 98%, sugarcane bagasse: 78%, wheat straw: 41%, banana leaves: 16% and maize cobs: 5%. The biological efficiency of the control substrate was 40% (Table 2).
The highest mushroom weight in different flushes for all the substrates was in the first flush, except for sugarcane bagasse and banana leaves.
|| Effect of substrates on yield of Pleurotus citrinopileatus
|Means followed by the same letter in the row are not significantly
different at p<0.05, *Fresh weight after four flushes
|| Biological efficiency of substrates for Pleurotus citrinopileatus
|Means followed by the same letter in the column are not significantly
different at p<0.05
||Days for completion of spawn running, fruiting bodies formation
and pinhead formation of Pleurotus citrinopileatus on different substrates
at the spawn rate of 5%
Pinhead formation was found to vary between 13 days and 31 days. Faster pinning occurred on bean straw (Table 2). By using bean straw, the number of days until production decreased (Table 3).
Whereas mycelia colonization of all substrates was complete at the end of spawn running period, the sawdust bags showed obvious thin incomplete colonization even up to the end of incubation period (Table 3).
Bean straw emerged as the most suitable substrate for cultivation of the indigenous
Pleurotus citrinopileatus. Bean straw showed the shortest colonization
period and the highest biological efficiencies and yields. Substrate composition
and structure is important for vegetative growth and fruiting bodies development
(Mshandete, 2011). Compared to the control, using bean
straw reduced the number of days until production by 10 days resulting into
shorter crop cycles for growers and minimizing the exposure of the production
substrate to pest infestations, especially sciarid (Lycoriella mali [Fitch])
flies. A study has shown that the sciarid fly may complete its life cycle in
25 days at 21°C, while 35 to 38 days are required at 18°C (Royse,
Timely disposal of spent substrate may help to minimize the build up of fly
populations on a mushroom farm (Royse, 2002). The superiority
of bean straw as a growth medium for the efficient mycelial growth of Pleurotus
sp. further reaffirms the previous findings regarding its suitability as a growth
medium for the propagation of mycelia of most wild mushrooms we have cultivated
including Pleurotus (Kimenju et al., 2009).
Bean straw is an ideal medium due to its nutrient content that can fulfill the
nutritional needs of this mushroom.
In all the cases, first flush fruit bodies gave much more yield than second
and subsequent flushes. There was decrease in mushroom yield in subsequent flushes.
These results agree with those of Kimenju et al.
(2009). Sawdust performed the least amongst the substrates tested. Sawdust
presented the longest spawn running time exposing the substrate for a longer
time to competitors such as weed molds and bacteria. Further, the mycelia density
in sawdust was observed to be thin and scanty which implies that the nutrients
present in the substrate was not sufficient to nourish a vigorous and luxuriant
growth. In the wild however P. citrinopileatus was found growing naturally
in Kakamega forest on the dead logs and branches of indigenous trees namely
Antiaris toxicaria (Pers.) Lesch. (Moraceae), Polyscias fulva
(Hiern) Harms (Araliaceae), Ficus thonningii Bl. (Moraceae) suggesting
that if nutritionally improved sawdust could be a suitable candidate as a substrate.
Thus there is a need to reinvestigate the appropriate formulation of saw dust-based
medium. For instance, in a side experiment for spawn production, addition of
wheat bran at the rate of 5% to sawdust, stimulated luxuriant mycelia growth
and early fructification.
This study recommends bean straw as a new substrate for cultivation of the
indigenous Pleurotus citrinopileatus at spawn rate of 5% which is being
reported for the first time in Kenya. This breakthrough in growing this mushroom
at our pilot plant is a major incentive for growing wild mushrooms and will
catalyze their adoption by farmers. If properly harnessed, this species can
be used as direct source of protein and bioactive compounds for the people while
generating livelihood, contributing to food availability and promoting environmental
protection in the countryside.
We would like to thank the Director, Kenya Industrial Research and Development Institute (KIRDI) and the management for providing the funds and necessary facilities to carry out this study under the project: Characterization and Domestication of wild edible mushrooms in Kenya. We would also like to thank Dr. Calvin Onyango for assistance in data analysis.