Organically based strategies used by small-scale farmers in Lesotho for the sustainable management of soilborne diseases
Abstract
English: Damping-off of vegetable seedlings caused by Rhizoctonia solani
Kuhn., Pythium ultimum Trow. and Fusarium oxysporum Schlecht. cause
serious losses in seedbeds in Lesotho. Composts prepared from poultry,
cattle, pig and sheep manure and commonly used by Lesotho farmers were
shown to decrease disease severity and increase plant biomass. Cattle, pig
and poultry manure composts gave the best disease suppression and
stimulated the growth of vegetable seedlings. Composted sheep manure
however, did not suppress damping-off nor increase seedling biomass. Seed
germination was also significantly suppressed in this compost. High
concentrations of phytotoxic elements were possibly responsible for this
phenomenon. Disease suppression was also investigated in field studies.
Composted cattle, pig and poultry manures significantly suppressed seedling
damping-off. Sheep manure compost was also able to reduce damping-off
severity under field conditions but to a lesser extent than the other three
composts.
General microbial activity in field soil including fungal populations
present in the four tested composts was evaluated in the laboratory using
FOA. Composted cattle, pig and poultry manure displayed a significantly
higher level of microbial activity and consequently yielded more fungal
colonies. The lowest microbial activity was observed in composted sheep
manure.
Research conducted on the suppression of R. so/ani, P. ultimum and F.
oxysporum with crude extracts of Rhamnus prinoides L. Herit, Artemisia afra
Jacg. ex Willd., Leucosidea sericea Eckl. & Zeyh and Melia azedarach L,
confirmed their ability to suppress these pathogens. Mycelial growth of R.
so/ani, F. oxysporum and P. ultimum was inhibited in vitro by extracts of R.
prinoides, L. sericea and A. afra. The growth of these pathogens was
however not significantly suppressed by extract of M. azedarach. The plant
extracts were also able to suppress damping-off of seedlings when added to
soil. Populations of R. solani, F. oxysporum and P. ultimum in soils treated
with these extracts were also significantly reduced. Disease reduction was
highest 7 and 14 days after treatment with the extracts.
The combination of composted animal manures with plant extracts
resulted in a reduction of general soil microbial activity, especially fungi.
Microbial activity was most reduced in cattle, pig and poultry manure
composts while the microbial activity in composted sheep manure was not
affected by plant extracts. In fact in some cases, the application of plant
extracts resulted in an increased microbial activity in sheep manure. Disease
suppression in greenhouse studies was not negatively or positively affected
by the addition of plant extracts.
The present study confirms that composted manure of cattle, poultry
and pig as used by Lesotho farmers, can be effectively used to control
damping-off of vegetable seedlings in seedbeds. The use of sheep manure is
however still questionable due to its negative effect on seed germination and
general plant growth. Extracts of L. sericea, A. afra, R. prinoides and M.
azedarach as used by Lesotho farmers, also have the potential to suppress
soilborne pathogens. They can be used to control soilborne diseases either
individually or in combination with animal manure composts. Afrikaans: Vooropkoms-afsterwing van groentesaailinge wat deur Rhizoctonia
so/ani Kuhn., Pythium ultimum Trow. en Fusarium oxysporum Schlect.
veroorsaak word, lei soms tot ernstige verliese in saadbeddings in Lesotho.
Kompos wat met bees-, vark-, skaap- en hoenderbemesting voorberei is, en
algameen deur selfversorgende boere in Lesotho benut word, is in die
glashuis- en veldproewe met betrekking tot hul siekteonderdrukkende
vermoeëns ondersoek. Met die uitsondering van skaapbemesting, was die
intensiteit van saailingsiektes wat deur bogenoemde patogene veroorsaak
word beduidend minder terwyl die biomassa van saailinge ook aansienlik
toegeneem het. Kompos wat met skaapbemesting voorberei is het ook
saadontkieming onderdruk, In verskynsel waarvoor hoë konsentrasies
fitotoksiese verbindings moontlik verantwoordelik was.
Die algemene mikrobiese aktiwiteit van gewone leemgrond asook die
van die vier tipes kompos hierbo genoem, was in die laboratorium met behulp
van fluorosien-diasetaat (FOA) geëvalueer. Kompos wat met bees-, vark-, en
hoenderbemesting voorberei is. het 'n beduidende hoër vlak van mikrobiese
aktiwiteit getoon en dienooreenkomstiog ook meer swamkolonies in kultuur
opgelewer. Skaapbemesting het In beduidend laër mikrobiese aktiwiteit as
grond en die ander bemestingstowwe getoon.
Navorsing is op die siekte-onderukkende vermoë van ru-plantekstrakte
van Rhamnus prinoides L. Herit, Leucosidea sericea Eck!. & Zeyh., Artemisia
afra Jack. ex Willd en Me/ia azedarach L. uitgevoer. AI vier plantsoorte het
vooropkomsafsterwing van groentesaailinge, wat deur bogenoemde patogene
veroorsaak word, aansienlik verminder wanneer dit tot grond-groeimedia
toegvoeg was. Miseliumgroei van die drie patogene was ook in vitro deur
ekstrakte van R. prinoides, L. sericea, en A. afra geïnhibeer maar nie deur dié
van M. azedarach nie. Siekte-onderdrukking was mees beduidend tussen
sewe en veertien dae na behandeling van die grond met die onderskeie
ekstrakte.
In Kombinasie van gekomposteerde dierebemestingstowwe met
plantekstrakte het tot 'n afname in die algehele mikrobiese aktiwiteit daarvan
gelei. Die grootste afname het in bees-, vark-, en hoenderbemesting
plaasgevind terwyl kompos met skaapbemesting nie beïnvloed was nie. In
sommige gevalle het daar met skaapbemesting selfs 'n toename in
mikrobiese aktiwiteit plaasgevind. Die siekte-onderdrukkingsvermoë van die
groeimedia het stabiel gebly.
Die studie bevestig dat die gekomposteerde dierebemestings wat
selfversorgende boere in Lesotho gebruik effektief is in die bekamping van
saailingsiektes van groentegewasse. Voorts, het ru-plantekstrakte van R.
prinoides, L. sericea, M. azedarach en A. afra ook potensiaal, alleen of in
kombinasie met dierebemestingstowwe, om grondgedraagde plantpatogene
te onderdruk.