Abstract
Propolis has been used by man for millennia for its antimicrobial and pharmaceutical
properties. However, its use as an agricultural antimicrobial agent has only recently been
assessed. This study assessed the use of an ethanolic extract of propolis (EEP) for the
control of avocado fruit fungal pathogens. Qualitative analyses of EEP indicated
flavonoids as the main antimicrobial constituents. Quantitative analyses detected 16.35
mg ml-1 total flavonoids and 3.28 mg ml-1 total phenolics. The Minimum Inhibitory
Concentration (MIC) of EEP was determined as 5 mg ml-1 against Colletotrichum
gloeosporioides, Pestalotiopsis guipinii, a complex of Colletotrichum gloeosporioides
and Pseudocercospora sp. (CgP complex), Verticillium sp., Fusarium sp. and Monilia
sp., isolated from avocado fruits, using the agar dilution method, at a concentration
gradient from 1 to 10 mg ml-1. Electron micrographs of Pestalotiopsis guipinii,
Colletotrichum sp. and Colletotrichum gloeosporioides/Pseudocercospora sp. (CgP
complex) incubated on agar media containing EEP clearly indicated signs of cell wall
damage with large pores within the hyphae. Conidial germination of Colletortichum sp.
and P. guipinii was inhibited by 98.95 % and 40.41 % respectively by EEP. Trees
infected with Colletotrichum sp., P. guipinii or CgP complex conidia were incubated
within greenhouse conditions and treated with 5 mg ml-1 EEP at weekly intervals from
once every week to once every six weeks. Disease indices from experimental and control
trees were similar but noticeable control of CgP disease symptoms was observed from
treatment with EEP. ‘Fuerte’ avocado trees were treated with copper hydroxide, borehole
water or 5 mg ml-1 EEP during the 2006-2007 growing season. All fruit were similar
after harvesting with respect to pre-harvest disease. The occurrence of post-harvest
diseases was analysed after simulations of import and export markets. EEP treated fruit
were similar to bore-hole treated fruits (control). Similar results were observed after trials
to assess the use of EEP as a post-harvest dip. The stem-end of prematurely harvested
‘Fuerte’ fruit were dipped into 5 mg ml-1 EEP, and incubated until ripe, to assess control
of stem-end rot (SER). EEP reduced the occurrence of SER by 30 %. EEP was further
assessed to inhibit infection or disease spread by Colletotrichum conidia. Fruits were
inoculated with Colletotrichum conidia and either treated with 5 mg ml-1 or 10 mg ml-1
EEP either after or before infection. The fruits were incubated until ripe. Both treatments
reduced the occurrence of disease (P < 0.001). In conclusion, EEP did not efficiently control disease in the field, but showed high potential as a future fungicide for avocado
fruit. Optimisation of EEP includes higher concentrations, the addition of stickers, and/or
more frequent spraying of trees.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/6888 |
| Date | 14 April 2009 |
| Creators | Giovanelli, Lorenzo Corrado |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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