Title page for ETD etd-04292005-141941


Document Type Master's Dissertation
Author Mphahlele, Mogalatjane Patrick
URN etd-04292005-141941
Document Title Honey bee dissemination of Bacillus subtilis to citrus flowers for control of Alternaria
Degree Magister Institutiones Agrariae
Department Plant Production and Soil Science
Supervisor
Advisor Name Title
Prof L Korsten Committee Chair
Prof R Crewe Committee Co-Chair
Keywords
  • citrus diseases and pests biological control
  • alternaria diseases control
  • honeybee
  • phytopathogenic microorganisms biological control
Date 2004-04-20
Availability unrestricted
Abstract
The initial phase in the development of a biological control strategy is screening of biological control agents. Secondary to this phase is the establishment of accurate, effective application techniques. However, successful control requires a thorough understanding of all factors affecting the relationship between host plant, pathogen and other microbes. The purpose of this study was to screen and identify potential bacterial antagonists against Alternaria, a fungal citrus pathogen, attachment of the antagonists to bees, and bee dissemination of the antagonist to citrus flowers. A total of 568 bacterial epiphytes were screened on agar plates for antagonism against Alternaria. Only eight of these isolates, which were identified as Bacillus subtilis, B licheniformis, B. melcerons, B. polymyxa, B. thermoglycodasius, B. sphaericus, B. amiloliquefaciens, and B. coagulans, showed inhibitory effects on the growth of Alternaria. The most effective isolates were B. subtilis and B. licheniformis. Further screening was done with B. subtilis and B. subtilis commercial powder (Avogreen). These bacteria were sprayed on citrus flowers for colonisation studies. Mean populations of B. subtilis and the commercial powder recovered from the flowers were 104 and 103 cfu/stamen respectively. The organisms colonised the styler end and ovary of the flowers when observed under scanning electron microscope (SEM). Avogreen was placed in an inoculum dispenser, which was attached to the entrance of the hive. Honeybees emerging from the beehive acquired 104 cfu/bee. The powder attached to the thorax and thoracic appendages, as revealed by SEM. One active beehive was placed in an enclosure with fifteen flowering citrus nursery trees in pots for dissemination trials. Mean populations of commercial B. subtilis recovered from the flowers visited by bees were 104 cfu/stamen. Electron microscope studies revealed that the antagonist was colonising the styler end and ovary of the flowers. Field dissemination studies were unsuccessful due to low yields.

2003 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria.

Mphahlele, MP 2003, Honey bee dissemination of Bacillus subtilis to citrus flowers for control of alternaria, MInstAgrar dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-04292005-141941/ >

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