Title page for ETD etd-09042009-172734


Document Type Master's Dissertation
Author Fourie, Michelle Louise
Email mlfourie@zoology.up.ac.za
URN etd-09042009-172734
Document Title The potential of wheat, maize, lucerne, and soybean as plant borders to reduce aphid-transmitted virus incidence in seed potatoes
Degree MSc
Department Zoology and Entomology
Supervisor
Advisor Name Title
Dr K Kruger Supervisor
Keywords
  • wheat
  • maize
  • lucerne
  • soybean
  • virus
  • seed
  • Gauteng
  • South Africa
  • crops
Date 2009-04-15
Availability restricted
Abstract

Crop borders have the potential to reduce transmission of non-persistent aphid-borne viruses provided a virus non-host is used as a border plant. Alatae (winged aphids) landing in these crop borders purge their mouthparts of the virus by initial probing behaviour on the virus non-host plant before moving into the field proper. The plant species used affects aphid landing because aphids respond to visual and olfactory cues emitted by their host plants. In addition, crop borders could enhance within-field diversification of agro-ecosystems, thereby increasing the number of food sources available to alatae migrating into potato fields.

The objective of the present study was to determine preference of aphids for selected agricultural crops to identify a potential border crop that could be used as a trap crop as well as a virus sink. To evaluate the potential of lucerne, maize, soybean and wheat as border plants for potato fields, a semi-field trial was undertaken at the University of Pretoria Experimental Farm, Gauteng, South Africa. The four crops were chosen based on discussions with seed potato producers. Aphid abundance, alatae landing rates and aphid species assemblages were compared between the four crops and potato using different collecting methods (leaf counts, sweep-netting and green bucket traps) to eliminate any bias caused by sampling methods. In addition, species overlap and composition of the alatae were compared between a heterogeneous planting in Pretoria and a homogeneous planting in Christiana, western Free State, South Africa. The aim was to determine whether it would be possible to use the plant(s) identified as potential border crops in the semi-field trial in Pretoria as a border crop in the seed potato production region in Christiana.

Results from different sampling methods regarding species composition and abundance on different crops in Pretoria varied according to the method used. Therefore, more than one method should be used when sampling aphids to avoid bias. According to the green bucket trap catches, aphids alighted more frequently on crops they colonized. This suggests that alatae have the ability to select their preferred host plant, if available within a habitat patch, in the pre-alighting phase. Overall, aphid species composition for colonizing and non-colonizing species on maize and wheat was more similar to potato than lucerne and soybean. Based on results of all three methods combined, maize and wheat were identified as the two crops with the highest potential to be used as crop border plants.

Similarity of aphid assemblages between Pretoria and Christiana, based on species composition and abundance, was relatively low. However, comparing presence/absence data, species overlap between the two regions was relatively high, suggesting most of the variation between the two regions was mainly due to differences in aphid abundance. Therefore, maize and wheat could be planted as trap border crops in Christiana. In addition, most aphids landing in potato fields in Christiana do not colonize potato. The most typifying species in this region have been recorded on Poaceae and are vectors of PVY, the most prevalent and important of the non-persistently transmitted viruses in South Africa and other potato-growing regions throughout the world.

Copyright 2008, 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.

Please cite as follows:

Fourie, ML 2008, The potential of wheat, maize, lucerne, and soybean as plant borders to reduce aphid-transmitted virus incidence in seed potatoes, MSc dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-09042009-172734/ >

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