Near-isogenic genotypes 1684/Tugela and 2199/Tugela containing D. noxia resistance ex SA1684
[PI 137739 (Dn1)] and SA 2199 [PI 262660 (Dn2)] were studied in terms of antibiosis, antixenosis
and tolerance, population development of D. noxia under field conditions and the probing behaviour
of D. noxia. The susceptible cultivars Betta and Tugela were included for comparison. A sister line
of 1684/Tugela, the commercial cultivar TugelaDn, was used to characterise the constitutive and
induced components of the resistance to D. noxia. Mechanism of resistance studies showed
antibiosis present in both resistant genotypes. No antixenosis was recorded in 2199/Tugela, with
only low levels present in 1684/Tugela. 1684/Tugela was able to retain the same leaf area and
plant dry mass as 2199/Tugela under a much higher aphid infestation level and both lines were
significantly more tolerant than Betta, but did not differ from Tugela. Betta and Tugela showed
higher infestation levels, both in terms of percentage tillers infested and number of D. noxia per
tiller, and lower yields than the resistant genotypes. The initial rapid increase of D. noxia
populations started in the beginning of October and peak aphid numbers were in early to mid-
November. EPG data reflecting the probing behaviour of D. noxia revealed distinct differences
between the resistant cultivars and the susceptible Betta and Tugela. The influence of resistance
in 1684/Tugela and 2199/Tugela on the probing behaviour of D. noxia is different indicating that
they contain two different genes, with different modes of action. While resistance in 1684/Tugela
was generally reflected by disturbances in phloem activity, the resistance in 2199/Tugela was
associated with a high number of short probes denoting some host recognition or epidermal factor
involved in the resistance. Constitutive resistance in TugelaDn influenced the time taken by D.
noxia to reach sustained phloem feeding. There was no evidence of surface or epidermal factors
influencing probing behaviour in this genotype. D. noxia probing on induced resistant TugelaDn
was characterised by a reduction in phloem activities on preinfested plants. D. noxia feeding on five
day induced resistant plants showed more E2 fractions shorter than ten minutes and fewer E2
fractions longer than 60 minutes indicating a reduction in the ingestion of nutrients. In the case of
both constitutive and induced resistance, initiation of phloem ingestion appears easier on
susceptible Tugela with a higher number of single phloem salivation periods on the resistant
genotype. Yield data for five susceptible and 15 resistant cultivars was analysed quantifying the
percentage yield retained under severe infestation. Cultivars with D. noxia resistance from the
same donor accession did not react in a similar way, neither was there any indication that they
show the same measure of compensation for D. noxia damage. Compensation for aphid
infestation was observed in some of the cultivars where higher yields were recorded from some
infested cultivars than from cultivars kept aphid free throughout the trial. In the 2000 season, the
variation in percentage yield retained between resistant cultivars equalled 63.2%, in the 2001
season 85.0 % and in the 2003 season 41.3%. This study confirms that the interaction between
the aphid and each host genotype is unique. The expression of host plant resistance is not only
dependent on the donor accession utilised, but also the genetic background in which it is deployed.
Furthermore, environmental factors can also significantly influence the performance of host plant
resistance to D. noxia.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-06132007-133159 |
| Date | 13 June 2007 |
| Creators | Tolmay, Vicki Louise |
| Contributors | Dr W.F. Tjallingii, Prof CS van Deventer |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-06132007-133159/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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