An in depth review is given of Host Plant Resistance research on
borers in general, and on B. fusca in particular. The general
biology and economic importance of B. fusca are also discussed.
Several aspects of the general methodology of breeding for
resistance to B. fusca are discussed. These topics include
collection of overwintering larvae, termination of diapause,
field infestation methodology and damage assessment.
Approximately 20 first instar larvae were applied to the plant
whorl when plants were about 30 - 40 cm tall. The primary method
of damage assessment was to evaluate leaf damage on a 1 to 5
scale. Further criteria for selection of resistant germplasm are
assessment of stunting due to stem boring and yield at harvest.
The effect of plant resistance on B. fusca was investigated. There
were clearly defined differences in leaf damage evident between
different maize genotypes. Heritability of this resistance was
demonstrated, and presumed to be an additive mechanism that
reduced insect feeding, indicating antibiosis. There were
significant differences between the number of larvae recovered
from whorl tissue of different cultivars. This was ascribed to
two resistance mechanisms exerting their effects within the first
few days' feeding by larvae. One mechanism was short lived, but
effective, antibiosis resulting in larval death, while the other,
also short lived, was repellence, resulting in larval migration.
Both mechanisms resulted in fewer larva feeding in the plants.
Another longer lasting resistant mechanism affected larval growth
and mass gain, resulting in smaller larvae. These mechanisms were
found to be heritable traits.
Differences in levels of resistance affecting larval mass gain
were also determined for various parts of the tassel. For all
inbreds, the peduncles were more susceptible than the tassel Cultivars also differed in the levels of resistance in the stern
tissue. Resistance in leaf tissue did not necessarily mean that
resistance occurred in the stern of that genotype. Some cultivars
had resistance mechanisms present in both leaves and sterns, some
had only one resistance mechanism in either part, and some were
totally susceptible.
The effect of the borer on the plant was investigated. Leaf
damage was found to not be of any consequence, but severe stern
damage caused extensive yield losses. There was good correlation
between leaf damage and stern damage. Yield loss was most
pronounced in longer season hybrids than in quick maturing
hybrids.
Methodologies utilized in the development of inbreds,
populations and hybrids are discussed. It was concluded that
borer resistant hybrids do have a place in the commercial
market. However their performance under conditions of low or no
infestation must be similar to that of other susceptible hybrids
because control measures for B. fusca are not excessively
expensive. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1989.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/10875 |
| Date | 09 June 2014 |
| Creators | Barrow, Michael Ronald. |
| Contributors | Bosman, Ted., Samways, Michael J. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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