Resistance in maize to the maize stalk borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae)

Abstract

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.