Breeding Wheat for Resistance to Insects

Larvae of the wheat midge, Sitodiplosis mosellana (Gehin) feed on the surface of wheat seeds for about 10 days beginning when pollination occurs. A few wheats have a high level of antibiotic resistance to the larvae, which suppresses their growth and development. Nearly all larvae develop successfully on susceptible wheats. Analysis by HPLC of seed extracts produced by alkaline hydrolysis revealed rapid changes in the levels of p-coumaric and ferulic acids during early seed development. Seed infested by wheat midge larvae showed induced changes in the dynamics of these phenolic acids. The most resistant wheats had a higher constitutive level and a more rapid induction of ferulic acid than susceptible wheats. Levels of ferulic acid exceeding 0.35 μg/g fresh weight were associated with a high mortality of newly hatched larvae. In one wheat line, resistance also was associated with induced production of p-coumaric acid. The induction of ferulic acid was similar in wheat from the laboratory and field, except in one resistant wheat that produced higher levels in the field. In ripe seeds, resistant and susceptible wheats had similar levels of phenolic acids.

Inducible Production of Phenolic Acids in Wheat and Antibiotic Resistance to Sitodiplosis mosellana

The wheat midge Sitodiplosis mosellana (Gehin) occurred in all wheat-growing areas of Manitoba during 1993–1997, with 95% of spring wheat fields having some seeds infested by larvae. The level of infestation varied, but each year in excess of 20% of seeds were infested in some fields. Infestation levels in adjacent fields were more similar than in fields separated by a few kilometres. Within fields, the infestation was similar at the edge and near the centre. Wheat midge larvae also overwintered in, and adults emerged from, fields in all wheat-growing areas of Manitoba. Adults emerged from the end of June to the end of July most years, and the peak period for adult flight was mid-July, about 1 month later than in parts of Europe where winter wheat predominates. The timing of the emergence was similar from place to place and year to year. Females constituted 95% of insects caught in a flight trap. The first 10% and 50% of the flight occurred on 9 and 16 July, respectively, and the timing of the flight was not related to growing degree-days. In early August, mature larvae began dropping from wheat heads. The timing of infestation of spring wheat was variable among years because of differences in timing between midge flights and the susceptible heading stage of the crop. Nevertheless, the wheat midge flight usually coincided with the susceptible stage of the spring wheat crop.

Distribution and seasonal abundance of Sitodiplosis mosellana (Diptera : Cecidomyiidae) in spring wheat

Cultivars of winter wheat, Triticum aestivum L., previously identified as possible sources of resistance to wheat midge, Sitodiplosis mosellana (Gehin), were crossed with spring wheat to produce lines with a spring growth habit and assure synchrony between insect and plant. Many of the lines showed low levels of infestation by wheat midge in the field, and 21 of these were tested for resistance in the laboratory. All test lines exhibited resistance, ranging from 58 to 100% suppression of larvae and 70 to 100% suppression of seed damage, compared with a susceptible line. Larval development was delayed and survival was reduced on all lines. This antibiosis was associated with a hypersensitive reaction in the seed surface. The hypersensitive reaction, or feeding damage by young larvae before they died, reduced the biomass of some infested resistant seeds by 28% compared with over 60% for infested susceptible seeds. Some lines also reduced the level of infestation either through oviposition deterrence or a resistance which prevented newly hatched larvae from establishing on the seed surface. A few lines also reduced the hatching rate of wheat midge eggs. The resistance was equally effective in field trials during two consecutive summers in Manitoba and Saskatchewan, with at least a 20-times difference in the level of infestation between susceptible and resistant wheats. No larvae could develop to maturity on some resistant lines. Large plots of one resistant line produced less than 1% as many larvae as a typical susceptible wheat, and the larvae that did survive produced few, small adults. This resistance is the first documented case of a high level of true resistance to wheat midge in spring wheat, distinct from asynchrony between the insect and susceptible stage of the plant. The antibiosis component of the resistance is currently being incorporated in cultivars suitable for production in western Canada.

Resistance to Sitodiplosis mosellana (Diptera : Cecidomyiidae) in Spring wheat (Gramineae)

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0008347X00015984

Susceptibility of red spring wheat, triticum aestivum l. cv. katepwa, during heading and anthesis to damage by wheat midge, sitodiplosis mosellana (géhin) (diptera: cecidomyiidae)

Annual canarygrass and oats were found to be free of natural infestations of wheat midge (Sitodiplosis mosellana Gehin) in northeastern Saskatchewan. Six-row barley cultivars had low infestations and triticale, rye, wheat and durum wheat, high levels of infestation. Differences among susceptible cultivars were frequently due to asynchrony of plant susceptibility and midge oviposition.Key words: Sitodiplosis mosellana Gehin, wheat midge, cereals, cultivars

A. T. Wright

Papers

Wheat midge infestation of spring cereals in northeastern saskatchewan