ISSN:
1570-7458
Keywords:
aphid-resistance
;
lucerne
;
alfalfa
;
Medicago sativa
;
spotted alfalfa aphid
;
Therioaphis trifolii f. maculata
;
antibiosis
;
bioassay
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract In autumn 1981 there were widespread reports of a reduced level of antibiosis in lucerne crops and field trials where cultivars selected for resistance to the aphid, Therioaphis trifolii f. maculata, had been used. On our field trial, the plot of ‘CUF 101’ lucerne was infested to a level about 40% of that on the aphid-susceptible ‘Hunter River’, compared with an average of about 3% over the two years before and the two years after. An experimental study of possible causes using a bioassay technique on cloned plants representing the spectrum of resistance in CUF 101 indicated that loss of resistance was temporary and occurred apparently randomly among the tests, but that certain treatments increase the frequency of its occurrence. Lowered temperatures and the use of either young regrowth or senescent lucerne, each increased the frequency of loss of resistance. Inundation of lucerne by large numbers of aphids did not affect the expression of resistance directly, but the few progeny that survived to adulthood on partly-resistance lucerne were habituated and were then able to interact with the plants to increase the apparent frequency of breakdown of resistance. Plants which showed the loss of resistance developed aphid populations between 4x ad 25x those when they expressed their normal resistance level. Investigations suggest that the situation in autumn 1981 may have been the result of a prolonged and massive immigration of aphids into lucerne crops, which, on the aphid resistant cultivars allowed surviving aphids to exploit maximally the combined effects of factors causing some loss of resistance.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00188241
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