Euphytica (2000) 114, 77-85

Sijun Zheng, Betty Henken, Willem Wietsma, Eri Sofiari, Evert Jacobsen, Frans A. Krens and Chris Kik (2000)
Development of bio-assays and screening for resistance to beet armyworm (Spodoptera exigua Hübner) in Allium cepa L. and its wild relatives
Euphytica 114 (1), 77-85
Abstract: The beet armyworm (Spodoptera exigua Hübner) is the most important pest in tropical Allium cultivations. All shallot (Allium cepa L. group Aggregatum) cultivars are susceptible to this pest.Therefore accessions from three wild Allium species, namely A. galanthum Kar. et Kir., A. fistulosum L. and A. roylei Stearn, next to A. cepa L. were used to screen for resistance. First of all, a reliablebio-assay had to be developed. To this end transparentplastic cages with in total 5 plants of one accession per cage were placed on perlite in a heated greenhouse. Five 3-day old larvae were inoculated on each plant. Eight days after inoculation the number of surviving larvae per cage and the mean fresh weight per larva was determined. The lowest larval survival (36%) was found on A. roylei. This was not, however, significantly different from other Allium accessions. Significant differences were found in the fresh weight per larva fed on different Allium accessions. The larvae survived on A. roylei had a very low fresh weight (10.3 mg per larva), while those on an accession of A. fistulosum had the highest fresh weight (45.1 mg per larva). The larval fresh weight on A. roylei was lower than all the other accessions except from the tropical shallot cultivar Bawang Bali. To check whether or not a toxic compound was involved in the resistance present in A. roylei, ten accessions from four Allium species were screened. Five 3-day old larvae were inoculated on regularly replaced leaf material of each accession of Allium species. No significant differences were found in mean fresh weight per larva and mean survival of larvae among different accessions. There were also no significant differences in pupal weight and developmental time. All larvae became pupae 10 days after inoculation. The data indicate that there is notoxic compound present in A. roylei. These results are underlined by the observation in the greenhouse bio-assay that A. roylei plants were equally damaged by the beet armyworm compared to other Allium species.The results obtained so far therefore suggest that introduction of resistance to S. exigua via the exploitation of variation for resistance to the beet armyworm in A. roylei is unclear and that genetic engineering using Cry sequences could provide a way forward.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Link to article at publishers website
Database assignments for author(s): Chris Kik

Research topic(s) for pests/diseases/weeds:
resistance/tolerance/defence of host

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Spodoptera exigua	Onion/garlic/leek (Allium)