SCREENING FOR ANTIXENOSIS RESISTANCE TO FLEA BEETLES, PHYLLOTRETA-CRUCIFERAE (GOEZE) (COLEOPTERA, CHRYSOMELIDAE), IN RAPESEED AND RELATED CRUCIFERS

A laboratory method to screen crucifer seedlings for antixenosis resistance to flea beetles, Phyllotreta cruciferae (Goeze), is described. The method utilizes a plexiglass arena with a foam base to hold 30- by 50-mm vials containing individual seedlings of 10 entries (10 seedlings per entry) in a 10 X 10 layout. In each arena, nine test entries and a standard entry are compared in a Latin square design. Flea beetles are allowed to feed on seedlings for about 30 h, and then the damage to individual seedlings is estimated using a visual rating scale. A rating of one arena can be completed in about 15 min. Seedlings at the arena edge often suffer more damage than those in the centre of the arena, but the effect of this variability in damage is minimized by the Latin square design. Use of border (guard) rows and columns does not eliminate the edge effects. The use of arenas without borders, and a single damage rating where the damage to the standard entry is about 50% of the cotyledon area, are considered ideal for initial screening to identify sources of flea beetle resistance. The method detects entries that differ by as little as 18% damage using a single arena with 10 replicate seedlings per entry. No significant antixenosis was found among 19 cultivars of Brassica napus L. and B. campestris L., but one accession of B. carinata L. and two accessions of Sinapis alba (L.) exhibited antixenosis.