Potato Aphid Assays. The results of our assays with
isolates WU6a through WU11 are summarized in Table
2. Plants carrying Mi had a strong negative impact
on the aphid isolates from France and The Netherlands,
and these isolates established signiÞcantly lower
numbers on tomato plants with Mi than on plants that
lacked the gene. In contrast, isolates WU7-NJ, WU8-
NC, and WU10-CA were virulent on tomato plants
bearing Mi, and established similar numbers on plants
with and without the gene. Aphid color could not be
used to predict the potato aphid isolatesÕ responses to
Mi. Of the two avirulent isolates, WU9-NE was green
and WU11-FR was red. Of the three virulent isolates,
WU10-CAwas green, andWU7-NJandWU8-NCwere
red.
The results for isolate WU5-CA are summarized in
Fig. 1. WU5-CA readily colonized the two tomato
varieties carrying Mi, and established large numbers
on resistant plants in all three assays (the average
aphid numbers per leaßet per resistant plant ranged
from 88 to 191 aphids). The relative numbers of
Fig. 1. Six plants per genotype were challenged with
WU5-CA aphids, and the number of aphids on the two most
infested leaßets per plant was counted. Bars represent the
average number of aphids per leaßet, per plant. The standard
error bars represent plant-to-plant variation for each treatment.
The near-isogenic lines Moneymaker (mi/mi) and
Motelle (Mi/Mi) were used for assays 1 and 2, and the
near-isolines CastlerockII (mi/mi) and Sun6082 (Mi/Mi)
were used for assay 3.