Ipomoea (Sweetpotato/Kumara) Post-Entry Quarantine Testing Manual

and the average number of peritichous flagellae is 8-11. On PDA media, depending on the
moisture content, young colonies can be circular, convex, smooth and entire, or sculptured
with irregular margins. After 4-5 days, both types of colonies resemble a fried egg, with a
pinkish, round, raised centre and a lobed periphery, which later becomes feathery.
7.1.5 Microscopic inspection for mites
Microscopic examination of plants for regulated mites is a required test on the Ipomoea IHS.
7.1.5.1 Tetranychus evansi
Recommended method
For each plant, use a hand lens to inspect the underside of all leaves for mite eggs, nymphs,
adults and symptoms of mite presence. Following this, for each plant, the 3 youngest leaves
of each plant plus any suspect leaves showing the presence of mites must be collected for
further examination using a binocular microscope. For species identification, both male and
female mites must be collected. Male mites should be mounted laterally onto a microscope
slide and female mites should be mounted dorsally to expose the diagnostic characters. To
improve transparency, the mites can be cleared in lactic acid under a table lamp prior to
mounting.
Interpretation of results
If mites are present the following symptoms may be observed on the underside of leaves;
webbing, distinct small yellow spots (which get larger over time), leaf browning and in
extreme cases the leaves may shrivel up and die. Overall, plant vigour and growth may be
affected (Fig. 1.4).
Mites of the Tetranychus genus can be green, yellow, orange or red in colour. Adult males
are smaller than the females for all Tetranychus spp. T. evansi female mites are reddish in
colour and the males are straw-coloured with a more pointed abdomen (Fig. 1.3).
Species level identification requires examination of the male aedeagus (i.e. the male
genitalia). For T. evansi, the male adeagus will appear upright at a 90ºC angle.
Ipomoea Post-Entry Quarantine Testing Manual · November 2012
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