Shiraz disease

Question 1

Vector

Answer 1

Mealybug

Question 2

Where does it occur?

Answer 2

Only in SA

Question 3

Cultivars

Answer 3

Shiraz, Merlot, Malbec

Question 4

Shoots

Answer 4

green rubbery that are not subjected to normal lignification = pendant format

numerous lenticels in close proximity

as the season progress, lignification is completely amiss. Change clour from green to black followed by die back

Question 5

Leaves

Answer 5

Discoloured red

Question 6

Other consequences

Answer 6

Unproductive and die later

Question 7

Characteristics not based on shoots

Answer 7

floppy appearance + decreased vigour = noticeably smaller vines

regrowth at an advanced stage of leaf drop

leaves have a pattern of discolouration + delayed leaf drop

Question 8

Bunches

Answer 8

small, green, undeveloped - due to poor set, and small poorly developed flower clusters

Question 9

What internal parts are infected?

Answer 9

cambium and cambium derivatives of shoots and bunches = disturbed differentiation patterns in secondary phloem and secondary xylem

Question 10

Characteristic anatomical changes:

Answer 10

1. cambium indented between the xylem rays in the direction of the pith imparts a dramatic wavy appearance
2. differentiation of abnormally large amounts of phloem at the expense of xylem
3. absence of secondary phloem fibres
4. no or poorly developed cork cambium and cork
5. underdeveloped or absent primary phloem
6. atypical xylem with small compressed wood vessels

Question 11

Physiological reactions

Answer 11

low
sugar [] & anthocyanin []
high
TA []

canes : reduced strach