Module_2_Vegetative_Cycle_and_Dormancy

Question 1

What are the main phases of the grapevine annual cycle?

Answer 1

Budburst → Shoot growth → Flowering → Fruit set → Berry development → Leaf senescence → Dormancy.

Question 2

When does the grapevine annual cycle begin and end?

Answer 2

Begins with budburst in spring and ends with leaf fall in autumn followed by dormancy.

Question 3

What determines the timing of budburst in grapevines?

Answer 3

Mainly temperature; buds burst after accumulating sufficient heat units once chilling requirements are met.

Question 4

What is ‘chilling requirement’ in grapevines?

Answer 4

The period of cold temperatures needed during winter to break endodormancy.

Question 5

What term describes the period when buds are alive but not actively growing?

Answer 5

Dormancy.

Question 6

What are the three stages of bud dormancy?

Answer 6

Paradormancy, endodormancy, and ecodormancy.

Question 7

What causes paradormancy?

Answer 7

Growth inhibition due to physiological signals from other parts of the vine (e.g., apical dominance).

Question 8

What causes endodormancy?

Answer 8

Internal physiological factors within the bud itself preventing growth even under favorable conditions.

Question 9

What is ecodormancy?

Answer 9

Growth is prevented by unfavorable external conditions such as low temperature or water stress.

Question 10

How is dormancy broken in grapevines?

Answer 10

Exposure to sufficient chilling followed by warm conditions triggers budburst.

Question 11

How does hydrogen cyanamide (e.g., Dormex) assist in dormancy breaking?

Answer 11

It mimics the effect of chilling, stimulating earlier and more uniform budburst.

Question 12

Why is uniform budburst important in vineyards?

Answer 12

Ensures even shoot development, flowering, and fruit ripening.

Question 13

How does apical dominance influence shoot growth?

Answer 13

The actively growing shoot tip produces auxin that suppresses growth of lateral buds.

Question 14

What happens to apical dominance when the shoot tip is removed?

Answer 14

Lateral buds below the cut break and grow, increasing canopy density.

Question 15

What hormone maintains apical dominance in shoots?

Answer 15

Auxin (indole-3-acetic acid, IAA).

Question 16

Which hormone can overcome apical dominance and promote budburst?

Answer 16

Cytokinins.

Question 17

How does pruning timing affect dormancy and budburst?

Answer 17

Late pruning delays budburst and can help avoid spring frost damage.

Question 18

What environmental cues influence leaf senescence in grapevines?

Answer 18

Decreasing day length and temperature during autumn.

Question 19

What happens physiologically during leaf senescence?

Answer 19

Chlorophyll degrades, nutrients are remobilized to permanent structures, and abscission occurs.

Question 20

Where are carbohydrate reserves stored during dormancy?

Answer 20

In roots, trunks, and canes as starch.

Question 21

Why are carbohydrate reserves important for spring growth?

Answer 21

They provide energy for early shoot and root growth before photosynthesis resumes.

Question 22

What is the main environmental factor initiating dormancy?

Answer 22

Declining temperature and day length in late autumn.

Question 23

How do carbohydrate reserves vary through the year?

Answer 23

Depleted during spring growth and replenished after harvest during post-harvest photosynthesis.

Question 24

Why is post-harvest leaf retention important?

Answer 24

It allows continued carbohydrate accumulation before leaf fall.

Question 25

How can drought stress affect vine dormancy preparation?

Answer 25

Premature leaf fall reduces carbohydrate storage and weakens vine vigor next season.

Question 26

What management practice helps synchronize budburst in cool climates?

Answer 26

Application of dormancy-breaking agents or late pruning.

Question 27

How can insufficient chilling affect budburst?

Answer 27

Leads to delayed, uneven, or poor budburst.

Question 28

How is vine phenology typically recorded?

Answer 28

Using the modified Eichhorn-Lorenz (E-L) growth stage scale.

Question 29

What is the E-L stage range for budburst?

Answer 29

Stages 4–7 (green shoot tips just visible to shoots about 10 cm long).

Question 30

Why is accurate phenology tracking important?

Answer 30

It guides management timing (spraying, irrigation, canopy management, etc.).

Question 31

How does temperature accumulation relate to vine growth?

Answer 31

Growth depends on heat summation—expressed as degree-days above a base temperature (~10 °C).

Question 32

What is the approximate base temperature for grapevine growth?

Answer 32

10 °C.

Question 33

Why might delayed budburst be desirable in some regions?

Answer 33

To avoid spring frost damage to emerging shoots.

Question 34

How does pruning wound bleeding relate to vine physiology?

Answer 34

It indicates reactivation of xylem sap flow as roots resume activity before budburst.