Chapter 19: Flowering & Fruiting in Fruit and Nut Crops

Chapter 19: Flowering & Fruiting in Fruit and Nut Crops

Grafting in Fruit Cultivars

  • Many tree fruits and vine fruits are cultivated using grafted plants.

  • Reasons for Grafting a Fruit Cultivar onto Different Rootstock:

    • To enhance plant size by controlling growth through selection of rootstocks or interstocks.

    • To improve resistance to soil-borne pests and diseases.

    • To provide better adaptability to harsh soil conditions.

Tree Size Control via Rootstocks

  • Tree Size Regulation:

    • Tree size can be limited or stimulated through rootstock choices.

    • Various rootstocks vary in vigor:

    • Malling 9 (M9): Very dwarfing rootstock.

    • Malling-Merton 111 (MM111): Semi-dwarfing rootstock.

    • Malling 2: Known for its invigorating effect.

    • MM104: Exhibits a very invigorating growth effect.

Soil-borne Organism Resistance

  • Certain rootstocks exhibit resistance to pests and diseases:

    • Some are less susceptible to nematodes and Verticillium wilt.

    • Example: European grapes die when planted in infected soil due to grape root louse but show resistance when grafted onto American grape rootstock.

Resistance to Soil Conditions

  • Rootstocks can improve resistance to:

    • Unfavorable soil conditions (heavy clay, saline, poorly drained soils).

    • Low winter temperatures that may damage the plant.

Cambial Layer Alignment in Grafting

  • Importance of Cambial Layer:

    • The cambial layer, responsible for secondary growth, must align between scion and rootstock.

    • This alignment allows for the successful “knitting” of the cells from both plant parts, promoting successful grafting.

Graft Compatibility

  • Graft incompatibility can arise when scion and rootstock lack botanical relationship:

    • There should be some relationship (at least within the same family).

    • Best success is when both parts come from the same genus.

Types of Grafting and Budding

  1. Bark Graft:

    • Utilized for various applications in plant propagation.

    • Involves a specific method of cutting and securing the graft for successful take.

  2. Cleft Graft:

    • Primarily used for top working an existing tree trunk.

  3. Four-Flap Graft:

    • Used for cultivar perpetuation, particularly in pecan trees.

  4. Whip or Whip & Tongue Graft:

    • Also known as splice or splice & tongue graft; used for cultivar perpetuation.

  5. T-bud:

    • Employed for cultivar perpetuation through specific bud grafting techniques.

  6. Patch-bud:

    • A method used for cultivar perpetuation focusing on delivering viable buds to the rootstock.

  7. Chip Budding of Japanese Maple:

    • Involves scion selection for cosmopolitically desirable foliage; undesirable foliage is removed from the rootstock.

Pruning and Training of Fruit Trees

  • Importance for Development:

    • Promotes strong trunk and scaffold branch system.

    • Ensures branches are well distributed to prevent excessive shading.

    • Aids in supporting heavy fruit loads without risking branch breakage.

  • Functions of Pruning and Training:

    • Regulate production of fruits effectively.

    • Rejuvenate older trees to foster productive fruiting branches.

    • Control excessive flowering by pruning away some branches.

    • Balance between fruiting and vegetative growth to maintain a healthy tree.

    • Facilitate the removal of dead or broken branches and improve light penetration.

    • Aid in insect and disease management by keeping the tree open and manageable.

    • Help limit the overall size and/or height of the trees.

Cultural Practices for High-Quality Fruit Production

  • Good cultural practices aim to produce a large quantity of high-quality fruits, emphasizing the significance of understanding flowering and fruiting processes.

Flower Bud Initiation

  1. Process of Initiation:

    • Involves a structural change at the vegetative growing point located in the leaf axil or fruiting spur leading to mature flower development.

    • E.g., peach trees initiate from axil buds and apple trees from fruiting spurs.

Factors Affecting Flower Initiation

  • Heavy pruning combined with nitrogen fertilization promotes vegetative growth.

  • Old, low-vigor trees are less likely to develop productive fruiting branches.

  • Severe drought during the initiation period can hinder flower bud formation.

Types of Dormancy in Flower Buds

  • Dormancy Types and Effects:

    • In autumn and early winter, buds experience Rest:

    • They do not grow even under optimal conditions due to internal physiological blocks.

    • Accumulation of abscisic acid (ABA) and low levels of gibberellins (GAs) are responsible for this block.

  • How to Release Rest:

    • Sufficient chilling exposure (vernalization) terminates the rest period.

    • This reverses growth inhibitor and promoter ratios leading to awakening of dormancy.

  • In late winter, budding exhibits Quiescence:

    • Non-resting buds cease growth due to unfavorable environmental conditions (low temperature, lack of water).

Correlative Inhibition

  • Induction of dormancy can also occur due to correlative inhibition:

    • Lateral buds restrained from growth due to the inhibitory effects of auxin originating from the apical dominance.

Stages of Flowering and Fruit Development

  1. Pollination and Fertilization:

    • Occurs in spring after flower bud expansion; favorable conditions lead to fruit set and development.

  2. Maturation Stage:

    • Fruits still attached to plants undergo:

      • Cell enlargement.

      • Accumulation of carbohydrates and flavor constituents.

      • Decrease in acids.

      • Flesh texture may change (softening may or may not occur).

  3. Ripening Stage:

    • Ripening follows maturation and may occur pre or post-harvest, involving:

      • Flesh softening.

      • Development of specific flavors.

      • Increase in juice content.

  4. Senescence Stage:

    • Post-ripening, fruit growth ceases and aging initiates:

      • Senescence can occur pre or post-harvest.