Crop Propagation: Seeds and Germination

Introduction

• Crop establishment can be achieved through seeds or vegetative propagation
• Field crops and vegetables utilize seeds
• Potatoes, sweet potatoes, sugarcane, fruit trees and vines use vegetative propagation
• Good propagation material equates to successful production
• Yield potential depends on genetic characteristics and cultivation conditions

Propagation by Seed

• Seed is often a small cost item but is frequently overlooked
• Good seed requirements:
  • Genetically pure and true-to-type
  • Well-developed with uniform size and without damage
  • Clean, free from weeds, foreign material, and disease
  • High germinability (90-100% in lab) with even germination
• Seed sources:
  • Certified seeds from seed companies are the best
  • Using part of a crop for seed increases risk of reduced Genetic uniformity and quality
  • New cultivars can be found from agricultural research stations

Germination Process

• Germination refers to the food utilization process which involves respiration
• Monocots preserve the endosperm until germination
• Dicots have cotyledons that absorb endosperm during seed maturation
• Stored food, both insoluble and soluble, is necessary for respiration and successful germination

Types of Germination

• Fast germinating seeds exhibit seed coat rupture within 1-2 days after wetting
• The radicle is the first organ to emerge
• The plumule follows the radicle
• Germination is complete when the radicle emerges from the seed and the seedling can photosynthesize
• Epigeal germination mainly occurs in dicots
• Hypogeal germination occurs in monocots

External Conditions for Germination

• Crucial for germination are sufficient moisture, oxygen, temperature, and light
• Any deficiency prevents germination
• A suitable temperature range is necessary
  • Cool seasons mean lower temperatures
  • Warm seasons require higher temperatures
  • Alternating warm and cool temperatures affect germination
• 50-70% of field capacity is appropriate
• Seed moisture should be at 26-75% for germination
• Water enters through the micropyle, hilum, and seed coat
• After that water is absorbed by the embryo, scutellum, and endosperm (imbibition)

Oxygen and Light Requirements

• Some seeds are impervious to gases
• Seeds require oxygen that comes from water
• Sowing too deep or excessive water limits oxygen
• Light and dark conditions are necessary
• Small-seeded crops require light to prevent deep planting
• Absence of light is important as well

Seed Quality

• Embryo injury prevents germination
• Broken seeds increase disease infection
• Mature seeds are preferable for stronger plants
• Small seeds can equate to small seedlings

Seed Dormancy and Longevity

• Mature seeds that do not germinate under favorable external conditions demonstrate dormancy
• Factors inducing dormancy:
  • Thick or hard seed coat
  • Seed coat interfering with oxygen uptake
  • Immature embryo
  • Mature embryo needing specific changes
  • Germination inhibitors present
  • High maturity temperatures
• Field crop seeds last 5-10 years
• Weed seeds can exhibit longevity
• Optimum storage conditions:
  • 5-7% moisture
  • No oxygen
  • Temperatures of -5 to 15°C

Treatments to Break Dormancy

• Scarification is used for thick or hard seed coats.
  • This involves mechanical or chemical abrasion
• After-ripening occurs during the period of dry storage
• Stratification involves a cold and moist period

Implements and Planting Practices

• Seeding equipment is adjusted to crop and circumstances
• These circumstances can include soil moisture, soil type, and seed size
• This can also include the need for simultaneous fertilizer or herbicide application
• Accurate seed measurement and even planting depth are important
• Planters of potatoes, seeds and vegetables vary
• Equipment like broadcast spreaders and liquid fertilizer tanks are available
• Planting time requires consideration for the crops and environment
  • This also includes evasion of disease and pests
• Summer crops are planted after enough rain >50-100mm
  • This helps avoid drought at critical periods
  • Avoid late planting/ irrigates crops
• Winter crops need consideration for early planting
  • This can help with spring frost damage
  • Focus on maximum vegetative growth
• Perennial crops - Plant into clean ground spring or autumn

Soil conditions and planting depth

• Sandy vs. clay soils impact plant depth
• Warm vs. cool soils impact plant growth
• Epigeal vs. hypogeal germination types impact plant growth
• Seed sizes impact plant growth

Planting Depths and Seed Sizes

• Planting depth is between 6mm to 75mm
• Max depth for emergence from 25 to 200mm
• Smaller seeds require shallow planting, while bigger seeds need deeper planting
• Representative crops vary based on seed size
  • White clover and turf require 660,000 to 11,000,000 seed size quantity
  • Cotton requires 900 to 20,000

Density, Nutrients, and Planting patterns

• Plant density is determined by the nature of the crop and environment
• Too few plants means not fully utilizing production potential
• Too many plants means competition and lowers crop efficiency
• High biological yield means more dry matter and less competition
• Density helps with nutrients and moisture
• Limited moisture and fewer nutrients can impact light and taller plants

Vegetative Practices

• Asexual reproduction involves taking a portion of a plant and regenerating it
• Most fruit trees and vines are vegetatively propogated
• This applies to potatoes, sweet potatoes and sugarcane
• Also includes many ornamental plants

Rootstock and Apomixis

• Commercial fruit orchards utilize rootstocks
• These rootstocks are tolerant of unfavorable conditions
• Rootstocks are resistant to soil born pathogens
• They can also alter the tree's growth
• Apomixis refers to the production of seed without fertilization
  • It is genetically identical to the mother plant
  • The only downside is long juvenile phase
• Parthenocarpy (for bananas) is the practice of planting with no seeds
• Nucellar poly-embryony helps clone rootstock for citrus

Reproduction types and embryo development in seed plants

• Nucellar embryony leads to a poly-embryonic seed

Cuttings

• Severed vegetative plant can regenerate a full plant
• Stem cuttings can come from many plants
• Leaf cuttings can generate new roots
• Root cuttings are how to propagate trees
• Environmental conditions can help stem cuttings
• Mist beds and bottom heat help softwood cuttings
• Begonias show good examples of leaf cuttings
• Flat cuts should be on top with slanted cuts on bottom, for plant root cuttings

Layering

• Involves rooting stems while attached to a plant
• To help root initiation, you need etiolation, girdling and hormone
• There are multiple types: Tip, serpentine, etc

Vegetative Propogation Techniques

• Three-step propagation
  • Establish culture
  • Multiply
  • Transplant
• This leads to some virus/disease free material for bananas
• Cambium zones in budding stem cuttings must touch
• There are multiple other vegetative methods
  • Bulbs such as onions
  • Corms include gladiolus
  • Rhizomes such as ginger
  • Stolons such as runners
  • Stem tubers, such as potatoes
  • Root tubers, such as dahlias
• Each of these show unique characteristcs in a growing enviornment