seedling establishment

8/8/2019 Seedling Establishment

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Seed germination andseedling establishment

Objectives of today·s lecture

Learn about horticultural practices that are

used to promote seed germination andseedling growth

Prenatal and postpartum care of plants



Seed germination and seedlingestablishment

2 major uses of seeds inagriculture

Plant part that is harvestedfor food, either directly or after processing

Used for propagating plants a $23 billion market for seeds

worldwide



Why are seeds used for plant propagation?

Advantages

relatively inexpensive

many seeds produced from a singleplant

convenient for storage

naturally dormant in many cases long shelf life

disease free propagation

few pathogens carried by seeds




Disadvantages

Genetic segregation of traits - plants grown

from seed may not be genetically identical tothe parent plant; examples include:

Seed produced from plants that are self-

incompatible, e.g. apples Seed produced from F1 hybrids, e.g. onions, sweetcorn




Disadvantages

Time to maturity

Apple trees grown from seed may grow for 10years before bearing fruit

Potatoes grown from seed take 2 years to produce

tubers



Important criteria for seeds used in propagation

Viability and vigor

percent seed germination

rate of germination

rate of seedling growth



Important criteria for seeds used in propagation

For most horticultural crops viability and vigor are maintained when seed are stored at:

low temperatures

low humidity

Note that these are the opposite of the

conditions that promote germination



Long term storage of seeds

Seeds of many species are kept under refrigeration for long term storage

National Seed Storage Lab in Colorado

repository for many species

important for preservation of germplasm, a gene

bank stored in liquid nitrogen

seed are regrown every few years



Seed quality

Seed quality is important in commercial sales

Federal and state regulations

Indiana requires all seed to be tested (by the StateChemist·s Office) and labeled

percent pure seed

percent weed seed

percent germination date of testing



Conditions for seedgermination

Successful seed germination requires

Viable, vigorous seed

Adequate moisture

Supply of oxygen

Appropriate temperature

Protection from pathogens and pests



Seed dormancy

Some seed will NOT germinate under standardconditions; seed are dormant

require specific treatments (temperature, abrasion,light) to break seed dormancy and before seed willgerminate



Breaking seed dormancy

Stratification

Scarification



Methods of seeding

Direct seeding

Seeds are planted where the plants will

grow to maturity or harvest Convenient to use

Adaptable to mechanization

Not well suited for very small seed Obtaining a good stand of plants requires

soil preparation



Methods of seeding

Indirect seeding Two stage process with seeds germinated in a

nursery before being transplanted to field Ensures good stand establishment

Crop matures earlier

Increased costs More difficult to mechanize

Higher level of crop management



Conditions for seedgermination

Successful seed germination requires

Viable, vigorous seed

Adequate moisture

Supply of oxygen

Appropriate temperature

Protection from pathogens and pests



Moisture is required for seed germination

Seed survive at very low moisture

Germination starts with imbibition,uptake of

water into the seed Once seed are imbibed and development is

initiated, the seedling is very sensitive todehydration



Moisture for germination

Maintaining an adequate supply of water is essentialfor good germination

In greenhouse (indirect seeding) thorough watering after seeding

monitoring of soil moisture and regular watering or

misting using plastic wrap to retain water

Beware! Many pathogens thrive under high humidity

conditions



Moisture for germination

Direct seeding

preparation of seed bed

good contact between soil particles and seedsfacilitates uptake of water into seed

planting at appropriate depth

deep enough so the soil doesn·t dry out shallow enough that the seed will emerge before its

reserves are exhausted



Oxygen is readily available if seed isplanted in a well drained, porous medium

- soil or greenhouse mix

Oxygen deprivation results fromwaterlogging, flooding or other soil

drainage problems

Germination requires oxygen



Temperature

Requirement varies betweenspecies

Temperature can be adjusted ingreenhouse

use of ´bottom heatµ

In the field, planting depends onenvironmental conditions andweather, not necessarily thecalendar



Protection from pathogens

Developing seedlings are a rich source of food for microbes

Seedlings are relatively unprotected cuticle and other defenses are not fully

developed in young seedlings

Many fungal pathogens cause ´dampingoffµ of seedlings

Phytophthora, Pythium, Rhizoctonia



Protection from pathogens

Preventive measures include:

soil pasteurization (180ÜF, 30 min)

using purchased sterilized soil mix

clean containers

controlling moisture

using clean seed

use of fungicides, seed treatments



Seed coatings

Seeds can be coated with a variety of

compounds to enhance germination and

seedling growth Fertilizer - to stimulate growth

Insecticide - to prevent insect damage

Fungicide - to inhibit growth of fungalpathogens



Specialized seeding methods

Hydroseeding

Spray application of primed seed in a mix

containing mulch and fertilizer



Other seeding methods

Liquid drilling

Seeds are germinated under controlled conditions,

until the radicle emerges Germinated seeds are mixed into a gel that contains

fertilizer

Mixture is sown in prepared field

Pre-germinated seed promotes rapid growth of seedling



Conclusions

Seeds are living organisms, handle with care

Successful establishment of seedlings requires

a rapid transition from dry seed to autotrophicplant

A variety of horticultural practices are used to

promote seedling establishment

seedling establishment

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