5 things to consider before buying hybrid seeds

Hybrid plants are a crossing between two selected parent plants achieved via controlled pollination  (see how are plants propagated). The seeds produced by this process are called F1 or F1 Hybrids. These hybrids will exhibit very specific qualities. Hybrids have quickly come to dominate the seed market. However, in spite of their increased market presence of hybrids, there are several factors to be considered. They can be summarized as follows:

Loss of Genetic Diversity

The massive shift to the use of hybrids has resulted in a severe reduction in seed varieties. Between 1984 and 1987, 54 of the 230 American and Canadian mail-order seed companies went out of business. With their closure, 943 non-hybrid varieties, or approximately 19% of all varieties, were lost. This trend continues based on the evolving demands of the agriculture industry, i.e. extreme consolidation and the globalization of supply chains. However, genetic diversity must be maintained as it is essential to the survival and adaptability of any given species (see crop wild relatives), something that will be increasingly relevant as a result of changes in climate and pest adaptations.

Higher Prices

Hybrid seeds are typically more expensive due to the financial investment required by the seed companies in order to develop new strains. Investment in this respect relates to finding two suitable partner plants and hand-pollination. The higher cost is passed on to growers. Growers who are producing for the market must then pass on the costs to consumers.

Non-saveable Seeds

Seeds from hybrids cannot be saved as the offspring will be genetically unpredictable. As a result, growers are forced to purchase new seeds each year. This puts undue financial stress on small-scale growers, which further contributes to the consolidation of the agricultural system. Further consolidation means more extreme shifts to mechanization which requires the use of chemicals that typically harm the environment and erode the relationship between food producer and consumer.

Private Property Rights

Unlike open-pollinated seeds, hybrid seeds are patented. This means that the genetic rights to the plants belong to the company producing the seeds rather than being a public good. With seed companies becoming increasingly consolidated, the power and control continue to become concentrated. In 2007, three companies – Monsanto, Dupont and Syngenta – controlled 47% of the world’s seed market with Monsanto alone controlling one-quarter of the market. Since that time, Monsanto has merged with Bayer, Dupont merged with Dow, and Syngenta merged with ChemChina. These mergers resulted in the development of an extremely powerful oligarchy that has a stronghold on the world’s seed market. This chokehold means diminished autonomy and a world subjected to subversive tactics designed to broaden the companies’ influence in the world’s economy.

Commercial Focus

The hybrid varieties produced are typically designed for commercial growers. Therefore, the primary focus of plant breeders is tolerance for machine harvesting and processing, with flavor and texture being of minimal importance. Likewise, hybrid varieties are designed to ripen uniformly which is not necessarily of benefit to home or smaller producers who seek to extend the growing season over as long of a period as possible.

Sources:

Ashworth, S. (2002). Seed to seed: Seed saving techniques for the vegetable gardener. Decorah, IA: Seed Savers Exchange.
https://extension.illinois.edu/hortihints/0102a.html
https://garden.org/courseweb/course2/week2/page18.htm
http://news.agropages.com/News/NewsDetail—21186.htm

question: how are plants propagated?

New plants are created via plant propagation of which there are two types: sexual and asexual.

With sexual propagation, there are two sources of parental DNA resulting in the creation of a third living organism. Sexual propagation involves the floral components of the plant and is the result of the pollination of megagametophyte (egg). There are two types of sexual reproduction.

The first is open pollination, in which the seed produced will be identical to the genetically identical parent plants. Such plants have been inbred (see also the purpose of plant breeding and selection and why it is a never-ending story) to propagate the best qualities of a given variety. All heirloom plants are open-pollinated. The second form of sexual production is hybridization which occurs when two plant varieties are crossed to produce offspring with the best genetic traits of each parent plant (ex. one variety has powdery mildew resistance and one is drought tolerant). The F1 (first) generation plant will exhibit the positive effects of the inter-breedings. However, the following generations (F2, etc.) will produce unpredictable offspring.

The second form of sexual production is hybridization which occurs when two plant varieties are crossed to produce offspring with the best genetic traits of each parent plant (ex. one variety has powdery mildew resistance and one is drought tolerant). The F1 (first) generation plant will exhibit the positive effects of the inter-breedings. However, the following generations (F2, etc.) will produce unpredictable offspring.

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Sexual Reproduction, Photo Credit: b4Fa.org

Success in sexual propagation is not guaranteed and largely dependent on appropriate temperature, water, light, and oxygen levels. For example, if the temperature is too high, it is likely that the blossoms will drop preventing fertilization and ultimately reproduction. Sexual propagation is considered the more cost-effective form of propagation. Likewise, it is a way of preventing the transference of disease from the parent plant to offspring.

Asexual propagation occurs when a piece of a parent plant is removed from the parent plant and regenerates to create a new plant that is genetically identical to the parental plant. Such a form of propagation can be considered cloning. Common methods include grafts, separation, dividing, layering, and cuttings.

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Plant Cutting, Photo Credit: pubs.ext.vt.edu

sources:
https://extension.umaine.edu/gardening/master-gardeners/manual/propagation/plant-propagation/
http://www.cropsreview.com/plant-propagation.html

biological controls in horticulture and agriculture defined and explained

Biological control as it relates to horticulture and agriculture is the use of parasites, pathogens and predators to control pest populations and damage. These biological agents are known as natural enemies. The benefits offered by these biological agents is supported via conservation, augmentation and classical biological control tactics. Most parasites, pathogens and predators are highly specialized which make them ideal for targeted past management.

(see: Natural Enemies Handbook and the Natural Enemies Gallery)

Parasites

A parasite is an organism that lives and feeds on a host.  In this instance, these parasites are called parasitoids because they kill their hosts.  Parasites that infect insects can develop in or outside a host’s body.  Typically, only immature parasites (larvae) feed on hosts.  However, there are instances where the adult females of parasites feed and kill their hosts (ex. wasps that attack whiteflies and scales).  This makes parasitoids excellent for biological control.

Most parasitic insects are flies (Diptera) or wasps (Hymenoptera).  

horn_parasite1
Photo Credit: extension.umd.edu

Pathogens

A pathogen is a microorganism.  These microorganisms can infect and kill their hosts. There are natural enemies like certain bacteria, fungi, nematodes and viruses which can greatly reduce the populations of pests, such as aphids, caterpillars, mites and other invertebrates.  This often takes place under naturally occurring conditions (epizootic) like prolonged periods of high humidity and/or dense pest populations.  Pathogens can also be commercially purchased in the form of biological or microbial pesticides.  Some of the most commonly used pathogens for biological control include Bacillus thuringiensis (Bt), entomopathogenic nematodes and granulosis viruses.

bacillus_thuringiensis
Photo Credit: wikimedia.org

Predators

Predators are organisms that kill and feed on prey. Examples include predatory beetles, flies, lacewings, true bugs (Hemiptera) and wasps. Spiders are also included in this category, as well as predatory mites.  

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Photo Credit: coolearth.org

There is also classical biological control (importation) which is typically only used against exotic pests that have been introduced to a given area by mistake.  This is necessary due to the fact that many organisms that are not pests in their native habitat become pests as a result of a lack of natural controls in a new environment.  Before importation, the pest’s habitat is studied and natural enemies are identified.  The theorized control agents (natural control agents) are then collected and their use is tested in a controlled environment for efficacy before widespread action is taken.  This method is quite effective if proper control efforts are taken.  To ensure maximum effectiveness and reduce the probability of negative environmental impact, importation is only completed by qualified scientists with proper permits in a controlled manner.

The long-term benefits of importation and other biological control efforts are dependent on cooperation with and support from the public, as well as landscape managers.  

The safety of biological control has been questioned due especially in instances where exotic species are introduced to address problems with non-native/invasive species. However, when proper procedure is taken and control measures are used, biological control is considered safe for human health and the environment – especially in comparison to the widespread application of chemical control agents.  Furthermore, the negative impact of biological agents is often much less significant than the negative impact of an invasive species.  

To mitigate the environmental risk, biological control methods should only be used when proper research and management efforts have been made.  

source:

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74140.html

10 common plant disease symptoms

Loss of Turgor Pressure (decrease in water pressure within plant cell walls)
Causes: abiotic factors, bacteria, fungi, nematodes, insects
Examples: Ralstonia solanacearum, Verticillium dahliae, Bursaphelenchus xylophilus

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Photo credit: biology4isc.weebly.com

 

Enations (scaly leaflike structures that lack a vascular system)
Causes: viruses
Examples: Cherry raspberry leaf virus, Pea enation mosaic virus

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Photo credit:  fftc.agnet.org

 

Stunting (dwarfing or loss of vigor)
Causes: viruses, phytoplasma, fungi, nematodes
Examples: Rhizoctonia, Strawberry lethal yellows

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Photo credit: ucanr.edu/

 

Witches’ Broom (dense clustering of abnormally small twigs)
Causes: phytoplasma, fungi, insects, mites
Examples: Ash yellows phytoplasma, Sphaerotheca sp.

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Photo credit: economist.com

 

Galls (abnormal growths)
Causes: fungi, nematodes, mites
Examples: Gymnosporangium sabinae, Meloidogyne spp.

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Photo credit: isponature.com

 

Fruit and Seed Deformation (malformed fruit or seeds)
Causes: abiotic factors, viruses, bacteria, fungi, nematodes, insects
Examples: Catfacing tomatoes, Little cherry disease, Spiroplasma citri, Thrips palmi

catfacing_in_tomato
Photo credit: eorganic.info

 

Tumors (aggregates of cells that have multiplied excessively)
Causes: viruses, bacteria
Examples: Agrobacterium tumefaciens, Cryphonectria parasitica

tomato
Photo credit: cals.ncsu.edu

 

Gummosis (oozing of sap from wounds/cankers on fruit trees)
Causes: abiotic factors, bacteria, fungi, insects, injury to the cutting sites
Examples: Pseudomonas syringa, Colletotrichum gloeosporioides

cytospora-perennial-canker_oozing
Photo credit: utahpests.usu.edu

 

Rot (decay)
Causes: bacteria, fungi
Examples: Arruina carotovora, Ralstonia solanacearum, Phomopsis obscurans, Botrytis cinerea

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Photo credit: clemson.edu

 

Necrosis (death of cells or tissues)
Causes: abiotic factors, viruses, bacteria, fungi, nematodes, insects
Examples: Xanthomonas axonopodis, Fusarium oxysporum, Milbe Tetranychus cinnabarinus

fig2
Photo credit: srs.fs.usda.gov

For more information about plant diseases read:

A Brief Introduction to Plant Diseases

 

question: what is the difference between plant resistance and plant tolerance?

Plant tolerance is the characteristic of a plant that allows a plant to avoid, tolerate or recover from attacks from insects, among other things, under conditions that would typically cause a greater amount of injury to other plants of the same species. These inheritable characteristics are what influence the ultimate degree of damage caused by a pest. Tolerance in terms of agricultural production means that despite stress from a pest or disease, the production levels will remain above the economic threshold.

Resistance means that a plant completely immunizes itself from a particular stress.  This is typically a biotrophic pathogen infection. The host has a resistance gene which prevents the proliferation of the pathogen. The pathogen typically contains an avirulence gene which triggers plant immunity.

Resistance and tolerance are the best defense mechanisms of plants against pests. 

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developing new plants that are resistant to freezing  photo credit: phys.org

There are two main types of resistance: ecological resistance/pseudo-resistance and genetic resistance. Ecological resistance is resistance related to favorable environmental conditions at a given location at a particular time. This type of resistance can be broken down into 3 forms:

  1. Host evasion – this phenomenon occurs when a host passes through the susceptible stages very quickly or during a period when pests are fewer.  This type of resistance applies to an entire species population.
  2. Induced resistance – this type of resistance is the result of some type of changed condition for the plant, such as an increase in available nutrients or water
  3. Escape – this is more or less luck as there is an absence of infestation or injury to a host plant as a result of incomplete infestation.

Genetic resistance is resistance related to (you guessed it) plant genetics.  There are several types of genetic resistance:

Resistance based on the number of genes

  • Monogenic – controlled by a single gene which makes it easy to both incorporate and exclude in plant breeding programs
  • Oligogenic – controlled by a few genes
  • Polygenic – controlled by several genes
  • Major Gene Resistance – controlled by one or a few major genes (vertical resistance) 
  • Minor Gene Resistance – controlled by many minor genes; the cumulative effect of minor genes is called adult/mature/field/horizontal resistance

Resistance based on biotype reaction

  • Vertical Resistance – specific resistance against specific biotypes
  • Horizontal Resistance – effective against all known biotypes; nonspecific resistance

Resistance based on miscellaneous factors

  • Cross-Resistance – when resistance against a primary pest results in resistance to a secondary pest
  • Multiple-Resistance – different environmental stresses (e.g. insects, diseases, nematodes, heat, drought, etc.) results in a new resistance

Resistance based on evolution

  • Sympatric Resistance – resistance that is acquired through the coevolution of a plant and insect (which is why it is important to protect our native pollinators!); governed by major genes
  • Allopatric Resistance – not governed by a co-evolution; governed by many genes

There are three mechanisms of resistance in plants.

Antixenosis (non-preference) resistance mechanisms are those by which host plant has characteristics that result in non-preference for insects in terms of shelter, oviposition, feeding, etc. There are morphological or chemical factors that influence insect behavior and results in the poor establishment of insects. Plant shape and color can also be an important influencing factor.

Antibiosis is the negative effect of a host plant on the biology of an insect. This can include decreased rates of survival, development and/or reproduction and is a result of biochemical and biophysical factors. Antibiosis may be a result of the presence of toxic substances, the absence of essential nutrients or a nutrient imbalance. Physical factors, such as thick cuticles, glandular hairs and silica deposits, also contribute to antibiosis.

Tolerance is a plant’s ability to grow and produce an acceptable yield despite a pest attack. Tolerance is typically attributed to plant vigor, regrowth of damaged tissue and a plant’s ability to produce additional stems/branches.

Both plant tolerance and plant resistance are extremely important to IPM efforts as it helps to reduce costs and amount of other control tactics that need to be implemented. This includes improving the efficacy of insecticides and promoting non-chemical benefits like shifts in predator-prey relationships and reduced pest populations.

The benefits of the use of resistant cultivars are numerous as this method has a high level of specificity, is eco-friendly, lower cost and adaptable to a given situation. The benefits are limited only by the amount of time required to develop new cultivars in breeding programs and by a lack of known resistance genes that can be used. To identify and capture relevant genes, crop wild relatives are often used.