History of Canola Seed Development

A relatively new crop and the only one that was “made in Canada”, canola has become one of the world’s most important oilseed crops and a profitable choice for Canadian farmers in only a few decades. Learn about the biological history of the Brassica napus canola that we are familiar with today along with the variety development improvements that occurred as the uses, consumer preferences and agronomic preferences changed over time.

Overview

Canola varieties grown in Canada belong to the Brassica napusB. rapa or B. juncea species, which in turn belong to the much larger mustard family (Brassicaceae, formerly referred to as Cruciferae). Since B. napus and B. rapa species were first introduced in Canada, plant breeders have developed many more varieties. The development of these varieties with major improvements in agronomics, oil and meal quality greatly influenced the rapid expansion of the canola industry in Canada, especially during the last few decades. Improved seed quality increased the market for canola seed and its products. In 2002, canola quality B. juncea was introduced under contract production. There are considerable differences in agronomic characteristics and yield between varieties that growers carefully evaluate when selecting a variety to grow. Choosing the variety that is best suited to local conditions (i.e. the particular field) will maximize yield and profitability.

Brassica species and relatives

Canola is comprised of three species that are modified (using traditional plant breeding methods) forms of rapeseed or brown mustard:

  • Brassica rapa or Polish canola
  • Brassica napus or Argentine canola
  • Brassica juncea or canola quality brown mustard

Until the early 1990’s, Brassica rapa was referred to as Brassica campestris. The difference in species name arose from an error in classification made by the 18th century father of taxonomy, Carolus Linnaeus. He named the turnip producing Brassica species B. rapa. (“rapa” being Latin for root).

Linnaeus later discovered a related plant that he believed was different from B. rapa. He gave this vegetable oil producing plant the name B. campestris. A review of his classification by taxonomists in the late 20th century found that the two plants in fact belonged to the same species and were cross fertile. Since Brassica rapa was the name first associated with the species, the decision was made to eliminate the use of the term Brassica campestris in favour of Brassica rapa.

B. rapaB. napus and B. juncea species belong to the Brassicaceae (Cruciferae or mustard) family. This family consists of about 3,000 species of plants found mainly in the northern hemisphere. The name crucifer originates from the arrangement of the plants flower petals-diagonally opposite each other in the form of a cross. Many Brassica species have been cultivated since prehistoric times for their edible roots, stems, leaves, buds, flowers and seeds. Members of the B. rapa species include turnip, Chinese cabbage and canola. Members of the B. napus species include rutabaga and canola. B. juncea species include mustard greens, various leaf mustards and brown or Indian mustard.

Rapeseed is closely related to other Brassica species like cabbage, cauliflower, kale, and brown and oriental mustard. The relationships are important to canola plant breeders since they provide wide sources of genetic features for research purposes. Figure 1 outlines the close relationships between Brassica species. B. napus, with its 19 chromosomes, originated about 1,000 years ago from a cross between B. oleracea (cabbage = nine chromosomes) and B. rapa (turnip = 10 chromosomes). The same is true for B. juncea, which originated from a cross between B. nigra (black mustard) and B. rapa (turnip).

Brassica crop relationships shown in the triangle of U
Figure 1. Brassica crop relationships shown in the triangle of U

More distantly related to rapeseed are the species Sinapis alba (white mustard) and Sinapis arvesis (wild mustard). These two species were formerly referred to as Brassica hirta and Brassica kaber, respectively. Besides wild mustard, the Brassicaceae family also contains a host of weed species including:

  • stinkweed – Thlapsi arvense L.
  • wild radish – Raphanus raphanistrum L.
  • shepherd’s purse – Capsella bursa-pastoris (L.) Medic.
  • dog mustard- Erucastrum gallicum (Willd.) Schulz
  • flixweed- Descurainia sophia (L.) Webb.
  • common peppergrass – Lepidium densiflorum Schrad.
  • ball mustard – Neslia paniculata (L.) Desv.

History of canola in Canada

History suggests that rapeseed was cultivated as early as 2000 B.C.E. in India, and was introduced into China and Japan about 35 B.C.E. References to its use or that of a close relative appear in the earliest writings of European and Asian civilizations. Rapeseed plants have the ability to grow at relatively low temperatures with far less heat units required than other oilseed crops. Therefore, rapeseed was one of the very few oil sources that could be successfully grown in temperate extremes. This led to rapeseed being grown in Europe as early as the 13th century. In later centuries, rapeseed was used for both cooking and lighting, as its oil produced a smokeless white flame. Rapeseed had a rather limited industrial acceptance until the development of steam power, when it was discovered that rapeseed oil would cling to water and steam washed metal surfaces better than any other lubricant. It was this special property that led to the introduction of rapeseed into Canada.

The need for Canadian rapeseed production arose from the critical shortage of rapeseed oil that was needed by Allied forces during World War II and were supplied by Canada to break the blockade of European and Asian sources in the early 1940s. The oil was urgently needed as a lubricant for the rapidly increasing number of marine engines in naval and merchant ships.

Argentine type (B. napus)

Prior to World War II, rapeseed had been grown in Canada but only in small research trials at experimental farms and research stations. The trials showed that rapeseed could be successfully grown in both eastern and western Canada. Due to the need for rapeseed oil production in the spring of 1942, a small amount of seed from research trials was distributed to a few experimental farms and stations. However, only 1,200 kilograms (2,645 pounds) was harvested that fall. A considerably larger quantity of seed than this was required for planting in 1943 to relieve the serious shortage of rapeseed oil. This led to the location and purchase of 19,000 kilograms (41,000 pounds) of rapeseed from United States seed companies. This B. napus seed had originally been secured from Argentina. Therefore the name “Argentine” rapeseed was widely used in the early years of production and is still used in Canada as an unofficial name for B. napus varieties. This seed was sown on 1,300 hectares (3,200 acres) in 1943 with a harvest of one million kilograms (2.2 million pounds). Growers received a good return for their production which stimulated an expansion of B. napus acreage the following year. The development of hybridization systems (Ctyoplasmic Male Sterility) with resulting high yield, shorter maturity, disease and pod shatter resistance has led to the dominance of B. napus in the Canadian growing regions.

Polish type (B. rapa)

A Shellbrook, SK farmer in 1936 obtained some rapeseed from a friend or relative in Poland. He grew this seed in his garden for a few years and found the plants well-adapted. However, at this time, there were no established markets in Canada for rapeseed. With the war approaching, and the release of information about the need for rapeseed production, the Shellbrook farmer increased his seed supply and sold seed to his neighbours. Due to the Polish origin of both the farmer and the seed, the species he grew became known in Canada as “Polish” rapeseed. It was later established that this rapeseed belonged to the B. rapa species. Since seed of the B. rapa species was widely distributed at the outset of production, it dominated the acreage for a few years. Yield tests showed that B. napus out yielded B. rapa. However, the earlier maturity and greater shatter resistance of B. rapa made it better adapted to short season growing areas.

Canola quality B. juncea

Canola oil quality B. juncea was developed through traditional breeding methods by Agriculture and Agri- Food Canada (AAFC) Saskatoon, SK Research Centre and Saskatchewan Wheat Pool (SWP). B. juncea is the same species used to produce oriental and brown mustard varieties. In 2002, SWP introduced the first two varieties, Arid and Amulet, under contract production. This species is more suitable to the hotter, drier regions of the southern prairies and will be most adapted to the brown soil zone. B. juncea pods do not shatter as easily as other canola varieties therefore producers will be able to straight combine the crop

Variety development

Variety development is a team effort that involves plant breeders, pathologists, crop quality chemists, physiologists and agronomists, as well as highly trained technicians to back up these professionals. The plant breeders make crosses among promising materials and select for yield and quality characteristics. After several years of selection, promising lines are entered into private and public evaluation trials called Co-operative Tests that are located at over 20 locations across western Canada. After one year of testing in private trials plus one to two years in the public Co-operative Tests, the lines that meet all the required standards for oil quality, yield, herbicide tolerance and disease resistance are evaluated by the Western Canada Canola/Rapeseed Recommending Committee. Lines that meet the criteria of the Committee are recommended to the Canadian Food Inspection Agency for registration.

It usually requires eight to 10 years from the initial crosses until a variety is registered. Rapeseed breeding began soon after the crop was introduced at AAFC, Saskatoon. Other rapeseed breeding programs were initiated at the University of Manitoba in Winnipeg, MB in 1953 and at the University of Alberta, in Edmonton, AB in 1969 to develop more regionally adapted varieties.

Rapeseed varieties

The original seed stocks of the B. napus species from Argentina contained a mixture of plant types, and were not licensed. However, these seed stocks provided the genetic material for the development of Canadian B. napus varieties. Similarly, the B. rapa seed stocks originally from Poland were not licensed, but were utilized in breeding programs for the development of later varieties.

Early breeding programs concentrated on improvements in agronomic characteristics and in oil content. The first rapeseed variety licensed in Canada was released from AAFC Saskatoon. Here’s a list of rapeseed varieties and when they were introduced:

  • Golden (1954) – a B. napus selection from Argentina with improved oil content and lodging resistance (AAFC, Saskatoon)
  • Arlo (1958) – a B. rapa Swedish variety
  • Nugget (1961) – a B. napus selection from Argentina with improved oil
  • Tanka (1963) – a B. napus selection from Golden with improved yield and seed size (University of Manitoba)
  • Echo (1964) – a B. rapa selection from Polish with improved yield (AAFC, Indian Head, SK)
  • Target (1966) – a B. napus selection from Tanka with a major improvement in maturity, plant height, oil content and yield (University of Manitoba)
  • Polar (1969) – a B. rapa selection from Polish with improved oil and protein content (University of Manitoba)
  • Turret (1970) – a B. napus selection from Target with improved maturity, oil contents and yield (University of Manitoba)

Currently over 100 varieties are registered for planting in Canada. Life science/seed companies continue to innovate and improve varieties for pest resistance, lodging, pod shatter, and maturity, resulting in higher yield potential and reduced risk for farmers who grow these varieties.

Fatty acid profiles in edible oils

Edible vegetable oils are made up of fatty acids. The types of fatty acids determine whether a vegetable oil is used for edible or industrial purposes. Certain fatty acids such as linoleic acid are considered essential in human diets since they cannot be synthesized by the body but must be obtained from the diet. All of the rapeseed varieties presented above produced oils containing large amounts of eicosenoic and erucic acids which are not considered essential for human growth. A comparison of rapeseed oil and oil from early canola varieties to other vegetable oils is shown in Table 1. A comparison of current canola oil and other edible oils or dietary fats are available on CanolaInfo.org.

Table 1. Comparative analysis of fatty acid contents of vegetable oils

Major fatty acids (%)

Low erucic acid rapeseed (LEAR) varieties

As early as 1956, the nutritional aspects of rapeseed oil were questioned, especially the high eicosenoic and erucic fatty acid contents. Canadian plant breeders responded quickly with isolation of rapeseed plants with low eicosenoic and erucic acid content-by 1960 for B. napus and 1964 for B. rapa. These desirable characteristics were then bred into suitable varieties. Here’s a list of low erucic varieties introduced:

  • Oro (1968) – the first low erucic acid B. napus selection from crosses between Nugget and an unlicensed forage crop cultivar Liho, which contained low erucic acid (AAFC, Saskatoon)
  • Zephyr (1971) – a B. napus selection from an Oro X Target cross with improved oil and protein content (AAFC, Saskatoon)
  • Span (1971) – the first low erucic acid B. rapa variety developed from low erucic acid selections from Polish and Arlo (AAFC, Saskatoon)
  • Torch (1973) – a B. rapa selection from Span with improved yield (AAFC, Saskatoon)
  • Midas (1973) – a B. napus selection from crosses between Target and a low erucic acid source with yields equal to Target but lower in protein content (AAFC, Saskatoon)

The development of low erucic varieties represented a major quality improvement and allowed Canada to first establish a maximum level of five per cent erucic acid in the oil component of the seed. Continual improvements in canola varieties through plant breeding have allowed this maximum to be reduced to less than two per cent erucic acid, which is currently the world standard.

Low erucic acid and low glucosinolates canola varieties

While the rapeseed oil quality changes were being bred into suitable varieties, plant breeders were also working hard with animal nutritionists to change the meal quality. Rapeseed meal is an excellent source of protein with a favourable balance of amino acids. However, the use of rapeseed meal in rations was limited by its glucosinolate content. Most plants of the mustard family contain glucosinolates. Glucosinolates are responsible for the pungent odour and biting taste, which ranges from the hot flavour in mustard seed and horseradish, to the more subtle flavours of rutabaga and cauliflower.

The glucosinolates in rapeseed led to palatability and nutritional problems when fed to livestock and poultry. The glucosinolates break down into other compounds during crushing and feed formulation. High levels of glucosinolates in rations fed to livestock and poultry resulted in reduced feed efficacy. For this reason, plant breeders searched for genetic material low in glucosinolates. In 1967, seeds from plants of the Polish variety Bronowski were found to be low in glucosinolates. This genetic source for low glucosinolates content was then utilized to develop low erucic, low glucosinolate varieties.

The University of Manitoba developed the first low erucic acid, low glucosinolate variety, Tower, in 1974. The term “double low” is used to describe varieties with low erucic acid and low glucosinolate levels. In 1977, two more “double low” varieties were registered, the first Polish variety, Candle, developed by AAFC, Saskatoon, and the second Argentine variety, Regent, developed by the University of Manitoba. Canada became the first country in the world to produce large quantities of rapeseed with low erucic acid in the oil and low glucosinolates in the meal.

This new improved quality in the seed, oil and meal needed a name to distinguish the commodity from common rapeseed. The term “canola” derived from “Canadian oil” was adopted. The term “canola” is not just a Canadian term and is no longer an industry trademark. Canola is defined in Canadian food acts, feed acts and the Seeds Act. The official definition of canola is: “An oil that must contain less than two per cent erucic acid, and less than 30 micromoles of glucosinolates per gram of air-dried oil-free meal.” Except for specialty fatty acid varieties like high erucic acid destined for specialty industrial markets, the varieties registered in Canada must be of canola quality.

Canola oil quality B. juncea was developed by AAFC, Saskatoon and Saskatchewan Wheat Pool by changing the fatty acid profile to that found in B. napus and B. rapa and reducing the erucic acid and glucosinolates levels to the canola standard.

Herbicide-tolerant canola

Conventional canola is tolerant to a variety of herbicides. Through mutagenesis and gene transfer, plant breeders have developed canola that is tolerant to specific herbicides or groups of herbicides. Here is a list:

  • Triazine-tolerant canola (TTC) was developed to allow growers to plant canola on fields infested with cruciferous weeds such as wild mustard, stinkweed, ball mustard and a number of other weeds, many of which cannot be controlled by herbicides in conventional canola. Unfortunately the triazine resistance from the B. rapa weed (bird’s rape) is due to a cytoplasmic mutant, which meant that TTC varieties yielded considerably less when compared to conventional canola varieties under weed-free conditions. Early work on triazine-tolerant canola took place at the University of Guelph, with the first B. napus variety, OAC Triton, registered in 1984.
  • In 1995, the first imidazolinone-tolerant (Pursuit + Odyssey herbicidesB. napus variety “45A71” was registered. This variety and others contain a tolerance trait that was developed through mutagenesis by Cyanamid (now BASF).
  • In 1995, the first transgenic B. napus variety, Quest, was registered. Quest is tolerant to the herbicide glyphosate (Roundup) and was developed by Monsanto.
  • Innovator and Independence were granted registration in 1995. These transgenic B. napus varieties were developed by Aventis and contain a gene that provided resistance to the herbicide glufosinate ammonium (Liberty).
  • In 1999, several bromoxynil-resistant varieties-295 BX, Armor BX, and Zodiac BX-were developed by the University of Manitoba.

From 1995 to 2001, over 100 herbicide-tolerant varieties were recommended for registration.

Hybrids and synthetics

A canola hybrid is simply the result of crossbreeding two lines of canola. Research in the greenhouse showed that making hand crosses between two distantly related lines of canola resulted in yields that were up to 45 per cent higher than either parent line. This increased yield is the result of heterosis or hybrid vigour. The more distantly related the parents, the greater the resulting hybrid vigour. However, producing hybrid seed by hand for large volumes of seed is economically impractical. Since B. napus varieties are mainly self-pollinated, the self-pollination of the parent lines must be controlled to make hybridization commercially feasible.

To date, several approaches have been taken to develop hybridization systems in B. napus. The first relatively successful programs utilized more traditional hybrid breeding methods such as cytoplasmic male sterility (CMS). Researchers discovered that some Brassica species and close relatives had male-sterile cytoplasm (material surrounding the nucleus of a cell). At the cellular level, fertility is controlled by an interaction between the cell nucleus and cytoplasm. The CMS systems for canola hybridization depend upon this mutation in certain cytoplasmic bodies that result in failure to develop functional pollen or anthers. Use of CMS allowed canola breeders to produce canola female plants that either fail to make pollen, fail to shed pollen or make pollen that is unable to cause self-fertilization. The hybrid system is normally composed of three components- a male-sterile Line A, a maintainer Line B and a restorer Line R (Figure 2).

CMS hybrid breeding method
Figure 2. A traditional hybrid breeding method called cytoplasmic male sterility (CMS) which is composed of a male-sterile Line A, a maintainer Line B and a restorer Line R

Female plant flowers from Line A have a sterile cytoplasm and do not produce pollen and cannot self-pollinate. This CMS characteristic is inherited maternally. Therefore, when a CMS female Line A, is crossed with a genetically identical maintainer Line B that produces pollen, all the seed produced retains the CMS trait. The restorer Line R is genetically different from Line A and contains nuclear genes that compensate for the defect in the cytoplasm and restore fertility to the hybrid cross. The first commercial CMS B. napus hybrid, Hyola 40, was registered in 1989 by Advanta Seeds. This was quickly followed by the very popular hybrid Hyola 401 in 1991.

A novel hybridization system was developed by Plant Genetic Systems in Belgium through biotechnology. This system involves the use of two parental lines. The first parental line is male sterile, does not produce viable pollen grains and cannot self-pollinate. A gene isolated from a common soil bacterium and inserted into the parental line causes this nuclear male sterility. The gene controls production of a specific enzyme in a specific anther cell layer and at a specific stage of anther development resulting in no pollen production. The second parental line contains another gene, obtained from the same common soil bacterium that produces an inhibitor enzyme that counteracts the sterility enzyme in the first parental line to restore fertility. A gene that confers tolerance to the herbicide glufosinate ammonium (Liberty) was inserted into both parental lines. When the two lines are crossed, the progeny is a 100 per cent true hybrid. And since fertility is restored, the hybrid plants are fully fertile and produce seed. The first Liberty-tolerant hybrids (called 3850 and 3880) were registered in 1996 by Aventis (which became part of Bayer CropScience and is now BASF).

Hybrid breeding techniques, while reasonably successful in B. napus, have not been successful in B. rapa variety development. An alternative breeding method to exploit the heterosis available in the Brassica family is the production of “synthetic” varieties. Synthetic canola varieties are developed by blending seed from one parent with seed from another parent and growing out the mixed seed to produce a Certified synthetic seed (Figure 3).

Synthetic B. rapa canola breeding and multiplication
Figure 3. Synthetic B. rapa canola breeding and multiplication

Synthetics of B. rapa are usually composed of two, or at most three, parental lines. The resulting Certified synthetic seed composed of a mixture of hybrid and parental plants tends to be more stable over a wider range of environmental conditions than conventional varieties. In comparison, a synthetic canola variety is usually intermediate between conventional varieties and hybrids in terms of capturing heterosis. B. rapa canola is self-incompatible, meaning the plant cannot self-pollinate with pollen from a flower on the same plant, but must pollinate with other plants in the field. This self-incompatibility in B. rapa is an advantage in making synthetic varieties. The first B. rapa synthetic varieties, Hysyn 100 and Hysyn 110, were registered in 1994 by Advanta Seeds.

Synthetics of B. napus are developed from two or more parental lines, which are then mixed in equal proportions (although not always) and grown in isolation. As B. napus is self-compatible and the degree of outcrossing is dependent on insect pollination, there will be varying degrees of crossing between the parental lines. The seed of the next generation will be a mixture of the parental lines and all possible hybrids between them. For example, a three parent synthetic would include the original three parental lines and the three possible hybrids. This process can be continued for another generation before the seed is released as Certified. As the degree of outcrossing is variable, it is difficult to predict what levels of heterosis will be achieved in the commercial seed. The first synthetic B. napus variety registered in Canada was Synbrid 220 in 1997. The success of hybridization to exploit heterosis and yield gain has removed B. napus synthetic lines from commercial production.

Winter canola varieties

Winter (fall-seeded) rapeseed is widely grown in parts of Europe and Asia. The term rapeseed is used, but many of the varieties have similar erucic acid and glucosinolate content to Canadian varieties and fit the canola definition. Winter rapeseed greatly out yields spring types as shown by Swedish yield data in Table 2.

Table 2. Average yield in Sweden of four types of rapeseed

Early winter varieties introduced and registered in Canada were of European origin. Since they did not meet the standards for glucosinolates, they were rapeseed varieties. However, later breeding work in Europe and eastern Canada produced winter canola varieties. The first Canadian-bred winter canola, OAC Winfield, was developed by the University of Guelph, in Guelph, ON and registered in 1988. In western Canada, winter canola is not grown commercially because of unsatisfactory winter hardiness. An occasional crop of a hardy variety may survive some winters in the southern prairies, but attempts to grow it consistently have always failed. Winter canola is slightly less winter hardy than winter barley that also rarely survives prairie winters. A major increase in winter hardiness is required for successful production in western Canada. Varieties with this degree of winter hardiness have not likely been observed to date anywhere in the world.

Research trials by the University of Guelph have shown that winter canola has limited potential for some areas of Ontario. Where winter canola successfully overwinters, it will outyield spring canola by 40 to 50 per cent. Management studies at many locations throughout Ontario have shown that winter canola has the best chance of winter survival and high yields when grown on well-drained, lighter-textured loam soils and on sandy loam soils in southern Ontario with good snow cover. Winter survival is not very good on heavy clay soils or soils with poor drainage due to heaving.

Specialty fatty acid varieties

Canola oil is accepted around the world as a healthy oil low in saturated fat. However, there are markets available for oils with specific oil characteristics for special functions. Specialty fatty acid canola varieties are tested and recommended for registration by the Specialty and Contract Registration Committee, a sub-committee of the Western Canada Canola/Rapeseed Recommending Committee. Specialty varieties are restricted to contract production through private companies.

High erucic acid rapeseed (HEAR)

Prior to the reduction in erucic acid levels which produced canola, rapeseed oil was used both for edible and industrial purposes. The high levels of erucic acid made the oil useful in the production of lubricants. Today there remains a market for a significant acreage of high erucic acid rapeseed oil for use in plastics, lubricants, lacquers and detergents.

Plant breeders increased the erucic acid level in conventional rapeseed to produce high erucic acid rapeseed (HEAR). At the same time, they reduced the glucosinolate levels so that the meal from HEAR varieties was more readily marketable as a livestock feed. The first HEAR (B. rapa) variety, R-500, was developed at the Agriculture and Agri-Food Canada Saskatoon, SK Research Centre. It produced a high glucosinolate meal. The second HEAR (B. napus) variety, Reston, was registered in 1982 by the University of Manitoba, in Winnipeg, MB. It contained 40 to 48 per cent erucic acid and medium glucosinolate levels. It was de-registered in 1989. Since then many HEAR varieties have been developed and released by the University of Manitoba.

Low linolenic and low linolenic/High oleic canola

Plant breeders also recognized that by manipulating other fatty acids different nutrient and processing characteristics could be produced in the resulting oil. The first variety in this category was developed at the University of Manitoba and registered in 1987 under the name Stellar. Stellar had a reduced linolenic fatty acid content (three per cent), which resulted in significant improvements in the processing and keeping quality of the oil. High linolenic acid makes oil go rancid. Since Stellar, companies such as Cargill Specialty Canola Oils, Pioneer Hi-Bred and Dow AgroSciences have registered varieties with modified fatty acid profiles, such as high oleic, low linolenic or high oleic and low linolenic.

Future variety developments

For the past decade varieties have changed rapidly as new quality and agronomic characteristics have been introduced. If Canadian canola plant breeders are as successful as they have been in the past, there will be many breeding improvements to look forward to in the next decade. Potential breeding improvements that plant breeders are working toward (or continue to improve on) include:

  • resistance/tolerance to drought stress
  • frost tolerance (late spring and early fall frosts)
  • elimination of green seed
  • improved nutrient use efficiency
  • even lower saturated fatty acid content
  • early maturing B. napus for shorter frost-free areas
  • new herbicide tolerance
  • disease resistance – ex. to clubroot, blackleg, sclerotinia, verticillium stripe, etc.
  • insect resistance – ex. to flea beetle, root maggot, cabbage seedpod weevil, etc.
  • cold temperature tolerance for improved germination and emergence
  • higher yielding hybrids
  • pod shatter and pod drop resistance

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