Appendix I: Best Management Practice Program for the CLEARFIELD® Brassica juncea Production System

Best Management Practice (BMP) Program for the  CLEARFIELD® Brassica juncea Production System

Developed by  BASF Canada

Table of Contents

1. CLEARFIELD Production System
   1. Introduction
   2. Key Sustainability Issues
2. CLEARFIELD Production System - Guiding Principles
3. Resistance Management in the CLEARFIELD Production System
   1. Herbicide Resistance Management using an Integrated Weed Management (IWM) Approach
   2. Development of Resistance
   3. Identifying Weed Resistance
   4. General Recommendations to Minimize Development of Weed Resistance
   5. Chemical Control
   6. Cultural Control/Crop Management
4. Integrated Weed Management (IWM) in the CLEARFIELD Production System
5. Controlling Volunteers from CLEARFIELD Brassica juncea
   1. Summary
   2. Important Reasons for Control of Volunteers
   3. Cultural and Chemical Options for Volunteer Management
   4. Management of Volunteer CLEARFIELD B. juncea
6. Managing Out-cCossing to Non-CLEARFIELD Crops and Weeds
   1. What is Out-Crossing and gene flow?
   2. Description of Brassica juncea Varieties with Clearfield Technology
   3. Potential for Out-Crossing in Clearfield Brassica juncea
   4. Potential for Out-crossing to Species related to Brassica juncea
   5. Potential for Out-Crossing to Canola
7. Managing Out-Crossing of CLEARFIELD Brassica juncea to Related Species
8. References

CLEARFIELD Production System

Introduction

Brassica juncea (L.) Czern. species is drought and heat tolerant and therefore naturally suited to the southern prairies. This is the main reason that traditionally mustard has been produced in the southern prairies, while canola was grown in the northern grainbelt. In recent times, economic pressure for crop diversification and precipitation patterns have led to increased canola production in the brown and dark brown soil zones. However, based on a three year study conducted by Agriculture and Agri-Food Canada (AAFC) in Swift Current, scientists concluded that oriental mustard (B. juncea) is better adapted to semiarid conditions than canola.

There are two additional agronomic characteristics of B. juncea that are attractive to producers. Firstly, it has very good resistance to blackleg disease, which is now wide spread in Saskatchewan. One of the other important agronomic features of B. juncea is its shattering resistance. The pods of B. juncea do not shatter as easily as B. napus, therefore it has greater potential for straight combining. Saskatchewan Wheat Pool and AAFC conducted experiments from 1998 to 2001 to test whether juncea canola had as much potential to be straight combined as B. rapa or mustard. Over the four year study, there was no significant difference in yield between swathing and straight combining juncea canola.

Canola quality juncea has the same agronomic advantages and suitability to the southern prairies as does oriental or brown mustard varieties, without the limited market and price volatility associated with the mustard market. However, broad spectrum weed control in conventional juncea remains an issue. The development of CLEARFIELD juncea canola will give producers an effective broad spectrum weed control tool while allowing canola juncea to retain its status as non GMO in international markets.

Key Sustainability Issues

The users, developers and marketers of herbicide tolerant cropping systems are responsible for sustaining the production system and must address the key issues of:

• Herbicide resistance management using an integrated approach.
• Control of herbicide tolerant crop volunteers.
• Managing out-crossing to non-CLEARFIELD crops and weedy relatives.

These key sustainability issues form the basis for our stewardship plans for crops grown using the CLEARFIELD Production System. The CLEARFIELD Brassica juncea Stewardship Plan, like those for other CLEARFIELD crops, can be summarized by the following guiding principles:

CLEARFIELD Production System - GUIDING PRINCIPLES

There are a number of GUIDELINES that must be understood and followed by Agronomists and Growers when using CLEARFIELD Production Systems.

• DO NOT exceed a maximum of 2 exclusive Group 2 herbicides on any one field, in any 4 year period
• ALWAYS follow an Integrated Weed Management (IWM) program that includes a wide range of herbicides, cultural practices and crop rotations in order to manage weed populations and minimize weed seed development
• ALWAYS control volunteers in the season following a CLEARFIELD crop
• USE practices which minimize the likelihood of out-crossing to similar crops or related weeds
• Scout fields for weeds or volunteer crops that are uncontrolled by herbicides
• FOLLOW the Best Management Practices outlined in the our CLEARFIELD Stewardship Guide for each crop

Resistance Management in the CLEARFIELD Production System

Herbicides have been grouped based on their mode of action. Herbicides that are in Group 2 are those classed as ALS/AHAS inhibitors. BASF markets herbicides that are in the imidazolinone chemical family and they are members of Group 2. Herbicides such as ABSOLUTE, ODYSSEY SOLO and ADRENALIN used in the CLEARFIELD Production System are examples of Group 2 herbicides. BASF is therefore a key stakeholder in resistance management of ALS resistant weeds.

BASF is committed to maintaining the efficacy of all of its herbicides in order to provide growers with effective, high performance, environmentally sound products for many years. The key to the performance of CLEARFIELD Production Systems is effective weed resistance management. BASF is committed to delivering sustainable cropping systems that incorporate best practice principles. The CLEARFIELD Production System provides alternative options for growers within a well-managed rotation.

Herbicide Resistance Management using an Integrated Weed Management (IWM) Approach

The objectives of herbicide resistance management are to achieve weed control while preserving the value of each herbicide and each herbicide group for the longer term. An integrated approach to weed control is the Best Management Practice to delay the onset of weed resistance to herbicides. Integrated weed management involves the use of a range of methods available to the grower in order to provide effective weed control in crop. The use of herbicides is one of a number of useful tools available to growers.

Development of Resistance

Herbicide Resistance Action Committee (HRAC) is an industry initiative which fosters co-operation between plant protection manufactures, government, researchers, advisors and farmers. The objective of the working group is to facilitate the effective management of herbicide resistance. HRAC has identified a number of factors to consider when evaluating herbicide resistance risk. The most important factors influencing a plant's potential to develop resistance are:

• Biology and genetic make up of the weed species in question: Points of consideration include the following. Weeds that are extremely susceptible to an herbicide, are prolific seed producers and have a large amount of genetic variation within the species may have a greater potential to become resistant to an herbicide. The initial frequency of naturally occurring resistant biotypes in a weed population influences a weed population's potential to develop resistance. Also, the relative fitness or vigor of resistant weed biotypes affects resistance development. Generally speaking, for any particular weed species, the greater the initial frequency of resistance and the greater the fitness of the resistant biotype, the greater the potential for herbicide resistance to develop.
• History of herbicide use and mode of action: continuous use of the same mode of action herbicide for several consecutive years, without tank mixing or sequentially applying herbicides with other modes-of-action, may increase the risk for resistant populations to develop. The greater the selection pressure exerted by an herbicide, the greater the potential for resistance. Although a higher rate of application or sequential applications results in a high level of weed control, it also represents an increased potential for the development of resistance. Likewise, lower herbicide rates, which provide less effective weed control, exert less selection pressure. Label herbicide rates are a reflection of efficacy trials that indicated best control and crop yield responses. Some herbicides, including Group 2 herbicides, have a greater ability to select for resistant weeds then others because of the frequency of resistance alleles in weedy populations.
• Crop management practices: weed control that relies solely on herbicide use and does not combine tillage or other cultural practices with herbicide applications may increase the potential for resistant populations to develop. This includes using crop rotation practices that allow for non-chemical options for weed control as well influence the ability to rotate herbicide type and frequency of use.
• Environmental conditions: environmental conditions that are not conducive to herbicide breakdown in the soil may increase the potential for resistant populations to develop. Continuous dry weather can slow the breakdown of many herbicides (e.g. imidazolinones). High soil pH inhibits the breakdown of some herbicides like SU's. The longer a herbicide persists, the longer it exerts selection pressure on a weed population, particularly if there are multiple weed flushes in one growing season.
• Weed seed bank/Seed soil dormancy: a high soil seed bank within an individual field increases the selection pressure, which in turn increases the likelihood of resistance developing. Seed soil dormancy will also impact on resistance development. Plants with longer soil dormancy will tend to exhibit slower resistance development since selection pressure is reduced. Seeds that can survive for years in the soil may slow the onset of resistance. Weeds with a long seed life may create a large seed bank in the soil. This seed bank serves as a buffer against genetic changes in the weed population, since the seeds do not normally all germinate within one year. Conversely, weed seed with a short seed life germinate within one or two years. This rapidly depletes the quantity of susceptible weed seed and gives any resistant seed a competitive advantage when a selection pressure is applied.

Many exceptions to these generalizations exist, and this makes it difficult to predict which species will develop a resistant population. The time required for a weed population to develop resistance will vary, and depends on many factors, including:

• Selection pressure exerted by the herbicide;
• Herbicide rotation patterns;
• Seed germination dynamics;
• Use of herbicide combinations with different modes of action;
• Initial frequency of naturally occurring resistant individuals in the weed population; and
• The relative vigor of resistant biotypes of weeds.

Based on these factors, models have been developed to predict the development of resistance in a weed population. Current models provide an indication of the development of resistance; these indications are an essential input to the development of resistance management strategies and practices.

Identifying Weed Resistance

It is important to avoid confusing herbicide failure caused by weed resistance with herbicide failure caused by other factors. All other possible reasons for poor herbicide performance should be ruled out before considering the possibility of resistance. These include application error and poor environmental conditions at the time of herbicide application. Shifts in weed populations from susceptible species to species that are less sensitive can also cause weed control problems. Herbicide resistance should be suspected under the following conditions:

• A weed species that is normally controlled by the herbicide now escapes treatment, while other weeds on the label are controlled.
• Other factors such as application error or adverse weather conditions are ruled out.
• Irregular shaped patches of a weed develop in the field and are not controlled with the particular herbicide or herbicide group.
• Weed control records for the field indicate repeated use of a particular herbicide, or herbicides from the same herbicide group.

General Recommendations to Minimize Development of Weed Resistance

Following is a discussion and proposed strategies for managing ALS herbicide resistance in weed populations under the CLEARFIELD Production System. The guidelines for managing the development of weed resistance presented here are consistent with recommendations put forward in provincial crop protection guides and WREAP.

Development of herbicide resistant weeds can be avoided or delayed through good management practices. The recommendations listed below take into consideration many of the points discussed so far and are designed to provide an integrated approach to weed management in order to prevent or delay the onset of weed resistance. Three key areas of integrated weed management are chemical control, cultural practices and crop management.

Chemical Control

Know your herbicide groups.

• Reliance on one product, or on products within the same group may eventually lead to weed resistance. Understanding herbicide classification by product group is necessary to develop an effective weed management strategy.

Keep records of herbicide application.

• Herbicide application records and field mapping are necessary to effectively rotate herbicide groups.

Always read and follow herbicide label recommendations.

• The rate of herbicide recommended provides the most effective control over a wide range of environmental conditions. This will help to ensure weed seed is not added to the seed bank, while minimizing selection pressure.

Use tank mixes or sequential applications of herbicides that have different modes of action.

• Tank mixes allow you to control weeds in more than one way by combining two or more modes of action on the same weed. In order to be effective, both active ingredients need to provide control of the target weed. This minimizes selection pressure and delays the development of weed resistance.

Rotate among herbicide groups.

• Rotate among herbicide groups for both grass and broadleaf weed control. Alternating products used according to mode of action is one of the most effective means of delaying development of weed resistance. Use the minimum number of applications of any one herbicide or herbicide group per season.

Utilize non-selective herbicides.

• Non-selective herbicides applied pre-emergence are an effective means of controlling early flushes of weeds and/or weed escapes. They should be used in conjunction with an in crop herbicide that has an alternative mode of action.

Cultural Control/Crop Management

Cultural (non-chemical) weed control practices do not exert any chemical selection pressure and can help to reduce the level of weeds in the soil seed bank. These practices are important components of an integrated weed control strategy.

Use crop rotations, notably rotations from broadleaf crops to grass crops, winter seeded and spring seeded crops, perennial and annual crops.

• Different crops can help to alter the weed spectrum. It also makes it easier to rotate between herbicide groups.

Plant competitive crops.

• Crops vary in their ability to compete with weeds. Crops such as barley that establish a heavy stand are much more competitive with weeds then crops such as lentils or flax. In most instances, crop competition will increase with higher seeding rates and planting varieties with a tall stature. A competitive crop can reduce weed pressure.

Seed early.

• Early seeding generally leads to better crop establishment and increased competitive ability. Delayed seeding of most crops results in a potential yield loss and is not recommended.

Plant quality seed/Increase your seeding rate

• Certified seed offers a number of benefits and helps to ensure a uniform stand that will compete more effectively with weeds. A more dense plant canopy offers more weed competition.

Combine tillage and/or timely cultivation with herbicide treatments, if practical.

• Direct seeding has been shown to reduce the number of annual weeds over time. However, if your crop production system includes spring cultivation, seed as soon as possible after working the ground to give the crop a head start over the weeds.
• An effective weed management strategy is comprised of multiple weed control options. Herbicide tolerant cropping systems provide yet another mechanism for effective weed control and should be considered as one of the tools for managing the development of weed resistance.

Integrated Weed Management (IWM) in the CLEARFIELD Production System

CLEARFIELD Production System crops are tolerant to the imidazolinones, which are Group 2 herbicides. Group 2 herbicides work by inhibiting acetolactate synthase, an enzyme that is required for the production of the amino acids leucine, isoleucine and valine in plants. Group 2 herbicides are known as "ALS inhibitors".

Continuous use of Group 2 herbicides may result in the selection of weed biotypes with a resistance to this Group of herbicides. Preservation of the effectiveness of this Group of herbicides is vital for efficient and cost-effective agricultural production in Canada. Therefore effective management strategies for weed control delay or avoid the potential for the development of resistant weeds is an important focus of the CLEARFIELD production system.

In addition to the general chemical and cultural control recommendations outlined in the previous section, a number of specific management strategies outlined below, should be followed when using the CLEARFIELD Production System. Growers and agronomists should give consideration to each of the following points, in order to develop an integrated weed management system when using CLEARFIELD crops as part of their production system.

• Make only one application of a Group 2 herbicide per season.
• Apply no more than two (2) exclusive Group 2 herbicides in any four (4) year period on the same field. The use of no more than two applications in four years will slow the development of resistance. Consideration should be given to less frequent use to delay the onset of resistance development. This includes the use of Group 2 herbicides both within the CLEARFIELD Production System and in conventional crops.
• If a Group 2 herbicide has been applied as a pre-emergence application, DO NOT apply further Group 2 herbicides to that crop. Make any further post-emergence applications with herbicides from a different mode-of-action group.
• Where it is possible, care should be taken to avoid applications of Group 2 herbicides in consecutive years unless at least two years previous effective weed control has been achieved, with methods other than the use of Group 2 herbicides.
• Farm practices, herbicide and crop rotations should be developed which allow for the use of alternative mode of action herbicides.
• Where Group 2 resistance is suspected within a weed population, testing of the relevant weeds should be carried out prior to the use of crops in the CLEARFIELD Production System.
• Integrated Weed Management should be undertaken on a field-by-field basis. Specific field planning should take into consideration the history of the field well as the future use options.
• Resistance management guidelines for other herbicide Groups, especially Group 1, should be taken into account when developing and planning rotations.

Crop rotation and CLEARFIELD Brassica juncea

The wait period between canola crops recommended is three years (Source: 2003 Canola Growers Manual). This one in four year cropping rotation is recommended to help manage build up of weeds, disease, and insect pests that are common to canola. The same management issues that lead to a recommended three year wait period between canola crops also are pertinent to juncea canola. Brassica juncea has the same recommended cropping interval as canola.

Studies have demonstrated that crop rotations with high canola frequency have more cruciferous weeds such as stinkweed. Proper crop rotation will allow different herbicides to be used for weed control. For example, a much wider range of herbicides are recommended for use on cereal crops compared to canola. This is especially true for juncea canola that has even fewer herbicides than canola recommended for in crop use. Rotating crops allows for the possibility of rotating herbicide groups and therefore helps delay the development of weed resistance.

Brassica oilseed crops such as canola grown in a short rotation tend to have more problems with diseases such as blackleg and seedling root rot. Other common canola diseases include sclerotinia stem rot and to a lesser extent alternaria black spot. The current juncea canola varieties available are susceptible to sclerotinia. Recommended waiting periods between canola crops to help manage these diseases range from 2-4 years. The intervening cropping years will allow producers to rotate herbicide groups to help manage the build up of herbicide resistant weeds.

Similarly, crop rotation is the cultural control practice recommended for a number of insect pests of canola that are common on the prairies. Production of alternate crops such as cereals will again create the opportunity for the producer to rotate herbicide groups used in his weed management program.

The yield benefit of crop rotation has been demonstrated in each of the three prairie provinces. In studies where yield of canola planted in various stubble types was examined, canola yield was higher on cereal stubble compared to canola stubble (2003 Canola Growers Manual). Numerous factors including climatic conditions, management practices and soil productivity all have an impact on the yield benefit associated with crop rotation. However, the benefits of crop rotation for management of weeds, diseases and insect pests is well documented. The ability to rotate herbicide groups in a more diverse crop rotation associated with canola production will delay the onset of herbicide resistance.

Controlling Volunteers from CLEARFIELD Brassica juncea

Objective: control of all volunteers from CLEARFIELD crops before flowering.

Summary

• Best Management Practice is to control volunteer plants in the year following when a CLEARFIELD crop has been grown.
• Do NOT rely on Group 2 herbicides to control CLEARFIELD volunteers. Group 4 herbicides are the most commonly used management tool for control of CLEARFIELD Brassica juncea volunteers. Certain Group 5 and 6 herbicides are also recommended for volunteer canola and mustard control.
• Volunteers from CLEARFIELD Brassica juncea will be controlled by all herbicides currently registered for control of conventional Brassica juncea, except for imidazolinone herbicides SOLO, ODYSSEY and PURSUIT.
• Clean up of farm equipment during all stages of sowing, harvesting, storage and transport are important in the effective control of volunteers.
• Best Management Practice is to make volunteer control part of weed, pest and disease management strategies for the farm.

Important Reasons for Control of Volunteers

• Volunteer plants act as competitive weeds in following crops or pastures.
• Volunteers may be important in the build-up and spread of major diseases.
• Volunteers increase the risk of herbicide tolerance spreading from cross-pollination of volunteer plants and conventional plants of the same crop species in neighbouring fields.

Cultural and Chemical Options for Volunteer Management

A number of cultural and chemical control options are available to control volunteers including:

• Minimize seed losses at harvest
• Close attention to timeliness of harvesting.
• Correct adjustments in the header.
• Seal all holes and cracks in harvesting equipment which allow spillage, even of small quantities of seed, (especially in the table, front elevator and grain tank).
• Clean out harvest equipment before switching fields.
• Practice good hygiene at harvest and during transport of grain. Secure loads to prevent losses during transport.
• Practice good stubble management after harvest in light of crop rotation decisions. Leaving Brassica juncea seed on the surface will increase seed mortality and help to reduce the seed bank population in the soil.
• Use pre-seed glyphosate application to control weeds and volunteers that emerge prior to seeding.
• Control volunteers along field edges and borders.
• Control ALL volunteers in following crops with proper selection of in-crop herbicides or other agronomic practices such as tillage where appropriate.
• Keep good field records of herbicides used in previous crops and herbicide-tolerant varieties in neighbouring fields to develop effective plans for controlling volunteers.
• A crop of the same species should not follow a CLEARFIELD crop, as controlling volunteers within the same crop species is difficult. Generally speaking, this would also not be a good agronomic practice for disease and weed management.

Management of volunteer CLEARFIELD B. juncea

The small seed size and large number of seeds produced by each B. juncea plant make juncea canola a crop that potentially may produce a large amount of volunteer plants. However, weed survey results indicate Brassica juncea is not a serious volunteer weed problem (Leeson et al., 2005). In the weed surveys conducted during 2001-2003, Indian mustard (Brassica juncea) was ranked 131st most common with a frequency of <0.1% of fields. In contrast, canola/rapeseed ranked 14th and wild mustard was ranked 24th most commonly occurring weed. Seed dormancy and farm management practices are the two most significant factors influencing the persistence of volunteer Brassica juncea.

Despite a long history of cultivation in western Canada, B. juncea has not become an abundant weed, and therefore there is good reason to conclude that it does not have the weedy characteristics of wild mustard and may be less prone than B.napus and B.rapa to become a problem as a volunteer weed. Dormancy has been studied more extensively in B.napus than in either B. juncea or B.rapa. Mature seed of B.napus has virtually no primary dormancy (Lutman, 1993). The vast majority of either Brassica juncea or Brassica napus will germinate within the year after crop harvest. Gulden, et al., (2003) found where canola was followed in rotation by wheat for three consecutive years that after 1, 2 and 3 winters, maximum persistence of 44, 1.4 and 0.2% of the original seedbank was observed, respectively.

Volunteer canola has been shown to persist for at least 4 years in rotation in western Canada (Legere et al. 2001). The duration of persistence is dependent on a number of factors and may be linked to canola genotypes varying in the potential for induction into secondary dormancy. Gulden, et al., (2003) classified 6 canola genotypes on the basis for potential for the development of secondary seed dormancy. Canola genotypes classified as high potential for secondary dormancy exhibited 6 to 12 fold greater persistence then those classified as having medium potential. Large seed size was also found to be associated with secondary dormancy.

To date we are not aware of these types of studies being initiated with B. juncea or B. rapa. However, B. juncea has some attributes that may reduce its volunteer weed potential in comparison with B. napus, such as shatter resistance, smaller seed size and thin seed coat in yellow-seeded varieties. Brassica rapa has had a reputation for being more persistent in the soil than B. napus.

Farm management practices will have a significant impact on volunteer weed problems. Starting in the fall after a crop of B. juncea has been produced and into the next cropping season, there are numerous opportunities to successfully manage volunteer B. juncea. Volunteer B. juncea is easily controlled by several common herbicides, and can be controlled through normal weed control practices commonly used by western Canadian producers.

The first opportunity is in the fall of the year the crop is grown. Practising good stubble management after harvest and leaving B. juncea seed on the surface will increase seed mortality and help to reduce the seed bank population in the soil. Depending on moisture conditions, a significant amount of volunteer B. juncea may germinate in the fall immediately after harvest. These volunteers will be effectively managed with freezing temperatures prior to winter.

The following season there are a number of options available to control volunteer CLEARFIELD B. juncea. Pre-seed control with glyphosate or other non-selective products is a common practice in western Canada for the control of early germinating grass and broadleaf weeds as well as winter annuals. Volunteer CLEARFIELD Brassica juncea that has emerged in the spring will be controlled during this common weed control operation.

As indicated earlier, cereal crops are one of the most common rotational crops with canola or Brassica juncea. Volunteer CLEARFIELD B. juncea will be effectively controlled by a whole range of Group 4 (growth regulator) and Group 6 (photosynthetic inhibitors) herbicides that are commonly used in wheat and barley for annual broadleaf weed control. The following list highlights options for volunteer CLEARFIELD B. juncea control in cereal crops. The herbicides are listed by active ingredient and herbicide Group, not trade name. The list of commercial products available to control volunteer Brassica juncea would actually be larger.

If CLEARFIELD wheat is grown as part of the 4 year crop rotation with CLEARFIELD juncea (Group 2 herbicide use recommended in only 2 out of 4 year rotation), the herbicides available for use on CLEARFIELD wheat will effectively control volunteer CLEARFIELD juncea. The two CLEARFIELD wheat herbicides commercially available are ADRENALIN SC and ALTITUDE FX. Both of these herbicides combine herbicides with different modes of action (Herbicide Group 2 + Group 4). ADRENALIN SC is a pre-mix of imazamox + 2,4-D. ALTITUDE FX is a co-pack of imazamox + fluroxypyr + MCPA. Consideration of herbicide resistance management and volunteer CLEARFIELD crop control was an integral part of our commercial decision on CLEARFIELD wheat herbicide offers.

Likewise, some of the SU herbicide offers on the market are co-packed with Group 4 herbicides. Harmony K and Refine M are two examples of SU product offers that will control volunteer CLEARFIELD juncea. As with our CLEARFIELD wheat herbicides, use of these products on a cereal crop following juncea should only be done in 2 out of 4 cropping years. The use of an SU herbicide without the addition of a Group 4 tank mix partner is not recommended for volunteer CLEARFIELD Brassica juncea control in cereals; Volunteer weed control will not be satisfactory to manage this CLEARFIELD plant.

Peas are a much less common rotational crop following Brassica juncea. In peas a number of options are available for control of volunteer CLEARFIELD Brassica juncea. Basagran Forte (Group 6) can be used at low rates in-crop for volunteer CLEARFIELD Brassica juncea control. Additional in-crop options available to control volunteer CLEARFIELD Brassica juncea include: MCPA sodium salt (Group 4) or Sencor (Group 5).

In summary, Brassica juncea does not pose a serious threat as a volunteer weed. Numerous weed management tools, cultural and chemical are available to effectively control volunteer CLEARFIELD Brassica juncea. These tools are part of the normal weed control practices commonly used currently by western Canadian producers. Management of volunteer CLEARFIELD Brassica juncea will not require any significant change in weed control practices.

Managing out-crossing to non-CLEARFIELD crops and weeds

What is Out-crossing and Gene Flow?

Gene flow is the movement of gametes, zygotes (seeds), individuals, or groups of individuals from one place to another and their subsequent incorporation in the gene pool of the new locality (Slatkin, 1987). Gene flow is a natural biological process and in plants it primarily occurs via pollen or seed dispersal (Levin and Kerster, 1974). The relative importance of gene flow to population genetic structure depends on the distance between donor and recipient populations, population size, how long the process has been in effect, and whether the new gene confers any fitness advantage to the recipient population (Waines and Hegde, 2003).

Out-crossing (or cross-pollination) is a type of mating in plants in which a male gamete of one individual fertilizes a female gamete of another individual (Waines and Hegde, 2003). The term out-crossing generally refers to mating within a species and the term has been used synonymously with gene flow (Gleaves, 1973; Handel, 1983). However, as defined earlier, gene flow can occur through means other then cross-pollination. We will restrict this discussion to pollen-mediated gene flow (out-crossing).

A wide range of factors influence the ability of a given plant to out-cross with others, including synchrony of flowering, stigma receptivity, pollen production, pollen dispersal, pollen viability and environmental factors. The likelihood of out-crossing varies greatly from species to species and variety to variety. Successful out-crossing may result in the offspring displaying characteristics of both parent plants.

The risk of out-crossing can vary between crop and weed species. The focus for management must be on the control of volunteers and managing herbicide tolerant crops and related species.

Description of B. juncea Varieties with CLEARFIELD Technology

There are both vegetable and oilseed types of B. juncea, possibly of different origins. Both types are considered to be natural amphidiploids (AABB genome, 2n=36). It is believed to have derived from natural interspecific hybridization between B. rapa (AA genome, 2n=20) by B. nigra (BB genome, 2n=16) crosses.

CLEARFIELD Brassica juncea was developed by mutagenesis and inter-specific crossing with CLEARFIELD B. napus, followed by backcrossing to B.juncea. It was not derived from recombinant DNA technology, i.e. it is not genetically engineered (GE)". These varieties have been bred to have tolerance to the BASF imidazolinone herbicides, ODYSSEY and SOLO.

Potential for Out-crossing in CLEARFIELD Brassica juncea

All B. juncea varieties have an annual growth habit. Fertilization of ovules usually results from self pollination, although interplant outcrossing rates of 20 - 30% have been reported (Rakow and Woods, 1987). Bees are the primary pollen vector, because the pollen is heavy and sticky and it is not carried great distances by the wind. Cross pollination of neighbours can also result from physical contact of the flowering racemes. Successive generations of B.juncea arise from seed from previous generations.

Potential for Out-crossing to Species Related to B. juncea

Interspecific and intergeneric crosses have been made between B. juncea and its relatives, however, many have been made artificially through ovary culture, ovule culture, embryo rescue and protoplast fusion. Warwick et al. (2000b) have done an extensive review of the interspecific and intergeneric hybrids of B. juncea and related species that have been obtained sexually.

Wild mustard (Sinapis arvensis) is the most abundant of the B. juncea weedy relatives in western Canada. A plant from the cross between B. juncea and S. arvensis was backcrossed into B. juncea and into S. arvensis (Bing et al., 1991). The resulting plants were weak or sterile and produced no seed on open pollination suggesting that this cross would not result in the natural transfer of traits from either species being stably inserted into the other species.

Warwick (2004) also demonstrated that gene flow from B. juncea to S. arvensis is possible. However, the hybrids formed have reduced pollen fertility and do not produce seed when back-crossed with either parent. In the rare situation where hybrids form with the unreduced genome of B. juncea, and have the potential to back-cross to S. arvensis, the herbicide tolerant trait is not stably incorporated into the S. arvensis genome. No interspecific hybrids involving S. arvensis have been confirmed in nature (Warwick et al., 2000a).

Lefol et al. (1997) investigated the production of hybrid seeds between B. juncea and dog mustard (Erucastrum gallicum) or wild radish (Raphanus raphanistrum) using reciprocal crosses. They did not use embryo rescue, so that their measurements referred to seed production which might occur under natural conditions. The R. raphanistrum x B. juncea cross failed to produce any seed, and the viable seed produced from all the other crosses was not considered to be hybrid. Thus the probability of intergeneric crosses between these two weedy species and B. juncea seems to be low.

Potential for Out-crossing to Canola

Numerous studies have been conducted with canola that demonstrate the amount of pollen movement decreases dramatically as the distance from the pollen source increases (Stringham and Downey, 1978, Downey, 1999, Scheffler et al. 1995). In other experiments, less than 0.03% cross pollination was observed when the pollen source was 30 meters away (Staniland et al., 2000). This work on pollen dispersal was done primarily with small scale field trials. Others have suggested that pollen moved over greater distances (Hall et al., 2000).

In terms of related crops, Bing et al. (1991) reported that, there was potential for hybrids between B. juncea, B. napus and B. rapa to produce viable seed that could survive to the next generations.

Warwick (2007) summarized results of ongoing pollen flow studies from transgenic Brassica napus to Brassica juncea. These studies have documented gene flow of 0.005% at distances of up to 200 meters.

Managing out-crossing of CLEARFIELD Brassica juncea canola to related species

Evidence indicates that the herbicide tolerant gene does not confer any competitive advantage to plants unless specific herbicides are used. It does not result in increased weediness or invasiveness of the species. Herbicide tolerant plants created through out-crossing can be managed in the same fashion as herbicide tolerant volunteers.

As discussed in the section titled "Management of volunteer CLEARFIELD B. juncea," the combination of crop rotation, farm management practices and the numerous chemical and cultural methods of weed control available for volunteer B. juncea control will all contribute to effective control of both B. juncea volunteers or any hybrid created through out-crossing.

The following practices should be followed to help in minimize the potential for out-crossing to occur.

• Control all volunteers in the season after growing CLEARFIELD B. juncea canola. (Refer to earlier section, Controlling Volunteers with CLEARFIELD Technology).
• Practice a diverse crop rotation that facilitates use of herbicides from different herbicide groups.
• Avoid planting CLEARFIELD B. juncea canola adjacent to canola or mustard cultivars which have different herbicide resistance traits.
• Maintain hygiene along fence-lines where different canola varieties may germinate.
• Cover loads during transport to avoid dispersing seed.

References

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