A novel looking
canola plant could be the key to disease avoidance in canola.
New approach to sclerotinia management |
Stephen Denys
Growers attending Zeneca Seeds Performance Trials
this past summer had to take a second look at one particular variety being demonstrated
for the first time. What growers saw was the first canola variety to produce flowers
without petals. This unique new technology is called apetalous canola, and it may
literally change the way canola is pictured in the field.
"The theory behind the apetalous technology is that by having no petals, the food
source for sclerotinia spores is removed, which greatly reduces the risk of disease
development", says Greg Buzza, Research Manager for Zeneca Seeds in Canada.
Sclerotinia is a major foliar disease in canola that causes millions of dollars in damage
each year. It is estimated that at least 9 percent of canola fields are sprayed with a
fungicide each year to limit the losses caused by the disease.
The development of apetalous canola was initiated after Zeneca Seeds researchers
investigated the sclerotinia disease cycle. "Initial Sclerotinia infections usually
occur at the same time as the onset of flowering in canola", says Bill Greuel,
Product Development Agronomist with Zeneca Seeds. Greuel describes the infection process
as part of the lifecycle of the disease. "Initially overwintering sclerotial bodies
germinate in the soil and produce apothecia, which are small fruiting bodies that produce
ascospores. These ascospores, or fungal seeds, are released into the air and land
throughout the canola canopy." Greuel says the ascospores require dead tissue to
germinate, which is provided by flower petals. "Petals infected with ascospores fall
on leaves and on the axils of plant stems. As the petals decay, they provide a food source
for the germinating ascospores." Greuel says the lesions that we see on stems and
leaves, is the result of the fungal growth. "As the fungus grows it produces a
substance called oxalic acid, which breaks down the pectin in the cell walls causing the
white soft rot associated with sclerotinia and causing the economic damage associated with
the disease."
Greuel says this is where apetalous canola comes in. "By taking away that initial
food source of dead and decaying petals, the amount of sclerotinia can be reduced, but not
necessarily eliminated". He notes that ascospores can still infect dead sepals, which
are the small green spinelike structures that flank each of the four petals on a canola
flower. In addition, if sclerotial bodies germinate later in the growing season, they can
also infect dead leaves which have senesced and fallen off of the stem. The advantage to
apetalous canola is that it delays the onset of any possible infection, increasing the
production capacity of the plant.
The first apetalous variety recently completed its second year of coop testing, but final
data was not available when this article was written. However in the first year of coop
testing the experimental apetalous variety ZNA005 yielded 3% higher than the average of
the check varieties (Excel, Legacy and Defender). The variety also has an R rating for
blackleg and was rated as being two days earlier than the check varieties for maturity.
From a quality perspective, the initial indication is that the variety will more than meet
the criteria for registration in Western Canada with a 0.40% protein premium, and 0.75%
oil premium over check varieties. In the 1998 Zeneca Seeds Seed Performance Trials program
the variety showed yields in a range comparable to other
varieties on the market with similar quality characterisitics. If registered in 1999,
Zeneca Seeds will have limited seed volumes of this initial apetalous variety.N1598 |
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