Author Topic: Breeding Brassicas for Swede Midge tolerance  (Read 598 times)

Oxbow Farm

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Breeding Brassicas for Swede Midge tolerance
« on: 2018-10-13, 07:08:42 AM »
Swede Midge (Contarinia nasturtii) is an old world midge species that has been recently introduced and established in North America.  It arrived on our farm approximately 5-6 years ago when we began to see visible economic damage, primarily on Siberian/Russian Kale (B. napus) and collard greens (B. olearacea).  Other market gardeners in our area have had severe economic damage to broccoli and cabbage, which are not important crops for our farm. We essentially never grow broccoli and only grow a small amount of cabbage for our own use. 

B. napus kales of the Siberian/Red Russian type are highly attractive to swede midge in general.  The mode of action is the midge lays eggs on the meristems of the host plant, the larvae then hatch and feed on the meristem by producing a enzyme that dissolves the meristem tissue.  This results in total or partial destruction of the meristem/growing point.  Severely affected plants basically melt into a pile of snot for want of a better description. This seems to be a result of secondary infection by fungal or bacterial rotting organisms.  Lesser affected plants simply have scar tissue form in place of the apical meristem, resulting in broccoli and cabbage without heads and kale plants that stop growing from the apex.  The plants then start growing from side meristems to a greater or lesser degree.  Minimally affected plants will simply show a deformed growth pattern before resuming normal growth. 

Swede midge seems to be rapidly expanding its range, and its distribution is extremely patchy even in my local area which has seen midge for almost a decade now.  Some farmers have had severe midge damage for 8 years while others only a few miles away have not seen damage or only began seeing it within the last few years.  But it has been reported in Missouri and Michigan already.  Damage from swede midge seems to be more severe in N. America vs in Eurasia, possible due to lack of predator/parasite relationships present there. 

In short, this species is a total PITA.  There does appear to be some differences in varieties ability to tolerate midge.  I have been attempting in a half-serious way to select for midge tolerance in napus type kale using the mass selection of a collection of varieties and then growing on the parent plants with the least severe damage symptoms.  Thus far, the single variety I have grown that is most resistant is a Tim Peters variety available from Adaptive Seeds called Bare Necessities.  The most susceptible variety I have grown was another Peters variety called Russian Frills, which previously was my FAVORITE napus kale for market. But midge turn into a pile of snot by the first of June.

Currently I've got a mix lot of seed from two generations of selection that I'm calling Peskimidgi Pesternomi Grex.  I am interested in sharing/collaborating with other midge afflicted growers on further developing this.  I'd like to have more folks screening for midge tolerance so we can get some good midge tolerant lines and then be able to select for nice leaf shapes and colors etc.  Right now Peskimidgi is highly variable and gets some questioning looks from my customers.

Diane Whitehead

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Re: Breeding Brassicas for Swede Midge tolerance
« Reply #1 on: 2018-10-15, 09:45:50 PM »
How are they spread?
Victoria, British Columbia, Canada
cool mediterranean climate  warm dry summers, mild wet winters,  70 cm rain,   sandy soil

Oxbow Farm

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Re: Breeding Brassicas for Swede Midge tolerance
« Reply #2 on: 2018-10-16, 04:50:53 AM »
They're on the wind.

bill

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Re: Breeding Brassicas for Swede Midge tolerance
« Reply #3 on: 2018-10-17, 12:44:26 PM »
Are there varieties with greater resistance grown where the midge is native?