Wednesday, April 23, 2014

Broccoli and Napa Cabbage On-Farm Plant Breeding Projects at Fifth Crow Farm, in Pescadero, CA by Steve Peters

Open-pollinated, on-farm breeding offers important advantages to the farmer/breeder to adapt a crop to his or her unique environment. 

Fifth Crow Farm is a certified organic produce farm located near the Pacific coast in central California, a few miles from the picturesque town of Pescadero. The region is both blessed and challenged by the maritime climate. Summer and winter temperatures are moderate, and days are often foggy.

The good folks at Fifth Crow, Teresa Kurtuk, Mike Irving, and John Vars, were gracious enough to allow us to undertake a plant improvement project on their land. Over a delicious farm-fresh lunch, we discussed strategies for integrating the seed work with their on-going vegetable farming activities.

For this location, I chose to work with two OP brassicas; a Napa-type (heading) Chinese cabbage called Nozaki Early, and an heirloom broccoli called Early Green, favored for its high-yielding production of side shoots. In the commercial trade, both of these crops are dominated by F1 hybrid varieties, which means that farmers cannot save their own seed. We feel it is necessary to offer more choices of good quality open-pollinated varieties for seed sovereignty and food security.                        

My goal from the outset was to develop a vigorous and reliably-heading Napa cabbage, and a broccoli with tight, well-formed heads, and extended harvest.  Seedlings were placed in the field in early May. We planted about 750 transplants for each crop. 

The Napa cabbage seedlings were covered until mid-June, to protect them from flea beetles. The large populations provided me the opportunity to select only the very best plants (about 10% of the total) for seed production.

All selections were made prior to any flowering, to avoid pollination from culls. Chosen plants are flagged, and left to mature. This approach has the added benefit of allowing harvest for fresh produce of any plants not to be saved for seed.

With the Napa cabbage, I was selecting for sturdy, dense, upright heads of substantial size. The ideal form was  barrel shaped, however, I allowed for some variation in the size and shape, if a plant showed outstanding vigor.

 Culling began as soon as the floating row cover was removed, in mid-June. This plant was rogued-out, as it was a premature bolter. Rejects made great kimchee!

 Plants were also removed if they had loose heads, were stunted, or had other forms considered off-type. The maritime climate of this region provides an extra-long window of good brassica growing conditions. However, Napa cabbage, when sown in spring, has a tendency to form looser, more open heads because of increasing day length at this time.  Similarly, the florets of broccoli are also more open in spring plantings. The summer planting, with decreasing day length conditions, results in tighter, better-formed heads, and is generally considered the optimal planting time for these crops.

I chose to plant in spring deliberately, when days are lengthening, in order to observe plants in less than ideal conditions. This exaggerated the individual plant differences within the population, allowing for easier discrimination. Under perfect conditions, phenotypic variations could go unnoticed.

Within a few weeks we noticed a large number of sickly plants in both crops, particularly among the Napa cabbage.

On pulling these up, we discovered the problem: club root, or Plasmodiophora brassicae. It is caused by the invasion of a phytomyxea, a soil-borne plant parasite, into the roots, creating the obvious clubbed roots and hampering the plant's ability to uptake moisture and nutrients. More than one quarter of the population of both crops was removed due to this disease. These plants went into the landfill rather than the compost or to the chickens, to reduce the chance of spreading the infection.

While the entire field harbored this disease, certain areas were especially hard-hit, as can be seen by the gap in the middle of the plot above. At first this seemed like a disaster, but we quickly realized that, rather, it might be an opportunity to select for club root tolerance in our crops.

The broccoli was also affected by club root, though not as seriously as the Napa cabbage. 

The first Napa cabbage plants began flowering in late June, and by late July every remaining plant was flowering.

 Brassicas are insect pollinated, as might be guessed by the fairly showy and colorful flowers. Bees will travel up to a mile in search of nectar, so it is important to isolate seed crops from other flowering brassicas of the same species. Napa cabbage is Brassica rapa, the same species as turnips, and broccoli raab.

 This Early Green broccoli displayed good form and was left for seed. Broccoli is Brassica oleracea. This species also includes cauliflower, cabbage, kale (except Siberian kale), collards, Brussels sprouts, kohlrabi, and Chinese broccoli.

A great example of a big plant with many side shoots.

 I experimented with leaving the center head for seed on some plants, while harvesting it on others and allowing the side shoots to produce all the seed. There was not much difference in seed yield per plant between these approaches; therefore I recommend harvesting the center head for fresh produce...enjoy!

           Let the fun begin! All remaining plants (55 Napa cabbage; 72 broccoli) intermated promiscuously! No fear of cross-pollination between the two distinct species.

 The seed harvest window for the broccoli lasted for about 3 weeks - from late September to mid-October.  Whole plants, including roots, were pulled, then thoroughly dried in a sheltered, airy space.

Each plant was harvested and processed individually. Seed yields per plant ranged from 1-20 grams (2/3 oz) for Napa cabbage and 6-95 grams (over 3 oz) for broccoli.

The threshing step, i.e., removing the seed from its pod and stem, was accomplished by hand-rubbing. 

Seed from each plant was kept in its own labeled bag.

A small, round-holed screen allowed for all the seed (and a little chaff) to drop into the container below. 

Not quite clean...yet.

 The final cleaning step is to gently spill the seed in front of an electric fan. Before electricity, this winnowing was accomplished by tossing seed and chaff up in the wind. Lighter chaff is blown away, heavier, viable seed falls onto a tarp or container for collection.

With the cleaning process completed, the seed is put in individual bags. We have now begun year 2 of the project. Last year was the initial field selection. This year we will conduct the progeny testing. For both the Napa and the broccoli, we have planted 30 seeds from each of the 50 highest seed-yielding plants from last year. In a few weeks we will transplant out the most vigorous 15 plants from each of these, for a total population of 750 for each crop. In the coming year, I will evaluate each group of fifteen plants as a distinct "family". This is called progeny testing. As I discover superior families, I will eliminate the less desirable groups. I call this sheparding the good genes. More on this process in a future blog.

1 comment:

  1. Thanks Moria for sharing your Broccoli and Napa Cabbage On-Farm Plant Breeding Projects with us. Your article very well described the process and journey of your project. Keep updating about your projects.

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