Seed harvest

8. Harvest the seeds and either plant immediately or store seeds in cool, dry conditions. If you will be storing the seeds or have more than you can use at the moment, label the seed packets in such a way that you can track their genetic history later on.

Harvest the seeds: Once the siliques are fully brown and dry you can harvest the mature seeds within. Try not to let the plants become too dry, as the siliques become prone to shattering and you may lose the seeds that fall out as you manipulate the plants. If you’re harvesting seeds from just one or a few siliques, a folded-up 4”x6” note card (see seed tray, figure 3) is sufficient: just crack the silique(s) between your fingertips and let the seeds fall onto the tray. Once all seeds have been recovered, take a look at them to see whether they are round and full or shriveled or otherwise crappy. If it’s the latter, you may need to plant extra seeds to start the next generation, since the germination rate may be reduced. Gently fold the note card lengthwise and pour the seeds into an appropriate receptacle. We use coin envelopes (#2 or #3 Kraft stock), but anything that can keep them secure and dry during storage is fine. Coin envelopes work well because they are stackable and provide plenty of space for labels. They also ‘breathe’, preventing accumulation of moisture or humidity that may result if seeds were harvested ‘a little green’. Try to avoid harvesting and storing plant debris with your seeds; it can also be a source of moisture that could promote precocious germination of seeds or growth of fungi and molds during storage. Place seeds in a cool place for long term storage, preferably over desiccant in a sealed (e.g., Tupperware) container.

Labeling seed packets: Before describing our preferred system for recording details of seed stocks held in storage, we need to be clear on one more bit of terminology—the notion of seed families. It’s not a complicated idea, but we’ve found that it takes a while for many of our students and other users to grasp its meaning. It’s simply a term used to reflect the fact that all of the seeds harvested from a silique or whole plant should have the same mother and the same father and are thus siblings—they constitute a family (sans mom and pop). Depending on the genetic constitution of the parents, the sibling seeds in a family may be genetically uniform (if the parents were homozygous at the relevant locus/loci) or they may differ if the parents were heterozygous at one or more loci. In either case, the seeds constitute a single family, and just as we use surnames to designate most human families, each seed family should get a unique identifier. It is tempting to use a descriptive and literal designation scheme—e.g. “selfed seeds from albino segregant grown on the window sill in June, 2009”—but such a system quickly spirals out of control if you want to be able to track the genetic provenance of seed stocks through multiple generations of selfing or crosses.

We recommend a numerical system in which each seed family received or harvested is assigned a serial number that is recorded on the seed packet or other container and entered into a spreadsheet with a fuller description of genetic attributes. For example, let’s say that Scott and Rick send you seeds harvested from an albino/+ heterozygote parent. ¼ are predicted to be +/+ , ½ to be alb/+, and ¼ to be alb/alb homozygotes. Upon receipt of the seeds, you should assign to the seed family the next available number in your stock list—let’s say it’s 103. You can add whatever additional information that you want or will fit on your seed packet, but make sure that “103” is written at the top of the packet. So now, with your heart racing and your mind spinning with anticipation of seeing what the plants will look like, you plant them out. In short order, you will see that about ¼ of the resulting plants will be distinctly yellow/pale green and ¾ will be just as green as the wild type FPsc plants (from your seed family stock #1) that you grew as controls. Wow! you think, that’s a cool 3:1 ratio among plants in family #103; maybe I can help my students to recognize that among the phenotypically wt sibs in that family, 2/3 are heterozygous for the alb allele, so you have them self-pollinate all wt plants and collect the seeds. How would you designate the plants and how will you designate the progeny seed families?

The individual plant designation is as simple as naming humans (although reversed): surname + given name. Thus, sibling plants in the albino family 103 can be designated 103-1, 103-2, 103-3, etc. When seeds produced by self-pollination of, say, plant 103-2 are harvested they, too, constitute a family (although mom and dad were technically the same individual and that may be where students get confused) and so merit a unique identifying number or surname (e.g., stock #104 derived from self-pollination of plant 103-2). Ink and bytes are cheap, so you can add all of the descriptive verbiage that you want in the hard-copy lab notebook or spreadsheet and some amount can be added to the seed packet. The key to being able to trace the genetic history of your seed stocks, though, is a consistent system of designating both individual plants and individual seed families.