Soybean seed integrity question

[blueadzuki]

Hi all,

I was wondering if anyone who has grown soybeans regularly could clarify something for me. While surfing the web I came across a statement that just does not make sense to me, namely that if the seed coat on a soybean is at all damaged in any way (cracked, hole, stress line) the bean inside becomes completely unable to germinate, 100% of the time. This seems to be a little odd to me. Granted I can understand if a damaged seed coat reduced viability of a bean, either by allowing in viruses or bacteria, or messing up the imbibing process (casung the seed to swell in a manner sufficently irregular to rip it apart) but I have difficulty believing that it can be 100% loss. I mean, cracks and chips in seed coats are common for soybeans, the seed coats are usally brittle. stress cracks seem common as well, and don't seem to seriosly cut down on germination (indeed there seems to be a strain (based on pictres) that has stress cracks along the seed coat of the whole population, if the statment was true, wouln't that type be extinct?)This is actually of some concern to me, as if it is true than my plan of segregation my black skinned soybeans into green kerneled and yellow kerneled strains (i.e cutting a little window into the skin of each seed to check the color before I plant) won't work. I the statement an exaggeration so that some will grow (or failing that, is there something I can paint over the cuts to "fake" an intact seed coat?)

[mjc]

It isn't true for any other bean or pea, that I know of.

Like you said, damage does reduce the viability...but by 100%?

I find that very unlikely.

[grunt]

I can't believe that would be true. I can not think of a growth regulating mechanism that could make that happen, particularly on a seed that had had skin integrity breached for only a very short time. I'm not even sure it would be likely on long term integrity breaches, unless storage conditions were pretty bad.
Where was the post originating from? = A hot humid climate might lead to fairly rapid seed deterioration, but that's the only thing I can think of that might have influence.
I put the question to myself as "how would the seed body (which does the germination) know if the skin was broken". Doesn't make any sense to me.
Probably posted by someone who had old or poorly stored seed that didn't germinate for him.

Thinking farther about it, I would expect the opposite to be true = higher germination of seed that did not have to "break through" an intact skin. But that's just my opinion.

[blueadzuki]

Jan 12, 2011 16:28:56 GMT -5 grunt said:

Thinking farther about it, I would expect the opposite to be true = higher germination of seed that did not have to "break through" an intact skin. But that's just my opinion.

Well, while I (of course) do not believe the orginal statment to be true (if I did, I never would never have started this thread in the frist place!) but I can sort of see a few points where the person might have gotten this sort of idea.
A seed coat crack on the hilum side could easily damage the hypocotyl of the seed; on a soybean the hypocotyl is very large very brittle, and very exposed (at least while the seed is dry) Try and peel of all of the seed coat of a soybean while it is dry (this is easier to do with the black skinned ones than most of the white ones, the skin on most black types does not adhere as strongly to the cotyledons as it does on most white ones) and you will snap off the hypocotyl at least half the time.
The other problem that can occur with a lot of modern soybeans is that a whole in the skin can effect how fast the varios areas of the bean imbibe water. By constricting the bean's expansion the seed coat evens out the rate of swelling, so that the whole bean swells up uniformly. Put a whole in that and that section often starts sucking up water faster than the rest of the bean. In many cases this can result in the bean actually tearing itself apart as it swells, with the pressure of the expanding areas casung that crack at the base of the hypocotyl again (being thin the hypocotyl is one of the first places to swell, the areas of the cotyledons it attaches to, one of the last).
If anyone else ever needs to window a soybean, my adive is to do it on the side of the seed perpendicular to the hilum, as close to the middle as you can. That way the hole is over no seam on the inside of the bean, and the chance for being torn up is minimized.