Testing Sugar Levels in Individual Kernels

[Joseph Lofthouse]

I have been doing more and more testing with
the equipment and techniques that I expect to
use while developing a sugary enhanced
multi-colored sweet corn.

With my current equipment it is possible to
test the sugar levels in individual kernels,
(if I use kernels near the base of the cob
and not at the tip).

My technique is:

Use a knife to cut off a a few kernels near
the base of the cob, cutting deeply to get
the whole kernel.

Nick the kernel to break the skin.

Use my fingers to squeeze the juice into a
micro-centrifuge vial and centrifuge for a
few minutes.

Use a tiny pipet to transfer the juice onto the
measurement window of the refractometer and
read the percent sugar.

My plan is to do a preliminary screening on each
plant by squeezing some juice from a dozen
or so kernels directly onto the window of the refractometer,
and only do individual kernel testing on the cobs
who's percent sugar falls into the range that
homozygous cobs would be expected.
(I also am able to test individual kernels without
centrifuging. The results are +/- 2% sugar but that
is more than enough accuracy to differentiate between a
kernel with 10% sugar and one with 30%. I'm really
thinking a centrifuge is not needed. )

Since all of my pollen is theoretically
sugary enhanced, then while I am testing the individual
kernels if any of them are not high sugar then the mother
plant was not homozygous for se. If I test 7 individual
kernels on a cob, there is a less than 1% probability that I
would accidentally select for a non-se+ mother. I figure
that I'll start by testing 3 individual kernels, that aught
to eliminate about 90% of the cobs that are not homozygous
for se.

My equipment is:

A Beckman 5414 centrifuge running on a
300 Watt inverter attached to the truck battery.

Refractometer RHB-32ATC

The more I think about it the more I think I'll just take
a couple of rolls of colored yarn, and the refractometer
out to the field, and test each cob, until I have made a
determination. Then tag the plants, Green for se+,
Yellow for one se gene, and red for normal sweet corn.

Regards,
Joseph

[raymondo]

Looks like you're set to go. Good luck with it. I'll be watching with interest.

[spero]

Are you confident you can get this 2% (or even 3%) refractometer reading ? I hope you are right. I have only one experience. I bought the refractometer for this purpose. I squeezed out some corn juice onto the plate and did not get what I thought was a readable reading. I put it away. After your earlier discussion, I tried squeezing some juice and letting it settle, and was able to get a clear reading.
Given that, I had planned to buy a bunch of little containers, go down the row cutting and squeezing kernels & leaving the juice by the plant, then come back down the row to do readings. Squeeze & read is what I was hoping for.

[Joseph Lofthouse]

Apr 20, 2010 10:02:40 GMT -5 spero said:

Are you confident you can get this 2% (or even 3%) refractometer reading ?

With my refractometer, and with the (old) corn that I have been buying at the grocery store the reading is very fuzzy, so I can't say for sure if it is 10% sugar or 13%, but it is easy to tell the difference between 13% and 30%.

I squeezed out some corn juice onto the plate and did not get what I thought was a readable reading. I put it away. After your earlier discussion, I tried squeezing some juice and letting it settle, and was able to get a clear reading.
Given that, I had planned to buy a bunch of little containers, go down the row cutting and squeezing kernels & leaving the juice by the plant, then come back down the row to do readings. Squeeze & read is what I was hoping for.

My best guess at this point is that I will squeeze the juice directly onto the sample window of the refractometer. I have tiny microcentrifuge vials and a centrifuge but based on my results with grocery store corn I'm expecting that they will not be used/needed.

Regards,
Joseph