genetics, environment, and ? random gene expression?

bower · March 11, 2012

Very curious about the phenotype of seedlings and how to select at an early stage which plants I want to grow. This time, I am also mystified by differences I cannot explain simply by genetics nor by environment.

Last year I purchased seed and grew several Black Sea Man. The 2011 seeds were germinated in cold conditions: I had one early start and it was a very leafy, vigorous and productive plant. I also grew some later starts which were less sturdy and leafy, which I attributed to their later germination - environmental conditions. I saved seed from two fruit from the early vigorous plant. I test germinated both batches of seed in early February this year, using bottom heat, and kept 6 seedlings from each fruit. One batch had been presoaked and germinated one day earlier, so had a slight head start.

These seedlings were transplanted into 3" pots and have been growing in a west window under lights in a cold environment. They are all quite vigorous in spite of cold (a little purple here and there) and are ready for a transplant.

What I discovered is that half of the seedlings have a different internode phenotype. The different phenos "leafy" vs "long" occurred in both seed batches (4/2) and were not correlated with position vis a vis the lights or the cold window, apparently a random 50% distribution of trait over 12 seedlings, which cannot be attributed to seedling environment. The two phenotypes are attached below (or see the album).

To clarify the lack of direct genetic differences, BSM is the only potato leaf I grew last year, and all seedlings are PL so no cross is suspected. Second, the vigorous plant from which seed was taken was situated some distance from the later ones, and surrounded by a lot of RL tomatoes in between, so a cross within the population is also not suspected. Both fruit produced seed that produced both 'leafy' and 'long' phenotype seedlings.

I have been reading with great interest some older threads here about determinate vs indeterminate plants, and differences found by different growers often attributed to environment or perhaps a mutation. I appreciate the formal definition of determinate vs indeterminate by the internode spacing of flowers, but this is also apparently inadequate to categorize the actual variation in growth habit which we need to discuss and understand, for practical purposes (at least, some of us need to! I excuse everyone who lives in tomato heaven!

).
In the present example, I cannot account for the difference in pheno by genetic difference nor by environment, except to speculate that this is a random gene expression for growth habit which produces two phenotypes in equal proportions. Since tomato is a selfing plant, mechanisms for diversifying within the homozygous state are advantageous - and they appear to be present. Does anyone have some science on this?

I wish I had the space to grow out and test both of them, but I am in the north here, with limited greenhouse space. The 'leafy' plant produced early tomatoes and big clusters for me, so I am inclined to ditch the others. On the other hand, I think the ones my mom grew were the 'long' pheno, and produced well for her indoors in 3 gallon pots, with smaller clusters over the whole plant. Both phenos produced new side shoots with flowers after being topped.

So many growers here have vastly more experience than I. Please enlighten me with your observations!

salix · March 12, 2012

An interesting question, and mystery. Sorry I cannot help at all with an answer, but I look forward to reading any reply from one of our resident gurus.

maf · March 12, 2012

I wouldn't attach too much significance to the spacing of the first pair of leaves, in my experience it can vary. Observe for a few more internodes and confirm the pattern is repeating. Are there any other differences between the plants?

If there is a genuine difference in phenotype between the plants, one possible explanation could be that the vigorous and productive plant from 2011 was an F1 hybrid; an accidental cross-pollination that occurred in the seed supplier's mother plant; and any differences you are now seeing are the natural segregation of the F2 population.

bower · March 12, 2012

Quote:

Originally Posted by maf

I wouldn't attach too much significance to the spacing of the first pair of leaves, in my experience it can vary.

Yes, I'm just looking for an explanation of the early variance. And looking for early selection cues for my own purposes, within a (presumed) homozygous batch of seedlings. I saved seed from the 'leafy' type plant last year because it was a more compact growth habit and big clusters of fruit early on. I didn't expect the seed to produce any 'leggy' type plants.

Quote:

Originally Posted by maf

Observe for a few more internodes and confirm the pattern is repeating. Are there any other differences between the plants?

One thing I noticed is that the 'leggy' ones' stems are a bit more slender than the 'leafy', and their height is more uniform between both batches of seed - one of which was started a day earlier. In the 'leafy' group, the two plants with a day's head start are noticeably taller than the others.
There's certainly no detectable difference in leaf shape - although maybe PL's are more uniform in leaf shape than RL types. I'm growing a number of other PL's this year, and it would be hard to tell any of them apart at this stage. Whereas the RL's are all distinctive, even when small.

I moved half of each group to larger pots today - didn't notice any difference in root volume.

Quote:

Originally Posted by maf

If there is a genuine difference in phenotype between the plants, one possible explanation could be that the vigorous and productive plant from 2011 was an F1 hybrid; an accidental cross-pollination that occurred in the seed supplier's mother plant; and any differences you are now seeing are the natural segregation of the F2 population.

This seems less likely, since both 'leafy' and 'leggy' plants were produced by the original batch of seeds and also had the same fruit shape and size, recessive colouring, and quality of fruit. It would have to be a cross with a virtually identical variety.

Thanks for your advice! I guess I'll have to grow out at least one of each, and see whether these differences are maintained as they get bigger, in the way that they did from the original seed source.

March 11, 2012	#1
bower Tomatovillian™ Join Date: Feb 2012 Location: Newfoundland, Canada Posts: 6,794	genetics, environment, and ? random gene expression? Very curious about the phenotype of seedlings and how to select at an early stage which plants I want to grow. This time, I am also mystified by differences I cannot explain simply by genetics nor by environment. Last year I purchased seed and grew several Black Sea Man. The 2011 seeds were germinated in cold conditions: I had one early start and it was a very leafy, vigorous and productive plant. I also grew some later starts which were less sturdy and leafy, which I attributed to their later germination - environmental conditions. I saved seed from two fruit from the early vigorous plant. I test germinated both batches of seed in early February this year, using bottom heat, and kept 6 seedlings from each fruit. One batch had been presoaked and germinated one day earlier, so had a slight head start. These seedlings were transplanted into 3" pots and have been growing in a west window under lights in a cold environment. They are all quite vigorous in spite of cold (a little purple here and there) and are ready for a transplant. What I discovered is that half of the seedlings have a different internode phenotype. The different phenos "leafy" vs "long" occurred in both seed batches (4/2) and were not correlated with position vis a vis the lights or the cold window, apparently a random 50% distribution of trait over 12 seedlings, which cannot be attributed to seedling environment. The two phenotypes are attached below (or see the album). To clarify the lack of direct genetic differences, BSM is the only potato leaf I grew last year, and all seedlings are PL so no cross is suspected. Second, the vigorous plant from which seed was taken was situated some distance from the later ones, and surrounded by a lot of RL tomatoes in between, so a cross within the population is also not suspected. Both fruit produced seed that produced both 'leafy' and 'long' phenotype seedlings. I have been reading with great interest some older threads here about determinate vs indeterminate plants, and differences found by different growers often attributed to environment or perhaps a mutation. I appreciate the formal definition of determinate vs indeterminate by the internode spacing of flowers, but this is also apparently inadequate to categorize the actual variation in growth habit which we need to discuss and understand, for practical purposes (at least, some of us need to! I excuse everyone who lives in tomato heaven!). In the present example, I cannot account for the difference in pheno by genetic difference nor by environment, except to speculate that this is a random gene expression for growth habit which produces two phenotypes in equal proportions. Since tomato is a selfing plant, mechanisms for diversifying within the homozygous state are advantageous - and they appear to be present. Does anyone have some science on this? I wish I had the space to grow out and test both of them, but I am in the north here, with limited greenhouse space. The 'leafy' plant produced early tomatoes and big clusters for me, so I am inclined to ditch the others. On the other hand, I think the ones my mom grew were the 'long' pheno, and produced well for her indoors in 3 gallon pots, with smaller clusters over the whole plant. Both phenos produced new side shoots with flowers after being topped. So many growers here have vastly more experience than I. Please enlighten me with your observations!

March 12, 2012	#2
salix Tomatovillian™ Join Date: Dec 2007 Location: north central B.C. Posts: 2,310	An interesting question, and mystery. Sorry I cannot help at all with an answer, but I look forward to reading any reply from one of our resident gurus.

March 12, 2012	#3
maf Tomatovillian™ Join Date: Jun 2010 Location: England Posts: 512	I wouldn't attach too much significance to the spacing of the first pair of leaves, in my experience it can vary. Observe for a few more internodes and confirm the pattern is repeating. Are there any other differences between the plants? If there is a genuine difference in phenotype between the plants, one possible explanation could be that the vigorous and productive plant from 2011 was an F1 hybrid; an accidental cross-pollination that occurred in the seed supplier's mother plant; and any differences you are now seeing are the natural segregation of the F2 population.