Freckles

Scabitha

One person's beauty mark is another person's mole.  So it is, I think, with “freckles” on tomatoes.   My first experience with this trait was with seed I got in trade of the variety Scabitha, which was attributed to Brad Gates at Wild Boar Farms.  I was impressed.  The fruit was meaty and tasty and the skin had random gold flecks that were interesting and unique.  One of the plants from this seed appeared to be an outcross, with smaller heart shaped fruit and a different expression of the “freckles” trait.  I made a cross to the true-to-type Scabitha, and saved OP seed from the odd ball.

Freckled Strawberry

Next year the odd ball got odder, and the first F1 showed that the “freckles” were heritable, and partially dominant.  Again I saved seed of the oddest of the oddballs (Freckled Strawberry) and made more crosses.

Dora x Scabitha F1

In the meantime I started trying to learn more about this unusual trait.  Here’s what I think is going on.   Fruit pox and Gold Fleck are physiological disorders that are often found together but are considered separate conditions (reference here). Fruit Pox is described as small cuticular disruptions 
found at random on the fruit surface. The number can vary from a few to many.  Gold Fleck shows up as small irregular shaped dark green spots at random on the surface of immature fruit which turn to a gold color as fruit ripens. Number of spots can vary from few to many.  There are reported genetic differences in susceptibility to these conditions (see here), and Scabitha and some of my lines seem genetically predestined to Pox and Gold Fleck – hence the “freckled” phenotype.

Mature/Immature fruit

Here’s a photo showing the Gold Fleck phenotype on immature green fruit and on a mature red fruit.  In my various Freckled Strawberry lines the green fruit stage is heavily peppered with black dots, which will later turn gold.  Although  high expression of the pox phenotype is a little over the top, moderate freckling in the F1/F2's look interesting.  There does not appear to be any relationship between "freckles" and any important horticultural traits (e.g yield, taste or fruit texture).  

Immature Freckled Strawberry

Freckled Child

A few other observations:  the “freckled” phenotype is influenced by environment, with higher expression later in the season; one F2 plant appears to have pox, without gold fleck – so maybe these conditions are somewhat independent; and there are other freckled phenotypes that are probably not related (e.g. WBF Freckled Child).


An August 2011 update:  in a new “freckles” breeding line I was able to find a plant with fruit that had gold fleck (freckles) and without fruit pox (scabs).   Interestingly in this fruit the freckles seemed to align in a fashion that suggested lateral “stripes” of gold spots.  I crossed this plant to a darker skinned/fleshed tomato hoping for gold on dark purple.  That’s a combination you can’t do with the gs (green stripe) gene – see the breeding for stripes blog entry.  Also this year we found an unusual variation on the freckled phenotype in a F3 plant from the cross Scabitha x Boar's Hoof -freckles w/o pox, but the freckles are tan, not gold.

Freckles in stripe pattern

(Boars Hoof x Scabitha)F3

Jessica (the plant pathologist) thinks this project is a dry hole, and wants nothing to do with it.  Mark is intrigued … but on his own on this one.  For now Mark, ever the optimist, is avoiding using the term pox, in favor of “freckles”.  More to come as Freckled Strawberry is stabilized and several Scabitha or Freckled Strawberry F2’s get planted out this spring.

Sept 2013 update - We have been able to introgress Aft (anthocyanin fruit) into our Freckled Strawberry germplasm.  The desired effect was gold freckles on a indigo skin (like bright stars on a night sky).  This is a work in progress, but looking interesting.  In this photo there are two fruits from the same plant, one fully ripe from deep in the canopy (no direct sun, no anthocyanin) and one from the top of the plant (below in photo) showing anthocyanin accumulation on the side of the ripening fruit exposed to the sun.  We like the look of these, but they are not yet stable.

The photo below was taken at our NC breeding nursery in  July 2014.  Two plants in a row of a hundred showed this very striking gold freckles on indigo.