Follow-up on White Drupelets in Blackberries

Yesterday I posted on why white drupelets occur in blackberries.  Well, the “why” that we know or think we know.  I also looked at the genetic make-up of certain cultivars.  Today, I went into the blackberry plantings here in Poplarville looking for white drupelets.  Since the season is almost over on some cultivars it wasn’t easy — there just weren’t enough berries, but I did find a few.  I was able to find them on ‘Ouachita’, ‘Kiowa’, ‘Chickasaw’, and ‘Sweetie Pie’.  I took some data on it too.  I harvested all the berries I could find that had white drupelets.  I counted the number of berries for each cultivar and from each berry counted the number of white drupelets.  I got an average and a range.  Plus, I took Brix measurement of the sugar content in the white drupelets compared to normal drupelets (I only did this for ‘Sweetie Pie’ because it was the only one that had a large enough sample).  Below is what I found:

Cultivar     # of berries    Avg. # white drup.    Range    Brix (white) Brix (normal)

‘Ouachita’       2                          2                   1-3

‘Kiowa’            5                          4.4                1-13

‘Chickasaw’    6                           2.7                1-9

‘Sweetie Pie’   45                         2.9                1-17        3.9             10.2

You may recall from yesterday that I broke down the genetic components of ‘Apache’ and ‘Kiowa’.  I will do that again for those I looked at today.

Ouachita:

Thornfree 25%, Brazos 25%, Darrow 17.1875%, OP (unknown) 18.75%, SIUS 68-1-8 12.5%, and US 1482 1.5625%

Kiowa:

Brazos 50%, Thornfree 18.75%, Darrow 12.5%, Wells Beauty 12.5%, and Brainerd 6.25%

Chickasaw:

Darrow 43.75%, Brazos 31.25%, Thornfree 12.5%, and Wells Beauty 12.5%

Sweetie Pie:

Brazos 43.75%, Humble 25%, Thornfree 18.75%, and Darrow 12.5%

As you can see ‘Brazos’, ‘Darrow’, and ‘Thornfree’ are mixed up in all of these cultivars.  Clark and Moore (2005) report that ‘Ouachita’ had low to no incidence of white drupelet in Arkansas. It has 25% ‘Brazos’ compared to ‘Kiowa’ at 50%, ‘Sweetie Pie’ at 43.75%, and ‘Apache’ at 31.25%. It appears likely that ‘Brazos’ has a role, but the extent is unknown. The field data doesn’t really tell us much because of the lack of replication and the few number of data points.  But with more it may be able to narrow down the genetic culprit of white drupelet.

The sugar content of the white drupelets was substantially lower than normal drupelets.  To me this suggests that the sugar may have not been there to begin with.  The texture and thickness of the skin are different than normal drupelets. At what stage does the drupelet abort from normal development?  This type of thing would be very difficult (or impossible) to replicate in a controlled environment.  I will continue to look at this issue and perhaps do a more in-depth study next year.

Below are some ‘Sweetie Pie’ fruit with white drupelets.  Just because it had the most white drupelets of the cultivars I looked at, it should not be an indictment of this cultivar.  It is later ripening that the others and thus had more fruit to sample.

'Sweetie Pie' fruit with white drupelets

‘Sweetie Pie’ fruit with white drupelets

Clark, J.R. and J.N. Moore. 2005. ‘Ouachita’ Thornless Blackberry. HortScience 40:258-260.

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