Strictly speaking about Portuguese, "condal" is an adjective which refers to Count. A Count ruled over a countship or "condado" in Portuguese. The equivalent in Britain comes from the Anglo-Saxon word "Earl".

earl
n.

1. A British nobleman next in rank above a viscount and below a marquis, corresponding to a count in continental Europe.

An earl ruled over a shire or earldom and later over counties.

I think that "nobreza condal" thus refers to that part of the nobility who ruled over counties (condados). This could be refered to as "county nobility". Depending on your context, you may want to use a more loose term such as "landed nobility".

Like most of the county nobility and gentry, Lord Chaworth took up arms in defence of the monarch. Mrs. Hutchinson says he was ‘high in the Royal party,’ and on war becoming inevitable he fortified his house at Wiverton, and made it a garrison for the King.
http://www.nottshistory.org.uk/Brown1896/wiverton.htm

The county magistrates in England were appointed on the recommendation of the Lord Lieutenant. There were property qualifications to be met, set low enough for small landowners to be eligible, but the problems of recruitment were often serious. The county nobility often showed a marked reluctance to sit on the bench.
http://web.bham.ac.uk/1848/document/saville.htm

The Saracen's Head was for many years the chief hotel of the city, and was much patronised by the county nobility, and also by distinguished strangers.
http://gdl.cdlr.strath.ac.uk/airgli/airgli0104.htm

For all practical purposes the battle ended with the virtual annihilation of the Hungarian army. The king, 28 magnates, 7 prelates,about 500 noblemen, 10,000 infantryman and 4,000 cavalrymen losttheir lives. [472] In conclusion one thing has to be said about the gravelosses suffered by the aristocracy and the county nobility. They mayhave been narrow-minded, selfish, irresponsible, and foolhardy men,but they certainly rode heroically in the forefront of that fatal attackwhich carried the country to its destruction!
http://www.hungarian-history.hu/lib/warso/warso26.htm



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Note added at 9 hrs (2008-04-14 02:43:04 GMT)
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A suggestion for your sentence:

"The persisten meddling of xxx in the affaird of the trans-Minho region can be traced back to the ancient tradition(s) of the county nobility of xxx"

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Note added at 9 hrs (2008-04-14 02:44:31 GMT)
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sorry, had some spelling mistakes:

persisten = persistent
affaird = affairs


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Note added at 9 hrs (2008-04-14 02:45:47 GMT)
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According to your note, the sentence should end with:

"to the ancient tradition(s) of the Galician county nobility"

Suerte.