The origin of the grapefruit will probably never be known with certainty but further light has been cast recently on its development in the Caribbean region during the 17th and 18th centuries.
It seems most probable that grapefruit originated by natural hybridization of pummelo with pollen from sweet orange and importantly inheriting two noteworthy traits, one from each parent. The sweet orange’s nucellar embryony has enabled the grapefruit to be propagated by seed reproduction, while the pummelo’s red pigmentation characteristic has been exploited in improved varieties.
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This variety was produced by irradiating seed from the Hudson variety in 1959. Flesh of the Star Ruby is slightly redder than Hudson and it remains the most deeply pigmented grapefruit variety yet developed. Externally, the rind is as smooth and fine as that of Flame and is generally more blushed, often equal to that of Rio Red but somewhat better background color.
In addition to these two good and important characteristics, Star Ruby is almost invariably seedless, rarely having more than one or two seeds in a minority of fruit. The rind is thin like Flame, and is slightly thinner than Rio Red. The flesh has a high juice content and is as sweet as or sweeter than Marsh and other pigmented varieties.
Ruby was discovered as a bud mutation of Thompson in 1926 in Texas and was patented in 1934.
Ruby matures at about the same time as Thompson but has better internal quality as well as better internal and rind pigmentation. The color is better than Thompson and apart from the color, Ruby is virtually identical to Marsh in most other fruit characteristics and typically has few seeds.
There are two possible origins of the Marsh variety: one suggests it originated as a root sprout from a seedy variety, probably Duncan, around 1880, while other proposed it was of seedling origin from around 1850.
The tree is vigorous and very productive, attaining large size although regarded as being more cold-sensitive. Marsh fruit is slightly smaller than Duncan but far less seedy, having typically just two or three per fruit.
The juice sacs are smaller and the pulp has a somewhat smoother and lighter appearance than Duncan. It has very slightly thicker rind but a high juice content of sweet flavor that is of rather high acidity early in its season. It reaches minimum maturity standards at about November, and it may hang later than Duncan.
This is the most recently introduced pigmented variety which, like Star Ruby, was developed from bud wood of a Ruby Red seedling in 1988.
Rio Red trees are vigorous with an open growth habit like that of Ruby and Ray Ruby. The fruit shape is generally good. It is somewhat later maturing than Flame and Star Ruby often by two weeks or more before rind color is fully developed. However, for most of the season the external appearance is quite impressive with deeply blushed areas where adjacent fruit have touched. The somewhat thicker rind is more than compensated for by softer flesh with an exceptionally high juice content. Like other pigmented varieties, seed content is low, usually in the range of one to three per fruit.