Post by till on Jan 6, 2021 4:04:50 GMT -5
Hello together,
I have tried to gather information how acidity is inherited in crosses of acidless citrus with sweet and acid citrus. Here I want to present my findings.
To the background: I wanted to breed hardy sweet Poncirus hybrids, believed that the percentage of Poncirus genes should be over 50%, requiring at least an F2 generation, but was then frustrated that all hybrids with Poncirus are very sour, that sweetness is a recessive trait. Recessive traits are frustrating for any breeder. A F1 cross of Poncirus and sweet citrus is sour although it definitely contains the allel for sweetness in one copy. A F2 cross between such Poncirus hybrids will most probably be also sour because sourness is a dominant trait. So it could be that I get a very promising F2 cross that is hardy and even tasty but sour. Can I use it for breeding sweet F3 hybrids? I do not know for sweetness is a recessive trait. That means this F2 hybrid may contain the allel for sweetness in one copy or it does not. I can make no selection on the basis of its phenotype. If I can make no selection I have to keep too much plants and will come to my limits.
So I searched for a way to create sweet F1 hybrids. My idea was, as I said in the old forum, to create hybrids with acidless citrus and Poncirus. I hoped that a cross between acidless citrus and acidic Poncirus is much less sour and such tastes somewhat sweet so that I can identify the presence of alleles for sweetness right from the beginning.
But is that possible? The answer is in short: No!, except with acidless pummelo and its hybrids (Chandler, Valentine). I shall tell why.
My sources are:
“Noemi Controls Production of Flavonoid Pigments and Fruit Acidity and Illustrates the Domestication Routes of Modern Citrus Varieties” by Eugenio Butelli, Concetta Licciardello, Chandrika Ramadugu, ..., Giuseppe Reforgiato Recupero, in Current Biology 29, 158–164 (2919)
“Absence of Acidless Progeny from Crosses of Acidless x Acidless Citrus Cultivars” by James W. Cameron and Robert K. Soost, in Journal of the American Society for Horticultural Science 104(2), 220-222 (1979)
“Acidity and Total Soluble Solids in Citrus Hybrids and Advanced Crosses Involving Acidless Orange and Acidless Pummelo” by James W. Cameron and Robert K. Soost, in Journal of the American Society for Horticultural Science 102(2), 198-201 (1977)
www.chemistryworld.com/news/genes-that-make-lemons-sour-revealed/3010199.article
I am not a botanist and my knowledge of genetics is very limited but what I grasped is this:
Acidless citrons, oranges and limes contain two defective copies of a certain “Noemi” gene. The defect is largely the same in all cultivars. The “Noemi” gene, if complete, allows the production of anthocyanin and the accredation of acids in the fruit. So all acidless citrons, oranges and limes cannot produce red (violet) color in leaves, twigs and flowers, their seeds are totally pale in color because they have no complete “Noemi” gene. Acidless varieties often have acidic counterparts and sometimes appear to be mutants of acidic varieties. Their acid counterparts contain at least one complete copy of the “Noemi” gene. That means one functional “Noemi” gene is enough to produce sour fruits. Low acidity is a recessive trait in oranges, limes and citrons.
Two limelike varieties are different: Pomona sweet and Millsweet. They contain one defectice copy of the “Noemi” gene and one otherwise mutated. So they do produce anthocyanin and do produce acids but their fruits are sweet and acid content is low.
Acidless pummelo is a different story. Acidless pummelo contains two homologous alleles for low acidity but they seem to be different than those of the before mentioned varieties. Crossing experiments are revealing here. When you cross acidless pummelo with acidic citrus it will lower the acidity level of its offspring. You won’t get acidless offspring but offspring with lower acidity than the sourer crossing partner. Moreover, when you cross acidless pummelo with acidless limes and oranges (probably citrons behave the same) you will NEVER get acidless offspring. The cross between Sweet Palestinian Lime and acidless pummelo produces even as much acids as would be expected for a cross between acidic lime and acidless pummelo. Cameron and Soost tried to explain that in two ways. They suggested that acidless varieties are chimeras with respect to the allel for lo acidity or that the genetic constitution of acidless pummelo is different than that of acidless oranges etc. The latter understanding seems to be the right one as later genetic studies suggest. The best explanation for the behaviour of pummelo crosses is that the acidless pummelo parents provides one complete and functional copy of the “Noemi” gene so that its hybrids with other acidless citrus are fully able to produce high levels of acid in their fruits that are only partially reduced by the differently structured gene for low acidity from the pummelo parent. The different nature of the pummelo gene can also be seen in the fact that Valentine pummelo hybrid is low in acidity and does produce anthocyanin (bloody fruits).
Some additional notes before I try to draw practical conclusions:
Sweet limes seem to be chimeras with respect to low acidity and are thus not a got choice for breeding experiments.
Besides the “Noemi” gene, scholars discovered a gene complex that is responsible for the accreditation of HIGH acidity levels in lemons (and probably other citrus). The activity of the gene should, as far as I see, be dependent on a complete “Noemi” gene. Would somebody be able to make a genetic scan of his or her young hybrid plants he could predict whether they will bear sweet or sour fruits.
Practical conclusions:
- All crosses between acidless oranges, limes and citrons with sour citrus will be sour.
- Selfing F1 hybrids of acidless oranges, limes and citrons will result in about ¼ of acidless offspring.
- F1 crosses with acidless pummelo (or its hybrids Chandler and Valentine) will result in significantly less acidic offspring (for Chandler and Valentine around 50%). Acidity levels range between below 1% acids in the case of sweet crossing partners and 2-4% acids in the case of sour crossing partners. That means hybrids with acidless pummelo and Poncirus will probably taste sour but less so than pure Poncirus (5-7% acids). So the phenotype of your hybrids will clearly show to you if the gene for low acidity is present.
- Selfing F1 crosses of acidless pummelo will result in about ¼ of acidless offspring.
- I do not know what will come from crosses between Millsweet or Pomona Sweet and sour citrus. I suppose offspring will be sour because one complete “Noemi” gene suffices to produce sour fruits when the variety is essentially sour (i. e. sour if it had a functional “Noemi” gene).
Thank you for reading my long text! Those who have better insights into genetics are welcome to add something or correct me.
=====
Sorry to the first readers: I got confused with the hybrid generations in my original post, said F2, F3, F4 hybrids but meant F1, F2, F3 hybrids. I have corrected myself now. Sorry for the confusion.
I have tried to gather information how acidity is inherited in crosses of acidless citrus with sweet and acid citrus. Here I want to present my findings.
To the background: I wanted to breed hardy sweet Poncirus hybrids, believed that the percentage of Poncirus genes should be over 50%, requiring at least an F2 generation, but was then frustrated that all hybrids with Poncirus are very sour, that sweetness is a recessive trait. Recessive traits are frustrating for any breeder. A F1 cross of Poncirus and sweet citrus is sour although it definitely contains the allel for sweetness in one copy. A F2 cross between such Poncirus hybrids will most probably be also sour because sourness is a dominant trait. So it could be that I get a very promising F2 cross that is hardy and even tasty but sour. Can I use it for breeding sweet F3 hybrids? I do not know for sweetness is a recessive trait. That means this F2 hybrid may contain the allel for sweetness in one copy or it does not. I can make no selection on the basis of its phenotype. If I can make no selection I have to keep too much plants and will come to my limits.
So I searched for a way to create sweet F1 hybrids. My idea was, as I said in the old forum, to create hybrids with acidless citrus and Poncirus. I hoped that a cross between acidless citrus and acidic Poncirus is much less sour and such tastes somewhat sweet so that I can identify the presence of alleles for sweetness right from the beginning.
But is that possible? The answer is in short: No!, except with acidless pummelo and its hybrids (Chandler, Valentine). I shall tell why.
My sources are:
“Noemi Controls Production of Flavonoid Pigments and Fruit Acidity and Illustrates the Domestication Routes of Modern Citrus Varieties” by Eugenio Butelli, Concetta Licciardello, Chandrika Ramadugu, ..., Giuseppe Reforgiato Recupero, in Current Biology 29, 158–164 (2919)
“Absence of Acidless Progeny from Crosses of Acidless x Acidless Citrus Cultivars” by James W. Cameron and Robert K. Soost, in Journal of the American Society for Horticultural Science 104(2), 220-222 (1979)
“Acidity and Total Soluble Solids in Citrus Hybrids and Advanced Crosses Involving Acidless Orange and Acidless Pummelo” by James W. Cameron and Robert K. Soost, in Journal of the American Society for Horticultural Science 102(2), 198-201 (1977)
www.chemistryworld.com/news/genes-that-make-lemons-sour-revealed/3010199.article
I am not a botanist and my knowledge of genetics is very limited but what I grasped is this:
Acidless citrons, oranges and limes contain two defective copies of a certain “Noemi” gene. The defect is largely the same in all cultivars. The “Noemi” gene, if complete, allows the production of anthocyanin and the accredation of acids in the fruit. So all acidless citrons, oranges and limes cannot produce red (violet) color in leaves, twigs and flowers, their seeds are totally pale in color because they have no complete “Noemi” gene. Acidless varieties often have acidic counterparts and sometimes appear to be mutants of acidic varieties. Their acid counterparts contain at least one complete copy of the “Noemi” gene. That means one functional “Noemi” gene is enough to produce sour fruits. Low acidity is a recessive trait in oranges, limes and citrons.
Two limelike varieties are different: Pomona sweet and Millsweet. They contain one defectice copy of the “Noemi” gene and one otherwise mutated. So they do produce anthocyanin and do produce acids but their fruits are sweet and acid content is low.
Acidless pummelo is a different story. Acidless pummelo contains two homologous alleles for low acidity but they seem to be different than those of the before mentioned varieties. Crossing experiments are revealing here. When you cross acidless pummelo with acidic citrus it will lower the acidity level of its offspring. You won’t get acidless offspring but offspring with lower acidity than the sourer crossing partner. Moreover, when you cross acidless pummelo with acidless limes and oranges (probably citrons behave the same) you will NEVER get acidless offspring. The cross between Sweet Palestinian Lime and acidless pummelo produces even as much acids as would be expected for a cross between acidic lime and acidless pummelo. Cameron and Soost tried to explain that in two ways. They suggested that acidless varieties are chimeras with respect to the allel for lo acidity or that the genetic constitution of acidless pummelo is different than that of acidless oranges etc. The latter understanding seems to be the right one as later genetic studies suggest. The best explanation for the behaviour of pummelo crosses is that the acidless pummelo parents provides one complete and functional copy of the “Noemi” gene so that its hybrids with other acidless citrus are fully able to produce high levels of acid in their fruits that are only partially reduced by the differently structured gene for low acidity from the pummelo parent. The different nature of the pummelo gene can also be seen in the fact that Valentine pummelo hybrid is low in acidity and does produce anthocyanin (bloody fruits).
Some additional notes before I try to draw practical conclusions:
Sweet limes seem to be chimeras with respect to low acidity and are thus not a got choice for breeding experiments.
Besides the “Noemi” gene, scholars discovered a gene complex that is responsible for the accreditation of HIGH acidity levels in lemons (and probably other citrus). The activity of the gene should, as far as I see, be dependent on a complete “Noemi” gene. Would somebody be able to make a genetic scan of his or her young hybrid plants he could predict whether they will bear sweet or sour fruits.
Practical conclusions:
- All crosses between acidless oranges, limes and citrons with sour citrus will be sour.
- Selfing F1 hybrids of acidless oranges, limes and citrons will result in about ¼ of acidless offspring.
- F1 crosses with acidless pummelo (or its hybrids Chandler and Valentine) will result in significantly less acidic offspring (for Chandler and Valentine around 50%). Acidity levels range between below 1% acids in the case of sweet crossing partners and 2-4% acids in the case of sour crossing partners. That means hybrids with acidless pummelo and Poncirus will probably taste sour but less so than pure Poncirus (5-7% acids). So the phenotype of your hybrids will clearly show to you if the gene for low acidity is present.
- Selfing F1 crosses of acidless pummelo will result in about ¼ of acidless offspring.
- I do not know what will come from crosses between Millsweet or Pomona Sweet and sour citrus. I suppose offspring will be sour because one complete “Noemi” gene suffices to produce sour fruits when the variety is essentially sour (i. e. sour if it had a functional “Noemi” gene).
Thank you for reading my long text! Those who have better insights into genetics are welcome to add something or correct me.
=====
Sorry to the first readers: I got confused with the hybrid generations in my original post, said F2, F3, F4 hybrids but meant F1, F2, F3 hybrids. I have corrected myself now. Sorry for the confusion.