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Thursday - May 10, 2012

From: Houston, TX
Region: Southwest
Topic: General Botany
Title: Carolina wolfberry blooms but doesn't produce fruit
Answered by: Nan Hampton

QUESTION:

I have had my carolina wolfberry for 2 years now ( I got it at the Wildflower center), it seems to be doing well, creeping all over the flower bed with some branches on the ground up to 6 ft long. It is also blooming every season, however I have never seen any fruit on it. Bees visit it when it is in bloom also. So I have no idea why it will not fruit. Your site says the flowers are bisexual. Does that mean on the same plant, and so it doesn't need another plant for pollination? Please help. Thanks

ANSWER:

Plants have a wide variety of sexual reproductive systems.  They may be dioecious—meaning that the male flowers and female flowers are on separate plants [e.g., Ilex vomitoria (Yaupon)].   They can be monoecious, with separate male and female flowers occuring on the same plant [e.g., Zea mays (corn)].  Lycium carolinianum (Carolina wolfberry) has a third system with all flowers having both the female and male parts together in the same flower.   These flowers are referred to as perfect, or complete, flowers.  One term used for plants with flowers containing both male and female parts is hermaphrodite.  The term bisexual is another way to say that the flowers have both male and female parts in a single flower.  Your wolfberry is, indeed, bisexual with the flowers containing both male and female parts. 

Many flowers are capable of self-fertilization.  For example, Pisum sativum (garden pea), the plant Gregor Mendel used for his now famous genetic experiments, readily self-fertilizes.  For some of his experiments Mendel had to clip off the stamens before the pollen formed to keep the peas from self-fertilizing. However, even though the wolfberry has perfect flowers, it cannot self-fertilize—thus, your lack of fruit.   The reason the pollen from the flower can't fertilize the ovary is due to a phenomenon called self-incompatibility (SI).  This system is present in some plant familites, but not in all families.  SI involves two closely-linked genes—one is expressed in the female style with two copies (the copies may be identical or slightly different) and the other gene is expressed in the male pollen with only one copy.   If the form of the gene in the pollen doesn't match either of the genes in the style, then the growth of the pollen tube continues down the style to the ovary and fertilization occurs resulting in fruit.  However, If the form of the gene in the pollen matches either of forms of the genes in the style, then the growth of the pollen tube down the style to the ovary ceases and no fertilization occurs.  The pollen from your plant will definitely match one of the forms of the gene in the style and fertilization will not occur.  You can read more about this in an article by Anna Rasmussen, Amherst University: Sweet carolinianum:  A study of allelic diversity in the S-RNAse gene of Lycium carolinianum.

Here is a more in-depth discussion:  Self-Incompatibility:  Avoiding Inbreeding.

For your wolfberry, the flowers bloom and the pollen falls on the style, but no fruits can develop because the gene in the pollen matches one of the genes in the style.  In order for you to have fruits on your plant, you need another plant nearby to furnish pollen to fertilize your plant.  Ideally, the other plant should not come from the same source as the plant you already have.  Having a different source will help insure that the plants have different forms (alleles) of the SI genes from those of your wolfberry.

 

 

From the Image Gallery


Carolina wolfberry
Lycium carolinianum

Carolina wolfberry
Lycium carolinianum

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