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Cucurbit Genetics Cooperative Report 22:28-30 (article 11) 1999

A Tendrilless Mutant in Watermelon: Phenotype and Inheritance

Bill Rhodes

School of Plant, Statistical and Ecological Sciences, Poole Agricultural Center, Clemson University, Clemson, SC 29634

Xingping Zhang

Hollar Seeds, P.O. Box 106, Rocky Ford, CO 81-67-0106

Vance Baird and Halina Knapp

School of Plant, Statistical and Ecological Sciences, Poole Agricultural Center, Clemson University, Clemson, SC 29634

Introduction. Lin et al (1) described the mutant branchless with half the number of branches at the first five nodes. They reported this phenotype to be due to a single recessive gene bl.

We observed that the mutant did not produce tendrils in the field or greenhouse (2) and decided to characterize it more fully. A pruning experiment was conducted to test the hypothesis that the mutant loses the ability to differentiate a vegetative bud after the 4thor 5th node. To test whether the root system affects the mutant phenotype, we conducted a grafting experiment. We again examined the inheritance of the mutant when crossed with a normal and a dwarf phenotype.

Methods. Three treatments of five plants each were used in the Pruning Experiment: (1) the shoot tip was removed at the 10th node, as were the axillary buds for the first five nodes, 2) the shoot tip only was removed at the 10th node, and (3) no pruning was done.

Grafting Experiment: five wild-type scion were grafted on mutant rootstock and five mutant scions were grafted on wild-type rootstocks.

Inheritance Studies: The mutant (T) crossed with wild types A and B and a dwarf type C, and the F1, F2 and BC populations were scored for the trait.

Results. Photos 1 to 9 are arranged from left to right on the page.

Photo 1 (wild type) exhibits the normal arrangement of floral bud and tendril at a node. Photo 2 (mutant) shows a profusion of floral buds and no tendrils. Photo 3 exhibits two female flowers with abnormally long peduncles. Photo 4 compares the terminal shoot tip of a normal plant, with developing tendrils, normal leaflets and floral buds (left) and the terminal shoot tip of a mutant plant with no tendrils, abnormal leaflets and a cluster of floral buds (right). Photo 5 shows the chronological transformation of leaves on a mutant plant from an almost normal oak-like leaf appearance to a triangular shape with edges curling inward. The emerging leaves gradually lose their lobing and become triangular toward the end of the shoot. The tendrilless mutant, previously described as branch less (1) has more pleitropic effects. Branches are not produced after the 5th or 6th node. the vegetative meristems gradually become floral meristems. Tendrils and vegetative buds are replaced by flowers, with a significant number of perfect flowers, and growth becomes determinate.

Photo 6 of mutant plants, from left to right, shows that: (1) removal of the shoot tip at node 10 and the axillary buds for the first five nodes eliminates the ability of the mutant to produce any branches; (2) removal of the shoot tip at node 10 encourages branches at the first five nodes; and (3) no pruning at all results in a plant with two branches. Photo 7 of wild-type plants shows that : (1) removal of the shoot tip at node 10 and the axillary buds for the first five nodes results in lateral branches above the first 4-5 nodes; (2) removal of the shoot at the 10th node only results in the emergence of four lateral branches and (3) the unpruned wild-type has two branches.

Rootstock did not affect the mutant tendrilless (T) phenotype (Photos 8 and 9). Photo 8 shows the foliar development of the grafted branch of the mutant phenotype along with the lateral branches of the normal stock plant. In Photo 9, a similar pattern is seen.

The results of the inheritance studies are given in Tables 1 and 2. In Table 1, the cross between the two lines with normal phenotypes and the mutant resulted in F1 plants with normal phenotype and F2 plants that are segregated 3:1 for the tendrilless trait. In Table 2, a cross between the same tendrilless parent and a dwarf parent resulted in normal F1 plants. The backcross progeny from the tendrilless parent fit a 1:1 normal:tendriilless segregation, but the backcross progeny from the dwarf parent did not fit a 1:1 normal:dwarf segregation. In the F2 progeny, the tendrilless segregated 3:1 normal:tendrilless. The inheritance of the dwarf character in line C has not been determined, but the expression of the tendriolless phenotype does increase the number of individuals scored as dwarf phenotypes.

Conclusions. The tendrilless pleitropic mutant behaves like a simple recessive trait that eliminates vegetative buds above the 4th or 5th node We propose the notation tendrilless and the symbol tl for this recessive gene instead of the descriptor "branch less".

Table 1. Segregation in F2 from two crosses of normal (A,B) x tendrilless (T) parent.

Parents, Progeny

TI- phenotype1
tl- ohenotype
Expected Ratio
G17 AB (A)
ASS-1 (B)
B242 (T)
(AxT) F2
(BxT) F2


1 Phenotype is described in Results.  

Table 2. Backcross and F2 progeny from tendrilless (T) x normal parent (C).

Parents, Progeny
B242 (T)
YF91-1-2 (C)
T x C
(TxC) x T
(TxC) x C
(TxC)F2 1993

Photos 1-5 (left to right, top row): 1. Normal tendril and floral bud at a node. 2. A profusion of buds on T branch. 3. Two female flowers with abnormally long peduncles on a T branch. 4. A normal shoot tip (left) with tendrils, multilobed leaflets, buds and a T shoot tip with no tendrils, 3-lobed leaflet, and bud cluster. 5. Left to right, a sequence of multilobed leaves on a T-branch to 3-lobed leaves with inward-curling edges. 6. (bottom row) Branching pattern of three T plants, after losing axillary buds from first five nodes as well as shoot-tip at node 10; only the same three treatments applied as described in 6. 8. Development of a plant with a wild-type stock and a T scion. 9. Development of a plant with a T stock and a wild-type scion.


Literature Cited

  1. Lin, D., T. Wang, Y. Wang, X. Zhang and B.B. Rhodes. 1992 The effect of the branch less gene on plant morphology in watermelon. Cucurbit Genetics Coop. Rpt. 15:74-75.
  2. Zhang, X., B. Rhodes, V. Baird and H. Skorupska. 1996. A tendrilless mutant in watermelon: Phenotype and development. HortScience 31(4):602 (Abstract).
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