SEX DETERMINATION IN SEEDLINGS OF CAROB
SCIENTIFIC NAME: Ceratonia siliqua
FAMILY: Fabaceae
SUMMARY
Reaction of plant tissue treated with Mandl paint was assessed in plants undergoing spring flush of growth. This reaction was similar to that obtained some years ago on tissue from mature trees at Hamel Nursery during spring.
Seedling stock were used in the current tests. Following assessment of sex of the seedlings, proof of sexing accuracy will be sought by outplanting the seedlings and/or grafting to mature stocks to monitor later sexual development. No conclusions could be drawn about reactions from hermaphrodite individuals.
Mandl paint is a pharmaceutical preparation mainly of Iodine and Glycerin used to treat severe throat infections. - Editor
AIM
To validate a reasonably simple field test to determine sex of Carob Bean seedlings in infancy, i.e. up to possibly 8-9 months old.
MATERIALS
Twelve seedlings of Carob of unknown gender, supplied by Mr L. Marshall of Armadale. Earlier tests on material in autumn of 1989 gave no reaction to Mandl paint, although this material had been taken from trees on the same property.
The tests also used Mandl paint, razor blades, tags for seedling numbering, and plastic bags for transport of material collected.
METHOD
(a) Plant Material Used
Small twiglets (up to approx. 3-4 mm diameter), with leaflets attached, were cut from seedlings after these were labelled with numbers, 1 - 12. Twiglets and leaf material collected were given numbers corresponding to those of the parent plant. All material collected was put in a plastic bag to keep moisture in the material collected.
(b) Staining
Oblique sections were cut from twiglets and the central mid-rib of compound leaves. Each exposed surface was immediately dipped in Mandl paint solution and left to stand for approximately 2-3 minutes.
At the end of this time, positive staining had occurred to a greater or lesser extent, as indicated in the Table.
(c) Assessment of Staining
Sexing of each numbered piece of material was attempted, based on the strength and location of the staining, i.e. criteria used for sexing was as follows:
1) Deep blackish purple stain in a concentric ring around the central tissue was regarded as indicating a female specimen.
2) Dark staining of scattered flecks over most of the cut section, with some bunching or blobs of darkened tissue around the central tissue, was regarded as indicating a male specimen.
(d) Rationale of Staining Reaction Assessment
It is reasoned that female trees need to develop, or have established, suitable translocatory tissue to carry starches and sugars rapidly to developing fruiting processes. This orientation of conducting tissue therefore results in concentration of starch and sugar solutions during spring growth flush, and is required at an early age so that it is in place as the tree develops. Mandl paint contains the elements iodine and potassium in solution, and is known to react strongly with starches, and possibly sugars, at this time of the year.
The correctness of this reasoning will be checked by outplanting seedlings for later verification of these assessments. Hermaphrodite individuals will tend to complicate the test, but indecisive reactions may be indicative of this type of plant.
Table 1. Reactions to Mandl Paint, tests on carob (Ceratonia siliqua)
| Sample Number | Twiglet | Leaflet | Assessed Sex |
| 1 | Pale to mid purple | Pale to nil | Male |
| 2 | None | Pale, scattered | Male |
| 3 | Dark purple | Dark staining | Female |
| 4 | Dark purple | Pale | Female |
| 5 | Mid to dark colour | Dark purple/black | Female |
| 6 | None | Dark | Female (poor sample) |
| 7 | Light purple/black | Nil or pale in circ. bundles | Male |
| 8 | None | Dark to mid-colour and pale (2 samples) | Female (poor sample) |
| 9 | Dark purple/black | Dark colour, dried out quickly | Female |
| 10 | Dark .. scattered | Medium colour | Female |
| 11 | Mid to dark, scattered greenish periphery | Nil or pale | Male |
| 12 | Dark, circular | Dark, circular | Female |
CONCLUSION
1. It is concluded that Mandl paint does react with a broad spectrum of starches and sugars present in Carob twiglets and leaves during spring periods of growth flush.
2. By study of the arrangement of the staining positions of tissue, the sex of individual plants may be identified.
3. Hermaphrodite plants are regarded as those plants which give an indecisive reaction. More investigation is required in this area of the technique.
4. Proof of the ultimate validity of the technique can only be had through observation of outplanting of the test plants, or grafting to mature trees to hasten the results.
5. The staining reaction is perishable. Approximately 24 hours after treatment, the staining is no longer evident. Fixing of the reaction will be necessary for storage of reacted specimens. Fixing could not be done in these tests because of lack of reagents.
ACKNOWLEDGEMENTS
My thanks and gratitude are expressed to Mr Marshall for his patience and cooperation in these tests.
DATE: January 1993
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