by
Y. Roederer and R. Bellefontaine1
INTRODUCTION
Neem (Azadirachta indica A. Juss., Meliaceae) is grown in many tropical regions, especially Central America, the Caribbean, South America, Asia and Africa. It regenerates naturally in many countries, and can even become invasive.
Collecting seeds (drupes) on the trees and sowing them immediately does not pose major problems, since viability is adequate during the first few weeks.
In spite of the importance of neem in many countries, it has not been possible up to now to carry out thorough and satisfactory provenance trials of the species in field trials, due to the fact that conservation of seeds poses serious problems: seeds received for such trials have proved to have very low or even zero germination rates. For reasons of short viability of the seeds, it is also likely that the genetic base of present-day populations grown as exotics in a number of countries, have a very narrow genetic base and date back to a few, limited introductions.
This consideration encouraged CTFT to undertake some research on viability of neem seeds of various origins, available at CTFT, Nogent-sur-Marne (Collet 1988; Roederer 1985, 86, 87).
REVIEW OF LITERATURE AND EARLIER TRIALS
As mentioned above, neem has the reputation of rapidly losing its germinative capacity. D.B. Webb et al (1984) consider that it decreases considerably already after 2–3 weeks. According to other references to problems of storage and viability of neem, the germination percent rapidly declines after 4 (sometimes 8) weeks, and drops to close to zero after 1–2 (seldom 4) months.2
Trials on germination of neem were undertaken in 1985 in the Centre National de Semences Forestières (CNSF), Burkina Faso (Ouedraogo et al 1985). They were aimed, in particular, at assessing the effect of varying stages of fruit maturity on storability of the seeds. In one of the experiments, three seedlots from fruit collected on the same day from the same mother tree were tested:
Immediate pulping and drying in the sun for four days was carried out under identical conditions for the three seedlots.
After 30 days of observation on the germination at room temperature in airtight boxes containing moistened sand, the results of these first trials indicated that a) and b) types of seeds gave better results, as compared with very ripe fruit.
Nagaveni et al (1987) confirmed that fruit collected from the ground had a viability period of 8–10 days, whereas fruit picked from the tree, of yellowish-green colour, pulped and put to dry in the shade for 2 days, had a germination rate of 80% for the first four months. After 6–7 months, germination had dropped to 50%, and dropped even further in the subsequent months.
In Nigeria, B.S. Ezumah (1986) found germination rates of 81–86 percent when seeds (from 9 different localities) were sown immediately after collection.
Ezumah also mentions other interesting results concerning treatment and germination:
pulping the fruit immediately after collection, or alternatively leaving it in a heap for a few days before pulping, did not affect the percentage of germination; however, the former method is more time-consuming and therefore more costly;
germination was adversely influenced by temperatures above 30°C; conversely, low temperatures (6–7°C) inhibited germination; germination rates were higher at 26°C than at 30°C;
the percentage of germination for seeds sown immediately after collection did not notably differ according to whether seeds were sown: (i) fresh; (ii) after 8 days of air drying at room temperature (26°–28°C); or (iii) after 8 days of drying in the sun (30–34°C). However, the moisture content of the seeds decreased from 35–40% in treatment (i); ±16% in treatment (ii); and ±10% in treatment (iii). Therefore the third method, which is also cheap, is recommended for the time being;
germination was, in general, better in nursery conditions than in the steady temperatures in the laboratory; day-night fluctuations seem to have had a beneficial effect on germination.
Concerning storage, Ezumah states that for all provenances the percentage of germination in laboratory conditions rapidly declined, whatever the method of storage, as follows:
after 4 weeks, germination was only 60 and 45% respectively, in seeds kept at room temperature (26°–28°C) and in a refrigerator (6°7°C);
after 12 weeks, in both cases, the percentage of germination was under 5%.
A team of three scientists in Thailand (1) assessed the influence of a range of drying and storage conditions (Chaisurisri et al. 1986). After immediate transport and pulping following collection, the seeds were submitted to various tests. It appeared that:
germination percent remained between 60 and 85% in most trials for the first 12 weeks; it dropped sharply between the 12th and the 16th week, and was equal to zero after 24 weeks (6 months);
the most efficient method was sun-drying in a glasshouse, as compared with drying in partly dehumidified air at 25°C; and at room temperature.
The following findings emerged from the study:
for drying, 2 days' sun-drying in a glasshouse is recommended;
seeds stored at 15°C in cotton bags keep a higher germinative capacity than those stored in tight containers;
none of the tested treatments led to maintaining a high germination rate after 12 weeks.
In summary, all observations and trials reviewed conclude that neem seeds lose their viability 2 to 6 months after collection.
OBSERVATIONS OF THE CTFT SEED LABORATORY
It should be stressed that the findings given below are not based on systematic trials, but are drawn from observations made on various seedlots stored with their endocarp, for various periods of up to several years in tight containers, in a coldroom with controlled temperature (+ 4°C) and moisture (about 30%).
After removing the shells and discarding a few dried out, rotten or abnormal seeds, the seeds were put to germinate in pre-moistened sand in tight transparent plastic germination boxes, at a temperature of 25°C (Collet 1988; Roederer 1985,86,87). The observation period for germinative capacity was set at 30 days. Moisture content of tested seeds ranged from 5 to 8%, that of the endocarp was approx. 11%.
Germination of these seeds, cleared of their endocarp, was satisfactory after 64 months of cold storage (42% for seedlot 83/4002N from Maroua, Cameroon), to very satisfactory after 17 months (75% for seedlot 86/5904N from North Cameroon).
It should be noted that details on collection history (date, stage of fruit maturity, number of mother trees, picking from the tree or gathering from under it, etc.); and post-collection handling (pulping, drying, storage); as well as ambient conditions at the time of shipping from Cameroon to France, were not always known with precision.
CONCLUSIONS
Neem seeds have the reputation of not keeping adequate viability for a long time. It is generally considered that after 2 to 6 months' storage, germination percent is near or equal to zero.
However, some observations made on seedlots which had been stored for several years at CTFT indicated that seeds without endocarp had an acceptable germinative capacity (42%) after over 5 years of storage.
These provisional findings should be confirmed by systematic experiments carried out with adequate quantities of seeds. Additional trials dealing with the effects of seed maturity and treatment of the fruit, and determining more precisely development in time of germinative capacity of the seeds, should also be carried out.
Information on how germination capacity could be maintained in the medium term, will make it possible to arrange international provenance trials of this relatively widespread species, as a basis for adequate broadening of the genetic base of the material used in exotic plantation programmes.
REFERENCES
Chaisurisri K., Ponoy B. & Wasuwanich P. 1986 Storage of Azadirachta indica A. Juss. seeds. The Embryon, Vol. 2, No. 1, 19–27, Sept. 1986. ASEAN Canada Forest Tree Seed Centre, Muak Lek, Saraburi, Thailand.
Collet C. 1988 Rapport de stage au Laboratoire de graines CTFT. July 1988, 9 pp. Centre Technique Forestier Tropical, Nogent-sur-Marne, France.
CTFT 1989 Fiche monographique: Azadirachta indica. Bois et Forêts des Tropiques, No. 217. Centre Technique Forestier Tropical, Nogent-sur-Marne, France.
Ezumah B.S. 1986 Germination of storage of neem (Azadirachta indica A. Juss.). Seed Science and Technology, 14, 593–600.
Nagaveni H.C., Ananthapadmanhaba H.S. & Rai S.N. 1987 Note on the extension of viability of Azadirachta indica. Myforest 23, 4, 245.
Ouedraogo A.S., Some L.M., Bance C. & Bellefontaine R. 1985 A Specialized Technical Institution for Forest Seed in the Sahelian and Sudanian zones: Direction des Semences Forestières, Burkina Faso. FAO, Forest Genetic Resources Information No. 14, 10–14. (Une structure technique spécialisée pour les semences forestières sahéliennes et soudaniennes): la Direction des Semences Forestières du Burkina Faso. FAO, Informations sur les ressources génétiques forestières, No. 14, 11–16.)
Roederer Y. 1985,86,87 Various internal reports, CTFT seed laboratory. CTFT, June 1985, August 1986, July 1987.
Webb D.B., Wood P.J., Smith J.P. & Henman G.S. 1984 A guide of species selection for tropical and sub-tropical plantations. OFI, Oxford, 256 pp.
1 Manuscript received August 1989
