Anyone who has had experience with Macadamia propagation knows that the germination of Macadamia seed is very erratic. In the first place, a given lot of seed, even newly fallen, freshly harvested seed, seldom germinates 100 per cent. In the second place, germination of the seeds which do grow does, not occur simultaneously, the first seedlings may appear within three or four weeks of the time the seeds have been placed for germination, the last may not appear until six months later. A few years ago, Hamilton (2, 3) carried on a study of Macadamia seed germination in order to determine some of the causes of irregularity. It found that much of the variation was due to clonal differences, i.e. that some clones or varieties consistently give a higher percentage of germination than others, also, that germination of all seeds which are going to germinate eventually is completed in a much shorter time in some varieties than in others, thereby yielding more nearly uniform lots of seedlings. Additional sources of variation are time of storage of the seeds and conditions of storage between harvesting and planting. Subjecting them to some form of treatment before planting enhances the rapidity and uniformity of germination of many kinds of seeds. Among such treatments are scarification of the seed coats with an abrasive substance, softening the seed coats by soaking the seeds in hot water or in strong acid or lye solutions, removal of the seed coats, and many others. The principal effect of the treatments is, of course, to allow water to reach the embryo more easily and quickly than would occur normally, thereby initiating more rapid and uniform germination. Because of the irregularity of germination of intact Macadamia seed, the question is often asked if there might not be some advantage in cracking the shells or removing the kernels from the shells entirely before placing for germination. The question has been answered more or less categorically by Hamilton (2) who stated, "Although the husk around the seed should always he removed before planting, it is neither necessary nor advisable to crack or remove the hard shell, which surrounds the embryo. It has been noted that when the shell is cracked before planting, the majority of the embryos rot rather than germinates. It is not known whether this is due to injury to the embryo in cracking or removing the seed coat or whether some other factors are involved. Cracking the shells mechanically actually lowers the percent of germinating seed and for this reason is not recommended." Since it is desirable to have rapid and uniform germination in nursery practice, the writers decided to look further into the matter of Macadamia seed germination, particularly of seed with the kernels removed from the shells. The results of our study are reported herein.

MATERIALS AND METHODS

All germination tests were carried out with seed of the integrifolia variety Keahou. This variety was selected because Hamilton (3) reported it to he the best variety from the standpoint of germination performance of the four varieties, which he tested in Hawaii. The seed used in our study was collected at the Schneider Orchard in Oceanside in January 1959. Observations were made on germination of seed under 14 more or less different treatments. The treatments and the results observed are given in Table 1. The reasons for handling the seed as indicated under various treatments will be discussed later in this section.
 

Table 1.—Macadamia seed treatments and
germination percentages
Treat Number	Treatment	No. Planted	No. Germination	% Germination
Whole nuts, newly fallen, untreated
1                            in soil, unoriented                                                                                    36                35                        97.2
2                           in sand, unoriented                                                                                    36                32                        88.8
3                           in vermiculite, unoriented                                                                           36                35                        97.2
Whole nuts, slightly dried, untreated
4                           in soil, unoriented                                                                                     36                33                        90.2
5                          in sand, unoriented                                                                                     36                30                        86.1
6                         in vermiculite, unoriented                                                                             36                36                      100.0
7                         in vermiculite, micropyle down                                                                     36                34                        94.4
Kernels. micropyle down, untreated
8                         in soil                                                                                                       36                  0                       00.0
9                         in sand                                                                                                      36                  0                       00.0
10                       in vermiculite                                                                                             36                  0                       00.0
Kernels. micropyle down, treated
11                      in vermiculite, dusted with Arasan SE-X                                                          36                 36                    100.0
12                      in vermiculite, watered with Arasan solution                                                     36                 34                      94.4
13                     in vermiculite, dusted with Zerlate                                                                  36                  34                      94.4
14                     in vermiculite, watered with Zerlate solution                                                     36                  33                      90.2

  All seeds were sown in flat boxes having inside dimensions of 15 in. x 15 in. x 6 in. These flats were filled to within one inch of the top with soil, sand or vermiculite used as germinating media. As noted in Table I, each flat was planted with 36 whole seeds or kernels. The seeds and kernels were placed so that the top was no more than one-fourth of an inch below the surface 0f the medium. All flats were planted on the same day and placed on the same bench in the greenhouse to insure as nearly uniform conditions as possible. No bottom heat was used, since during the time the experiment was in progress the temperature in the greenhouse was maintained at 65-85F. The experiment was initiated with planting on January 27 and terminated on April 20 with potting-off of the seedlings. Treatments 1, 2, and 3 correspond more or less to common nursery practices. Some growers germinate nuts in soil or soil mixtures, some in sand, and some in vermiculite. Other growers use composted sawdust, sponge rock, volcanic cinders, and other materials not represented in this experiment. Only mature nuts, which obviously had fallen from the tree, no more than three or four days previously were used. Since most Nurserymen simply drop the nuts onto the soil or drill them in without regard to orientation, the seeds in these treatments were handled similarly. Treatments 4, 5, 6, and 7 are essentially the same as the preceding three except that nuts, dried slightly until the kernels rattled, were used, and in the case of treatment 7 the nuts were oriented with the micropyle down. In attempting to extract kernels for use in other treatments, it was found to he virtually impossible to crack the nuts and remove the kernels without some damage to the kernels. The kernel is actually the complete embryo of the seed, consisting of the plant axis, or embryonic shoot and root, to which are attached two large hemispherical cotyledons or seed leaves. At maturity, and in the freshly dropped nut, the embryo is so full of moisture and so closely appressed to the shell that it and the shell can he separated from each other without damage to the embryo only with difficulty. Because Hamilton (2) mentioned damage to the embryo as a possible cause of reduced germination, it was thought desirable to extract the kernels without injury. To do this it was found necessary to dehydrate the nuts to a slight extent. The nuts used in all treatments from 4 through 13 were dried for two weeks at a temperature of about 80 F and a relative humidity of 15-20 per cent. They lost about 15 per cent of their weight as water loss under these conditions. The kernels became loose in the shell and were easily removed without the slightest damage following cracking with a simple hand cracker which has been described elsewhere (1. 4, 5). In treatments 4, 5. and 6, the nuts were drilled into the germination medium without respect to orientation. Treatment 7 was added to conform to subsequent treatments in which kernels were planted with the plant axis In a vertical position. The plant axis consists of plumule (embryonic shoot) and radicle (embryonic root). The radicle lies at the tiny opening (micropyle) at the apical end of the nut. In planting, therefore, whole nuts were placed with the micropyle end down, and kernels with the radicle down, corresponding to the normal orientation of roots and shoots of growing seedlings. In treatments 8, 9, and 10 kernels were planted just as they come from the shells. In treatments 11, 12, 23, and 14 kernels were treated with a fungicide in either of two ways, (1) dusting before planting, and (2) watering the flat with a solution of the fungicide. In treatment II the kernels were shaken in a paper hag with, a small quantity of Arasan SF-X until thoroughly coated. They were then planted and watered with domestic water without further treatment. In treatment 12 the kernels were planted direct from the nuts but were watered subsequently only with a solution of 3 teaspoonfuls of Arasan SF-X to a gallon of water. Treatments 13 and 14 were similar to 11 and 12 except that Zerlate was the fungicide used. We wish to point out that no particular considerations dictated the choice of Arasan and Zerlate in the selection of fungicides. They simply happened to be the most conveniently available when this experiment was begun. In the light of results to he reported, many other fungicides probably would have served the purpose just as well.

OBSERVATIONS AND DISCUSSIONS

Table 1 gives a summary of the 14 treatments under observation, the numbers of seeds planted, the numbers of seeds which germinated during the 12-week term of the experiment, and the percentage of seeds germinating. Treatments 1, 2, and 3 consisting of freshly fallen whole nuts planted without treatment with a fungicide and placed in flats without regard to orientation of the micropyle, and therefore of the embryo, resulted in 88.8 to 97.2 per cent germination. It is apparent that there were no great differences between soil, sand, and vermiculite as germination media. The percentage of germination was well above that observed in ordinary nursery practice. In a previous year, the writers planted 1297 seeds of the integrifolia type about two months after they had been harvested in Hawaii and shipped to California. These seeds yielded 428 seedlings, representing a germination percentage of 33.0. This percentage corresponds quite closely to those reported by Hamilton (3) for stored seed of four varieties. It is perhaps noteworthy that the highest percentage of germination reported by Hamilton for any variety using seed one month old was 55.0 per cent for the variety Keauhou. Hamilton did not report any germination percentage for freshly fallen seed. The reasons for the high germination percentages observed here as opposed to those observed in ordinary nursery practice are: 1) Only freshly fallen seed was used. In nursery practice, seed may be stored for various lengths of times and under various storage conditions with consequent effects upon ability to germinate; 2) only sound, mature seed was used. In nursery practice, seeds are usually planted without selection, consequently many old seeds and seeds which have dropped from the tree or been knocked off prematurely are sown with the good seeds; (3) As nearly ideal environmental conditions as possible were provided for germination. In many nurseries, conditions are often less than ideal, especially during the winter months when seedbeds with no provision for bottom heat get too cold for good germination. Germination percentages of the seeds in treatments 4, 5, 6, and 7 were just as good as in treatments 1, 2, and 3. These indicate that slight drying of the nuts to the point where the kernels rattle in the shells is not detrimental to the embryos and has no appreciable effect on ability to germinate. Also, there is no difference between nuts planted without orientation of the embryo and those planted with the plant axis in a vertical position with the radicle down and the plume up. In the light of these observations, one may conclude that germination percentages were not affected in treatments 8 through 14 by using kernels removed from partially dried nuts and planting them with the radicle down. No germination occurred in treatments 8, 9, and 10 in which kernels were planted without treatment upon removal from the shell. The reason for failure of germination was rapid decay of the kernels. Within 3 or 4 days after planting fungal mycelium could be seen on the surface of the medium, spreading out from centers immediately above the location of a kernel. By the end of a week the entire kernel was a soft, amorphous, foul-smelling mass, with no indication that the plant axis had begun to initiate growth. The fungus was identified as Rhibopus nigricans. It was not determined whether it was the primary cause of decay, or whether it moved in immediately after bacteria or other fungi had started decay. Germination percentages of treated kernels in treatments 11, 12, 13, and 14 were of the same order as those of treatments I through 7. The most effective treatment was dusting with Arasan SF-X before planting. Little or no decay of the cotyledons was noted, and the embryos germinated 100 per cent. Control of the fungus seemed slightly less effective in the other treatments, and decay of some areas of the cotyledons occurred on quite a number of kernels; not enough, however, to preclude germination entirely. Sprouting was more nearly simultaneous than was the case with whole seed, hut the plants as a group seemed to be less robust.

CONCLUSIONS

The principal reason for carrying on the germination test reported herein was to determine whether kernels could be removed from the shells and planted for more rapid and uniform germination than occurs ordinarily with whole nuts. The main conclusions to be drawn from the study are: I) That kernels can be planted for germination provided they are protected from decay continuously by means of a fungicide until the shoot and root are well developed. Although Arasan SF-X and Zerlate were used in this experiment simply as a matter of convenience, there seems good reason to believe that many proprietary fungicides would be equally effective; 2) Kernels planted without the protection of a fungicide deteriorate rapidly and fail to germinate regardless of the medium in which they are planted. Germination fails because decay attacks the cotyledons causing deterioration before the axis has a chance to initiate and develop vegetative root and shoot growth. Deterioration seems to occur just as rapidly in completely undamaged kernels as it does in kernels with cotyledons chipped during cracking of the shell or upon extraction. Doubtless, it is the same sort of decay, which precludes germination of nuts the shells of which are cracked hut not removed before planting. Other conclusions, which can be drawn from the observations, are: 1) The particular medium in which the seeds were planted did not seem to have any effect upon rapidity of germination or final percentage of seeds germinating; 2) Seed dried over a period of two weeks, enough for the kernels to rattle, showed no difference in germinahility in comparison with freshly fallen seed; 3) The first seedlings appear from both whole nuts and kernels at about the same time; that is in 3-4 weeks from planting. However, sprouting was more nearly uniform from kernels than from whole seeds. The former was complete in 6-7 weeks, the latter required the full 12 weeks of the experiment; 4) Orientation of the nut has no apparent effect on germination; 5) The seedlings from. whole nuts seemed to he more robust than those from kernels. The reason for this is not known, hut one might speculate that continuous coverage with fungicide had a retarding effect upon the developing seedlings. A final conclusion, which can he drawn is: that there is no advantage in removing kernels or cracking the shells of Macadamia nuts over planting whole nuts for germinating seedlings. Germination of whole fresh nuts results in just as good a percentage of seedlings recovered as planting kernels, one need not take the precautions necessary to prevent decay with whole nuts as one does with kernels, and the seedlings from whole nuts seem to grow more vigorously than those from kernels. *Associate Horticulturist, and Laboratory Technician, University of California Citrus Experiment Station, Riverside

LITERATURE CITED

I. Hamilton, R. A. Make your own nutcracker. Hawaii Farm Sci. 3(2):5-6. Oct. 1954.

2. . Problems in germinating Macadamia seed. Hawaii Farm Sci. 5(3): 3, 9 and 12. Jan., 1957.

3. . A study of germination and storage life of Macadamia seed. Amer. Soc. Hort. Sci. Proc. 70:209-212. Dec., 1957.

4. -. Make your own nutcracker. Calif. Macadamia Soc. Yrbk. 5:29. Mar., 1959.

5. Schroeder, C. A. A useful hand cracker for Macadamia nuts. Calif. Avocado Soc. Yrbk. 38:69. 1953-54.