Development and Evaluation of Macadamia Nut Varieties

DEVELOPMENT AND EVALUATION OF

MACADAMIA NUT VARIETIES*

R. A. Hamilton** and E. T. Fukunaga***

Reprint From CMS Yearbook 1973

INTRODUCTION

In Macadamia nuts and many other tree crops, which variety to plant continues to be a major source of interest and concern to growers, nurserymen, promoters and amateur enthusiasts. Macadamia nut "variety" refers specifically to selected clones usually propagated by grafting. Variety will be used in this context in the following discussion and evaluation of current development.

In most tree crops, there are usually far too many varieties. The total number of varieties depends upon the importance and stage of development of the crop. It is common to encounter exaggerated and misleading claims concerning relative merits and potential performance of varieties. This tends to make standardization and the choice of varieties to plant, somewhat difficult, confusing and arbitrary Macadamia nut growers are faced with the same type of variety problems that confront other tree crop producers.

Macadamia nuts have been grown as a commercial crop for less than 40 years. Named varieties have been available for only about 25 years however. Most of the existing varieties were selected, named and introduced rather quickly after grafting methods were perfected. More than 43 selected clones have been named and introduced as varieties since the first 5 clonal varieties were named described by Storey (5) in 1948. Before macadamias were grown successfully as a commercial crop, individual trees were sometimes given names and seed nuts from these trees sold at high prices. Names such as ‘Comet,’ ‘Eggshell’ and ‘Smooth Queen’ originated and were used in this mariner in Australia. Resulting seedlings from these named trees proved to be quite variable and were usually inferior to the parent tree. These names did not actually represent true horticultural varieties and the original trees were eventually lost or forgotten.

When a relatively new tree crop such as Macadamia shows promise as a commercial product, new varieties can evolve rather quickly. This is especially true when there are large numbers of wild and/or cultivated seedling trees available for observation and selection - This has happened in Macadamia where more than 43 selected clones have been named and described since 1947. This activity has taken place in 3 distinct areas: California, Hawaii and Australia.

Selection Standards

Standards used in Macadamia selection vary and seem rather arbitrary in some cases. Similarly, testing, especially for yield, quality and suitability for commercial production, was often incomplete. Selections were based mainly on superficial observation of the original seedling trees and nuts produced.

Named Clones

A survey of the literature and checking University of Hawaii trial orchard records reveals at least 7 clones from California with variety names. There are 12 more from Hawaii and 24 from Queensland and New South Wales in Australia. A total of 43 named varieties are listed in Table 1. This list is undoubtedly incomplete and a worldwide survey would probably reveal several more. The varieties in Table I include both ‘‘smooth shell’’ M. integrifolia and ‘‘rough shell’’ M. tetraphylla varieties as well as several hybrid clones. Table 1 lists 19 smooth shell varieties, 14 rough shell varieties and 10 others considered to be of hybrid origin.

Table I. Species and area of origin of 43 named varieties of Macadamia
Area of Origin
Number Australia Species Hawaii Species California Species
1 A.R. Nelson * Bond 23 * Burdick **
2 Amamoor ** Chong 6 * Faulkner *
3 Amanasco * Honakaa Sp. * Hall **
4 Ardrey ** Ikaika * Jordan *
5 Beaumont *** Nuuanu * Parkey *
6 Collard ** Pahau * Santa Ana **
7 Colliston ** Kakea *    
8 Daddow * Kau *    
9 Ebony *** Keaau *    
10 Elimbah ** Keahou *    
11 Flaxton ** Kohala *    
12 Gerber ** Wailua ***    
13 Gerber's hybrid ***        
14 Hinde *        
15 Howard **        
16 Maroochy **        
17 Oakhurst ***        
18 Own Choice *        
19 Rankine ***        
20 Rickard ***        
21 Renown ***        
22 Sewell **        
23 Stephenson **        
24 Teddington ***        
25 Tinana ***        
Species designation: Macadamia integrifolia * Macadamia tetraphylla ** Macadamia Hybrid ***

 

Hopefully, hybrid varieties might combine the best characteristics of both species. Actually they tend to resemble M. tetraphylla more than M. integrifolia, especially in nut characteristics and kernel quality. In Hawaii, no promising rough shell or hybrid selections have been found and rough shell varieties are not used in commercial orchards. All 5 varieties used for commercial planting in Hawaii are of the smooth shell M. integrifolia type. This trend is expected to continue since rough shell types are erratic and slow to come into bearing in Hawaii, and the nuts they produce have significantly lower percentages of grade 1 kernels than smooth shell varieties. There are approximately 50 new selections presently under intensive yield testing in Hawaii and all of then, are M. integrifolia clones.

All known varieties from both Australia and California have been imported for testing in Hawaii during the past 20 years. All except 4 of the 43 varieties in Table 1 have fruited and been tested in Hawaii. Evaluation of tree and nut characters has however shown only 5 varieties to be suitable for commercial growing and processing purposes.

In studying variety performance, it is interesting to note that nut characteristics of the some varieties appear to be very similar, regardless of whether they are grown in Australia or Hawaii. In a study conducted in 1962 (1), no significant differences were found in average nut size, percent kernel and shell thickness of 15 Australian grown varieties, compared with those of the same varieties grown in Hawaii (see Table 2.) Nuts of Hawaiian varieties grown in California however tend to be slightly smaller with lower oil content than when grown in Hawaii.

Judged by selection and processing standards used in Hawaii. ‘Faulkner’ has been the most interesting of the California varieties. It measures up well in most respects and probably could be used as a commercial variety in Hawaii, if necessary. The nuts are somewhat more variable in size than those of standard Hawaiian clones and kernel average somewhat smaller but production, quality and appearance of kernels are quite satisfactory.

Table 2. Comparison of means kernel percent and shell diameter of nuts from 15 Australian clonal selections grown in Queensland and Hawaii

Location Where Grown

Kernel Percent (by Wt.)

Shell Diameter ( inches )

Top to bottom Side to Side

Australia 33.8 1.04 0.99
Hawaii 33.6 1.08 1.02
Difference 0.2 .04 .03
Difference required for significance at 5% level

 

2.1

 

.044

 

.035

The 24 varieties originating in Australia include 8-M. integrifolia, 11-M. tetraphylla clones and 5 which, appear to be of hybrid origin. These varieties range from selections with large, thin-shelled nuts to those, which conform closely to Hawaiian selection standards. None of 20 Australian varieties, which have fruited in Hawaii, appear suitable for commercial growth or processing. Several are however, being utilized as parents for breeding work in progress. Australian varieties such as ‘Hinde’ and ‘Rickard’ hear well in Hawaii and initially appeared promising but produced excessive numbers of stick-tight nuts. This, of course, eliminated them from further consideration as commercial varieties. Selection standards in Hawaii, which have been kept high, have recently been revised upward. A brief review of current selection standards in Hawaii should be useful in evaluating named varieties from various sources.

Tree characteristics: Vigorous trees with dark green foliage, strong crotches and ascending rather than spreading branch structure, ‘Kakea’ as well as ‘Keaau’ and ‘Kau,’ the last 2 varieties introduced, have relatively upright growth habits compared with ‘Keauhou’ and ‘Ikaika’, which have spreading growth habits. More upright growth habit allows the planting of more trees per acre.

Nut and kernel characteristics: Medium sized nuts, 10-20 nuts per cluster, 65-68 nuts per pound, uniform in size, 38-48 percent kernel. Round, uniform, white or cream colored kernels without dark circles or off-color tops. Few on no stick-tight nuts and at least 95 percent No. 1 kernels as determined by flotation testing.

Production: A minimum annual production of 100 lbs. of in-shell nuts by well grown 8 year old trees in favorable location or at least 75 lbs. from 10 year trees in less favorable locations.

Variety Improvement Program

More than 800 numbered clones have been selected and tested in Hawaii during the past 38 years. Several of these might logically be considered varieties since they are as good or better than most named varieties. The majority of these numbered clones have already been discarded in the testing program however and it would therefore serve no useful purpose to discuss them further.

There are approximately 50 clonal selections presently undergoing yield tests in University of Hawaii trial orchards. These were selected according to high selection standards using the 5 standard commercial varieties as checks and include some very promising new clones.

These selections are now undergoing rigorous testing in a newly established variety trial planting. It is probably and even likely that one or more new selections will eventually meet or exceed present stated selection standards. A comparison of nut and kernel characteristics of 5 commercial varieties, "Faulkner'' and 6 promising new selections is provided in Table 3.

Tree characteristics take considerably longer to prove out and test objectively than nut and kernel characteristics. Initial selection of promising seedlings is made mostly on the basis of nut characteristics and preliminary observation of tree form, and productivity. However it takes at least 10 years to objectively evaluate bearing behavior of grafted trees under orchard conditions. Since most of the named varieties were given names on the basis of nut characteristics and observation of the performance of the original seedling tree, it is not surprising that so few have survived to become commercial varieties.

For those interested in selection statistics, between 80 and 90 thousand individual seedling trees of bearing age have been sampled and evaluated in selecting the 5 commercial varieties presently used in Hawaii. Compared to original seedling orchards in Hawaii commercial varieties produce about 4 times as many nuts per tree, which have about 10 percent more kernels, and an additional 10 percent more of grade 1 kernels. This calculates out to about 6 times more marketable kernels per tree from grafted orchards compared to the original seedling plantings.

What can be said about the potential for Macadamia variety improvement in Hawaii? Judge by present indications including new selections and genetics material on hand, present production per tree can be increased by about 25 percent, the percent kernel recovery from about 35 up to 45 percent and the percent of No. 1 kernel from about 90 up to 95 percent. This potential, if realized, could lead to an increase in production of No. 1 kernels per tree and per acre, up to about 70 percent.

 

Table 3. Comparison of nut and kernel characteristics in 12 Macadamia integrifolia cultivars grown in Hawaii

Standard Varieties Percent Kernel Nut Wt. (g) Kernel Wt. (g) Nuts per pound Percent No.1 Kernels (floaters) Kernel Appearance (cooked)
Keahou 39 7.2 2.8 63 85 good
Ikaika 34 6.5 2.2 70 89 fair
Kakea 36 7.0 2.5 65 90 good
Keaau 44 5.7 2.5 80 97 excellent
Kau 38 7.6 2.9 60 98 excellent
Hawaiian Agricultural Experimental Station Selection Numbers
781 40 7.8 3.1 59 98 excellent
790 40 7.0 2.8 65 99 excellent
794 38 6.1 2.3 75 94 good+
800 40 8.0 3.2 57 98 excellent
812 42 6.2 2.6 73 97 good+
830 44 5.9 2.6 77 95 good+
Faulkner 43 5.1 2.2 88 97 excellent
Mean of 5 Standard Varieties 38.2 6.80 2.58 67 92  
Means of 6 HAES Selection Numbers 40.7 6.83 2.77 67 97  

 

Five varieties are presently considered suitable for commercial planting in Hawaii. No one variety is however outstanding to the extent that it can be universally recommended over all others. Choice of varieties is still made largely on the basis of adaptation to location and preference of the grower. It is notable that the University of Hawaii Horticulture staff selected all the 5 commercial varieties and that they are smooth-shell M. integrifolia types.

Detailed descriptions of tree, nut and kernel characteristics of these varieties have been published (2), (3), (4), (5). The 5 varieties presently recommended for commercial planting in Hawaii are ‘Keauhou,’ ‘Kakea,’ ‘Ikaika,’ ‘Keaau’ and ‘Kau'. Brief descriptions of these varieties follow:

‘Keauhou’ is one of the oldest Hawaiian varieties, having been selected about 1935 and named in 1948. It has excellent nut and kernel characteristics but the tree is rather broad and spreading. It therefore requires wider spacing in the orchard than narrower more upright varieties. ‘Keauhou’ is not considered as hardy or wind resistant as ‘Ikaika’ or ‘Kau.’

‘Kakea’ is an excellent commercial variety, which has performed exceptionally well in long time yield trials at Poamoho, Waikea and Kona experimental farms. It is reasonably hardy, produces kernels of excellent quality and has been a consistently high producing, long-lived variety at all test locations. Its growth habit is more upright than ‘Keauhou’ so those young trees may need to be topped. Nurserymen consider ‘Kakea’ harder to graft than other varieties but skilled propagators are still able to get a high percentage of takes. ‘Kakea’ is one of the best and most reliable varieties for commercial planting in Hawaii.

‘Ikaika’ was selected largely because of its tree vigor and hardiness, it has been widely planted in areas where wind problems tend to limit tree growth and nut production. The nuts are rather thick shelled and the percent of kernel recovery 34 percent or less. ‘Ikaika’ is hardy and productive but its nut and kernel characteristics are not as desirable as those of other Hawaiian varieties are.

‘Keaau’ is a relatively new variety, first selected in 1948 and named in 1966. It has an upright growth habit permitting closer than average spacing in the orchard without undue crowding. ‘Keaau’ has outstanding nut and kernel characteristics with about 44 percent kernel and more than 95 percent of grade 1 kernels. The nuts are almost ideal for processing and the trees have performed well during the limited period this variety has been tested.

‘Kau’ is the most recently introduced variety. Although first selected in 1935, it was not officially named until 1971. ‘Kau’ is very much like ‘Keauhou in nut characteristics, kernel quality and productivity. The tree is however more upright and considered hardier and more wind resistant than ‘Keauhou,’ which it most resembles. ‘Kau’ is considered to be a relatively hardy, productive, wind resistant variety suitable for commercial planting in areas where it is adapted.

Conclusions

This concludes a progress report on the origin, status and performance of 43 named Macadamia varieties from 3 distinct areas. In all likelihood there will be new varieties named and introduced within the next 10 years. An active Macadamia breeding project is being continued in Hawaii. Selection standards can be expected to remain high because there are several good commercial varieties available for use as checks.

1.Published With the approval of the Director of the Hawaii Agricultural Experiment Station as Journal Series No. 1598.

2.Professor of Horticulture, University of Hawaii.

3.Horticulturist and Superintendent Kona Branch Station, Hawaii Agricultural Experiment Station.

 

LITERATURE CITED

1.Hamilton, R. A. and E. T. Fukunaga. 1962. Testing Australian Macadamia nut varieties in Hawaii. Hawaii Macadamia Producers Association First Annual Mtg. Pro. 27-32 pp.

2.Hamilton, R. A. and M. Nakamura. 1971. ‘Kau’ a promising new Macadamia variety. Hawaii Macadamia Producers Association 11th annual mtg. proc. 29-32 pp.

3.Hamilton, R. A. and H. Ooka. 1966. Keaau - a new commercial Macadamia. Hawaii Macadamia Producers Association sixth annual mtg. proc. 10-14 pp.

4.Hamilton, R. A., W. B. Storey and E. T. Fukunaga. 1952. Two new Macadamia nut varieties. Hawaii Agr. Expt. Sta. Cm. 36, 5 pp.

5.Storey, W. B. 1948. Varieties of the Macadamia nut for planting in Hawaii. Hawaii Agr. Expt. Sta. Ping. Notes 51,4 pp.