Development of Macadamia Nut Cultivars in Hawaii

DEVELOPMENT OF MACADAMIA NUT CULTIVARS IN HAWAII

R. A. Hamilton1 and Philip J. Ito2

Reprint From CMS Yearbook 1976

The Macadamia nut, M. integrifolia, a relative newcomer among crop plants of the world, is the first and only native food plant of Australia, which has achieved the status of a commercial crop. Most of the commercial development has taken place in Hawaii during the past 40 years. This state presently grows and processes more than 95 percent of the world’s production of this fine dessert nut. Macadamia nuts are now the most important tree crop in the state from the standpoint of acreage, production and value.

More than 100,000 seedling Macadamia trees have been examined and evaluated to date in a continuing selection and testing program begun in 1934 by personnel of the Hawaii Agricultural Experiment Station. From this wide selection of seedling trees grown in private orchards and experiment station plantings, 863 preliminary selections were made and are being intensively tested and evaluated. Most of the early selections have already been discarded as a result of preliminary screening and evaluation procedures. About 50 of the most promising selections, which have survived preliminary testing, have been grafted and set out in several field plots on Hawaii, Maui and Oahu. They are now in the process of being tested in trial plots and experimental orchards throughout the state.

Since Hawaii Agricultural Experiment Station horticulturists initiated breeding and selection works in 1934, nine cultivars have been named. These are: ‘Keauhou’, ‘Nuuanu’, ‘Kohala', ‘Pahau’ and ‘Kakea' in 1948 (6); ‘Ikaika' and 'Wailua’ in 1952 (5); ‘Keaau’ in 1966 (3) and ‘Kau’ in 1971 (2). Two other cultivars, 'Chong 6’ and ‘Honakaa Special’, although not officially named, have become known by these names and are still grown to a limited extent in the Kohala and Honakaa areas respectively. The nine University of Hawaii cultivars were named and introduced after yield trials, quality testing and objective evaluation of tree, out and kernel characteristics over a long period of time. These clones were first grown commercially under the original HAES test numbers, but were officially released after being named and described in Hawaii Agricultural Experiment Station publications.

Five cultivars, all of which have been selected, tested and named by University of Hawaii horticulturists, are presently planted and grown in commercial orchards in Hawaii. This situation is considered to be somewhat unique among other tree crop cultivars, most of which have originated by chance as superior seedlings selected by nurserymen, growers and amateur horticulturists, or imported from other areas or countries. Macadamia cultivars in Hawaii, on the other hand, have originated almost entirely as a result of breeding efforts and rigorous testing activities by Experiment Station horticulturists and plant breeders. Exacting selection standards have been set up and are constantly being revised upward. A summary of present selection standards used in evaluating new cultivars from various sources, including 30 introduced clones from other areas and countries since 1949, follows:

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 most recently introduced cultivars, have more upright growth habits than Keauhou and ‘Ikaika’, which have spreading growth habits. A more upright growth habit permits closer planting within the row and thus more trees per acre.

Nut and Kernel Characteristics:

Medium sized nuts with 10-20 nuts per cluster, 65-68 uniformly sized nuts per pound and 38-48 percent kernel. Uniform, round, white or cream colored kernels without dark circles or off-color tops. Few or no stick-tight nuts and at least 95 percent of grade 1 kernels having a specific gravity of less than 1.0 as determined by flotation testing in water.

Production:

A minimum annual production of 100 lbs. of in-shell nuts from well-grown eight-year-old trees in favorable locations and/or at least 75 lbs. from 10 year old trees in less favorable locations.

Named Hawaiian Macadamia Cultivars:

The first named Macadamia cultivars in Hawaii were described in 1948 by Storey (6). These were ‘Keauhou’. HAES 246, ‘Nuuanu’, HAES 336, ‘Kohala’, HAES 386, ‘Pahau’, HAES 425, and ‘Kakea’, HAES 508. ‘Ikaika’, HAES 333, and ‘Wailua’, HAES 475, were named by Hamilton, Storey and Fukunaga in 1952 (5). ‘Keau’, HAES 660 was named by Hamilton and Ooka in 1966 (3) and ‘Kau’, HAES 344, by Hamilton and Nakamura in 1971 (2). Two other cultivars previously mentioned, ‘Chong 6’ and ‘Honakaa Special’, although selected in the University of Hawaii selection program, were never officially named and described.

Recommended Cultivars:

Five cultivars are presently being planted and grown commercially in Hawaii. No one variety is outstanding enough to be recommended over all others. Choice of varieties is still made largely on the basis of adaptation to location and preference of individual growers.

Nut and kernel characteristics of the five main cultivars in Hawaii are listed in Table 1.

Table 1. Comparison of nut and kernel characteristics in seven Macadamia integrifolia cultivars grown in Hawaii

Cultivars Percent Kernel Nut Wt. (g) Kernel Wt. (g) Nuts Per lb.

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 very good
Keaau 44 5.7 2.5 80 97 excellent
Kau 38 7.6 2.9 60 98 excellent
Mean of 5 Named Varieties 38.2 6.80 2.58 67 92

Detailed descriptions of tree, nut and kernel characteristics of these cultivars have been published (1), (2), (3), (5), (6). The five varieties presently grown commercially in Hawaii are ‘Keauhou’, ‘Kakea’, ‘Ikaika’, ‘Keaau’ and ‘Kau’. Brief descriptions of these cultivars follow:

Keauhou- formerly known as HAES 246 is the oldest Hawaiian cultivar first selected in 1935 and named in 1948. The tree is broadly spreading in form with wide crotch angles and strong branch structure. It therefore requires wider spacing in the orchard than narrower more upright cultivars. It yields well and has attractive nut characteristics, but the kernel quality has proven somewhat marginal some years in certain location (4). ‘Keauhou’ is not considered as hardy or wind resistant as ‘Ikaika’ and ‘Kau’.

Kakea4- HAES 508 is an excellent commercial cultivar selected in 1936 and named in 1948. It has performed exceptionally well in long-time yield trials at the Poamoho, Waikea and Kona experimental farms. It is reasonably hardy, producing kernels of excellent quality and has been a consistently productive, long-lived variety in all test locations. Its growth habit is more upright than Keauhou’ and young trees often need to be topped. Nurserymen consider ‘Kakea harder to graft than other varieties but skilled propagators are able to get a high percentage of takes. ‘Kakea’ is one of the best and most reliable varieties for commercial planting in Hawaii.

Ikaika- HAES 333, was selected in 1936 and named in 1953, largely because it's early hearing tendencies, dark green foliage and vigorous tree characteristics. It has been widely planted in areas where wind problems are limiting factors in growth and production. The nuts are relatively thick-shelled so that recovery of grade 1 kernels is usually less than 30 percent. ‘Ikaika’ is hardy and productive but because its nut and kernel characteristics are not as desirable as those of other are Hawaiian cultivars are it is not being planted as extensively as before.

Keaau- HAES 660 is a relatively new variety first selected in 1948 and named in 1966. It has an upright growth habit permitting somewhat closer planting than most other cultivars without undue crowding. ‘Keaau’ has outstanding nut and kernel characteristics with 42 to 46 percent kernel and more than 95 percent of grade 1 kernels. The nuts are excellent for processing and the trees have performed well during the limited period that this variety has been tested.

Kau- HAES 344, is the most recently introduced cultivar. Although first selected in 1935, it was not officially named until 1971. Kau’ most resembles ‘Keauhou’ in nut characteristics and productivity but has appreciably better kernel quality in most locations. The tree form is more upright than Keauhou and it is also considered hardier and more winding resistant. ‘Kau is a relatively hardy, productive, wind resistant variety considered suitable for commercial planting in areas where it is adapted.

Compared to original seedling orchards in Hawaii, the five commercial cultivars listed in Table 2 have been found to produce approximately 4 times as many nuts per tree, which have about 10 percent more kernel and an additional 10 percent more of grade 1 kernels. This is calculated to be approximately 6 times greater yield of marketable kernels per acre than is produced on comparable seedling plantings of similar age. Nut and kernel characteristics of five promising new selections presently under advanced testing are also listed in Table 2 for comparison with those of five standard varieties. These new selections produce, on an average, nuts of about the same size as the standard varieties but the newer selections have higher percent kernel and a larger percentage of grade 1 kernels.

Table 2. Average nut and kernel characteristics of 10 Macadamia integrifolia cultivars grown in Hawaii

Standard Varieties Percent Kernel Nuts per Pound Nut Weight (g) Kernel Wt. (g) Percent Grade 1 Kernels (floaters) Kernel Appearance (cooked)
Keahou 39 63 7.2 2.8 85 good
Ikaika 34 70 6.5 2.2 89 fair
Kakea 36 65 7.0 2.5 90 very good
Keaau 44 80 5.7 2.5 97 excellent
Kau 38 60 7.6 2.9 98 excellent
Hawaiian Agricultural Experimental Station Selection Numbers
741 43 70 6.5 2.8 98 excellent
790 38 65 7.0 2.7 99 excellent
800 40 57 8.0 3.2 97 excellent
828 44 69 6.6 2.9 96 excellent
849 52 78 5.8 3.0 98 excellent
Mean of Standard Varieties 38.2 67 6.80 2.58 92  
Mean of 5 Promising Selections 43.4 68 6.78 2.92 98

Figure 1. Shell and kernel characteristics of 4 commercial Macadamia cultivars and 4 promising selection.

Upper: commercial cultivars; left to right: Keauhou, Kau, Kakea and Keaau.

Upper: unnamed new selections; Left to right: HAES 741, HAES 800, HAES 828 and HAES 849.

 

What predictions can be made about the future and improvement of commercial Macadamia cultivars in Hawaii? On the basis of new selections already under test and genetic material under observation, production per tree can be increased by about 25 percent over present cultivars. Percent kernel recovery can be improved approximately 10 percent from about 35 up to 45 percent and percentage of Grade 1 kernels from about 90 to 95 percent. This potential increase in useable kernels would amount to an increase of about 70 percent in production of Grade 1 kernels per tree and per acre. A comparison of the shell and kernel characteristics of the standard Hawaiian cultivars with those of promising new Hawaii Agricultural Experiment Station selections is shown by Figure 1.

About 50 new cultivars are presently being tested and 2 of these, HAES Nos. 741 and 800, will be named and released as soon as adequate scion wood can be made available.

An active Macadamia breeding project continues in Hawaii. Selection standards will remain high because excellent commercial cultivars are available and being used as checks in selecting superior new cultivars.

1.Professor of Horticulture, University of Hawaii.

2. Associate Professor of Horticulture, University of Hawaii, Hilo Branch Station.

LITERATURE CITED

1.Hamilton, R. A. and E. T. Fukunaga. 1973. Macadamia nut varieties. Hawaii Macadamia Nut Producers Association 13th annual proceedings. Pp. 34-37.

2.Hamilton, R. A. and M. Nakamura. 1971. ‘Kau’ a promising new Macadamia variety. Hawaii Macadamia Producers Association 11th annual proceedings, Pp. 29-3 2.

3.Hamilton, R. A. and H. Ooka. 1966. Keaau — A new commercial Macadamia. Hawaii Macadamia Producers Association 6th annual proceedings. Pp. 10-14.

4.Hamilton, R. A., A. L. Radspinner and P. J. Ito. 1975, A study of variation of Keauhou in percent kernel and grade 1 kernels at several locations. Hawaii Macadamia Producers Association 15th annual proceedings. Pp. 34-47.

5. Hamilton, R. A. and W. B. Storey and E. T. Fukunaga. 1952. Two new Macadamia varieties and an appraisal of the HAES named varieties. Hawaii Agricultural Experiment Station Circular 36. 5 pp.

6.Storey, W. B. 1948. Varieties of the Macadamia nut for planting in Hawaii. Hawaii Agricultural Experiment Station Progress Notes 51.4 pp.