By Russell T. Nagata
University of Hawaii at Manoa College of Tropical Agriculture and Human Resources Komohana Research and Extension Center
While the Kona district of Hawaii Island is traditionally known as the best avocado-growing area in the state, well-selected avocados, in general, will grow and fruit from sea level up to about 2,000 feet in elevation around the state.
Kona is reputed to be the best avocado-growing region because many of our cultivars originated from seeds that were planted in area coffee fields from which the best were selected and propagated based on their good fruit quality.
Many of those cultivars bear the surnames of the farmer on which farms the original tree grew. Avocados are harvested in Hawaii year round, but for the past few and next few months they should be more readily available than at other times of the year.
Many of us have trees growing in our yards, or know friends or relatives who are willing to share in their bountiful crop. Avocados are easy to grow, and by planting several selected cultivars that mature at different times of the year, your harvesting can be nearly year round.
While some people believe that avocados are bad for you due to their high oil content, avocados taste good and, believe it or not, are good for you. A one-cup serving of cubed avocado is more or less about 240 calories, due to the fat content ranging from 15 to 30 percent. However, most of that fat is monosaturated fat, the one that’s good for you.
Avocados are reported to contain over 20 vitamins and minerals considered necessary for good health and are a good source of dietary fiber (10 grams), potassium (higher than banana) and folic acid. Another reason to eat an avocado is that it is reported to be a natural mouthwash to eliminate bad breath.
Avocado, Persea americana, originated in tropical America and three races are recognized that reflect the harvest season, fruit and plant characteristics and adaptation to specific environmental niches.
The Mexican race is native to the highlands of Mexico and has anise-scented leaves, 8-ounce fruits with smooth, thin skins and ripen in six to eight months. It is the most cold- hardy and has oil content up to 3o percent. Seeds are loose and tend to rattle within the fruit when shaken.
The Guatemalan race is native to the highlands of Central America and has large 1-to-2-pound fruits which ripen within nine to 12 months and contain 8 to 15 percent oil. Fruits hang from long stems and skins are thick, bumpy, hard and brittle which contribute to the grittiness around the cut surface when eaten. Seeds are normally small and tightly held in the fruit.
The West Indian race originated in the lowlands of Central America and has fruit smaller than the Guatemalan race which mature between six and nine months. Fruits hang on short stalks, have smooth, leathery skins and seeds are large and generally loose within the fruit. Oil content ranges from 3 to 10 percent and generally lacks the smooth buttery texture of the other races.
From the descriptions of the three races, you might be wondering that they’re nothing like avocados you recently consumed. What you experienced can best be described as a combination of different characteristics from the races.
Perhaps it was a small fruit with a rich butter taste from the Mexican race but with a small seed that is a characteristic of the Guatemalan race. If this thought came to mind, you are correct in that many of our economically important avocado cultivars or varieties that we consume today are hybrids of the different races.
For the avocado, cross-pollination or hybridization is a natural process and goes a long way to explain why it is not recommended to plant a single avocado tree in your yard, especially if you don’t have neighbors with trees. It is also the reason you are encouraged to purchase a grafted tree instead of planting a seed from a good avocado you just ate.
All avocados generally flower during the same period and the number of months to maturity account for differing harvest dates. Pollination biology in avocados is classified as synchronous dichogamy, in which two types of flower opening known as types “A” and “B” are present.
In both flowering types, flowers open for two days with the female organs (stigma/ovary) being functional on the first day. When the flowers open on the second day, the male organs (anther/pollen) are functional. For type “A” avocados, female organs (ovary) are functional in the morning of the first day, and on the afternoon of the second day the male organs (pollen) become functional.
In type “B” avocados, the female organs are functional in the afternoon of the first day and the male organs are functional in the morning of the second day. Therefore, to maximize fruit number it is best that you plant both type A and B avocados for best pollination, especially if your neighborhood lacks avocado trees.
However, there is some overlap of morning and afternoon functioning and some self-pollination does occur, resulting in fruiting.
Some of the better-known type “A” cultivars are Greengold, Hass, Ohata and San Miguel. The better-known type “B” cultivars are Kahaluu, Malama, Murashige, Nishikawa and Sharwil.
For more information on this and other gardening topics, please visit the CTAHR electronic publication website at http://www.ctahr.hawaii.edu/Site/Info.aspx, or visit any of the local Cooperative Extension Service offices around the island. I can be reached at email@example.com.