How to Breed Hoyas
First and foremost, I have not yet known any new hoya variety released in the Philippines as a result of artificial pollination done either by ornamental breeders in any research institution or by amateur breeeders. I also haven’t succeeded in developing new hoya hybrids thru artificial breeding.
Unlike in other countries, particularly U.S.A., new hoya hybrids are produced and released every year due to active hoya breeding programs mostly done by amateur breeders. As of January 1, 2006, 13 hybrids were listed with the International Hoya Association (Fraterna Volume 19, Number 1). Michael Miyashiro is one of the famous hoya breeders who developed Hoya Kaimuki by artificially crossing H. archboldiana and H. macgillivrayi. This is just one of the many hoya hybrids he developed.
I can say that developing new plants through breeding is a long and tedious process, so passion, patience, and persistence are a must for anyone who wants to create new plant variety by artificial breeding. Of course, it will require time, space and some financial investment. I don’t mean to discourage potential hoya breeders, but with the information I learned from literatures, tips from known plant breeders and my humble experience in plant breeding, I hope to inspire them to do what other breeders and I failed to accomplish.
Hoya flowers develop from a structure commonly known as spur. The spur resembles a thickened stem and scarred with minute bracts, and arises from the leaf axil on each node. Its stalk is called a peduncle. Depending on the species, the spur persists as part of the plant after the leaves fell off or it may senesce and drop off after some time. Flowering is triggered by proper nutrition, light, temperature, humidity, and water. The more spurs that a plant has, the more flowers it can produce so do not cut the spurs for they produce successive blooms.
The flowers of hoya are arranged in group known as umbel. The shape of the umbel is determined by the length of the pedicel or the stalk of each individual flower. A globular or ball shaped umbel is produced when the pedicels are of the same length. A concave or flat umbel is formed when the pedicels are of varying lengths, being shortest at the interior and becoming longer towards the edge. The pedicels are rigidly curved and all flowers face downward in reaction to gravity. A convex or globose umbel is developed when the peduncle is in an upright position, against the pull of gravity. The umbel may be composed of just a few or an abundant number of flowers loosely arranged or in a compact form depending on the species.
It is very important that we know and can identify the different parts of the hoya flower. The individual flower is generally minute, or large in some species and usually lasts for only a day.
The flower contains both the male and female parts. It is regularly symmetrical and composed of five partly-fused sepals (calyx) and five fused petals (corolla). In the center is the crown (corona) composed of five fleshy coronal lobes (scales) shaped like a star, overlying the anthers. Beneath the corona is the head (stylar table) at the edges of which are 10 fused (or five bi-parted) stigmas. This structure encloses the two ovaries at the interior center of each flower, and a spongy material leads from the stigma to the twin ovaries.
The basic male part of a hoya flower is the anther which contains the pollinarium. Each pollinarium consists of two pollinia, the pockets that contain the pollen held together by a retinaculum which has a head,, waist, and hips. Of all flowers, only orchids are known to have pollinia that are very easy to handle that is why orchid breeding is very successful even to amateurs. We’ll see why it isn’t the case in hoya breeding.
The female parts of the hoya flower is contained in the stylar table. It is five-sided and consists of 10 stigmas fused into five pairs, on e pair at each side. The stigma itself is very small, a somewhat concave surface under the retinaculum. In other words, the retinaculum, which develops from a gland located in the middle of each side of the stylar tfible, covers the stigma.
Under the microscope, the receptive stigma is granular and spongy in appearance. These might explain why the stigmas of hoya are difficult to study. Access to the stigma has been likened to entering an ampitheater — the way is narrow and your space is limited.
THE POLLINATION PROCESS
First, select flowering plants that will be used as a male parent and as a female parent. The male parent plant will be the pollen donor, while the female parent will be the pollen receptor and will eventually produce the seeds. To pollinate, collect a pollinarium using a fine pointed-tip forceps, a needle with flattened tip or a dentist’s dental pick from a flower of the selected pollen donor.
Prior to depositing the donor pollen to the stigma of the female parent, break the retinacula and pick-up all of the pollinaria of the female parent using a fine pointed-tip forceps. This process is known as emasculation and is also a way to expose the female parent stigmas for pollen deposition.
After emasculation, deposit the pollinaria collected from the male parent on all the stigmas of the female parent. Put a label on the pollinated flower using a tag where the name of the female parent is written first followed by the name of the male parent and the date of pollination.
To ensure a successful pollination in hoya, the following must be considered:
1. The stigma of the female parent must be in a receptive condition. Stigma is receptive when a scent is emitted and/or nectar is secreted. Usually, at flower opening the stigma is already receptive. Flower opening in hoya occurs in late afternoon, early evening, and at night time. The scent emitted ranged from barely detectable to sharply spicy to delectably sweet to undesirably stinky. When nectar is secreted, the corona becomes moist or dripping wet.
2. Refrain from damaging the corona and the stylar table in the process of emasculation. Damaging the stylar table can cause earlier wilting of the flower.
FRUIT DEVELOPMENT AND MATURATION
The ovaries of hoya occur in pairs. They are located above the calyx and surrounded by the tissues of the staminal column. After the pollen is deposited on the stigma, pollen tubes germinate, elongate, and enter from the tip of the ovaries and fertilize the ovules within. The ovaries enlarge rapidly and develop into fruits.
Usually, after successful pollination of all stigmas, two fruits may develop from each pollinated flower in an umbel. Most of the time, however, only one fruit develops from the twin ovaries, but under favorable conditions, a whole cluster of fruits naturally develops from an umbel.
The fruit, often referred to as pod, is technically called a follicle. The follicle matures within 2-3 months from pollination. As it matures, it dries up and splits at just one side only. Splitting occurs longitudinally from the tip towards the base or pedicel-end. Prior to splitting, the individual follicle must be covered with a fine nylon net, gauze, old stocking, glassine, or plastic bag, or just taped near both ends to prevent unwanted dispersal of the precious seeds.
FROM SEEDS TO SEEDLINGS TO FLOWERING PLANTS
The ripe fruit splits open in the morning. The brown seeds found inside the follicle are individually attached to a silky tuft of white hair called a coma. The seeds easily separate from the placenta and due to their light nature and the resistance of coma to water, they are easily blown away even by the slightest breeze or your own breath. So, carefully isolate the seeds from the follicle and immediately sow them in a germination medium.
The medium that I use for seed germination is finely chopped fern roots called paslak. Prior to its use as germination medium, the fern roots should be boiled for at least 45 minutes or steamed in a pressure cooker for at least 15 minutes. The process is known as sterilization, a means to kill harmful microorganism in the medium.
After the fern roots have cooled down, place it in a clear plastic food container with holes provided at the bottom. Sow the seeds evenly on the surface of the medium. Once sowing is done, spray with water and cover with the lid. The relative humidity will be maintained by making it sure that the lid is tightly in place. Keep under diffused light condition. Germination will commence one week after sowing although in some species, it happens overnight. Then gradually transfer the container to a brighter location, but never under direct sunlight.
Transplant the seedlings using a potting mixture of equal parts of coconut coir dust and compost three months after sowing or when there, are already several pairs of true leaves. A mixture of one part garden soil and one part coconut coir dust can also be used as potting medium. Vigorous and well-rooted seedlings should be potted individually while the smaller or weaker ones should be composted first to give time for further development. After transplanting to individual pots, spray water to the seedlings. Always maintain the moist condition of the medium, but water only when the surface of the medium is already dry.
A month after transplanting and every month afterwards, apply a complete fertilizer solution either as drench or foliar spray at the rate recommended on its label. If controlled release pellet/granule will be used, the usual application is every three months. Initially, 3-5 pellets/granules are placed on the medium. The quantity is increased to 10-15 pieces or 1/2 teaspoon as the seedling grows larger.
Fertilizer high in nitrogen tends to produce longer or taller plants with more leaves, but it also depends on the light intensity. I use a balanced complete foliar fertilizer with micronutrients at 1 tablespoon per gallon of water every month and also apply 1/2 teaspoon organic fertilizer or compost into the medium every three months.
Flowering may commence as early as one year after seed-sowing, but it is highly affected by environmental factors especially light.