Overview of Our Anorectic Plant Research

Research-Greenhouse

Our research greenhouse

This provides an overview of our ongoing research and development work with species of Hoodia and other anorectic (appetite suppressing) plants. Materials derived from these plants are widely used in dietary supplements for weight loss, and have other potential uses in products under development. We will provide additional information on these activities in future updates of this website.

Our research program currently focuses on developing cultivars of anorectic plants in the family Apocynaceae, formerly Asclepiadaceae that are more suitable for efficient production under artificial cultivation conditions meeting requirements for organic certification. Species of primary interest include those in the genera of Hoodia, Hoodiopsis and Caralluma. Wild populations of many of these plants are declining because of habitat destruction, climate change, unsustainable harvesting practices and other factors. In response countries where these plants are endemic and international treaties are now restricting exports and trade in these species. Development of new cultivars should reduce pressure on wild populations and provide improved domestic access to the valuable materials that can only be produced from these plants.

We are also developing innovative, science-based products to be made from these plant materials for novel applications that we believe may be more effective than most currently available products and will provide consumers with greater assurance of freshness, content and freedom from adulterants.

Background

There are significant obstacles to growing the above plants in artificial cultivation. The most challenging problems relate to their slow growth and high susceptibility to pests and diseases, particularly when the plants are grown in high humidity and/or wet soil conditions. Most of these plants require prolonged periods of winter dormancy, infrequent rain and dry conditions during the winter. Here in Hawaii outdoor conditions are unfavorable. It rains frequently throughout the year and the highest amounts of rain usually occur in the winter months. The plants do well in greenhouses where water can be controlled and produce the medicinal compounds of interest but growing these slow growing plants indoors on a large scale indoors may not be economically feasible.

Pests and Diseases

The disease of greatest importance that affect all plants in this group is soft rot, and black spot disease or anthraconose affects all species of Hoodia, the genus of most commercial use. The agents that cause these diseases are of ubiquitous worldwide distribution and have been observed in both wild populations and plants in artificial cultivation. Under unfavorable growing conditions, particularly outdoors the diseases they cause can spread quickly, infecting and decimating entire plant populations. Plants grown indoors are also highly susceptible to mealybug infestations that can be difficult and expensive to control.

Soft Rot – In most cases soft rot is appears to be caused by Erwinia, species of Gram-negative bacteria in the family Enterobacteriaceae. (The taxonomy of these bacteria is currently undergoing revision). Soft rot reportedly can also be caused by Fusarium species or other fungal pathogens but we rarely find this in our collections. Soft rot infections usually begin in the roots where they may remain quiescent and unnoticed for prolonged periods of time. Prolonged wet conditions, weakening of the plants and other undetermined factors result in activation of fulminant disease. Activation apparently marks the onset of a highly motile swarming phase in the bacterial populations and the release of enzymes that dissolve cell walls. This allows the bacteria to spread rapidly upward through the vascular system of the plant resulting in liquefaction of the soft tissues and complete collapse of the affected aerial parts. Healthy appearing plants can turn to mush in less than a day from the onset of noticeable symptoms. No pesticides are effective for control of bacterial soft rot. Prevention by controlling growing conditions and development of disease resistant cultivars are the only methods likely to reduce the prevalence of soft rot to manageable levels.

The Hoodia seedlings in the photo below are the same cultivar of approximately the same age.  The plant on the left appeared healthy and the same as the plant on the right about one week before this photo was taken.  The plant on the left then contracted soft rot moving upward from the roots resulting in liquefaction of its soft tissues and complete collapse of the plant.  This shows the rapidity of soft rot disease progression.

Fulminant-Soft-Rot-of-Hoodia-gordonii

Fulminant soft rot of Hoodia

Black Spot or Anthracnose – This disease is caused by pathogenic fungi, primarily in the genus Colletotrichum and is usually associated with spider mite infestations. All species of Hoodia and Hoodiopsis triebneri are severely affected; we have not observed this in the species of Caralluma and Orbea that we work with, even when they are held in the same conditions and in close proximity to other infected plants. Areas of the plants bitten by the mites develop black lesions under the cuticle of the plants. These may spread from the area of the bites but usually do not advance if mite infestations are controlled. Areas of the plant affected by these infections stop growing and plants with severe infections may be stunted, fail to emerge from winter dormancy and eventually die. In our outdoor Hawaiian growing area the false spider mite Brevipalpus phoenicis is the primary vector of this disease. Warm, humid conditions and prolonged periods of rainfall promote infestations and 100% of plants exposed may develop black spot disease. While it is possible to control infestations and the affected plants may recover they are left with lesions that render them unusable for sale or consumption.

Black-Spot-Disease-on-Hoodia-gordonii

Black spot disease on Hoodia gordonii

Black-Spot-Disease-on-Hoodiopsis

Black spot disease on Hoodiopsis triebneri

Mealybugs – Hobbyists that specialize in keeping these asclepiad plants aptly describe them as “mealybug magnets”. Apparently many species of mealy bugs infest these plants and they can be easily introduced into areas where they were not previously present from imported plants. Once established in greenhouses they can be very difficult to eradicate without the use of systemic pesticides such as imidacloprid that are unacceptable for organic production. An example is Chorizococus brevicruris, the short-legged mealybug that apparently was introduced into our greenhouse in Maryland in 2006 in a shipment of plants from California. It took us several years to completely eradicate this pest from our nursery operations. In both Maryland and Hawaii mealybugs have been an ongoing problem in our greenhouses but plants grown outdoors have rarely been affected, perhaps controlled by predation.

Mealybug infestations usually begin on the tender buds of growing shoots. Unless quick brought under control their bites will stunt or completely stop plant growth. While insecticidal soaps, sulfur emulsions and other common non-persistent pesticides compatible with organic certification can be successfully used to control mealy bugs on the areal parts of Hoodia species they have not been effective in controlling mealy bug infestations on roots. Growing media for these plants must promote rapid drainage and usually consists of granular inorganic materials such as perlite, sand or volcanic cinders. These allow mealy bugs to enter the soil and dry growing conditions allow them to survive and attack subsurface stems and roots. If unchecked even small numbers of mealybugs on roots can stunt growth and kill plants. These infestations may go unnoticed until it is too late to save the affected plants.

Mealybugs-on-Hoodia-gordonii-Shoot

Mealybugs on a Hoodia gordonii shoot tip

Mealybugs-on-Hoodia-Root

Mealybugs on roots of Hoodia gordonii

Desirable Traits

To facilitate growing of these plants in artificial cultivation the traits we seek in new cultivars are listed below in order of priority:

  1. Resistance to soft rot.
  2. Tolerance of wet soil conditions.
  3. Extension of growing season by reduction or elimination of requirements for prolonged winter dormancy. Plants are also at greatest risk of disease when they are dormant.
  4. Faster growth and weight gain.
  5. Resistance to black spot disease.
  6. Ability to grow from cuttings to maintain, propagate and patent desirable cultivars. (Most of these plants are self-sterile so pollination by other plants is required to produce seeds, and these seeds may not exhibit the same traits of the seed producing plant). For plants that are potentially invasive the ability to propagate only self sterile cultivars by vegetative reproduction reduces also reduces risks associated with introducing these plants into areas where they are not endemic.
  7. Forms that would facilitate sustainable harvesting and easier production of materials from the plants: smaller, less sharp thorns; thicker shoots; rapid recovery from shoot removal and cutting wounds; presence of medicinal compounds at sufficient concentrations when the plants are mature enough for the first harvest.

Development and Selection of New Cultivars

We began research and development of new cultivars in 2005. The processes used consist of conventional plant breeding techniques, primarily the continuous selection of plants with desirable traits from those that survive exposure to adverse growing conditions in artificial cultivation in greenhouses and field trails.

To begin this process and maximize genetic diversity we obtained plants and seeds of as many different species and sources as possible. These were obtained from growers; we did not accept plant materials from wild populations. At the onset of this program plants were scarce and expensive, few reputable vendors were available, the identity of the supplied plants and seeds was often incorrect, some imports contained live pests and the viability of seeds was low. In recent years prices for plants have declined but there are still few sources and restrictions on international trade have severely limited the variety and availability of propagative material.

We are working with the following species in our research program:

Caralluma

C. fimbriata

C. foetida

 

Hoodia (focus of our research; includes intraspecific hybrids of these species)

H. currorii

H. currorii subsp. currorii

H. flava

H. gordonii

H. juttae

H. macrantha

H. officinalis

H. parviflora

H. pedicellata

H. pilifera subsp. annulata

H. pilifera subsp. pilifera

H. ruschii

 

Hoodiopsis triebneri

(Hoodia gordonii X Orbea vaga)

 

Caralluma-fimbriata

Caralluma fimbriata

From the plants and seeds of these species obtained from outside sources and cuttings subsequently made from the original plants, several thousand plants and seedlings were produced and used in numerous experiments involving various soil media, pesticides and artificial wet growing conditions in greenhouses and field tests in Maryland and Hawaii. Less than one percent survived with most lost to bacterial soft rot and culling. From the surviving plants with desirable characteristics cuttings were made and seeds for replanting were grown for use in additional experiments. This process is labor and material intensive, tedious and slow as it typically takes a minimum of about three years from planting seeds to grow a mature hoodia plant and produce new seeds.

Status of Cultivar Development

This long process of continuous selection and improvement has yielded about ten new cultivars of Hoodia gordonii and one of Hoodia parviflora. The first named Hoodia gordonii New Cultivar (HGNC) was a colchicine treated seedling grown in 2005 from lot of seeds obtained from Germany. HGNC showed improved resistance to soft rot, produces numerous shoots, has an exceptional ability to root from cuttings, and the plants contain the medicinal compounds of interest when grown in artificial cultivation. At least six successive generations of plants have been produced vegetatively from cuttings of this plant. The cuttings often bloom within 1-2 years of rooting, produce viable seeds when crossed with other Hoodia gordonii genotypes, and apparently other species of Hoodia. The other new cultivars are all from seed plants of this species except for the one cultivar of Hoodia parviflora, which is likely to be an intraspecific hybrid. Of the H. gordonii cultivars testing results, incomplete as of this writing indicate that the majority are tetraploid plants. This suggests that the selection criteria including large size and rapid growth favors polyploids, as is common for many other agricultural crops.

New-Tetraploid-Hoodia-Cultivar

One of our new tetraploid hybrid Hoodia cultivars

 

Product Development

Concomitant with our development of new cultivars we have been conducting research and development of new applications for materials derived from this group of plants. Most of this work was successfully concluded in 2014 and described in a provisional patent and proprietary information. We are currently considering partnerships with others to complete further development and begin manufacturing of these products.

Disclaimer

No statements on this website and none of our products are intended for use in diagnosing, treating, curing or preventing any diseases of humans, animals or plants. None of these products or statements have been evaluated by the U.S. Food and Drug Administration (FDA).