Articles:BULB CHAT November 2010 PDF Print E-mail
Sunday, 05 June 2011 16:13

Bulb Chat November 2010

Polyploidy in Haemanthus by Aart van Voorst

A Summary

Aart is a plant breeder and therefore had the facilities available to manipulate the ploidy of plants, that is, to increase the chromosome number. The plant characters are all contained within the genes arranged along the chromosomes, of which the plant has inherited 2 sets (diploid), one each from the male and female. Each species has a defined number of chromosomes located in each cell.

Polyploidy, usually a doubling of the number of chromosomes, is found naturally in many cultivars and can be recognized by the bigger flowers with longer-lasting qualities, stronger stems, etc. These are seen as favourable traits.

Aart started with wild plants and attempted to double the chromosome number resulting in tetraploid plants. This can be done with the aid of the chemicals, colchicine and oryzaline, which upset the normal cell division.

Why would one want to double the number of chromosomes in Haemanthus from 16 to 32? Firstly to increase the robustness of the plant and produce larger flowers, and, in triploid hybrids, to confer extra hybrid vigour.

Another advantage is to restore the fertility of interspecific hybrids, which can then be crossed using the natural pollinators. This can be seen in the wild with H albiflos X coccineus.

Because of the many possibilities it is necessary to have a defined goal in mind. Aart was working towards hybrids that stay evergreen, with flower colour other than the white with yellow pollen of H albiflos, specifically the red of coccineus.

The best method to obtain tetraploids is to apply 0.05% solution of colchicine to meristem cells.However the meristem of a mature bulb is deep within the heart of the plant. Bulblets can be induced to grow from a leaf/bulb by treating with hormones, and these can be treated with colchicine.

Germinating seeds also can be treated. Colchicine is applied on a piece of tissue to the growing tipat a temperature of >20oC for 1-3 days. The growing radicle is avoided, as the teratogen may kill the meristematic cells. If all seeds are treated, the embryos may all be different.

Aart started with wild plants and made a cross. Pollination may be difficult, and many self-pollinate. It is best to emasculate H albiflos (mother), and remove stamens, and then pollinate with H coccineus pollen by hand.

Results of the interspecific cross produced hybrids that produced buds after 3.5 years. There was a variation of leaf markings to none, but they were evergreen with a red flower (coccineus). The flowers

The success of the colchicine treatment can be checked by

a) Counting chromosomes in root tip cells. This is not always accurate as the original radical was not treated and may remain diploid.

b) Measuring stomata size. Tetraploids and diploids have different stomata sizes on the leaves.

c) Anthers of tetraploids are bigger than those of diploids .

The tetraploid H albiflos was crossed with a diploid H coccineus, resulting in a triploid hybrid with a pink flower.

Haemanthus are fast breeding, and can be propagated by tissue culture, whereas Clivia is very slow-growing in tissue culture.

Other possibilities:

H deformis x H coccineus cross produced red flowers but the leaves died at flowering.

H albiflos X humilis has been done, but not flowered yet. The leaves however are evergreen. There are differences in pollen grains of H humilis in nature, so it is surprising that the seeds are viable.

Cross -pollination is facilitated by the fact that H coccineus all seeds ripen at the same time.

Also H albiflos sets seed very easily.

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COLLECTION AND STORAGE OF SEEDS By Rod Saunders

The life of South African bulbs and corms is finite, so it is important to hand pollinate this season’s flowers to obtain seed for re-sowing the following season. This is particularly important for species of Sparaxis and Gladiolus which are quite capable of flowering themselves to death. After one has pollinated the flowers and the seeds have set and ripened, the next step is to harvest the seeds and store it until the correct season for sowing.

In Iridaceae, most seeds take about 6 weeks to ripen, with some exceptions eg Watsonias which take longer and some Moraea species which are ripe in 4 weeks. Ornithogalum, Albuca and Bulbinella seed is ripe about a month after flowering. As the capsules ripen they will change colour slightly, take on a shrivelled appearance and splits will appear in the capsules at the tips. At this stage the capsules may be harvested. Under certain conditions green spikes may be harvested and ripened in a jar of water to which a pinch or two of sugar has been added. As it is difficult to estimate the degree of ripeness of the seeds, I do not recommend this method unless one is desperate! If the seed is well formed in the capsules and the endosperm is solid and no longer milky then it is reasonably successful. Having said this, some seeds such as those of Lachenalias, with L. rubida a good example, have a long after-ripening period. The flowering stem dies off soon after seed set, and the whole spike separates from the bulb. In cases such as this, the spike with the green capsules can be collected, placed in a paper bag and left in a cool place to ripen.

Seed is very nutritious and is host to a number of parasites. It is therefore very important to treat the seed with an insecticide immediately it has been harvested. I always use Karbadust – it is freely available from nurseries and is relatively non-toxic to warm blooded animals. Do not use any product containing Gamma BHC as this will inhibit seed germination. The seed should be placed in a paper bag, Karbadust added, and the bag should be well shaken to ensure good coverage of the seeds. On sowing the seeds, the excess dust can be sieved off.

Seed longevity varies from genus to genus, and it can be increased by storing the seeds at 4°C. If stored at room temperature, most Irid seeds will germinate well for up to 2 years; for Gladioli and some Moraeas, it is less. As a rule, their viability is short. I have sown some 10 year old Dierama seed and obtained germination, but this is an exception. Agapanthus seeds are notoriously short-lived (about 3 to 6 months) and should be stored in a refrigerator. A cool dry place should be used for seed storage, away from light – better still, if you have the space, use a fridge.

In closing I have to stress how important hand pollination and seed collection is if you want to maintain the integrity of your bulb collection.

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From Connie Smits: A serendipitous find!

In a letter to John Manning

I have checked my garden diary to ascertain how and when I came to have M aristata in my garden - and this is what happened:-

I bought a potted plant of Asystasia gangetica at the George Herbarium plant sale in Oct 2004 and duly planted it in my front garden.  In August 2005 I noticed a plant with a single bloom of M aristata protruding from the Asystasia plant.  The following year there were 18 blooms!  I then sent a specimen to you for positive identification.  In Jan 2007 I uprooted the Asystasia so that I could collect the cormlets of the Moraea and plant them in pots for safe-keeping. Altogether I counted about 80 of these. Some of the larger ones produced flowers from mid-August to September 2007.  In May 2009 I replanted the corms (at least 200 of all sizes!) into a large trough.  These produced plants but no flowers.  This August/September there were 17 blooms and I anticipate many more in 2011!”

As Connie’s son is the Professor of Astronomy at UNISA, it seems serendipitous to know that the only natural home of this Moraea is at the Cape Town Observatory.

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In Memoriam:

We are very sad to report that Burger van Eeden, a member of IBSA of long standing, has passed away recently. He was very active in both conservation and cultivation, and will be greatly missed by all in IBSA. Our condolences go to his family.

We were also informed that Ernst Lotz, the husband of Lynette Lotz, an IBSA member of long standing, has passed away, after a long ilness. He was an engineer and lecturer, but very well known as a mountaineer - in his day probably the doyen of climbers in the Western Cape. He wrote the guide to the Jonkershoek Mountains: "Jonkershoek en sy Berge"; he made and cleared paths, giving access and confidence to thousands of nature lovers.

Our condolences to Lynnette and the family.

Last Updated on Thursday, 11 July 2013 16:23
 
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