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Re: [aroid-l] Colocasia hybrids

  • Subject: Re: [aroid-l] Colocasia hybrids
  • From: "Alex Burgess" <alexcburgess@hotmail.com>
  • Date: Wed, 14 Jul 2004 11:28:09 -1000

Dear Brian,

Following are two quotes taken from an article on the FAO website (http://www.fao.org/DOCREP/005/AC450E/ac450e00.htm#Contents) which may be the best tips for what you are trying to do:

1. "Natural flowering occurs only occasionally in taro, but flowering can be artificially promoted by application of gibberellic acid (see later). The inflorescence arises from the leaf axils, or from the centre of the cluster of unexpanded leaves. Each plant may bear more than one inflorescence. The inflorescence is made up of a short peduncle, a spadix, and spathe. The spadix is botanically a spike, with a fleshy central axis to which the small sessile flowers are attached. The spadix is 6-14cm long, with female flowers at the base, male flowers towards the tip, and sterile flowers in between, in the region compressed by the neck of the spathe. The extreme tip of the spadix has no flowers at all, and is called the sterile appendage. The sterile appendage is a distinguishing taxonomic characteristic between dasheen and eddoe types of taro. In eddoe types, the sterile appendage is longer than the male section of the spadix; in dasheen types, the appendage is shorter than the male section.

The spathe is a large yellowish bract, about 20 cm long, which sheathes the spadix. The lower part of the spathe wraps tightly around the spadix and completely occludes the female flowers from view. The top portion of the spadix is rolled inward at the apex, but is open on one side to reveal the male flowers on the spadix. The top and bottom portions of the spadix are separated by a narrow neck region, corresponding to the region of the sterile flowers on the spadix.

Pollination in taro is probably accomplished by flies. Fruit set and seed production occur only occasionally under natural conditions. Fruits, when produced, occur at the lower part of the spadix. Each fruit is a berry measuring 3-5mm in diameter and containing numerous seeds. Each seed has a hard testa, and contains endosperm in addition to the embryo."

2. "Flowering and seed set in taro are relatively rare under natural conditions. Most plants complete their field life without flowering at all, and some cultivars have never been known to flower. For many years, this characteristic was a great hindrance to taro improvement through cross pollination. However, the problem was solved when it was discovered that gibberellic acid (GA) could promote flowing in taro (Wilson, 1979).

Essentially, plants are grown from corms or cormels to the 3-5 leaf stage in the field, and then treated with 15,000 ppm GA, a process known as ?pro-gibbing? (Alvarez & Hahn, 1986). Alternatively, the plants could be multiplied in a seedbed, and pro-gibbed at the 1-2 leaf stage with 1,000 ppm GA. A third method involves leaving taro in the field at the end of the growing season and then pro-gibbing the first leaves that emerge at the onset of the next rainy season. Whichever method is used, pro-gibbed plants produce normal flowers 2-4 months after treatment.

Today, researchers are able routinely to induce flowering of both taro and tannia by the application of GA. Controlled pollination can then be carried out on the flowers that are produced. The resulting seeds, thousands per spadix, are first germinated in nutrient media in petri dishes. The plantlets are later transplanted to humid chambers in the greenhouse. When the seedlings have reached a height of 15-20cm, they can be transplanted to the field. The large genotypic and phenotypic variability resulting from this process affords the plant breeder ample scope for selection."

3. Following are some other sources:

These guys have successfully bred hybrid colocasias for disease resistance (a good thing to consider in your own program) and you could contact them to find out how they did it (or perhaps for a specimen or two!):

http://www.spc.org.nc/AC/arttaro.htm

Here's another article (I haven't read it) - you'll have to pay $12 for it:

http://www.actahort.org/books/380/380_70.htm

This article mentions taro breeding in Hawaii and you could contact the Hawaii CTAHR (I would try the Kauai branch) for further information:

http://www.kauaiworld.com/articles/2004/05/23/business/bus01.prt

The ancient Hawaiians revered taro literally as an elder brother to all mankind, and here is an excellent article which I highly recommend on traditional Hawaiian beliefs about taro:

http://www.earthfoot.org/lit_zone/taro.htm

I, too, am interested in colocasias, although I have never attempted to cross them. I live in Hawaii and grow several types, and if you are successful in crossing them I hope you would consider sharing your methods/results.

Incidentally, you may be interested to know that Hawaii has the largest number of taro varieties of anywhere I've seen, mostly heirloom varieties still surviving from the ancient Hawaiians. There are around 100 varieties remaining here, most unknown commercially and not easily available since many commercial growers here prefer the Chinese varieties and most of the 'old' varieties are only preserved by a few concerned Hawaiians, one of whom I know. Perhaps you could consider obtaining and growing some of these as an easier way to market or collect 'new' varieties, while helping to preserve the heirloom 'native' types.

There used to be over 300 types of colocasias grown in great quantities here prior to Captain Cook's syphilitic first contact, and the loss of 2/3 of these taro varieties (and nearly all the pure Hawaiians who originally developed them) is just another reason why Hawaii is considered by many to be the extinction capital of the USA!

Best of luck,

Alex




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