ROOTSTOCKS THAT HAVEN'T WORKED
CUSTARD APPLE ROOTSTOCKS
I refer to my article "The Backyard Garden" in Newsletter No.90, 1/95. The picture of the Gefner Custard Apple described as having four extra rootstocks of Mexican Soncoya (Annona purpurea) for support in cyclonic winds is wrong!
I have since found out that the rootstocks fit the description of Annona reticulata or Bullock's Heart. The tree in the middle, also originally on Annona reticulata, died of root rot recently leaving the remaining four as free-standing trees.
Whether Annona purpurea is any more resistant to root rot in this area than Annona reticulata now remains to be seen, as Annona purpurea is not yet available from the source where I got the trees originally.
The mix-up occurred because the Annona reticulata rootstocks were wrongly named as Mexican Soncoya in the first place. Thus we live and learn!
QUESTIONS THAT NEED TO BE ANSWERED
(1) In the DPI's book Growing Custard Apples, the variety Gefner is described as an Atemoyer cultivar. In the graft compatibility table, Atemoyer is shown to be incompatible with Annona reticulata as the rootstock. So why are my trees of Gefner on Bullock's Heart rootstock doing so well after three years? Could somebody please elucidate?
(2) Is Annona purpurea more resistant to root rot than other species as I have been led to believe? In the above-mentioned compatibility table, Annona purpurea is not listed amongst the rootstocks. Some updating of that table would be a help.
(3) What we need is a rootstock for Custard Apples resistant to flooding during heavy rain in the Cairns area for the backyard gardeners. What is now recommended for Atemoya cultivars for such conditions?
(4) Are there any superior rootstock clones in the pipeline as mentioned on page 21 of the above-mentioned book? And can they be vegetatively propagated by cuttings for more reliable results in the field and for more uniform trees?
In newsletter No. 90, in the same article, I described approach grafting the black mangosteen on the more vigorous yellow-fruited rootstock. That didn't work either! They made good unions, no doubt about that, but as soon as I cut away the roots of the black variety, the black scions left on the yellow rootstock just shrivelled up.
Perhaps it was only the cambiums that united without differentiating into the xylem and phloem conducting tissues.
When it is not clear as to whether something will work or not, you just have to try it out. A success or a failure just adds to the sum of one's knowledge. But at the same time, let us hear about it in the Newsletter please!
ROOTSTOCKS THAT HAVE WORKED SO FAR
This does not do well in Cairns and needs a stronger rootstock.
I have a Tamarillo, CYPHOMANDRA BETACEA syn. C. crassicaulis grafted onto a Potato tree, Solanum macranthum rootstock, now five years old and still growing strongly - grafted mid-1990.
The fruit from the scion variety is disappointing. This was originally grown from seed taken from a fruit from Woolworths. The same fruit is much nicer when grown in the cooler climate of Kuranda.
However, an improved variety has been grafted onto the original tree, so we will see how that goes in Cairns.
I have seen this passionfruit vine, PASSIFLORA LlGULARIS in Kenya during my good old colonial days but have yet to taste the fruit which I am told is delicious. It originates from mountainous areas in South Mexico and Central America.
According to Gardening in East Africa, edited by A. J. Jex-Blake: "It has considerable ornamental value with its large heart-shaped leaves and sweet-scented lilac-coloured flowers. The ripe fruit, of excellent flavour, is orange to orange-brown, sometimes shaded purple, and being enclosed in a hard shell can be transported without damage."
However, in Cairns it only grows weakly, possible because of our warm climate compared to its native habitat. It needs a stronger rootstock. At the Botanic Gardens, I approach grafted some plants of Passiflora ligularis onto the yellow passionfruit, Passiflora edulis flavicarpa, which does well in this climate, is vigorous and resistant to root rot diseases and nematodes. This was done on 6.12.1994, and once the grafts had taken, they were planted out and are now growing strongly. Two grafted Sweet Granadilla vines can be seen growing on the fence surrounding the rubbish bin area in the Rare Fruit section of the Botanic Gardens on Greenslopes Street.
Each vine has two root systems, its own plus that of the flavicarpa rootstock. The vines have now reached the top of the fence (August) so it looks promising.
DATE: September 1995
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