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Archive for the ‘Rootstocks’ Category

It has been a long held belief that Rosa x fortuniana Lindley is the only rootstock suitable for local conditions in Western Australia. Rosa x fortuniana Lindley has produced outstanding yields under conditions in Florida (McFadden 1962). The reasons for its superior performance include better adaptation to warm weather and sandy soils. Resistance to soil borne pathogens such as Pythium, Phytophthora,  Rhizoctonia and crown gall has been found in Florida trials. Hybrid vigour is also a possibility – Rosa x fortuniana Lindley is believed to be a hybrid of R. banksiae x R. laevigata. Superior uptake of iron during hot weather could also be a factor.

Rootstocks found in Western Australia include R. multiflora, R. x fortuniana, R. indica major, R. ‘Dr Huey’, R. manetti and R. canina inermis. Some of these are being used for inground cutflower production whereas others are used in the home garden as well.

Characteristics of a rootstock which are important include:
1) Ease of propagation
2) Lack of suckering
3) Disease resistance and/or tolerance to nematodes
4) Vigour
5) Tolerance of local conditions eg salinity, heat and drought.

Multiflora is noted as being more salt sensitive and more cold tolerant. It is less tolerant of alkaline conditions. It also picks up virus infections from the scion material very easily (however in Australia there is no virus free material, I can write separately on this topic). There are numerous lines of multiflora used internationally and at least two lines have been found Western Australia. One line is greatly lacking in vigor and displays a multitude of trace element deficiencies. Even the other line of multiflora seems susceptible to trace element deficiencies, especially copper and iron. Studies, both at the Department of Agriculture and overseas have shown it to be an ideal host to both root knot nematode and to lesion nematode, but particularly, root knot.

‘Dr Huey’ appears to perform quite well especially on heavier soils. In both McFadden’s study and in that of the Department of Agriculture, it came second to fortuniana. I have not seen any obvious problems with ‘Dr Huey’. It is reported to be susceptible to black spot which may be a problem in more humid climates.

R. manetti, used commercially, appears to have some degree of resistance to nematodes and has solved grower issues with trace element deficiencies. The growth is far superior to R. multiflora and on a par with ‘Dr Huey’.

R. canina, also used commercially, also appears to have some degree of resistance to nematodes. Studies overseas have supported this. R. canina is extremely tolerant of root knot nematode and reasonably tolerant of root lesion nematode (Coolen and Hendrickx, 1972). Growth is superior to multiflora and trace element deficiency symptoms not evident.

R. x fortuniana is planted extensively in home gardens and to a lesser degree in commercial inground production. It is definitely superior to multiflora. It does seem to have some issues with trace element deficiencies. One disadvantage is that it is more difficult to propagate. It also suckers more freely.

Trials in Florida (Gammon and McFadden, 1979) compared flower production between bushes on fortuneana, odorata, multiflora and manetti. Odorata produced the highest yields, followed by fortuneana, manetti and multiflora. They also found large differences in the accumulation of trace elements. Fortuniana accumulated five times more manganese than odorata but this was not related to flower yield. Odorata was a superior accumulator of potassium and under low nutrient conditions both fortuniana and odorata were good accumulators of nitrogen and potassium and this was related to flower yield.

The results of the trial at Medina Research Station (1980 to 1982) did seem to support the superiority of fortuniana, especially for bloom counts. However the following factors should be borne in mind:

• High pH water and soil (both around pH 8),
• Medina soil is a Spearwood sand unlike most of the soil in the metropolitan area with is much poorer in nutrient status, and
• Climate – Medina is recognised as being a particularly cold spot in winter.

All these factors could have a significant bearing on the performance of any rootstock. Finally the experiment at Medina lasted for only three years when the normal lifespan of a bush in the average home garden is many times that.

Summary
In Western Australia which has a hot climate and nutrient poor sandy soils prone to nematodes and with poor water holding ability, R. x fortuniana is the logical choice. However home gardeners often modify their soils to varying degrees which may decrease this advantage. In areas with colder night temperatures multiflora may perform better than on the Swan Coastal Plain. In the clayier soils of the scarp, ‘Dr Huey’ also does well.

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