Selecting rootstocks
Selecting the right rootstock for your orchard is very important. A healthy root system that is compatible with your chosen variety and well suited to its environment is essential if your orchard is to be a success (see Tables 1 and 2).
Rootstocks should be selected for their:
- ability to perform under your soil and climatic conditions
- resistance to pests and diseases
- compatibility with the variety you are planting
- positive impact on fruit yield and quality.
To choose the right rootstock you need to have all the relevant information. Factors which will impact on the performance of different rootstocks in your situation include:
- soil type and structure, depth, drainage, pH and salt content
- pests and diseases
- whether it is replant or virgin soil
- climatic conditions expected, for example, extreme summer and winter temperatures (frosts etc.)
- water quality (salt and pH) and the type of irrigation system (sprinklers, drippers)
- compatibility with the variety you intend to grow.
| Rootstock | Fruit size | Rind thickness | Rind texture | Fruit maturity | Sugar content | Acid content | Juice content |
|---|---|---|---|---|---|---|---|
| Trifoliata | med-large | thin-med | smooth-med | mid-late | high | high | high |
| Troyer citrange | medium | thin-med | smooth-med | mid | med-high | med-high | high |
| Rough lemon | large | med-thick | coarse | early | low | low | low-med |
| Volkameriana | med-large | med-thick | med-coarse | early | low | low | low-med |
| Swingle citrumelo | med-large | thin-med | smooth-med | mid-late | med-high | med-high | high |
| Sweet orange | medium | medium | medium | mid | medium | medium | medium |
| Cleopatra mandarin | small-med | thin-med | medium | mid | medium | medium | medium |
| Rootstock | Salinity tolerance | Calcium (alkalinity) tolerance | Suitability for sandy soils | Suitability for loamy soils | Suitability for poorly drained soils | Phytophthora resistance |
|---|---|---|---|---|---|---|
| Trifoliata | low | low | poor | good | good | high |
| Troyer citrange | medium | low | good | good | average-good | med-high |
| Rough lemon | low | medium | good | average | poor | low |
| Volkameriana | low | medium | good | average | poor | low |
| Swingle citrumelo | medium | low | average | good | good | med-high |
| Sweet orange | medium | high | average | average | poor | very low |
| Cleopatra mandarin | high | high | average | good | average | medium |
Prior to planting, obtain a comprehensive soil survey, including a soil profile description, of proposed orchard sites. This will help in rootstock selection and overall planning and management of the orchard.
When purchasing trees, ensure that they are free of major viroids and other diseases. Rootstock seed should come from a reliable source.
Budwood for propagation should be sourced from Auscitrus to ensure freedom from exocortis viroid (CEV) and other viroids that can affect tree health and vigour. Nurseries should be certified free of major diseases and have a good reputation for consistently producing high quality trees.
Benton citrange
This rootstock was developed by a NSW Department of Primary Industries rootstock-breeding program and selected for its tolerance to root rots (Phytophthora spp.) and compatibility with Eureka lemon. It is a hybrid of Ruby Blood sweet orange and trifoliate orange (P. trifoliata) and seed was first released to industry in 1984.
This stock has not been used in any volume in WA and it is likely that it will be superseded by Cox mandarin hybrid as a stock for Eureka because it is easier to grow and propagate in the nursery.
Benton produces trees with similar vigour to Troyer and Carrizo but there have been mixed results from trial plantings. It has performed well in some trials with Eureka, while other trials with oranges have been less encouraging. It is Phytophthora and tristeza-tolerant.
Compatibility
No reported incompatibility with Eureka lemon. It is compatible with most orange and mandarin varieties.
Local experience
This stock has not been extensively used in WA and not a lot of local information is available. Local nurserymen have described it as being difficult to propagate.
C35 citrange
Developed in California, this is a hybrid of trifoliate orange (P. trifoliata) and Ruby Blood sweet orange. It has not been extensively tested under WA conditions. There is some interest in it as an alternative rootstock for navel oranges because it reputedly produces medium-sized trees, around 25% smaller, than those produced by Troyer and Carrizo citrange. Yield and other characteristics are reputedly similar to other citranges.
It is tolerant of Phytophthora spp., citrus nematode and tresteza.
Compatibility
C35 should not be used with Eureka lemon as incompatibility issues have become apparent in both local and eastern states commercial plantings in trees as young as three years old.
Evaluation of a 1997 rootstock trial at Loxton Research Centre in South Australia has revealed C35 citrange also has compatibility issues with Navelina (Navelina 7.5 selection). Trees of this variety/rootstock combination performed adequately up to 10 years of age but significant tree deaths have occurred since then, while no deaths were observed in other variety/rootstock combinations. There is also a risk that C35 citrange will be incompatible with the closely related varieties Navelina 315, M7 and FJ Navel.
Local experience
Although this stock has been planted in large numbers in recent years, there is very little local information on performance over a longer time period. Evaluation in a Newhall navel rootstock demonstration block in Bindoon showed that trees grew well in the establishment stage, and yields were similar to those achieved by Troyer citrange at the same site. Eureka lemon plantings on C35 in Western Australia have failed and, in most cases, trees have been removed.
Cleopatra mandarin
Cleopatra is a small-fruited mandarin which has been used as a rootstock for many years. It has not been used extensively in WA. It is the most salt- and lime-tolerant of the commercially available stocks.
Trees are slow growing in the nursery. Early production tends to be poor, with trees taking a long time to settle into cropping.
Fruit quality is good but small fruit size has been an issue with some varieties. Trees perform well on both heavy and light soils, with best results on loam. Cleopatra is tristeza- and exocortis-tolerant and moderately susceptible to phytophthora root and collar rots. It is susceptible to citrus nematodes and not generally recommended for replant sites.
Compatibility
No compatibility problems have been reported and it is considered a good stock for most mandarin varieties.
Local experience
This stock has rarely been used in WA and very little local information is available. In a Newhall navel rootstock demonstration block at Bindoon, small fruit size was observed in the first few seasons. A good yield of small to medium-sized fruit was achieved in 2012 and size was better again in 2013.
Cox mandarin hybrid
This is a hybrid of Scarlet mandarin and trifoliate orange (P. trifoliata) which was bred by the NSW Department of Primary Industries at Gosford in the early 1960's. It was released in 1995 and is compatible with Eureka lemon (see Figure 1).
It has not been tested extensively under WA conditions. Cox is resistant to phytophthora root and collar rot. Seedlings are moderately vigorous and easier to grow than Benton citrange, making it more nursery-friendly.
Compatibility
Information on performance and compatibility (other than with Eureka lemon) is very limited.
Local experience
Eureka lemons planted on this stock in both Bindoon and West Gingin have grown excellent trees which have produced good yields. At a West Gingin site where trees were grown on bleached sand low in organic mater, Cox had stronger growth than Benton, possibly due to the mandarin component of its parentage being more adapted to poorer soil conditions.
Newhall navel on this stock in Bindoon has produced small to medium sized fruit.
Rough lemon (Citronelle)
Rough lemon was the most popular rootstock during establishment of the citrus industry in WA. It is still widely used for lemons and backyard plantings of oranges and mandarins.
It produces large, vigorous, highly productive trees that are drought-tolerant. It grows well on a wide range of soils but is particularly well adapted to deep sandy soils. It does not perform well on poorly drained soils and is sensitive to saline conditions.
Fruit quality can be poor. Poor skin colour and thick skins are a potential problem. Good water and nutrient management is important to get the best out of this stock.
Rough lemon is susceptible to citrus nematodes and phytophthora root rot and is not recommended in replant situations. It is tolerant of tristeza virus, and exocortis and xyloporosis viroids.
Compatibility
Rough lemon is unsuitable for some mandarins such as Ellendale and Satsuma types. As with Volkameriana, it should not be used with mandarins like Imperial that are susceptible to internal granulation (drying), especially in areas where this is a problem.
Local experience
This stock is no longer used extensively because of its susceptibility to phytophthora. Its main use is for Eureka lemon.
Yield has been quite good in a Newhall navel rootstock demonstration block planted at West Gingin in 1995. In the sandy soils there it out-yielded many stocks including Trifoliata and Swingle, especially in the early years.
As with Volkameriana, fruit sugar and acid levels are usually lower than with other stocks and can drop relatively quickly.
Fruit should not be left on the tree too long or it can become bland. Imperial mandarins on this stock have had problems with internal granulation (drying), especially on sandy soils.
Sweet orange
Seedlings of sweet orange have been used as rootstocks around the world for many years. Although widely used in the Sunraysia and Riverland in early plantings, it has not been widely used in WA because of its susceptibility to phytophthora root and collar rot, and citrus nematode.
Sweet orange does best on well-drained, deep sandy soils and can tolerate calcareous soils. It is sensitive to dry conditions and will not tolerate waterlogging. Fruit quality is generally good. It is tristeza- and exocortis-tolerant but not suitable for replant sites.
Compatibility
No incompatibilities have been reported.
Local experience
This stock has rarely been used in WA and very little local information is available. It did not perform well in a Newhall navel rootstock demonstration block in West Gingin.
Swingle citrumelo
Hybrids of grapefruit and trifoliate orange are referred to as citrumelos. Swingle has been the most widely and thoroughly tested of the many named and unnamed citrumelos throughout the world. It is a hybrid of Duncan grapefruit and trifoliate orange.
In Australia, Swingle initially attracted attention as an alternative to Troyer and Carrizo citrange for grapefruit, navel and Valencia oranges.
Tree size varies, depending on variety and soil type. Grapefruit are known to be very productive on Swingle overseas, while some navel oranges have performed well in Australia. It is thought to be more salt- and drought-tolerant than other trifoliate hybrids. Swingle will not perform well on shallow, poorly drained sites and highly calcareous soils.
Swingle is tolerant of Phytophthora spp., tristeza and the exocortis and xyloporosis viroids. It is resistant to nematodes and suitable for use in replant situations.
Compatibility
Swingle is incompatible with Eureka lemon and problems have been reported with some mid-season orange and mandarin cultivars. In WA there have been major incompatibility problems on Navelina and some orchards have suffered major decline and tree deaths at around 10 to 15 years old.
Recent problems with tree decline and death have also emerged with Daisy mandarin grown on Swingle.
Local experience
Swingle has been popular with many WA growers, particularly in the Bindoon/Chittering area. Recent incompatibility problems with Navelina and some other varieties have eroded that popularity.
It appears to be more salt-tolerant than some commonly used stocks and produces reasonable-sized, manageable trees. Experience suggests that vigour depends on soil type and climate. In general, it is more vigorous than Trifoliata — especially in the establishment years — and less vigorous than Troyer and Carrizo citrange.
In trials at West Gingin it has taken a while for trees to reach production and it is probably not suited to the light sands of this area. In trialing at Bindoon a number of trees of Newhall navel on this stock have showed symptoms of decline at around 10 years of age.
Trifoliata (Poncirus trifoliata)
Poncirus trifoliata or trifoliate orange has been used worldwide for many years and is commonly grown on heavy soils in WA. It produces small to standard-sized trees, depending on soil type. They bear well for their size, and fruit quality is good.
Trifoliata performs best on heavier clay loams to loamy soils and is not well suited to sandy soils where growth is slow. It is cold hardy but has poor drought tolerance and is poorly suited to saline and highly alkaline or acidic soil conditions.
This rootstock is resistant to citrus nematode, tristeza virus and some species of Phytophthora. It is very susceptible to the exocortis viroid. It is responsive to viroid dwarfing and suitable for use in replant sites.
Compatibility
Trifoliata is incompatible with Eureka lemon. Because of reports of incompatibility with some minor varieties, it should be used cautiously with untested varieties.
Local experience
Trifoliata has become less popular in recent years as it produces small trees that can take a long time to yield. It is not as tolerant of saline conditions — an increasing problem in some areas — as some other stocks. It is known for good quality fruit and is better suited to heavy soils. It has performed poorly in deep sands at West Gingin where trees are slow to reach a good bearing size.
Troyer and Carrizo citrange
Hybrids of sweet orange and trifoliate orange are referred to as citranges. These two citranges are virtually indistinguishable and are hybrids of Washington navel and P. trifoliata. Troyer citrange is the most widely used rootstock in Western Australia.
Both rootstocks are cold hardy, produce vigorous trees and perform well on most soil types. They will not grow well in calcareous soils or under saline conditions. Trees on these rootstocks can be prone to micronutrient deficiencies, especially on calcareous soils.
They are tolerant of the citrus tristeza virus, citrus nematode (Tylenchulus semipenetrans) and phytophthora root rot but are susceptible to severe strains of the citrus exocortis viroid. Both are responsive to viroid dwarfing and are suitable for use in replant sites.
Compatibility
Troyer and Carrizo citrange are compatible with most common citrus varieties except Eureka lemon. There is a long-term problem with Imperial mandarins that may be related to overgrowth at the bud union. Compatibility with some minor varieties is unknown.
Local experience
Troyer and Carrizo are grown under a range of conditions in WA. They are commonly known as ‘best bet’ rootstocks throughout the state and have performed well on the deep sands at West Gingin and heavier clay loams at Harvey.
Volkameriana (Volkamer lemon)
Volkameriana seedlings are fast-growing, vigorous and adaptable to a wide range of soil conditions. Like rough lemon, it will grow well in deep sands where some rootstocks struggle. Fruit quality is not as good as that produced on citrange and Trifoliata stocks, but it is reported to be better than that produced by rough lemon.
Volkameriana is not susceptible to tristeza virus or exocortis and xyloporosis viroids. It is susceptible to citrus nematodes and phytophthora root rot but less so than rough lemon. It is not recommended for replant situations.
Compatibility
Volkameriana is compatible with lemons, most oranges and mandarins. Mandarin varieties susceptible to internal granulation (drying), such as Imperial, should not be planted on this stock which has been shown to enhance this problem.
Local experience
This rootstock has performed quite well in a Newhall navel demonstration block planted at West Gingin in 1995. In the sandy soils it out yielded other stocks including Trifoliata and Swingle in the early years.
Sugar and acid levels are not as high as for many other stocks and can drop relatively quickly. Fruit should not be left on the tree too long or they can become bland.
Imperial mandarins on this stock have had problems with internal granulation (drying), especially on sandy soils.
Untested: Citrus macrophylla
This rootstock is untested in Western Australia but has been used in some orchards in eastern Australia. It is understood that commercial interest is based on its precocious fruiting habit. Trees are reputedly very vigorous in the early years and then slow quickly once fruiting commences.
Although fruit is large, fruit quality is reported to be poor with low sugar and juice content. It is very susceptible to tristeza virus, xyloporosis viroid and cold damage, however is resistant to phytophthora root rot and is salt-tolerant.
Fruit quality issues, particularly in sandy soils, mean that fruit may struggle to meet local and national standards. There is no strong recommendation for its use in Australia.
New rootstock evaluation
A number of new rootstock evaluation trials have commenced in Western Australia in recent years and these include some that were selected for tolerance to saline conditions and others which are hybrids of mandarin and trifoliata. It is anticipated that some results from these trials will be available in a few years time although it should be noted that rootstocks trials take many years to mature and provide conclusive results.
Six new Chineese rootstocks (Zao Yang, Tanghe, Ghana, Donghai, Anjiang hongju and Caoshi xiangju) were released in 2017 and seed of these is now available through Auscitrus. These rootstocks have not yet been extensively tested in Australia, however further information about their performance in different Australian regions will become available over time.
Acknowledgements
Mark Skewes from the South Australian Research and Development Institute provided information on C35 citrange incompatibility with Navelina.
Graeme Sanderson from New South Wales Department of Primary Industry provided information on C35 incompatibility with Eureka lemons.
This page updates Farmnote 16/2004 Citrus rootstocks for Western Australia by Kevin Lacey.