Sugarcane is closely related to the genera Erianthus, Narenga, Miscanthus and Sclerostachya. These genera including Saccharum are collectively known as the Saccharum complex and are expected to be sexually compatible at some levels (Bull & Glasziou 1979; Grassl 1980; Daniels & Roach 1987).
Miscanthus sinensis has been recorded in southern Western Australia, the central coast of New South Wales (Hnatiuk 1990), southern South Australia, southern Victoria and in two locations in Tasmania (Australia's Virtual Herbarium 2004) and locally is considered weedy (Lazarides et al. 1997). Miscanthus floridulus is a noxious weed overseas (Randall 2002). It has been found naturalised in Australia but has not been recorded as a weed (Australia's Virtual Herbarium 2004). Miscanthus nepalensis is recorded as locally invasive in New Zealand and Brazil (Randall 2002).
Narenga porphyrocoma has been collected from a single site in Queensland within commercial sugarcane growing areas (Australia's Virtual Herbarium 2004). Other species in the Miscanthus and Erianthus genera are listed in ‘A Global Compendium of Weeds’ (Randall 2002) as weeds of agriculture in Asia.
Some accessions of the Saccharum complex, such as Erianthus and Miscanthus are maintained in many sugarcane research station germplasm collections for sugarcane breeding in Australia.
Section 4.1 Gene Transfer to Cultivated Sugarcane and naturalised sugarcane
As indicated above, sugarcane flowering is variable in the field and the crop is exclusively vegetatively propagated. Sugarcane is a largely cross-pollinated species with a low frequency of selfing and pollen is dispersed by wind (McIntyre & Jackson 2001). No insect or animal vectors for sugarcane pollen are known. Pollen viability is low under natural environmental conditions (Moore 1976). Sugarcane pollen is rapidly desiccated after dehiscence, having a half life of only 12 minutes and no viability after 35 minutes at 26.5°C and 67% relative humidity (Moore 1976). Even under artificial conditions, storage of sugarcane pollen is difficult and has been the subject of intensive investigations by sugarcane breeders, who would like to store valuable pollen for desirable crosses.
Different varieties of sugarcane produce different amounts of pollen. Crossing and selfing therefore varied greatly. Analysis of seed derived from crossing studies showing seed set varied between 3.1-22.7% (Grassl 1980; Rao 1980) reflecting the poor viability of sugarcane pollen. In some case seed were uniform in size but up to 30% were smaller or shrivelled, however, most of them germinated (Rao 1980). Molecular methods have indicated that 0-17% of progeny from apparent hybrid crosses are actually the result of selfing (flower being fertilised by its own pollen, McIntyre & Jackson 2001). Selfing frequencies were found to vary dramatically between 0-18% (McIntyre & Jackson 2001) to 0-80% (Hogarth 1980).
Parents used in breeding programs are classified as male or female depending on relative amounts of viable pollen produced. Sex is often determined by aceto-carmine staining to determine the viability of pollen. Clones with <10% pollen viability are designated as female, clones with >25% viable pollen are designated as male. Clones with intermediate levels of viable pollen (10-20%) are classified as bisexual and may be used as either male or female parents (McIntyre & Jackson 2001).
Commercial breeding programs produce artificial crosses between Saccharum spp. hybrids under highly favourable conditions. Male and female arrows are set up inside canvas lanterns (pollen impervious canvas bags) with the male set above the female to allow pollen to be shed downwards onto the female flowers (Cox et al. 2000). However, sugarcane is not an ideal candidate for crossing in conventional plant breeding due to its characteristic non-synchronous flowering and low sexual seed viability (Selman-Housein et al. 2000).
Viable pollen of sugarcane would not be expected to disperse very far. Accordingly, cross-pollination would only be expected to occur to flowering sugarcane plants growing in close proximity. In addition, a very low rate of successful crosses would be expected due to the rapid loss of pollen viability.
It has been reported that species with the genus Saccharum can hybridise with other closely related species (Grassl 1980; Daniels & Roach 1987; Grassl 1980). However, such reports of hybridisation do not generally refer to modern sugarcane varieties (complex hybrids).
Gene flow between Saccharum spp. hybrids to other Saccharumspecies is likely to be low, because plants are likely to be harvested before flowering. If seed set happens, seedling survival is poor, and field management methods would limit survival of any volunteer plants.
None of five recognised Saccharum species (S. spontaneum, S. officinarum, S. robustrum, S. barberi and S. sinensis) are native to Australia. These species are maintained within sugarcane research stations as germplasm and can hybridise successfully with modern cultivars of sugarcane (Saccharum spp. hybrid). These species have been used in breeding programs to produce new varieties. Of these species only S. officinarum and S. spontaneum are recorded as naturalised in Australia. There is no records of native or endangered species having sexual compatibility with sugarcane in Australia (Daniels & Roach 1987).
There are a number of species within the Saccharum genus which are recognised as weed elsewhere, such as Saccharum arundinaceum, S. bengalense, S. floridulum, S. narenga, S. procerum, S. ravennae (Randall, 2002). These species have potential to outcross successfully with hybrid sugarcane but as mentioned above there have been no records of these species in Australia (Hnatiuk, 1990; http://www.cpbr.gov.au/avh.html).