Sorghum, artificial (PROSEA)
Sorghum, artificial perennial hybrids
- Family: Gramineae
- Chromosome number: 2n= 20, 40
- General: artificial perennial hybrids are usually known by their cultivar names, e.g., "Silk", "Krish"
- Philippines: batag (Tagalog), batad (Bikol), bukakau (Ilokano)
- Laos: lüay, khauz f'angx
- Thailand: ya khao fang.
Origin and geographic distribution
Being man-made hybrids, these are confined to areas where they have purposefully been sown or have since become naturalized. They have only been grown to a limited extent in South-East Asia, but "Silk" is widely grown in subtropical Australia.
Perennial sorghum hybrids are grown as short-duration perennial forages for grazing by cattle, but can be used for cut-and-carry forage or for hay and silage.
Foliage is very palatable to livestock and "Silk" has greater in vitro digestibility than S. × almum Parodi ("Crooble"). Total free sugars in the stem averaged about 20%. In common with other sorghum species, young herbage can accumulate dangerously high levels of HCN which may lead to prussic acid poisoning in livestock. There are 120-160 seeds/g.
Erect perennials with numerous tillers and stems to 4 m tall, with or without a few short rhizomes. Leaf-blade 25-40 mm wide, glabrous except for a few hairs close to the membranous ligule. Inflorescence a large open pyramidal panicle with secondary and tertiary branches, the branches sometimes drooping; spikelets in short, fragile racemes, paired, the lower one sessile and bisexual, with rigid shiny glumes which may be straw-coloured, reddish-brown or black, depending on cultivar, and which tightly enclose the caryopsis when ripe, the upper pedicelled and male; lemmas often awned.
"Krish" is a hybrid between S. halepense (L.) Pers. and S. roxburghii Stapf; it has not been utilized commercially to any great extent. "Silk" is a hybrid between "Krish" and S. arundinaceum (Desv.) Stapf. In the subtropics, "Silk" may easily be established in spring and shows rapid early growth, early tillering and an ability to compete with weeds. In contrast, "Krish" has poor seedling vigour and growth in spring is also slow; however, it outyields other sorghums provided it is not defoliated before 10 weeks of growth. "Krish" flowers much later than "Silk", which is later flowering than S. × almum cultivar "Crooble". "Krish" has been used as a source of resistance to sugar-cane mosaic virus in the breeding of grain sorghum ( S. bicolor (L.) Moench). One of the merits of "Krish" and "Silk" is that, unlike the weed-parent S. halepense , they can be eradicated without difficulty and hence do not pose a problem to any subsequent crop. However, this does not necessarily apply to other hybrid combinations.
Perennial sorghums are well-adapted to high temperatures and are well suited to areas receiving from 500-800 mm annual rainfall to periods of moisture stress. In Queensland, Australia, "Silk" is widely grown on clay soils, and has replaced S. × almum as a sown forage in these situations.
Perennial sorghum pastures may be established by seed into a cultivated seed-bed, either by broadcasting at 20-25 kg/ha or drilled in 1 m rows at 5-7 kg/ha. Perennial sorghum is usually sown in pure stands but can be sown with other grasses with or without legumes. Initally the mixtures grow more slowly, but they are more persistent. The sorghum then provides early grazing and contributes to the suppression of weeds. Perennial sorghums are compatible with cool season forages such as lucerne ( Medicago sativa L.), annual Medicago spp. or oats ( Avena sativa L.) and warm season legumes such as Neonotonia wightii (Wight & Arnott) Lackey or Lablab purpureus (L.) Sweet. Young plants or young regrowth should not be grazed owing to risk of prussic acid poisoning.
Perennial sorghums are normally grazed, although they are suitable for cut-and-carry systems of management or for hay or silage if not allowed to become too coarse. A recovery period in spring may be necessary to ensure persistence if pastures have been heavily grazed during the cool season.
In trials in Australia which led to its release, "Silk" consistently outyielded S. × almum "Crooble" by 24-78%. "Krish" outyields other forage sorghums late in the growing season. Under continuous grazing in sub-humid Queensland, Australia, steers grazing at stocking rates of 1.5-3 steers/ha averaged liveweight gains of 150 kg/head per year.
"Krish" shows a high degree of resistance to rust and blight, also to sugar-cane mosaic virus.
Genetic resources and breeding
Breeder's seed of hybrid cultivars and stocks of parental species are held by ATFGRC (CSIRO, Australia). The perennial hybrid sorghums are cross-pollinating plants which show a considerable degree of intra-varietal genetic diversity. Many perennial hybrid combinations have been produced experimentally and the wide range in variability in the genus allows the possibility of new improved cultivars. In Australia the difficulty in distinguishing between seeds of "Silk" and the noxious weed S. halepense has led to efforts to produce a cultivar with tan-coloured seeds by selection within "Silk".
The perennial sorghums have potential in sub-humid regions where yearly cultivation for sowing annual forages is undesirable and where permanent pastures are not required. In more humid regions, over a period of several years, annual forages are higher yielding when yields are averaged over the lifespan of the perennial forages.
Literature |1 | Ferraris, R. & Silvey, M.W., 1988. Sward productivity and seasonal animal production from perennial forage sorghums grazed at four stocking rates. CSIRO, Australia. Division of Tropical Crops and Pastures, Technical Memorandum No 56. 22 pp.
- Oram, R.N., 1990. Register of Australian herbage plant cultivars. CSIRO, Australia. pp. 66-68.