Lack of information on the feeding value and on the presence of deleterious substances in many species belonging to the genus Indigofera has limited the potential use of these species as feed and fodder legumes. To obtain such information, leaves and seeds of 46 accessions representing 19 species of Indigofera that had shown some agronomic value were incorporated into a semi-synthetic diet at 5% w/w (seed) or 20% w/w (forage). The diets were fed to groups of young rats for 4 weeks, and dry matter intakes and growth rates relative to control diets were measured. Selected organs were examined for any histological changes. Seed and forage samples were analysed for indospicine, a hepatotoxin, and for the presence of another potentially deleterious substance, 3-nitropropanoic acid. Thirteen of the accessions representing 8 species were readily eaten and did not depress growth rates relative to control feeds, and another 13 representing 10 species gave acceptable growth rates. Liveweight gains were less affected by forage diets than by those containing seeds. With the exception of those in rats fed on diets containing I. spicata and I. nigritana, the organs of all other rats were histologically normal. It is unlikely that the concentration of 3-nitropropanoic acid (0.5-3.4 mg g-1 dry matter) in any feed was high enough to cause any of the observed toxic signs. Indospicine was present in only 4 of the 23 species tested, including all accessions of I. spicata, and the concentration of indospicine was a good indicator of the toxicity of these feeds. It is concluded that accessions that had produced growth rates comparable to those of controls may be recommended as non-toxic feeds suitable for further testing.

A rapid evaluation of palatability and apparent toxicity of forage legumes, using a rat bioassay and requiring only 400 g of dried forage or 100 g of seed, is described. Vegetative material is included as 20%, or seed as 5%, of a nutritionally complete, 12% protein (casein) diet for rats. Voluntary intake and weight gain of rats on test diets are compared with results from standard diets given ad libitum and at restricted rates. It proved possible to distinguish toxicity from simple unpalatability by comparing the weight gain observed on test diets, with the expected weight gain estimated from the regression of weight gain on intake of the standard diet. The method is satisfactorily reproducible, and discriminated clearly between commercially acceptable forages and others known to be toxic, between young and old or between leaf and stem material of the same plant, and between raw and autoclaved seed. The method was used to screen forage from 340 accessions and seed from 110 accessions held in the Australian Tropical Forages Genetic Resources Centre of the CSIRO Division of Tropical Crops and Pastures. Of 150 species, mostly in the genera Cassia, Crotalaria, Indigofera and Tephrosia, only 40 could be classified as palatable and non-toxic to rats, though there was considerable variation between accessions of some other species. As the rat, which is the common laboratory test animal for plant compounds harmful to poultry, man and other monogastric animals, is likely to be more sensitive to ingested phytotoxins than ruminants in most cases, the technique provides a fast, cheap, conservative, preliminary screen of potential forages.

Dry matter production and quality of 20 Digitaria accessions, cut four- and eight-weekly, were compared at four sites in south-east Queensland differing in soils, rainfall and frost incidence over the period 1971-73. The wettest, least frosted site was at Beerwah (70 km north of Brisbane) and the two driest, most frosted sites were at Narayen (480 km north-west of Brisbane). Samford (near Brisbane) was intermediate in terms of rainfall and frost incidence. Dry matter production over the two years varied markedly with site, accession and cutting frequency, and there were interactions between all three. D. smutsii (CPI 38869) was well adapted to all sites and Narayen in particular, O. macroglossa (CPI 16267) was specifically adapted to Beerwah, and D. milanjiana (CPI 41 192) and the two D. smutsii accessions (CPI 38869,16778A) to Samford. Accessions of D. milanjiana, O. pentzii and D. setivalva also performed well at Narayen. Accessions differed in resistance to fire, frost, rust and insects, and in nutritional quality. However, all were adequate for ruminant nitrition. An examination of the quality of the accessions as standover winter feed at Narayen showed that frost lowered digestibility, and the sodium and potassium content of the herbage, but not to the level where animal nutrition would be affected.

Dry matter production and quality of 45 Digitaria accessions were measured over the period 1964-70. In three experiments at Samford, south-east Queensland, the accessions were fertilized with either 336 or 672 kg ha-1 of N a year and cut four-weekly. Both total and cool season production was measured. Highest annual yields were produced by D. smutsii (40,000 kg ha-1), D. macroglossa (37,000 kg ha-1) and D. decumbens (30,000 kg ha-1). D. decumbens yielded up to 5000 kg ha-1 dry matter between May and September compared with up to 6800 kg ha-1 from D. pentzii, 6700 kg ha-1 from D. macroglossa and 6400 kg ha-1 from D. smutsii. In two other experiments persistence and production of nine accessions were compared with those of Rhodes grass (Chloris gayana) on heavy, gilgaied clay soil at Meandarra, Queensland and with Panicum coloratum var. makarikariense on a shallow, self mulching, sedentary black earth at Southbrook, Queensland. D. decumbens showed the greatest potential for persistence and production at Meandarra and one strain of D. smutsii had the greatest yields at Southbrook. Digestibility and mineral content varied little between species and were generally satisfactory for animal production. Digitaria tended to be higher in phosphorus content than P. coloratum and C. gayana.

Cracking clay soils or vertisols occur in large areas of the subhumid regions of north-eastern Australia and frequently contain appreciable levels of salt in their subsoils. The comparative salt tolerance of some tropical pasture legumes was studied in pots with NaCl added to a clay soil to achieve electrical conductivities (saturated extract, ECe) over the range 2.0- 20.0 dS m-1. Tolerance, based on EC, at 50% of maximum growth (in parentheses) was in the order: Macroptilium atropurpureum cv. Siratro (10.6)> Macroptilium lathyroides cv. Murray (9.9) > Vigna trilobata (9.7) > Indigofera spicata (9.5) > Desmanthus subulatus (9.3) > Arachis pintoi (7.9) > Clitoria ternatea (6.4) > Stylosanthes scabra (5.6) > Indigofera schimperi (5.4) > Psoralea tenax (5.3) > Rhynchosia minima (5.1). The grass Panicum coloratum cv. Bambatsi was markedly more tolerant than any of the legumes studied, with 50% yield at an EC, of 16.4 dS m-1. Patterns of Na+ and Cl- uptake with increasing level of salt differed between species, but were not related to the degree oftolerance observed. The results are discussed in terms of the reported salinity tolerance of legumes generally and their implications to the search for persistent legumes for clay soils.