Growth responses of sugarcane to mycorrhizal spore density and phosphorus rate

Arbuscular mycorrhizal (AM) fungi, commonly found in long-term cane-growing fields in northern Queensland, are linked with both negative and positive growth responses by sugarcane ( Saccharum spp.), depending on P supply. A glasshouse trial was established to examine whether AM density might also have an important influence on these growth responses. Mycorrhizal spores ( Glomus clarum), isolated from a long-term cane block in northern Queensland, were introduced into a pasteurised low-P cane soil at 5 densities ( 0, 0.06, 0.25, 1, 4 spores/g soil) and with 4 P treatments ( 0, 8.2, 25, and 47 mg/kg). At 83 days after planting, sugarcane tops responded positively to P fertilizer, although responses attributable to spore density were rarely observed. In one case, addition of 4 spores/g led to a 53% yield response over those without AM at 8 mg P/kg, or a relative benefit of 17 mg P/kg. Root colonisation was reduced for plants with nil or 74 mg P/kg. For those without AM, P concentration in the topmost visible dewlap ( TVD) leaf increased significantly with fertiliser P (0.07 v. 0.15%). However, P concentration increased further with the presence of AM spores. Irrespective of AM, the critical P concentration in the TVD leaf was 0.18%. This study confirms earlier reports that sugarcane is poorly responsive to AM. Spore density, up to 4 spores/g soil, appears unable to influence this responsiveness, either positively or negatively. Attempts to gain P benefits by increasing AM density through rotation seem unlikely to lead to yield increases by sugarcane. Conversely, sugarcane grown in fields with high spore densities and high plant-available P, such as long-termcane-growing soils, is unlikely to suffer a yield reduction from mycorrhizal fungi.

Growth, sporulation and spore properties of bacillus stearothemophilus produced in chemically defined media

The nutritional requirements for the vegetative growth of B. stearothermophilus strains NCIB 8919, NCTC lO,OO3 (wild) were found to be DL-methionine, biotin, nicotinic acid, thiamin, glucose and mineral salts. Strains NCIB 8920 required in addition L-tryptophan. B. stearothermophilus NCTC lO,OO3 (mutant) grew in a medium containing only glucose and mineral salts. Separate chemically defined media for the growth of Bacillus stearothermophilus strains NCIB 8919, 8920, NCTC lO,OO3 (wild) and NCTC lO,OO3 (mutant) were developed. Optimally aerated culture of B. stearothermonhilus NCTC lO,OO3(mutant) required 1.0 x 10-4 M. Mn2+ and 2.4 x 10-3 M. glutamic acid for optimal sporulation. Specific nutrient depletion of growth affected percentage sporulation. Spore suspensions of B. stearothermophilus NCTC 10,003 (mutant) were prepared from media in which sulphate (SO4-), nitrogen (N-),phosphate (Po4-), carbon (C-), magnesium-carbon simultaneously (Ng-C-) depleted growth. The heat resistance, dormancy and chemistry of these spores varied considerably. B. stearothermophilus NCTC 10,003 10,00310,00(mutant) spores prepared from carbon depleted cultures containing high and low concentrations of calcium, iron or manganese showed variations in heat resistance,dormancy and chemical composition. Progressive increase in the concentration of medium calciumfrom 1.0 X 10-5  M to 1.4 X 10-4 M. progressively increased theheat resistance of B. stearothermophilus NCTC 10,003 (mutant) spores prepared from nitrogen depleted cultures (N-). The thermodynamic functions for germination rate, magnesium and manganese release of N- and SO4- spores were within the range expected of enzymic reactions. The thermodynamic functions for the breaking of dormancy in SO4- spores and that for the release of D.P.A. were identical. Sublethal heating of SO4- spores (96.5°C and below) induced dormancy in these spores, whereas heating above 96.5°C gave rise to heat activation. Pooled results of the chemical analyses of all spore types studied showed that the concentration of D.P.A. and calcium were positively related to heat resistance whereas magnesium concentration and Mg/Ca molar ratio were inversely proportional to heat resistance.