Effects of Low Dose Irradiation on the K-Value and Hypoxanthine Concentration of Fish Fillets

Fillets of five fish species were irradiated at 0, 1 and 3kGy to investigate whether the K-value test of freshness can be applied to irradiated fish. Following irradiation, the fillets were stored on ice and sampled regularly for K-value analysis. Hypoxanthine (Hx) and total nucleotide content were also determined on fillets of two species. K-values of irradiated fillets were generally lower than those of unirradiated controls. Hypoxanthine levels paralleled the K-value changes. These results indicated that quality standards based on K-values or Hx levels that have been set for unirradiated species cannot be directly applied to fish that has been irradiated. Total nucleotide content did not appear to be affected by irradiation.

Towards the development of a Cavendish banana resistant to race 4 of fusarium wilt: gamma irradiation of micropropagated Dwarf Parfitt (Musa spp., AAA group, Cavendish subgroup)

'Dwarf parfitt', an extra-dwarf Cavendish cultivar with resistance to subtropical race 4 fusarium oxysporum f. sp. cubense 9Foc), was gamma irradiated at a dose of 20 Gy and putative mutants were recovered with improved agronomic characteristics. Further screening of putative mutants for improved yield and fruit size, as well as a degree of resistence to fusarium wilt, led to the selection of a line (DPM25) with improved productivity when grown on soils infested with subtropical race 4 Foc. DPM25 was equal to the industry standard, 'Williams', in every agronomic trait measured and it consistently showed a lower incidence of fusarium wilt. Further improvement of field resistance to race 4 Foc is needed in DPM25 and further cycles of mutation induction and selction is an option discussed.

Effect of microwave radiation on seed mortality of rubber vine (Cryptostegia grandiflora R.Br.), parthenium (Parthenium hysterophorous L.) and bellyache bush (Jatropha gossypiifolia L.)

A trial was undertaken to evaluate the effect of microwaves on seed mortality of three weed species. Seeds of rubber vine (Cryptostegia grandiflora R.Br.), parthenium (Parthenium hysterophorous L.) and bellyache bush (Jatropha gossypiifolia L.) were buried at six depths (0, 2.5, 5, 10, 20 and 40 cm) in coarse sand maintained at one of two moisture levels, oven dry or wet (field capacity), and then subjected to one of five microwave radiation durations of (0, 2, 4, 8 and 16 min). Significant interactions between soil moisture level, microwave radiation duration, seed burial depth and species were detected for mortality of seeds of all three species. Maximum seed mortality of rubber vine (88%), parthenium (67%) and bellyache bush (94%) occurred in wet soil irradiated for 16 min. Maximum seed mortality of rubber vine and bellyache bush seeds occurred in seeds buried at 2.5 cm depth whereas that of parthenium occurred in seeds buried at 10 cm depth. Maximum soil temperatures of 114.1 and 87.5°C in dry and wet soil respectively occurred at 2.5 cm depth following 16 min irradiation. Irrespective of the greater soil temperatures recorded in dry soil, irradiating seeds in wet soil generally increased seed mortality 2.9-fold compared with dry soil. Moisture content of wet soil averaged 5.7% compared with 0.1% for dry soil. Results suggest that microwave radiation has the potential to kill seeds located in the soil seed bank. However, many factors, including weed species susceptibility, determine the effectiveness of microwave radiation on buried seeds. Microwave radiation may be an alternative to conventional methods at rapidly depleting soil seed banks in the field, particularly in relatively wet soils that contain long lived weed seeds.

Evidence for a stock discontinuity of snapper (Pagrus auratus) on the east coast of Australia

Allozyme electrophoresis was used to investigate the genetic stock structure of snapper, Pagrus auratus (Bloch and Schneider) on the east coast of Australia. Spatial variation in allele frequency was examined at nine polymorphic loci. The results support a single, relatively weak genetic disjunction among the P. auratus populations north of Sydney (latitude 33°52?) but south of Forster (latitude 31°58?) on the central coast of New South Wales. There was also evidence for genetic isolation by distance on the east coast. The influence of the East Australian Current (EAC) in transporting larvae to the south, coupled with the general northward migration pattern of adult snapper is believed to be responsible for maintaining a panmictic snapper population on much of the east coast of Australia.