Environmental controls on the spatial variability of savanna productivity in the Northern Territory, Australia

Gross Primary Productivity (GPP) is a critical measure of the health and sustainability of natural ecosystems. Understanding the magnitude, spatial patterns and processes of GPP will underpin predictions of the impact of climate change on the carbon cycle. In Australia, savannas account for one third of the terrestrial carbon stores and therefore, estimating the magnitude of savanna GPP and studying the spatial relationship between GPP and environmental determinants at the regional scale is essential in understanding ecosystem responses to increasing atmospheric CO₂ concentrations and climate change. In this study we employed an integrated approach combining in situ measurements, eddy covariance based flux tower data and remote sensing techniques to examine the role of environmental drivers in controlling the spatial variation in GPP of savannas in the Northern Territory (NT), Australia. We used field based light use efficiency (LUE), regional specific meteorology and Moderate Resolution Imaging Spectro-radiometer (MODIS) based fraction of absorbed Photosynthetically Active Radiation (fPAR) data to estimate GPP. The estimated GPP agreed quite well (only a 6% error) with GPP estimated from flux tower at the Howard Springs site. The spatial pattern of GPP along the Northern Australian Tropical Transect (NATT) was calculated and showed a strong gradient in GPP from the coast (12.50°S where rainfall was 1622 mm year⁻¹) to inland (17.73°S where mean rainfall was 643 mm year⁻¹) with a decrease of 77%. A decreasing trend in GPP with rainfall is noticed especially at the dry end of the transect studied. However, in the wet end and middle part of the transect (e.g. dominated by different Eucalyptus species), the response of GPP to changes in rainfall is reduced. This finding suggests that the influence of rainfall on various Eucalyptus species may be dampened by biotic factors. Our results suggest that future changes in precipitation driven by climate change may affect the future distribution and dynamics of GPP in northern Australia.     

Transgenic Cotton and Disease Resistance Genes

Success in conventional breeding for resistance to mycotoxin-producing or other phytopathogenic fungi is dependent on the availability of resistance gene(s) in the germplasm.Even when it is available,breeding for disease-resistant crops is very time consuming,especially in perennial crops such as tree nut crops,and does not lend itself ready to combat the evolution of new virulent fungal races.     

Diversity in nuclear DNA content and ploidy level of Hedychium species and hybrids

Hedychiums are multipurpose plants cultivated as ornamentals because of their multicolor and showy and scented flowers and as medicinal plants because of their essential oils that have been found to possess antimicrobial and insecticidal properties. There is often taxonomic and botanical confusion about Hedychium species and cultivars because of the apparent existence of more than one cytotype within several Hedychium species, most likely because of the ease with which these species hybridize. Nuclear DNA content (2C-DNA) was determined for the first time in 23 Hedychium species and hybrids. The 2C-values ranged from 1.70 pg to 3.98 pg. We also determined the chromosome number of one species, Hedychium stenopetalum, which was found to be diploid (2n = 2x = 34), supporting the widely held view that the basic chromosome number in Hedychium is x = 17, and the existence of different cytotypes is most probably attributable to natural hybridization. Our results should be helpful not only in clarifying the botanical and taxonomic confusion in Hedychium but also in paving the way for a sound breeding program for this increasingly important ornamental ginger.     

Pollen biology of ornamental ginger (Hedychium spp. J. Koenig)

An improved in vitro pollen germination assay was developed to assess the viability of stored Hedychium pollen. The effect of polyethylene glycol (PEG) (10, 15, and 20%, w/v) on pollen germination and tube growth was evaluated for Hedychium longicornutum and two commercial Hedychium cultivars, ‘Orange Brush’ and ‘Filigree’. Overall, the inclusion of PEG 4000 in the medium improved both pollen germination and tube growth for the three different genotypes tested and the results varied depending on genotype. In vitro germination was used to assess the viability of Hedychium pollen stored up to two months. Pollen nucleus status was determined for four Hedychium cultivars, ‘Orange Brush’, ‘Anne Bishop’, ‘Filigree’, and ‘Daniel Weeks’. Pollens of ‘Orange Brush’, ‘Anne Bishop’, and ‘Daniel Weeks’ were found to be binucleate but ‘Filigree’ was shown to possess both binucleate and trinucleate pollens. High pollen:ovule ratio values were obtained in several Hedychium taxa. The results obtained on the nuclear pollen status and pollen:ovule ratios will further our understanding of the pollination biology and help clarify the taxonomy and phylogeny of Hedychium species.     

Aspergillus flavus growth and aflatoxin production as influenced by total lipid content during growth and development of cottonseed

Aspergillus flavus infects several food and feed crops, such as corn (Zea mays L.), cotton (Gossypium hirsutum L.), peanuts (Arachis hypogaea L.), and tree nut crops and contaminates the seed with carcinogenic aflatoxins. These susceptible crops contain rich reserves of lipids and fatty acids. The nature of relationship between lipids and the ability of the fungus to infect and produce aflatoxins in mature cottonseed, a protein-rich animal feed, has been addressed previously. In this study, we tracked lipid accumulation in developing cottonseed (15–35 days post-anthesis [DPA]) and also the ability of an aflatoxigenic strain and an isogenic non-aflatoxigenic strain to grow and produce aflatoxins in planta. The aflatoxigenic strain Af-70 green fluorescent protein (GFP) and the isogenic, non-aflatoxigenic strain SRRC 1500 (fungal collections maintained at the Southern Regional Research Center) did not differ much in infection and colonization of cottonseed. The non-aflatoxigenic strain did not produce aflatoxin at all stages of cottonseed development, whereas the aflatoxigenic strain Af-70 GFP produced copious amounts of aflatoxin and it coincided with the increasing levels of lipids, especially in mature cottonseed (30–35 DPA). Fungal growth, as quantified by the GFP expression in the fungus, was highly correlated with toxin production.