ThesisApril, 2024
Australian native Oryza species have potential for commercial cultivation due to their high nutritional grain profile, and their long association with Australian First Nations peoples. These species exhibit potential as high-value, niche foods, with cultural significance and nutritional benefits, particularly in gourmet cuisine, tourism, dining establishments, and value-added products. Consequently, they are considered promising candidates for the development of a native rice-based industry. Commercialisation of the Australian native rice has the potential to support Australian First Nations enterprises in northern Australia.
In the wild, Australian native Oryza species exhibit high seed production. However, the challenge lies in the difficulty of efficiently harvesting their grains due to the inaccessibility of their wild habitats and risks such as estuarine crocodile encounters in northern Australia. Wild harvesting is therefore unlikely to ensure a reliable commercial seed supply. Thus, cultivation has been identified as necessary for the commercialisation of native Australian Oryza, guided by thoroughly researched agronomic protocols and an understanding of potential challenges. However, the basic agronomic protocols for the cultivation of these species are unknown. This thesis thus investigated the cultivation protocols of Australian native rice in order to develop options for their commercial production by Australian First Nations enterprises.
The first objective involved reviewing the factors and pathways utilised for the commercial cultivation of other wild rice species in order to identify the knowledge required to commercialise Australian native Oryza. Based on this review, a conceptual framework was developed for implementing a successful wild rice industry in northern Australia. Based on this framework, agronomic research was identified as a major first step for the commercial production of Australian native rice. Furthermore, planting density was identified as a key determinant for achieving high rice yield potential.
Planting density has not been investigated for Australian native rice. The second objective therefore investigated planting density by conducting a meta-analysis to quantify the effects of planting density on the rice yield of O. sativa cultivars. Results showed that high-density planting can improve the yield potential of O. sativa cultivars. This was attributed to an increase in the number of panicles per unit area, spikelet filling percentage, and 1,000-grain weight. The responses of rice yield to high-density planting varied according to the management practices. Increases in yield due to high-density planting were stronger at nitrogen (N) rates < 120 kg ha-1 than at N rates > 120 kg ha-1. This meta-analysis indicated the planting density range to be tested for Australian native rice, and that the N application rate could interact with the response of rice yield to density.
The findings from meta-analysis on O. sativa cultivars were used as a guide for subsequent shade-house trials on Australian native rice. The third objective investigated the effects of planting densities and N rates on the yield potential and grain quality of two Australian native rice species (O. meridionalis and O. rufipogon) in the dry and wet seasons. In the dry season, the maximum grain yield per area of the two rice species was achieved under the combination of a high-planting density at 10 x 10 cm spacing with a reduced N rate of 150 kg ha-1. In the wet season, substantial plant lodging occurred. A reduced N rate of 150 kg ha-1 combined with a moderate plant density at 15 x 15 cm effectively enhanced the yield potential in the wet season, while minimising the lodging rate in both rice species. In addition, the N rate significantly influenced the grain quality of both species. A reduced N rate of 150 kg ha-1 resulted in a lower protein content and a higher amylose content, both of which are potentially desirable grain quality traits.
This study supports the potential commercial cultivation of Australian native Oryza in northern Australia. This study also emphasises the importance of optimising agronomic factors such as planting density and N rate in maximising the grain yield and quality of Australian native rice species. Cultivation for commercial production of these native grains could provide economic options for Australian First Nations enterprises.