Dante Adorada

Characterizing the Saltol Quantitative Trait Locus for Salinity Tolerance in Rice

This study characterized Pokkali-derived quantitative trait loci (QTLs) for seedling stage salinity tolerance in preparation for use in marker-assisted breeding. An analysis of 100 SSR markers on 140 IR29/Pokkali recombinant inbred lines (RILs) confirmed the location of the Saltol QTL on chromosome 1 and identified additional QTLs associated with tolerance. Analysis of a series of backcross lines and near-isogenic lines (NILs) developed to better characterize the effect of the Saltol locus revealed that Saltol mainly acted to control shoot Na+/K+ homeostasis. Multiple QTLs were required to acquire a high level of tolerance. Unexpectedly, multiple Pokkali alleles at Saltol were detected within the RIL population and between backcross lines, and representative lines were compared with seven Pokkali accessions to better characterize this allelic variation. Thus, while the Saltol locus presents a complex scenario, it provides an opportunity for marker-assisted backcrossing to improve salt tolerance of popular varieties followed by targeting multiple loci through QTL pyramiding for areas with higher salt stress.

Durum wheat quality in high-input irrigation systems in south-eastern Australia

Abstract. To extend the production base of durum wheat in Australia, field trials were conducted on seven registered durum varieties across four seasons and six sites in locations where irrigation was supplied during crop growth. The purpose was to determine if the quality of the grain produced met the requirements for good milling and pasta-making quality and to understand the genotype, environment and their interaction in affecting yield and technological quality of the grain and derived pasta. High grain yields and grain protein were obtained, producing large grain weights, low screenings and low percentage of hard vitreous kernels. Yellow colour of semolina and pasta was reduced marginally but dough and other pasta technological characteristics were similar to typical dryland durum production, with some exceptions. Varieties were identified with potential for production under irrigation.

Bacteria associated with sheath browning and grain discoloration of rice in East Timor and implications for Australia's biosecurity

A survey of rice growing regions in East Timor (Timor Leste) conducted in 2010 has resulted in the identification of several bacterial species associated with sheath browning and seed discolouration. Bacteria were identified by partial sequencing of the 16s rRNA gene and comparison with sequences from GenBank and EZtaxon databases. Bacterial isolates of known pathogens of rice, corn and cotton were identified, along with non-phytopathogenic endophytes. This is an indication that the disease symptoms are likely to be the result of a pathogen complex rather than caused by a single species. Unfortunately, due to current lack of infrastructure in East Timor, definitive pathogenicity testing of these isolates could not be undertaken. However, it is imperative to increase the capacity of East Timorese to improve their diagnostic skills and management of diseases of rice, and ultimately increase productivity. Furthermore, it is important to heighten the awareness of East Timorese farmers of the importance of diseases in rice production. Evidently, there is a potential source of high risk bacterial pathogens in the rice production system in East Timor and this also poses a risk to Australia’s biosecurity. Potentially devastating pests and diseases of Australian agriculture currently present in Asia could spread into Australia via East Timor. There are a number of economically important diseases of rice that occur in Southeast Asia which do not currently occur in Australia.

First Report of Resistance to DMI Fungicides in Australian Populations of the Wheat Pathogen Zymoseptoria tritici

The erosion of demethylation inhibitor (DMI) fungicides effectiveness over time in Europe has been attributed to mutation sites in the 14α-demethylase encoded by the nuclear gene CYP51 (Cools and Fraaije 2013). These mutations first appeared in Europe in the 1990s, became widespread over the next 20 years, and were also recently reported in North America (Estep et al. 2015; Lucas et al. 2015). Zymoseptoria tritici has been present and causing disease on wheat (Triticum aestivum) in Australia for many decades and the use of fungicides for its control has become more common over the past 15 years. However, no significant changes in the field performance of fungicides have been noted by growers. To investigate possible undetected changes, we sequenced the CYP51 gene of 18 isolates cultured from wheat leaves collected in a commercial field on 1 July 2012 at Inverleigh, Victoria (–38.086743° S; 143.935783° E), and 3 isolates cultured from wheat leaves collected from trial plots on 22 August 2002 at Wagga Wagga,NSW (–35.044544° S; 147.316318° E). The nucleotide sequence of Z. tritici strain ST1 eburicol 14 alpha-demethylase (CYP51) gene (GenBank Accession No. AY730587.1) was used to design a set of three forward and three reverse sequencing primers across the known mutations. The sequence reads were assembled into contigs and checked for complete sequence. To generate an alignment of mature protein sequences, the mature protein sequence of ST1 (CYP51) gene was downloaded from NCBI to use as a reference. CYP51 nucleotide sequences were translated into amino acid sequences using all six possible frame shifts. These were aligned to the mature protein sequence of ST1 (CYP51) to identify the correct frame-shift sequence, enable the removal of intron sequences, and finally generate an amino acid alignment. Nucleotide and amino acid sequences are deposited in GenBank with Accession Nos. KT201543 to KT201563. Sixteen of the isolates from Victoria were carrying the Y137F mutation, one isolate carried the L50S-Y461S mutation, and one the L50S-S188N-N513K. The three isolates from NSW collected in 2002 contained no mutations compared with the reference accession. Fungicide sensitivities for propiconazole were determined at 50% effective concentrations (EC50) using rates of 100, 30, 10, 3, 1, 0.3, 0.1, 0.03, 0.01, 0.003, and 0.001 mg/liter, and the resistance factor (RF) of each isolate was calculated as fold change in the EC50 compared with that of the wild-type strains as per Cools et al. (2011), four replicates per isolate were performed. Results of the phenotypic assay of a subset of nine isolates (four Y137F mutants, one L50S-Y461S, one L50S-S188N-N513K, and three Wild-type) confirmed the elevated EC50 values for the mutations known to cause reduced sensitivity. The Y137F and L50S-Y461S mutants showed EC50 values of 1.08 and 1.03 mg/liter and RF levels in the range of 3.07 and 2.93. respectively, while the wild-type and L50S-S188N-N513K mutant had EC50 of 0.352 and 0.367 mg/liter, respectively. The EC50 values observed for the isolates appear higher than those found by Cools et al. (2011); however, the RF values are lower for both mutations. Further exploration of CYP51 mutations occurring in Z. tritici within the Australian cropping regions will be necessary to establish how widespread the Y137F and L50S-Y461S mutants are, and if others such as the S524T or the V136A, which are associated with higher levels of resistance to DMIs, are also present.

Genetic improvement of triticale for irrigated systems in south-eastern Australia: a study of genotype and genotype × environment interactions

Abstract. Research into winter cereal breeding in Australia has focused primarily on studying the effects of rainfed environments. These studies typically show large genotype × environment (GE) interactions, and the complexity of these interactions acts as an impediment to the efficient selection of improved varieties. Wheat has been studied extensively; however, there are no published studies on the GE interactions of triticale in Australia under irrigated production systems. We conducted trials on 101 triticale genotypes at two locations over 4 years under intensive irrigated management practices and measured the yield potential, GE interactions, heritability and estimated genetic gain of yield, lodging resistance and several other traits important for breeding triticale. We found that high yield potential exceeding 10 t ha–1 exists in the Australian germplasm tested and that, in these irrigated trials, genotype accounted for a high proportion of the variability in all measured traits. All genetic parameters such as heritability and estimated genetic gain were high compared with rainfed studies. Breeding of triticale with improved yield and lodging resistance for irrigated environments is achievable and can be pursued with confidence in breeding programs.

Occurrence of Winter Cereal Viruses in New South Wales, Australia, 2006 to 2014

Winter cereal viruses can cause significant crop losses; however, detailed knowledge of their occurrence in New South Wales, Australia is very limited. This paper reports on the occurrence of Wheat streak mosaic virus (WSMV), Wheat mosaic virus (WMoV), Barley yellow dwarf virus (BYDV), Cereal yellow dwarf virus (CYDV), and their serotypes between 2006 and 2014. Detection of WMoV is confirmed in eastern Australia for the first time. The BYDV and CYDV 2014 epidemic is examined in detail using 139 samples of wheat, barley, and oat surveyed from southern New South Wales. The presence of virus was determined using enzyme-linked immunosorbent assays. The results reveal a high frequency of the serotype Barley yellow dwarf virus - MAV as a single infection present in 27% of samples relative to Barley yellow dwarf virus - PAV in 19% and CYDV in 14%. Clear differences emerged in the infection of different winter cereal species by serotypes of BYDV and CYDV. These results are contrasted to other Australian and international studies.