Morphological,Structural, and Thermal Properties of Starch Nanocrystals Affected by Different Botanic Origins

Six types of starch nanocrystals were prepared from corn, barley, potato, tapioca, chickpea, and mungbean starches with an acid hydrolysis method. The yields and morphological, structural, and thermal properties of starch nanocrystals were characterized. Starch nanocrystals had yields ranging from 8.8 to 35.7%, depending on botanical origin. During acid hydrolysis, amylose was effectively degraded, and no amylose was detected in any starch nanocrystal. Shape and size of native starch granules varied between starches, whereas there was no obvious difference in shape among different types of starch nanocrystals. The average particle size of starch nanocrystals was mainly related to crystalline type of native starches. Compared with their native starch counterparts, changes in crystalline diffraction patterns of starch nanocrystals depended on the original botanical source and crystalline structure. Degree of crystallinity, melting temperature, and enthalpy of starch nanocrystals increased, whereas their thermal decomposition temperature decreased. Of six produced starch nanocrystals, potato starch nanocrystal had the lowest yield, degree of crystallinity, and onset and melting temperatures, the largest particle size, and obvious changes in crystalline diffraction pattern.     

Genetics of adult plant stripe rust resistance in four Australian wheats and the French cultivar 'Hybride-de-Bersée'

Long-term resistance to rust diseases depends on the identification and use of durable resistance sources or on the continuing use of new resistances and combinations of genes for specific resistance. These studies include four Australian wheats with intermediate, but inadequate levels of resistance and a French wheat ‘Hybride-de-Bersée’ (‘Bersee’), with reputed durable resistance to stripe rust. Studies of F₂ and F₃ populations from crosses with the susceptible ‘Avocet’ indicated that intermediate levels of adult plant stripe rust resistance in cultivars ‘Harrier’, ‘Flinders’ and ‘M2435’ were inherited monogenically, whereas King possessed two genes for resistance. Cultivars Harrier and M2435 possessed the same gene. Similarly, cvs. King and Flinders carried a gene in common. Like ‘Harrier’ and ‘M2435’, ‘King’ and ‘Flinders’ share common parents. The higher level of resistance in ‘Bersee’ was controlled by four genes. This conclusion was based on conventional genetic analysis, tests on F₂-derived F₇ single-seed descent lines and testcross progenies.     

Molecular mapping of adult plant stripe rust resistance in wheat and identification of pyramided QTL genotypes

The Puccinia striiformis f. sp. tritici (Pst) pathotype, 134 E16A+, detected in 2002 in Australia, produced relatively lower and higher adult plant stripe rust responses, respectively, on cultivars Kukri and Janz in comparison to the pre-2002 Pst pathotype 110 E143A+. Molecular mapping of adult plant stripe rust response variation among 180 Kukri/Janz-derived doubled haploid lines over 4 years, two each with Pst pathotypes 110 E143A+ and 134 E16A+, was performed. QYr.sun-7B and QYr.sun-7D were consistently contributed by Kukri and Janz, respectively. QYr.sun-7D corresponded to the genomic location of Yr18 and QYr.sun-7B remains to be formally named. QYr.sun-1B, QYr.sun-5B, and QYr.sun-6B were detected during more than one season irrespective of the Pst pathotypes used, whereas QYr.sun-3B was identified only during the 2003 crop season. QYr.sun-1A contributed by Janz, and QYr.sun-2A from Kukri, were detected only against Pst pathotypes 110 E143A+ and 134 E16A+, respectively. The DH lines showing better resistance than the either parent carried combinations of 4 to 6 QTL. These lines are currently being used as stripe rust resistance donors in wheat breeding programs.     

Genotypic and environmental effects on lupin seed composition

Currently, white lupin (Lupinus albus L.) is gaining importance due to its high nitrogen fixation capability and potential in sustainable crop production systems. Even though research conducted in Australia, Chile, Germany, New Zealand, and Portugal has indicated lupin's positive potential as human and animal food, such information from Virginia and adjoining areas of the United States is not available. In addition, effects of growing environment and genotypes on lupin seed composition need to be characterized to evaluate lupin's potential as a food and feed crop. Towards this end, seed of 12 lupin genotypes produced in Maine (USA) and Virginia (USA) were compared to determine genotypic and environmental effects on contents of protein, sugar, oil, various fatty acids, amino acids, and minerals. The protein content of dry seed was not affected by growing environment. However, growing environment had significant effects on contents of total sugar, amino acids, oil, fatty acids, and minerals. Significant variation existed among 12 lupin genotypes for various traits when composition of seed produced in Virginia was evaluated. The results indicated that site-specific evaluation of adapted lupin genotypes for chemical composition should be included in efforts to evaluate lupin's overall potential as a food or feed crop.     

Relationship between wheat rust resistance genes Yr1 and Sr48 and a microsatellite marker

A recombinant inbred line population derived from a cross between the winter wheat cultivars Arina and Forno was used to study the genetic relationship between genes Yr1 and SrAn1 in chromosome 2AL. Yr1 from Forno showed repulsion linkage (16·5 cM) with SrAn1 carried by Arina and was proximal to SrAn1 . Based on the chromosomal location of SrAn1 with respect to Yr1 and its ineffectiveness against the Australian Puccinia graminis f. sp. tritici pathotype 34-1,2,7 +  Sr38 , it was concluded that SrAn1 is distinct from Sr21 and was designated as Sr48 . An attempt was made to map more markers in the distal region of chromosome 2AL in order to determine the precise location of Sr48 . Unfortunately none of the markers tested mapped between Yr1 and Sr48 , with the latter being the most distal locus. However, close linkage was identified between Yr1 and the PCR-based molecular marker stm673acag. Genotyping with stm673acag amplified a 120-bp fragment in eight of nine genotypes carrying Yr1 . Avocet S was the only line tested without Yr1 that also amplified the 120-bp product. A 124-bp product was amplified in 40 Australian wheat cultivars known to lack Yr1. These results suggest that stm673acag could be used for marker assisted selection of Yr1 . Genotypes carrying both Yr1 and Sr48 were identified.     

Temperature-sensitive wheat stem rust resistance gene Sr15 is effective against Puccinia graminis f. sp. tritici race TTKSK

The wheat stem rust fungus, Puccinia graminis f. sp. tritici (Pgt), race TTKSK and related races pose a serious threat to world wheat production. Knowing the effectiveness of wheat stem rust resistance (Sr) genes against Pgt race TTKSK is fundamental in mitigating this threat through resistance breeding. Sr15 was previously identified as being ineffective against Pgt race TTKSK. Here, multirace disease phenotyping data, linkage analyses, allelism testing and haplotype analyses are presented to support the conclusion that Sr15 is effective against Pgt race TTKSK. Resistance to race TTKSK was mapped to Sr15 in a biparental population. Thirty-two accessions with Sr15 displayed seedling resistance phenotypes against race TTKSK. However, these accessions were susceptible as seedlings at high temperatures (22–25 °C), consistent with previous reports that the interaction between avirulent Pgt isolates and Sr15 is temperature-sensitive. Markers STS638, wri4 and KASP_IWB30995 were found to predict the presence of Sr15, suggesting the utility of these assays for marker-assisted selection in breeding programmes. The effectiveness of Sr15 to specific Pgt races and temperatures makes it a less-desirable TTKSK-effective gene. Wheat lines assayed as resistant to race TTKSK at the seedling stage may possess Sr15 and breeders should be aware of the limitations of Sr15 for conferring stem rust resistance.     

Identification of recombinants carrying stripe rust resistance gene Yr57 and adult plant stem rust resistance gene Sr2 through marker‐assisted selection

Many stem rust resistance genes have been formally named in wheat. Adult plant stem rust resistance gene Sr2 was mapped in the short‐arm of chromosome 3B. Stripe rust resistance gene Yr57, identified in Aus91463, was mapped about 5 cM away from Sr2 based on its linkage with Sr2‐linked marker gwm533. The objective of this study was to combine Sr2 and Yr57 in a single genotype. A mapping population containing 107 recombinant inbred lines was developed from a cross between Aus91463‐Yr57 and Hartog‐Sr2. This population was tested at the seedling stage in the glasshouse for variation in stripe rust response, and high temperature induced Sr2‐linked seedling chlorosis. The RIL population was screened for Sr2‐linked pseudo black chaff phenotype at the adult plant stage in field. Five recombinants carrying Sr2 and Yr57 in coupling were detected using phenotypic and marker data. Four recombinants also carried leaf rust resistance gene Lr23 from Aus91463. These recombinants are being used as triple rust resistance source in the Australian Cereal Rust Control Program.     

Aspects of wheat rust research in Australia

A National Wheat Rust Control Program, that has operated in Australiasince 1975, provides national pathotype surveys for the three rustpathogens, undertakes ongoing searches for new sources of resistance andcarries out genetic analyses of these sources, and provides rust screeningand germplasm enhancement support for breeders. The program wasexpanded in the 1980s to address problems arising from the introductionof wheat stripe rust. A new form of stripe rust, described as barley grassstripe rust, was first detected in 1998. Although virulent on some wheatseedlings this new rust appears to be a greater threat to barley. Molecularmarkers are expected to make an increasing impact on our ability to selectthe gene combinations needed to enhance the durability of resistance.