The Aegilops ventricosa segment on chromosome 2AS of the wheat cultivar 'VPM1' carries the cereal cyst nematode resistance gene Cre5

Previous studies showed that the intermediate level of resistance in bread wheat line ‘VPM1’ to pathotype Ha12 of the cereal cyst nematode could be conferred by an Aegilops ventricosa‐derived gene, CreX, in chromosome arm 2AS, which also carries the rust resistance genes Yrl7, Lr37 and Sr38. Near isogenic lines (NILs) differing for the presence and absence of the Ae. ventricosa‐derived linked genes Yrl7/Lr37/Sr38 were tested with cereal cyst nematode. Lines carrying Yr17 produced significantly fewer nematode cysts than the controls. An infested soil experiment produced better differentiation among resistant and susceptible genotypes. Susceptibility of ‘Trident’ indicated that linkage between CreX and Yr17 is incomplete. Microsatellite markers did not differentiate between ‘Trident’ and CreX‐carrying genotypes. However, Xgwm636 (104) was associated with the presence of Yr17 in all six genetic backgrounds. Since none of the reported cereal cyst nematode resistance genes is located in chromosome 2AS, CreX was designated as Cre5.     

Characterisation and origin of rust and powdery mildew resistance genes in VPM1 wheat

Summary The expression of rust resistances conferred by closely linked genes derived from VPM1 varied with environmental conditions and with genetic backgrounds. Under low light and low temperature conditions seedlings carrying Yr17 showed susceptible responses. Stem rust and leaf rust resistance genes Sr38 and Lr37 tended to confer more resistance at 17±2° C than at normal temperatures above > 20° C. These studies supported the hypothesis that Yr17, Lr37 and Sr38 were derived from Aegilops ventricosa, whereas Pm4b was probably derived from T. persicum. Studies on certain addition lines and parental stocks indicated that wheat cytoplasm may enhance the expression of Sr38.     

Exploring wheat landraces for rust resistance using a single marker scan

Marker-trait associations identified in diverse germplasm can be exploited in crop improvement programs. An attempt to establish such associations was made by evaluating 205 wheat landraces for stripe rust, leaf rust and stem rust responses in the field over three crop seasons. Diversity arrays technology was used to genotype the landraces and associations were identified using a single-marker scan. Sixty-eight markers were significantly associated with rust resistance. Several significantly associated loci coincided with the presence of known major genes or QTL for rust resistance. In contrast, many marker-rust response associations identified in this analysis for each of the three rust diseases uncovered new loci. Dual associations; stripe rust-leaf rust (1AL, 2BS, 2BL, 3DL, 5BS, 6BS and 7DL), leaf rust-stem rust (5BL) and stripe rust-stem rust (4BL and 6AS) resistance were also observed. These associations could enable a cost-effective targeted mapping of dual rust resistance. Some marker-trait associations identified in this study have been validated through genetic analyses and formal naming of resistance loci.     

Australian Uromyces viciae-fabae: Host and nonhost interaction among cultivated grain legumes

Uromyces viciae-fabae, rust of faba bean, parasitizes other legume crops such as lentils (Lens culinaris) and field peas (Pisum sativum) in some environments. In this study we examined the host range of two Australian isolates of U. viciae-fabae collected and purified from a faba bean crop and classified as U. viciae-fabae ex V. faba. Field pea (P. sativum), chickpea (Cicer arientinum), lupin (Lupinus spp.), lentil (L. culinaris), and mung bean (Vigna radiata) genotypes were tested with these isolates, as well as resistant and susceptible genotypes of the faba bean host. Race specificity for these two pathogen isolates was observed on Vicia faba, with two faba bean genotypes showing partial resistance. Both U. viciae-fabae isolates also colonized field pea seedlings and successfully produced uredinia under glasshouse conditions, despite this fungus not being known as a pathogen of Australian field pea crops. No sporulation of either isolate of U. viciae-fabae ex V. faba was observed on any of the remaining legume species tested. However, obvious differences in fungal growth were observed, ranging from small infection sites with very rare haustorium formation in mung bean to more extensive growth and the development of potential uredinial structures in chickpea. These observations are discussed in relation to the phylogenetic relationship of these host and nonhost species.     

Mapping of Aegilops umbellulata‐derived leaf rust and stripe rust resistance loci in wheat

Aegilops umbellulata, a non‐progenitor diploid species, is an excellent source of resistance to various wheat diseases. Leaf rust and stripe rust resistance genes from A. umbellulata were transferred to the susceptible wheat cultivar WL711 through induced homoeologous pairing. A doubly resistant introgression line IL 393‐4 was crossed with wheat cultivar PBW343 to develop a mapping population. Tests on BC₂F₇ RILs indicated monogenic inheritance of seedling leaf rust and stripe rust resistance in IL 393‐4 and the respective co‐segregating genes were tentatively named LrUmb and YrUmb. Bulked segregant analysis placed LrUmb and YrUmb in chromosome 5DS, 7.6 cM distal to gwm190. Aegilops geniculata‐derived and completely linked leaf rust and stripe rust resistance genes Lr57 and Yr40 were previously located in chromosome 5DS. STS marker Lr57/Yr40MAS‐CAPS16 (Lr57/Yr40‐CAPS16), linked with Lr57/Yr40 (T756) also co‐segregated with LrUmb/YrUmb. Seedling infection types differentiated LrUmb from Lr57. Absence of leaf rust‐susceptible segregants among F₃ families of the intercross (IL 393‐4/T756) indicated repulsion linkage between LrUmb and Lr57. YrUmb expressed a consistently low seedling response under greenhouse conditions, whereas Yr40 expressed a higher seedling response. Based on the origin of LrUmb/YrUmb from the U genome and Lr57/Yr40 from the M genome, as well as phenotypic differences, LrUmb and YrUmb were formally named Lr76 and Yr70, respectively. These genes have been transferred to Indian wheat cultivars PBW343 and PBW550, and advanced breeding lines are being tested in state and national trials.     

Inheritance and chromosome location of leaf rust resistance in durum wheat cultivar Wollaroi

The Australian durum cultivar Wollaroi produced low leaf rust responses in the field since its release in 1993. A recombinant inbred line population was developed from a cross of Wollaroi with a susceptible landrace Bansi. Monogenic inheritance of low seedling leaf rust response against the Puccinia triticina pathotype 104-1,2,3,6,(7),(11),13 was observed. This gene was temporarily designated as LrWo. A DArT based map of Wollaroi/Bansi was used to determine the genomic location of LrWo and it was mapped in chromosome 5BS. Following enrichment of the DArT map of chromosome 5BS with SSR markers, LrWo was flanked by gwm234 (7.2 cM) and wPt-1420 (20.3 cM) distally and proximally, respectively. A previously characterised gene Lr52 was also located on the chromosome arm 5BS, proximal to gwm234. Based on genetic association with the marker gwm234 at a similar distance, we concluded that LrWo could be either Lr52 or is another allele of this locus. Based on infection type comparison the latter argument seems more plausible.     

Characterization of stem rust resistance in old tetraploid wheat landraces from the Watkins collection

Stem rust is one of the important diseases of tetraploid wheats worldwide. One hundred and five landraces from the Watkins collection were assessed for seedling and adult plant stem rust response variation. Seedling resistance genes Sr8a, Sr8b, Sr9e, Sr9g, Sr12, Sr13, Sr17 and Sr23 were postulated in 28 genotypes using Australian and Indian Puccinia graminis f. sp. tritici pathotypes. Four genotypes possessed either uncharacterized seedling stem rust resistance gene(s) or combinations of known stem rust resistance genes with compensating avirulences among pathotypes used. Adult plant stem rust response assessments were made on 73 seedling susceptible genotypes in Australia and Ethiopia. Adult plant stem rust responses varied from 1 (very resistant) to 7 (moderately susceptible) on a 1–9 scale. The Ethiopian nursery was exposed to Ug99 (TTKSK) and JRCQC (virulent on Sr9e and Sr13). Some genotypes that exhibited high responses in Australia were scored low in Ethiopia. These results demonstrated the effectiveness of some resistance gene(s) that were ineffective in Australia. The opposite trend was also noted. Over 50 % genotypes exhibited commercially acceptable rust responses varying between 2 and 5 across sites and years. Genotyping with the Sr2-linked molecular marker csSr2 did not detect Sr2 in any of the genotypes. The marker gwm533 however detected the presence of Sr2 in eight genotypes. Stem rust resistant genotypes that carried varying levels of APR could carry new genes. Genetic analysis and deployment of these uncharacterized sources of seedling and APR in new cultivars will ensure durable stem rust control through increased diversity.     

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.     

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.