THE UNIVERSITY OF SYDNEY
IA Watson Wheat Research Centre, Narrabri, 2390, NSW Australia.
Kolumbina Mrva and Daryl Mares.
High levels of a high pI a-amylase in mature wheat grain (LMA) in the absence of sprouting but resulting from the impact of cool temperature on particular genotypes during grain filling, is widespread in Australian breeding programs and present in some commercial cultivars. Improved procedures have been developed to assist wheat breeders to identify and eliminate LMA-prone germ plasm. These procedures involve two steps: 1. the reliable induction of LMA using controlled environment cabinets to subject whole plants or spikes on detached tillers to a standard cool-temperature regime for 7-10 days beginning 25 days after anthesis and 2. the determination of any high pI a-amylase synthesized using a high pI-specific ELISA kit developed in collaboration with CSIRO Plant Industry in Canberra. In addition to its use in identifying LMA-prone genotypes, the ELISA kit also can be used to differentiate sprouting or LMA from retained pericarp a-amylase and sprouting from LMA. The latter distinction relies on the fact that in sprouted grain, the a-amylase is concentrated at the embryo end of the grain, whereas in LMA-affected grains, the amounts of enzyme in the proximal and distal halves of grains is usually similar. Details of these procedures will appear shortly in the Australian Journal of Agricultural Research.
Doubled-haploid lines in a mapping population that involves an LMA-prone parent were characterized for LMA in 2000. Initial analysis has identified a highly significant QTL associated with LMA. Details on this QTL will appear shortly following confirmation.
Sprouting was widespread again in New South Wales causing substantial economic and yield losses and a downgrading of quality. As in the two previous seasons, ripe grains affected by black point sprouted more readily than sound grains from the same sample. The possibility of a genetic linkage between sprouting and black point was investigated using the DH population 'AUS1408 (sprouting tolerant and black point susceptible)/Cascades (sprouting susceptible and black point resistant)' obtained from Dr. Peter Williamson at the Leslie Research Centre, Toowoomba, QLD, Australia. Equal numbers of the four possible recombinants were observed and we concluded that the two traits were not genetically linked. The mechanism involved in the black-point effect on sprouting remains unclear. Scanning electron microscopy of black point-affected grains revealed no evidence of cracking of the seed coat nor of fungal infestation.
As of April 2001, Kolumbina Mrva and Daryl Mares will be located in the department of Plant Science, University of Adelaide, Waite Campus, Glen Osmond, SA 5064, Australia.
THE UNIVERSITY OF SYDNEY
PBI Cobbitty and Department of Crop Sciences, Private Bag 11, Camden, NSW, 2570; and Sydney, 2006, Australia.
H.S. Bariana, J. Bell, R.A. McIntosh, J.D. Oates, R.F. Park, and C.R. Wellings.
After a long and distinguished career with the University of Sydney, Prof. R.A. (Bob) McIntosh retired at the end of July. Bob's association with the University of Sydney began in the late 1950s when he enrolled as an undergraduate student in the Faculty of Agriculture, and his professional career at the University began in 1960. Bob's achievements in the years since have earned him extensive national and international reputations as a wheat geneticist and rust pathologist. Dr. R.F. Park was appointed as acting director of rust research, and a search is underway to find a replacement for Prof. McIntosh. Ms. K. Kaur was appointed in March to replace G.N. Brown.
Conditions in Western Australia (WA) during the autumn and winter were dry following a wet summer. Outbreaks of stem rust in WA were reported from many areas in 2000 and, despite the dry conditions, a substantial spread of the disease occurred with high levels and significant yield losses in some crops. As in recent years, the predominant pathotypes in WA were 34-2 and 34-2,7. A new variant, 34-1,2,7, with virulence for Sr6 was detected from several sites in northern regions of WA. Pt 98-1,2,3,5,6, common in eastern Australia but not previously detected in WA, was detected in the Moorine Rock region, and one isolate also was identified from Merredin/Esperance. In eastern Australia, stem rust was observed on self-sown wheat in the Mallee around Lascelles/Hopeton in early August. The disease remained at low levels in eastern states, and samples received comprised primarily pt 98-1,2,3,5,6.
In WA, leaf rust became severe in the far northern wheat belt, was moderately severe in early sown crops in the east and southeastern areas, and occurred sporadically in the central and south-coastal areas. Many samples were received and all were identified as pt 104-1,2,3,(6),(7),11. Although the drought conditions in the northern regions of eastern Australia during 2000 did not favor rust development, generally better conditions in the southern regions led to widespread occurrence of leaf rust. The important development during 2000 was the detection of a new pathotype (104-1,2,3,(6),(7),11+Lr24) with virulence for the resistance gene Lr24. This pathotype was first detected on the Yorke Peninsula, South Australia, in October and subsequently in the lower and mid-north of SA, southern NSW, Victoria, and Queensland The most common pathotypes in south eastern Australia were pt 104-1,2,3,(6),(7),11, pt 104-1,2,3,(6),(7),11,12, and the Triller (Lr26 virulent) pt 104-1,2,3,(6),(7),9,11.
Fewer wheat stripe rust samples were received compared to previous seasons. The early isolates from Queensland and northern NSW were pathotype 104 E137 A-, which has been common in this region for many years. Samples were received from Camm (Yr17) wheat, and it is expected that these may yield the Yr17 virulent pathotype first detected last year. In general, we expect that the epidemic development and crop losses will be minimal despite favorable conditions in southern regions. In contrast, barley grass stripe rust (BGYR) was very common, especially in southern NSW. Isolates from barley grass have included both wheat and BGSR. Some stripe rust samples, presumably BGYR, were received from barley although crop losses are not expected.
Close repulsion linkage was determined between Sr39 and Sr36. A recombinant genotype was identified and will be progeny tested in 2001. Sr39 is closely linked with a leaf rust resistance gene Lr35. If the recombinant genotype carries Sr39/Sr36/Lr35, it would provide an excellent source of resistance to two rust diseases. Because of the close linkage it is likely that all three genes can be transferred together in a backcross program (H.S. Bariana).
A PCR marker linked with VPM1-derived rust resistance genes was developed and validated by testing in populations in work conducted in collaboration with E. Lagudah's group at CSIRO Plant Industry (H.S. Bariana).
A new stem rust-resistance gene from Ae. tauschii was identified and genetically characterized. Introgression of the gene into a hexaploid derivative of Meering was confirmed by rust testing. The gene is located in chromosome 2DS and is very closely linked with an RFLP marker that could prove useful in marker assisted selection (H.S. Bariana).
A genetic association was demonstrated between CreX and the VPM1 resistance Sr38/Lr37/Yr17 in collaborative work with Dr. J. Jahier, INRA-Station d'Amelioration des Plantes, BP 29, F-35653 Le Rheu Cedex, France. The gene was designated as Cre5 (H.S. Bariana).
A genetic association of a root lesion nematode-resistance gene RLnn1 with leaf rust resistance gene Lr20 was demonstrated in collaboration with Dr. K. Williams, South Australian Research and Development Institute (H.S. Bariana).
Studies of adult plant resistance to stripe rust using the test cross procedure were continued in field experiments in 2000. Cultivars studied included Janz, Dollarbird, Tasman, Pelsart, Cook, Cascades, Yarralinka, Shrike, Oxley, Currawong, Warbler, and Suneca. Studies of F2 populations in 1999 allowed a prediction of gene number. Selected populations were harvested and tested as F3 short rows in 2000. Although data summaries have not been finalized, reasonable agreement in the expected segregation patterns between F2 and F3 was found (K. Gossal, Ph.D. student, and C.R. Wellings).
Two further generations of backcrossing for the development of NILs with genes for leaf rust-resistance were made. International testing of the Cunderdin sib line used as the recurrent parent indicated that the line may be marginally late in maturity for some locations (R.A. McIntosh).
Genetic analysis of adult plant resistance in European wheat cultivars. A collection of about 150 European winter wheats, recently characterized for seedling resistance to leaf rust (R.F. Park), were rated for adult plant response in field tests. Selected lines with adult plant resistance were crossed to either Avocet R or Cunderdin sib to study the inheritance of the resistance. Additional crosses of many cultivars were made to the Australian wheat Spica, to provide genetic confirmation of the presence of Lr13 (A. Pathan, Ph.D. student, and R.F. Park).
Testcrosses were made to F1s involving lines carrying adult plant resistance to leaf rust and stripe rust (ex Dr. Singh, CIMMYT) and Avocet S. Unfortunately, all F2 material derived from these crosses sprouted because of the abnormally wet conditions at harvest and was discarded. This work will be repeated in 2001 (H. Miah, Ph.D. student).