Queensland Wheat Research Institute, P0 Box 2282, Toowoomba, Qid, Australia, 4350

Background and objectives
Crown rot of wheat and barley is a soilborne disease caused by Fusarium graminearum Schwabe Group 1. It has become a limiting factor to grain production in winter cereals in Queensland and northern New South Wales and is becoming a problem in parts of southern Australia. As the primary means of survival is in diseased tiller bases, the trend to greater retention of stubble has caused this disease to become more widespread and important. In Queensland, 15 of 17 bread wheat cultivars, all durum cultivars, and all barley cultivars are susceptible or highly susceptible to this disease. Sources of partial resistance have been identified in bread wheat (1), but not in the other cereals. To incorporate resistance into winter cereals, higher levels of resistance in bread wheat, and sources of resistance in durum and barley or closely related germplasm are needed. Appels and Lagudah have found sources of resistance to cereal cyst riematode, Septoria nodorum, Septoria tritici and rusts in accessions of Aegilops tauschii (=Triticum tauschii) (2). Ae. tauschii is considered to be the donor of the D genome of bread wheat. This paper reports on tests on wild relatives of bread wheat, durum wheat and barley to determine whether levels of resistance higher than that currently recorded are available.

Materials and methods
Resistance to crown rot was measured as severity of tiller discoloration in either mature plants inoculated in the field (1) or as severity of leaf sheath disease in inoculated seedlings grown at 25C for 3 weeks. Synthetic hexaploids (Durum x Aegilops tauschii) and their durum parents were screened as seedlings for their resistance to crown rot. In a subsequent experiment, the Ae. tauschii parents of synthetic hexaploid accessions with partial resistance, were also screened. To find germplasm that could be used in a durum breeding program, accessions of Triticum turgidum ssp. carthlicum, T. turgidum ssp. dicoccoides, T. turgidum ssp. dicoccon, T. turgidum ssp. turanicum were screened. Accessions of the wild relative of barley, Hordeum vulgare ssp. spontaneum were also screened as seedlings.

Results and conclusions
Thirty-six of 189 synthetic hexaploid accessions showed partial resistance to crown rot as seedlings; those tested in the field were also partially resistant. None of the durum parents showed resistance in the field although some showed a low level of resistance as seedlings. In contrast, 16 of 42 Ae. tauschii parents were partially resistant. Within tetraploid species, resistance was found only in accessions of T. turgidum ssp. carthlicum but not in any other subspecies. Preliminary tests with H. vulgare ssp. spontaneum indicate that some accessions are partially resistant. These tests show that some but not all of the wild relatives of wheat and barley possess resistance to crown rot. The finding of resistance in Ae. tauschii adds to the growing list of sources of resistance in this species (2). However, the finding of resistance in T. turgidum ssp. carthlicum indicates that resistance may be present in any of the three genomes of bread wheat. Further testing will investigate whether genes for resistance in different Triticum spp.and Ae. tauschii are different and whether the resistances can be combined to provide sources of higher levels of resistance to this disease.

1. Wildermuth GB, McNamara RB, 1994. Plant Disease 78, 949-53.
2. Appels R, Lagudah ES, 1990 Australian Journal of Plant Physiology 17, 253-66.