Abstract only

Stripe rust near isogenic lines (NILs) developed in Avocet S, a selection of the Australian wheat cultivar Avocet, overcome some of the problems associated with differential genotypes, which often have additional or uncharacterised resistance genes when used globally, and undesirable or variable growth habits that limit their usefulness in field nurseries. These NILs are currently used widely in pathotype monitoring, field trap plots and breeders? nurseries. However, a limitation of the Avocet NILs for pathotyping in the field has been an inability to distinguish components in pathotype mixtures. In order to improve this situation, especially for researchers in developing countries where adequate greenhouse facilities are often not available, combinations of two or more stripe rust resistance genes were developed by intercrossing the single gene Avocet NILs. Lines homozygous for the gene combinations were selected and confirmed through differential infection types, multipathotype testing, genetic analysis, and use of molecular and morphological markers. The use of well characterised pathotype collections is currently the most reliable and efficient means for postulating rust resistance genes. In total, 41 stripe rust gene combinations have been produced and confirmed. The seedling effective resistance genes involved are Yr1, Yr5, Yr6, Yr7, Yr9, Yr10, Yr15, Yr17, Yr24/Yr26, Yr27, Yr32 and YrSp. In some cases the adult plant resistance gene Yr18 is also included. Allelism prevented some combinations. For example, Yr5, Yr7, YrSp and YrJubII (from Jubilejna II) showed evidence of allelism at a single locus; Yr24 and Yr26 are alleles on chromosome 1B and are probably identical; and combinations of Yr9 (1BL/1RS) with genes in or near chromosome 1BS (Yr10, Yr15, Yr24 and Yr26) are not possible. Where possible the presence of particular genes is being confirmed by molecular markers. This will validate and confirm that markers reported in the literature can be used as a means of identifying the particular combinations largely assembled by non-marker means. One problem with such a large set of morphologically identical lines (apart from those with Yr10 and having brown chaff colour due to close linkage) is maintenance of the identity and purity of individual lines. For this, markers will be essential. Scientists will also be encouraged to store adequate quantities of seed under good storage conditions (sealed dry seed, at low temperatures in a refrigerator or deepfreeze). This will allow repeated sampling from the same seed sources over years without need for regeneration each year when errors are more likely to occur. Use of the combination lines in conjunction with the mono-gene lines will not provide classical race identifications, but if used strategically will go part way in resolving important pathotype diferences in targeted regions.

Global Wheat Program|Socioeconomics Program

English

Lucia Segura

INT3176

CIMMYT Staff Publications Collection