Genetic variation between and within Ethiopian barley landraces with emphasis on durable disease resistance

Landraces are known to be variable. Their resistance to diseases can be assumed to be durable. The durability of resistance in landraces can be due to the multiline principle or due to genetic durable resistance. To investigate the degree of variation both between and within landraces and what type of resistance is present 1800 single plant derived lines of IS Ethiopian barley landraces were studied for six traits among which resistance to two pathogens, Puccinia hordei, representing biotrophic fungi, and Rhynchosporium secalis, representing the hemi-biotrophic fungi.

The 1800 landrace lines were grown in 1991 and 1993 under field conditions a, Holetta Research Centre, Ethiopia and evaluated for scald (Rhynchosporium secalis) disease severity (DS) after infection from the naturally occurring inoculum. Earliness, plant height, leafiness and 1000 grain weight were also measured. All five characters varied greatly both between and within the landraces. The degree of association between DS and the other characters was investigated and earliness had an important effect on DS. The frequency of resistant genotypes within the landraces increased markedly with altitude. Complete resistance to scald occurred frequently. Lines fully resistant in one year could be fully susceptible in the other year indicating that the resistance of these lines was race-specific. It means, that for leaf scald at least a considerable part of the resistance found was race-specific. In this pathosystermthe multiline principle seems to operate to give durable resistance.

In 1990 over 1200 landrace lines, raised in the greenhouse, and each represented by five plants, were assessed at the young flag leaf stage for infection type (IT) and latent period (LP), the main component of partial resistance, after infection with barley leaf rust, race 1.2.1. This race was used because it carries virulence factors which can neutralize six of the nine known Pa-genes. Nearly all lines showed a high IT, which varied between 7 and 9 on the 0-9 scoring wale, indicating the absence of major genes for adult plant resistance in the landraces studied. For partial resistance the landraces showed a considerable variation both between and within the landraces. All landraces had at least some partial resistance.

In 1992 over 1700 landrace lines from the 18 landraces were grown in the greenhouse and evaluated for IT at the seedling stage after exposure to two barley leaf rust races (1.2.1 and A). Race A is virulent to fewer Pa-genes than race 1.2. 1. Nearly all lines assessed showed a high IT (8-9 on the 0-9 scale) to the two races. This again confirms the absence of hypersensitive major resistance genes in the landraces studied. Moreover, four Ethiopian and one Dutch barley leaf rust race were analyzed for their virulence patterns on the seedlings of the differential series of 11 barley cultivars together carrying nine Pa-genes and on 21 barley entries, 19 of which representing individual lines derived from 14 Ethiopian barley landraces. The Ethiopian isolates showed patterns of virulence/avirulence similar to those of European isolates. Again there was no evidence of the presence of effective major genes in the Ethiopian barley landraces and the multiline principle that might give these landraces durable resistance to barley leaf rust does not operate. The durable resistance to this pathogen is based on genetically durable resistance genes.

The inheritance of the partial resistance to leaf rust in the landraces was studied using 10 landrace lines and their F1, F2 and F3 or F4 progenies. At the F1, most crosses showed intermediate or recessive inheritance while a few crosses showed dominance. From the generation mean analysis some epistasis was also observed. At the F2, crosses segregated and distributed continuously ranging from the low to the high parent and in most crosses transgressive segregation was observed which was confirmed by the F3 or F4 data. The partial resistance in the eight landrace lines is based on some to several minor genes.