^AWA State Agricultural Biotechnology Centre, Murdoch University, Murdoch, WA 6150
^BPlant Research & Development Services, Agriculture Western Australia, South Perth, WA 6151

Introduction

Net-type net blotch of barley caused by Pyrenophora teres f. sp. teres occurs widely throughout the barley cropping regions of Australia. It reduces grain yield by up to 33% mainly through reduced grain size. Development of stable forms of resistance depends upon using barley lines resistant to the most prevalent isolates around Australia.

Materials and Methods

We have screened 69 barley lines from different barley breeding groups around Australia and elsewhere to identify sources of resistance for breeding. Most of these lines have some resistance to net blotch and some represent elite resistances. These lines were screened as seedlings in duplicate sets using net-type net blotch isolates prevalent in Western Australia (five isolates), Queensland (three isolates) and South Australia (one isolate) (Table 1). Inoculations of these lines were undertaken at the two leaf stage with a suspension of ~2 x 10⁴ spores /ml. Plants were incubated at 19-20°C with complete leaf wetness for the first 24 hr and symptom severity assessed on ninth day.

Table 1. Net-type net blotch isolates used to screen 69 barley lines.

The responses of 69 lines to nine isolates were subject to analysis of variance components using the program ASREML. In this analysis responses were estimated as Best Linear Unbiased Predictors (BLUPS). These estimates take into account experimental error and are better predictors of future performance than raw means.

Results and Discussion

For each line an overall rating (BLUP) and a variance across isolates were calculated (Figure 1). The most desirable resistances have low overall rating (BLUP) and low variance indicating resistance to the majority or all tested isolates.

Figure 1. Barley lines categorised into resistant, intermediate and susceptible using best linear unbiased predictors and variance.

Twenty four lines were resistant with variances up to 3.16 (Table 2). Forty one lines were intermediate with variance ranging 0.28 - 6.48. Four lines were susceptible with variances of up to 2.01. Barley lines Abyssinian, Beecher, Perun, Rika and Shannon had very higher variance (>4). The basis of high variance for these lines is shown as contrasting responses to the different isolates (Figure 2).

Figure 2. Barley lines with contrasting responses to net blotch isolates.

Barley lines that served to differentiate isolates included in this study were Abyssinian, Beecher, Dampier, Grimmett, Perun, Pompadour, Prato, Reinette, Rika, Shannon and Skiff (Table 1).

Table 2. Resistant barley lines ranked on overall net blotch response. Among these lines, those with the lowest variance were resistant to all isolates tested.

Resistant lines with low variance are the most useful sources to identify resistance genes for future breeding strategies for net-type net blotch. Four diverse lines WA 4794, Pompadour, CI 9214 and WPG8412-9-2-1 were selected to study inheritance of resistance and genetically map those resistances under the National Barley Molecular Marker Program. Doubled haploid lines from crosses with these parents have been generated and screening is in progress.

Acknowledgments

This research was supported by GRDC and the Western Region Malting Barley Improvement Programme. We thank G. Platz for providing net-type net blotch isolates.