A high‐throughput glasshouse bioassay to detect crown rot resistance in wheat germplasm

Abstract

A high-throughput and reliable seedling bioassay to screen wheat germplasm for crown rot resistance was developed. Single wheat seedlings were grown in square seedling punnets in a glasshouse and inoculated with a monoconidial Fusarium pseudograminearum isolate 10 days after emergence. The punnets were laid horizontally on their side and a 10-µ L inoculum droplet placed on the stem base. Seedlings were incubated at near-saturated relative humidity, and crown rot severity was assessed 35 days after inoculation. Studies on the duration of incubation period, inoculum concentration and temperature were carried out to optimize these parameters. Seedling growth at 25/15( ± 5) ° C in a glasshouse and 48-h incubation at near-saturated RH in darkness gave the best results. When crown rot resistance rankings of 16 Australian cultivars from the bioassay were compared with their field performance, Spearman's rank correlation coefficient was highly significant. This indicated that the seedling bioassay mimicked field resistance to crown rot in adult plants. A bootstrap resampling analysis showed little or no improvement in the coefficient of variation with an increasing number of replications, indicating a high level of precision and reproducibility. By detecting small but consistent differences in crown rot severity, the bioassay proved effective in large-scale screening for partial resistance: already over 1400 wheat genotypes have been screened. The high degree of precision makes this an invaluable tool in the understanding of pathogen aggressiveness, host specialization and parasitic fitness.

Pyramiding QTL increases seedling resistance to crown rot (Fusarium pseudograminearum) of wheat (Triticum aestivum)

“…This highlights the reproducibility of the Wildermuth and McNamara (1994) method used for assessing plant responses to seedling infection with F. pseudograminearum. A number of alternative methods for phenotyping seedlings infected with F. pseudograminearum have recently been reported (Mitter et al, 2006;Li et al, 2008). These approaches use conidial suspensions placed on the stem rather than a sub-surface band of ground, colonised grain as an inoculum.…”

Different genes can be responsible for crown rot resistance at different developmental stages of wheat and barley

“…The glasshouse-based assays are preferred for assessing seedling resistance. Clearly, seedling resistance may or may not reflect resistance of adult plants, although CR reactions obtained from several of the seedling-based assays show strong correlation with field rankings (Klein et al 1985;Wildermuth and McNamara 1994;Mitter et al 2006;Li et al 2008). Nevertheless, seedling resistance forms an essential part in minimizing CR damage.…”

Multilocus sequence analysis of Fusarium pseudograminearum reveals a single phylogenetic species

“…Crown rot caused by F. pseudograminearum is a chronic problem in Australia and is becoming recognised as more widely dispersed pathogen of wheat worldwide (Mitter et al 2006;Nicol et al 2004). The ability of strains and/or species from geographically separated locations to recombine, poses the danger of introducing virulence and/or toxigenic genes into local pathogen populations.…”