Culm discolouration as an indicator of Fusarium pseudograminearum biomass

Abstract

Disease severity of crown rot (Fusarium pseudograminearum) in winter cereal culms is typically assessed at harvest maturity by recording incidence of infection, whitehead production and discolouration of basal internodes. This study has investigated the relationship between the proportion of discolouration of individual internodes and the extent of host tissue colonisation by the pathogen, based on species-specific quantitative PCR (qPCR). Field-grown p l ots w er e u se d t o c om pa re vis ua l ra tin gs an d F. pseudograminearum DNA content of eight cereal genotypes (six hard white spring wheats, one durum wheat and one barley) at 16 and 22 weeks after planting (WAP) in 2009 and 2013. At 16 WAP (post anthesis -early milk development) strong correlations were present between visual discolouration and fungal DNA content per unit of tissue weight for internodes one, two and three in 2009 and 2013. At 22 WAP (harvest maturity) these relationships were only significant for internode two in 2009 and internode three in the 2013 trial. Differences in both visual symptoms and fungal DNA content between the genotypes occurred at both sample times, but the most significant distinction between genotypes was at 16 WAP. We conclude that visible discolouration of cereal culms is a useful indicator of fungal biomass in culm tissue, as estimated by qPCR. Furthermore, assessment of diseased culms at 16 WAP provides a stronger correlation with fungal colonisation and discriminates more clearly between disease reactions in different host genotypes, in comparison to assessment at harvest maturity.

Disease responses of hexaploid spring wheat (Triticum aestivum) culms exhibiting premature senescence (dead heads) associated with Fusarium pseudograminearum crown rot

“…The current study included a time-course examination of the impact of plant maturation on crown rot disease responses. While assessment was only performed in one year, the findings support those of Knight and Sutherland (2015), in which a plateau or reduction in F. pseudograminearum biomass was observed in two hexaploid spring wheat genotypes at maturity. The current study demonstrated that within cv.…”

“…Knight et al (2012) described similar variation in cereal seedling tissues, and supported the use of plant tissue dry weights as an alternative normalising factor. bioRxiv Timing of tissue collection may have a strong influence on crown rot disease measurement, along with individual cultivar growth patterns, growth stage and environmental variation (Hogg et al, 2007;Knight et al, 2012;Knight & Sutherland, 2015;Knight & Sutherland, 2016;Knight et al, 2017;Percy et al, 2012;Smiley, 2019;Stephens et al, 2008;Summerell et al, 1989). The current study included a time-course examination of the impact of plant maturation on crown rot disease responses.…”

“…The inoculated experimental trial was grown in the third year of the rotation. Further details of Wellcamp and Narrabri field site preparation, planting, inoculum production and inoculation are described by Knight & Sutherland (2015) and Knight et al (2017). Tamworth samples were from a trial planted in a field with naturally occurring crown rot inoculum.…”

Competition Between Fusarium pseudograminearum and Cochliobolus sativus Observed in Field and Greenhouse Studies

“…Disease severity score was calculated by summing the number of tillers in each severity category and multiplying by the value of the category, then dividing by the total number of tillers scored. Significant correlations between disease severity score and both Fusarium populations and yield have been reported (Hogg et al 2007;Knight and Sutherland 2015).…”

Fusarium crown rot caused by Fusarium pseudograminearum in cereal crops: recent progress and future prospects

“…The measurement of stem base browning is often used as a proxy for the evaluation of cereal germplasm for FCR resistance. Knight and Sutherland () found positive correlations between stem base browning and fungal biomass measured using qPCR in wheat and barley in a 2‐year field study. However, these correlations were significant for different internodes of infected plants in different years.…”