Development of an evaluation system for Fusarium resistance in wheat grains and its application in assessment of the corresponding effects of Fhb1

Authors: GONG, XUAN - Yangzhou University; HE, XIANYAO - International Maize & Wheat Improvement Center (CIMMYT); ZHANG, YUHUI - Yangzhou University; LI, LEI - Yangzhou University; XUN, ZHENGXI - Yangzhou University; Bai, Guihua; SINGH, PAWAN - International Maize & Wheat Improvement Center (CIMMYT); LI, TAO - Yangzhou University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2020
Publication Date: 6/8/2020
Citation: Gong, X., He, X., Zhang, Y., Li, L., Xun, Z., Bai, G., Singh, P.K., Li, T. 2020. Development of an evaluation system for Fusarium resistance in wheat grains and its application in assessment of the corresponding effects of Fhb1. Plant Disease. https://doi.org/10.1094/PDIS-12-19-2584-RE.
DOI: https://doi.org/10.1094/PDIS-12-19-2584-RE

Interpretive Summary: Fusarium head blight (FHB) is an important disease of wheat and barley that results in lower yields, shriveled kernels, and contamination with mycotoxins. Fhb1 is the most important and widely used resistance gene against FHB in wheat. Fhb1 has been shown to reduce disease spread within a wheat spike, but effects on other types of resistance were unclear. We used wheat lines with or without Fhb1 to study the direct effect of Fhb1 on kernel infection rate and kernel weight. The resistant and susceptible lines showed no differences in infection rate with the fungus. However, lines with Fhb1 showed a greater reduction in individual kernel weight than in susceptible lines. This was confirmed by microscopic observation of greater starch granule degradation in lines with Fhb1. This research clarified our understanding of different types of resistance to FHB. It also showed that the resistance gene Fhb1 provides no direct resistance to kernel infection or degradation.

Technical Abstract: Fusarium head blight (FHB) caused by Fusarium species is a globally important wheat disease. Host resistance to FHB is composed of multiple mechanisms, including resistance to initial infection (type I), disease spread (type II), toxin accumulation (type III), kernel infection (type IV), and yield loss (type V), of which the last three have been less studied. Traditionally, the Fusarium-damaged kernel rate (FDK; percentage of Fusarium-infected grains) from point- or spray-inoculated experiments was used as the parameter for type IV resistance, which may be problematic because of the influence of type II resistance. Here we propose a new definition for type IV resistance: that is, the resistance against Fusarium infection expressed in wheat grains that have the same chance in contact with the pathogen, under favorable temperature and humidity for infection. Fhb1 confers strong type II resistance, leading to significantly reduced FHB severity and FDK. To investigate the role of Fhb1 in type IV resistance, a pair of near-isogenic lines, R22W (Fhb1 carrier, resistant in terms of type II resistance) and S22V (non-Fhb1, susceptible), along with eight wheat genotypes differing at Fhb1 were inoculated at different grain development stages with Fusarium macrospores both in vivo and in vitro. The in vivo experiments with all florets inoculated demonstrated a significant reduction in thousand kernel weight (TKW) in inoculated grains, regardless of their Fhb1status and developmental stages. Surprisingly, R22W showed more TKW reduction than S22V, which was supported by the scanning electron microscopy observation that confirmed the more severe degradation of starch granules in R22W grains. The in vitro experiments demonstrated that grains from both R22W and S22V promoted fungal colonization, but no significant difference was found between the two lines. In summary, our results indicated that the proposed type IV evaluation system is effective in determining different grain resistance levels, providing novel tools for FHB resistance breeding. The finding that Fhb1 is not associated with type IV resistance enriches our understanding of this gene.