Seed treatments enhance photosynthesis in maize seedlings by reducing infection with Fusarium spp. and consequent disease development in maize

Authors: RODRIGUEZ-BRLJEVICH, CARLOS - Samosol; KANOBE, CHARLES - Iowa State University; Shanahan, John; ROBERTSON, ALISON - Iowa State University

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2009
Publication Date: 2/1/2010
Citation: Rodriguez-Brljevich, C., Kanobe, C., Shanahan, J.F., Robertson, A.E. 2010. Seed treatments enhance photosynthesis in maize seedlings by reducing infection with Fusarium spp. and consequent disease development in maize. European Journal of Plant Pathology. 125:343-347. Available: http://www.springerlink.com/content/w411360561r31um3/

Interpretive Summary: Maize is susceptible to infection by numerous species of Fusarium fungal pathogens. Disease symptoms caused by Fusarium species include early-season seedling blights (seed, root, and mesocotyl rot) and crown, stalk and ear rots in late season. Since seedling blights result in stand loss, virtually all maize seed planted in the US Corn Belt is treated with fungicide applied as seed dressing. The effectiveness of seed-treatment fungicides are usually evaluated in field trials, with emergence and plant height used as an indication of plant vigor, and yield used to demonstrate product effectiveness. However, these data provide very little information regarding the effects of seed treatments on infection of the maize plant by specific pathogens and subsequent disease development. Collection of such data relies on destructive sampling and assessments that may be subjective. An enhanced understanding of the effect of seed treatments on the Fusarium-maize pathosystem would enable better seedling disease management. Furthermore, data pertaining to the effect of seed treatments, if any, on the physiology of the developing maize plant would be of interest. Reduced photosynthetic performance has been associated with plant stress. In the tomato pathosystem, chlorophyll fluorescence (CF) was found to be a suitable indicator of plant stress as a result of infection. Similarly photosynthetic performance (as measured by CF) in maize plants infected with Fusarium was shown to be reduced compared with uninfected plants. Presumably, reduced photosynthesis in hosts that were infected by Fusarium occurred due to root and mesocotyl tissue damage associated with infection, as well as systemic colonization of the host that interfered with normal absorption and transport of water and nutrients by the roots and mesocotyl. Assessments of CF could serve as an indirect method to measure plant vigor reduction related to infection of germinating maize seedlings by soil-borne pathogens and/or an estimator of disease severity and therefore be a valuable tool to assess the effectiveness of seed treatments on seedling disease. Furthermore, CF measurements could be used to assess the effect of seed treatments on the photosynthetic performance of maize plants. The goal of this study was to enhance our understanding of the effect of seed treatment on the maize-Fusarium pathosystem and on photosynthetic performance of maize seedlings in the field. Our primary objective was to evaluate if CF measurements have a significant relationship with seedling vigor, disease severity and incidence of Fusarium infection of maize seedlings. Field trials were planted at the Iowa State University (ISU) Southeast Research Farm (SERF), near Crawfordsville, Iowa and the ISU Northeast Farm (NERF) at Nashua, Iowa. At both sites, the fields chosen had been in a continuous-maize rotation for four years to encourage Fusarium infestation. Maize seed was either treated with Cruiser Extreme 250® (azoxystrobin + fludioxonil + mefenoxam + thiomexoam) using a Gustafson® (modelBLT) seed treater or was left untreated. Plant height was assessed at growth stages V4 and V6. Root, mesocotyl and crown rot severity, incidence of Fusarium colonization and chlorophyll florescence (CF) (estimate of photosynthetic performance) were assessed at growth stages V2, V4 and V6. Stalk rot severity was assessed at growth stage R6. Results at both locations showed seed treatment reduced disease severity and incidence of Fusarium infection at all growth stages assessed. Measurements of the CF parameter 'PSII decreased significantly with increased disease severity and higher incidence of Fusarium at growth stages V2 and V4 at both locations, indicating that seedling disease due to infection by Fusarium negatively affects photosynthetic performance in maize seedlings. Furthermore, 'PSII measurements were greater in mo

Technical Abstract: The effects of a seed treatment on early season growth, seedling disease development, incidence Fusarium spp. infection, and photosynthetic performance of maize were evaluated at two locations in Iowa in 2007. Maize seed was either treated with Cruiser 2Extreme 250 ® (fludioxonil + azoxystrobin + mefenoxam + thiamethoxam) or not treated. Plant height was assessed at growth stages V4 and V6. Root, mesocotyl and crown rot severity, incidence of Fusarium spp. colonization and chlorophyll florescence (CF) (estimate of photosynthetic performance) were assessed at growth stages V2, V4 and V6. Stalk rot severity was assessed at growth stage R6. At both locations, seed treatment reduced disease severity and incidence of Fusarium spp. infection at all growth stages assessed. Measurements of the CF parameter 'PSII decreased significantly with increased disease severity and higher incidence of Fusarium spp. at growth stages V2 and V4 at both locations, indicating that seedling disease due to infection by Fusarium spp. negatively affects photosynthetic performance in maize seedlings. Furthermore, 'PSII measurements were greater in more vigorous seedlings as determined by plant height. Relationships occurred between mesocotyl rot severity at V4 and crown rot severity at V6 at both locations and crown rot at V6 and stalk rot at R6 at one location.