Recipient Organization
VIRGINIA POLYTECHNIC INSTITUTE
(N/A)
BLACKSBURG,VA 24061
Performing Department
Plant Pathology Physiology & Weed Science
Non Technical Summary
Gray leaf spot (GLS) of corn (Zea mays L.), initially a disease caused by the fungus, Cercospora zeae-maydis (Tehon and Daniels, 1925)(formerly known as C. zeae-maydis Group I) which is found in the United States, Canada, Mexico, and Brazil or Cercospora zeina (formerly known as C. zeae-maydis Group II) which is reported in the eastern third of the United States, Brazil, and sub-Saharan Africa (Wang et al., 1998, Dunkle and Levy 2000, Goodwin et al., 2001, Zhu et al., 2002, Okori et al., 2003, Shim and Dunkle 2005, Crous et al., 2006, Brunelli et al., 2008, and Meisel et al., 2009). No-tillage or reduced tillage maize production was recognized as the main contributing factor in GLS (Beckman et al, 1981; Beckman and Payne, 1982; Hilty et al, 1979; Latterell and Rossi, 1983; Roane et al, 1979; Stromberg, 1984; Stromberg and Donahue, 1986 and Asea et al., 2005). GLS is now recognized as one of the most significant yield-limiting diseases of maize worldwide (Lipps et al, 1998; Nutter and Jenco, 1992; and Ward and Nowell, 1998). GLS now poses a serious threat to maize production in many areas of the eastern United States, and more recently large areas of the U.S. Corn Belt and Africa (Lipps et al., 1998; Nowell, 1997; Nutter and Jenco, 1992; Nutter et al., 1994; Ringer and Grybauskas, 1995; Ward, 1996; Ward et al., 1999). GLS has become a serious disease in many parts of Sub-Saharan Africa. In the Republic of South Africa (RSA) GLS was first identified on the continent in the early 1990?s in KwaZulu-Natal Province and severe epidemics, resulting in significant economic losses, have occurred since the 1992/93 season (Givers and Lake, 1994). During my visit (February-March 1997) to RSA and Zimbabwe, I observed severe levels of GLS throughout the maize growing areas of KwaZulu-Natal and Zimbabwe. In addition to the United States and Africa, GLS has been reported in Brazil, Columbia, Peru, Trinidad, Costa Rica, Mexico, and Venezuela (Boothroyd, 1964; Chupp, 1953; and Latterell and Rossi, 1983). GLS has been recognized recently as a yield-limiting disease of maize in China (Coates and White, 1995), particularly in the Jilin Province (D.G. White3, personal communication).
Animal Health Component
(N/A)
Research Effort Categories
Basic
(N/A)
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
1. Evaluate selected commercial, public, and experimental hybrids, inbreds, and maize germplasm for resistance to Cercospora zeae-maydis, causal agent of gray leaf spot, under natural disease pressure in continuous no-tillage production. New sources of resistance to gray leaf spot will be identified and used for the development of hybrids for commercial production by seed companies. 2. Critically define the expression of disease and inheritance of resistance in newly identified resistant x susceptible F2 populations. Where applicable sources of resistance will be critically studied and QTLs for resistance will be mapped and molecular markers can be developed to assist in resistance breeding. 3. Evaluate new and novel fungicide chemistry for efficacy in control of GLS and correlate with yield losses with severity of leaf blighting. Better fungicide treatment strategies will be identified and promoted.
Project Methods
Objective 1: Hybrids are evaluated for resistance, grain yield, lodging, and grain moisture at harvest. Plot area is in continuous no-tillage maize production with abundant maize debris heavily infested with Czm. Hybrids will be no-tillage planted in four rows at a final population of approximately 58,000 plants/ha in a randomized complete block design with four replications. The two middle rows of each plot will be scored 3 to 4 times during the growing season for leaf blighting. A Disease Severity Index (DSI) ranging from 0-5 increments where: 0 = no symptoms; 1 = trace of lesions below ear leaf, none above; 2 = many lesions below ear with trace above ear; 3 = severe lesion development below ear and some lesions on leaves above ear; 4 = all leaves show severe lesion development, but green tissue is still visible; and 5 = all leaves dead. The two middle rows will be scored for lodging. Plants within these rows will be mechanically harvested to record grain yield and grain moisture. Grain yield will be expressed as 15.5% moisture as kg/ha and as bushels per acre. Objective 2: As resistant inbred germplasm is identified, it may be crossed with a susceptible inbred (e.g. B73 or Mo17) to produce an F2 population segregating for resistance to GLS. At least 750 individuals from an F2 population will be planted in single row plots in the GLS nursery with a no-tillage cone planter. The seed will be planted in 3.5-m long rows spaced 0.76 m apart. Plants tagged to maintain identity and self-pollinated and an F3 generation produced for possible further evaluation. Leaf discs from each individual will be used for DNA extraction and molecular characterization. Each plant will be scored for DSI and lesion type over a 5 or 6 week period when GLS lesions first appear. DSIs for individual plants within an F2 population will be used in statistical analyses for interval mapping for QTLs for resistance. Construction of a maize RFLP linkage map from F2 data will be based on the Mapmaker computer program (Lander et al, 1987). Objective 3: A high yielding, adapted and highly susceptible to Czm will be used. It will be planted in four row units in an identical manner described in Objective 1. Treatments will consist of fungicide compounds and/or combinations applied one or more times during the season to the two middle rows of each plot. Applications will be made with a CO2-pressurized backpack sprayer equipped with a single Tee-Jet 8004 flat fan nozzle. Fungicide solutions and a water control will be applied at 400kPa and delivering 235 l/ha. DSIs will be determined and plots will be mechanically harvested as in Objective 1. Grain yield at a standard 15.5% moisture, 500 seed weights, grain moisture at harvest, and percentage lodging will be determined for each plot unit. Data analysis for evaluating fungicide efficacy as determined by DSI will be subjected to regression analysis for grain yield, 500 seed weights, grain moisture, and percentage lodging at harvest using standard ANOVA techniques. Regression analysis will be used to associate DSI at a stage of maize developmental growth stage with grain yield.