Effect of Cercospora zeae‐maydis infested maize residue on progress and spread of grey leaf spot of maize in central Uganda

Abstract

The spread of grey leaf spot caused by Cercospora zeae-maydis from infested maize residue on the soil surface and progress over time were studied under tropical conditions at two locations in central Uganda, Kabanyolo and Namulonge, using a susceptible local cultivar, LP16. Infested maize residue collected the previous season was used as the inoculum source in varying amounts; 80% coverage, 40% coverage and 0% soil coverage were used to simulate no tillage, minimum tillage and maximum tillage with complete burial of residues. In all the seasons, disease spread was adequately described by a power law model, whereas disease progress over time was equally well represented by both Gompertz and logistic models. The time factor was highly significant (P < 0.05) for disease development, indicating both increases in disease intensity over time and change in gradients with time. The amount of infested residue on the soil surface in the maize planting was highly significant (P < 0.05) for slope (b) and intercept (a) of the linearised disease gradient. The gradient parameter (b) based on the average for the four directions from the residue source ranged from -0.96 to -0.08 in the second cropping season of 1999, from -2.16 to -0.01 and from -0.87 to -0.03 in the first and second seasons of 2000, respectively. The distance from the infested residue significantly affected foliar disease, but the direction from the residue inoculum source did not, nor was the distance by direction interaction significant. However, interactions between amount of residue and distance were significant. Percentage leaf area affected by grey leaf spot, the areas under disease progress curves and disease intercepts decreased with distance at both locations, but rate of disease increase (r) was generally constant with distance from residue source at Kabanyolo, but not at Namulonge. The relationship between disease severity and amount of residue cover appeared to be affected by the level of background inoculum. At Kabanyolo, where little background inoculum was present, differences were detected in disease severity parameters between the no-residue plots and residue plots, whereas at Namulonge, where high background levels existed, there was no effect of residue on disease.

Local dispersal of Puccinia striiformis f. sp. tritici from isolated source lesions

“…Several studies examining rust dispersal in crop canopies have been undertaken. However, sources of inoculum for these studies have most often contained enough propagules to form several, in some cases several thousand, initial infections on individual plants (Willocquet et al ., ), on several plants within a focal area (Asea et al ., ; Sackett & Mundt, ), or on entire fields (Gitaitis et al ., ). More recently, it was demonstrated that the highly local dissemination of wheat leaf rust requires the study of individual lesions if the full epidemiological impacts of dispersal gradients are to be understood (Lannou et al ., ).…”

A review on threat of gray leaf spot disease of maize in Asia

“…The infected residue of a previous crop left over the soil surface is the principal source of inoculums. There was a strong positive correlation between the amount of infected maize residue and disease inoculums (Asea et al, 2002;de Nazareno et al, 1993a). They reported that disease intensity was higher in a high residue treated plot than a non treated plot.…”

Identification and diversity of tropical maize inbred lines with resistance to common rust (Puccinia sorghi Schwein)

“…The major foliar diseases of economic importance in the mid‐altitude and highland ecologies of ESA are northern corn leaf blight (NCLB) caused by Exserohilum turcicum (Pass.) Leonard & Suggs (Pratt et al., 2003; Vivek et al., 2010), gray leaf spot (GLS) caused by Cercospora zeae‐maydis Tehon & Daniels (Asea et al., 2002; Bigirwa, Pratt, Adipala, & Lipps, 2001; Menkir & Ayodele, 2005; Ward, Stromberg, Nowell, & Nutter, 1999), and common rust caused by Puccinia sorghi Schwein (CABI, 2019; Fininsa & Yuen, 2001; Vivek et al., 2010).…”