Temporal progress of southern rust in maize under different environmental conditions

Abstract

The progress of the severity of southern rust in maize (Zea mays) caused by Puccinia polysora was quantified in staggered plantings in different geographical areas in Brazil, from October to May, over two years (1995-1996 and 1996-1997). The logistic model, fitted to the data, better described the disease progress curves than the Gompertz model. Four components of the disease progress curves (maximum disease severity; area under the disease progress curve, AUDPC; area under the disease progress curve around the inflection point, AUDPCi; and epidemic rate) were used to compare the epidemics in different areas and at different times of planting. The AUDPC, AUDPCi, and the epidemic rate were analyzed in relation to the weather (temperature, relative humidity, hours of relative humidity >90%, and rainfall) and recorded during the trials. Disease severity reached levels greater than 30% in Piracicaba and Guaíra in the plantings between December and January. Lower values of AUDPC occurred in later plantings at both locations. The epidemic rate was positively correlated (P < 0.05) with the mean daily temperatures and negatively correlated with hours of relative humidity >90%. The AUDPC was not correlated with any weather variable. The AUDPCi was negatively related to both variables connected to humidity, but not to rain. Long periods (mostly >13 h day-1) of relative humidity >90% (that corresponded to leaf wetness) occurred in Castro. Severity of southern rust in maize has always been low in Castro, thus the negative correlations between disease and the two humidity variables.

Genetic diversity, population structure and AFLP markers associated with maize reaction to southern rust

“…The high temperatures observed in the first crop might be inadequate to the P. polysora development, exceeding the 25 °C, described as optimum to the pathogen (Godoy et al 1999;Raid et al 1988). Furthermore, according to Godoy et al (2003) late sowings commonly show higher inoculum presence which, associated to ideal weather conditions, can result in severe epidemics of southern rust.…”

Reaction of selected common bean germplasm accessions to bacterial brown spot in South Africa

“…The AUDPC indicates total disease intensity (Campbell and Maiden, 1990), expressing the dynamics of an epidemic as a single value (Haynes et al, 2004). Godoy et al (2003) reported that AUDPC values are indicative of long-term environmental effect such as climate, as opposed to temporary factors such as temperature.…”

Global risk levels for corn rusts (Puccinia sorghi and Puccinia polysora) under climate change projections

“…These values allow the disease to persist in India, Madagascar and New Zealand. The maximum cardinal temperature for preceding infection period of P. polysora was estimated at 42°C and for the infection period the value ranges from 27 to 32°C (Cammack, ; Godoy et al., ; Pivonia & Yang, ). In agreement with the previous experimental values, the TTHS was set at 34°C and its accumulation rate at 0.0002 per/week.…”

“…In crops, fungal and bacterial diseases are mainly dependent on the availability of a susceptible host, but climate is also a key determinant influencing the pathogens’ rate of growth, infection and dissemination (Godoy et al., ; Pavgi & Dickson, ). In the cereal rusts, temperature and humidity are the major determining factors for spore germination, penetration, establishment and spread of the disease (Pavgi, ).…”