Spatial distribution and association of factors influencing the Gibberella ear rot development and accumulation of mycotoxins in maize grains in multiple agroecosystems in Ethiopia

Abstract

Maize (Zea mays L.) is an important crop globally, including in Ethiopia, where it plays a significant role in food security. However, fungi, particularly Fusarium species, pose significant threats to food safety and security worldwide. Among these fungi, the Fusarium graminearum species complex (FGSC) is a major pathogen that causes Gibberella ear rot (GER) in maize. In addition to reducing yield, FGSC pathogens produce harmful mycotoxins, primarily deoxynivalenol (DON), Deoxynivalenol-3-glucoside (DON-3G), zearalenone (ZEN), and nivalenone (NIV). Thus, disease assessment was conducted to identify the distribution of GER, as well as the associated production practices and biophysical factors, affecting the disease development in southern and western Ethiopia during 2020 and 2021. This study also aimed to analyze the concentrations of mycotoxins (DON, DON-3G, and ZEN) in field samples. The survey revealed significant differences (p < 0. 001) in GER intensity and grain yield loss across the assessed zones. The highest disease severity and corresponding estimated grain yield loss were observed in West Wallaga, while the Gurage zone had the lowest disease severity and yield loss. All the maize samples (n = 52) contained ZEN, while more than 75% of the samples tested positive for DON and DON-3G. Mycotoxin contamination levels ranged from 1 to 4291 µg kg⁻¹ (a mean 635 µg kg⁻¹) for DON, 1 to 1554 µg kg⁻¹ (a mean 174 µg kg⁻¹) for DON-3G, and 6 to 2236 µg kg⁻¹ (a mean 202 µg kg⁻¹) for ZEN. The frequency and levels of mycotoxins in this study were greater than those reported in previous studies on maize in Ethiopia. This could be attributed to less adoption of the recommended production practices by most farmers in the area and varying environmental factors that could favor the disease. Moreover, 25% of the maize samples exceeded the European Union's recommended value for ZEN and DON in unprocessed cereals. The severity of GER disease was significantly and positively correlated with biophysical factors like insect and weed infestations, but significantly negatively correlated with production/agronomic practices such as the correct fertilizer applications and use of resistant/tolerant maize hybrids. The right sowing date and cropping methods also significantly influenced the variation in GER disease intensity among the maize farms. Furthermore, there was a strong positive association between disease severity and the concentrations of DON, DON-3G, and ZEN in maize kernels. Overall, the study highlighted the necessity for integrated approaches to manage GER and associated mycotoxins. The role of agronomic practices under varying environmental conditions is not fully understood, but implementing preharvest ear rot management strategies can help mitigate GER disease and the associated mycotoxin risks.