Gibberella is a widespread fungus posing significant challenges in agriculture. This fungal genus can cause considerable damage to various crops. Its presence leads to reduced crop yields and diminished quality, impacting farmers and the broader food supply.
Understanding Gibberella
Gibberella is a genus of fungi, with Gibberella zeae being the most recognized species in agriculture. This fungus is also known by its asexual form, Fusarium graminearum, and is a plant pathogen. It survives and overwinters on crop residues, such as corn stalks and wheat straw.
The fungus produces spores, which are dispersed through wind, rain splash, or insects to susceptible host plants. Warm temperatures, typically between 25°C and 28°C, combined with high humidity, create favorable conditions for the growth and spread of Gibberella zeae.
Diseases Caused by Gibberella
Gibberella zeae is responsible for several plant diseases, notably Fusarium Head Blight (FHB) in small grains like wheat and barley, and Gibberella Ear Rot (GER) in corn. FHB, also known as scab, primarily affects the heads of small grain cereals, causing premature bleaching or blighting of spikelets. Infected spikelets may show pink or orange spore masses, especially during wet, humid weather. Infected kernels become shriveled, discolored, and lightweight, often referred to as “tombstones”.
In corn, Gibberella zeae causes Gibberella Ear Rot, characterized by a reddish-pink or sometimes white mold that starts at the ear tip and spreads downwards. The mold can grow between kernels and underneath the husk, sometimes causing the husk and silks to adhere tightly to the ear, giving it a “mummified” appearance. Infection often occurs through the silk channels during silking, particularly when cool, wet, or humid conditions persist. Secondary infections can also happen through wounds caused by insects, birds, or hail, allowing the pathogen to enter the kernels.
Mycotoxins and Their Impact
Beyond causing visible disease symptoms, Gibberella zeae produces harmful compounds called mycotoxins. The most common mycotoxins associated with Gibberella infection are deoxynivalenol (DON), often called vomitoxin, and zearalenone (ZEN). These mycotoxins pose health risks to both humans and livestock when consumed through contaminated grain.
Deoxynivalenol (DON) can cause digestive issues, including vomiting and feed refusal, particularly in swine, leading to weight loss. In humans, consumption of DON-contaminated wheat can lead to symptoms such as headaches, abdominal pain, and diarrhea. Zearalenone (ZEN) is an estrogenic mycotoxin that can mimic natural estrogens in mammals, leading to reproductive problems in livestock, such as infertility and reduced fertility, especially in pigs. The presence of these mycotoxins in crops leads to significant economic losses due to reduced grain quality, lower market prices, and rejection of contaminated loads at grain elevators.
Managing Gibberella and Its Diseases
Managing Gibberella and its associated diseases involves agricultural practices aimed at reducing fungal inoculum and minimizing infection. One effective strategy is to select and plant crop varieties with improved resistance or tolerance to Gibberella ear rot and Fusarium head blight. While no entirely resistant varieties are available, some hybrids offer defensive mechanisms that can slow fungal growth.
Proper crop rotation is also beneficial, as the fungus overwinters in crop residue. Rotating small grains with non-host crops like soybeans can reduce pathogen inoculum in the soil. Tillage practices that incorporate crop residues into the soil can also break down infected plant material, reducing fungal survival and spore production. Fungicide applications, particularly around the flowering stage for wheat and silking for corn, can help protect plants from infection and reduce disease severity. Post-harvest grain management, including drying grain and proper storage, is important to prevent further mold development and mycotoxin accumulation.