While the global banana planting industry is developing rapidly, banana crops are suffering from various diseases. The most typical and threatening one is banana fusarium wilt. Banana wilt is also known as yellow leaf disease, banana Panama disease, or banana fusarium. For banana crops, it is a devastating soil-borne disease. The pathogen is Fusarium oxysporum.
The disease was first reported by Joseph Bancroft in Australia in 1874 and was first discovered in Hawaii in 1904. Since Brandes proved that the pathogen(Fusarium oxysporum) is pathogenic in 1919, banana fusarium wilt has shown large outbreaks of varying degrees in growing areas around the world. From 1935 to 1939, the disease had a serious impact on the banana planting industry in South America. In the 1950s, the disease broke out in Panama, Colombia, Costa Rica, Honduras, and other countries, and about 40,000 square hectares of banana plantations were destroyed.
At present, the disease is widely distributed in major banana-producing areas such as Africa, Asia, Australia, and tropical America. In fact, almost all banana-growing areas suffer from the banana fusarium wilt. The world banana industry is facing the most serious threats and challenges in its history.
Why is Fusarium oxysporum so harmful
Fusarium oxysporum is a typical soil-borne disease. The pathogen can survive in the surface soil in the form of hyphae and chlamydospores for a long time. It has been documented that the pathogenic chlamydospore spores can survive in the soil for as long as 5 years and can withstand harsh environments. This provides ample opportunities for pathogen infection, spread, and harm.
Pathogens invade from the injured roots of the host, spread upward along with the vascular bundles and spread to the upper part of the leaves and pseudostem, and produce toxins or colloids to block the host’s transport tissue, and eventually cause the host’s entire plant to wither and die.
After infecting the host, Fusarium wilt has a certain incubation period. It takes about 1-2 months to inoculate the sprouts, and it takes more than 3-5 months for the infection to occur under natural conditions.
The local incidence of the disease is very high, the affected fields have obvious disease centers, and the speed of transmission is fast.
Fusarium oxysporum can be spread over long distances through seedlings with bacteria, agricultural machinery, and equipment. At the same time, pathogens can also spread through short distances through diseased plant residues, conidia, agricultural tools, irrigation water, nematodes, etc. The hot and rainy climate is conducive to the infection and spread of banana wilt.
At the same time, acidic soil, low organic matter, heavy soil quality, poor drainage, poor soil permeability, and improper farming management are all conducive to the occurrence of this disease.
Symptoms of Banana Fusarium Wilt
The typical characteristics of banana wilt are plant withering and vascular bundle discoloration and rot, which can be infected from the young to the adult stage.
The first symptom of the diseased plant is that the lower leaves turn into a special yellow, and expand from the edge of the leaf to the middle of the leaf ridge. The petiole near the leaf sheath begins to bend, and finally, the whole leaf changes from yellow to brown and hangs upside down beside the pseudostem.
At the same time, the leaves also developed successively from bottom to top, turning yellow, drooping, browning, and withering until the last top leaf withered. From the onset to the rot and fall, the diseased plant can generally remain upright for 1-2 months, and then due to the influence of certain bacteria or nematodes on the host’s vascular bundle, the symptoms of banana wilt may change.
After pathogenic bacteria invade the host, they mainly produce toxins, hormones and enzymes, and other active substances that harm the host plant. Banana Fusarium wilt bacteria toxin contains fusaric acid and dehydrofusaric acid.
Among them, fusalic acid is one of the main toxins of Fusarium wilt. It can reduce the vitality of plant cells by inhibiting the activity of host defense enzymes, increasing active oxygen in cells, changing cell membrane permeability or membrane potential, and disrupting host physiological metabolism.
At present, there is no effective chemical agent for controlling banana fusarium wilt. Planting disease-resistant varieties, crop rotation with aquatic crops, and biological control are currently more effective ways to prevent banana wilt.
The biological control of banana wilt has just started, mainly focusing on the screening of antagonistic bacteria of banana wilt and indoor control experiments. Tests have proved that the control effect of Trichoderma harzianum on banana wilt is 48% to 51%; Pseudomonas fluorescens can induce plant resistance to inhibit banana wilt, and Bacillus subtilis also has a better control effect. Experiments have proved that the combination of planting of resistant varieties and application of biocontrol bacteria can achieve more than 95% of the control effect on banana wilt.
According to research, it has been found that Trichoderma can effectively inhibit the activities of Fusarium oxysporum through a series of anti-parasitic, antibiotic, bacteriolytic, and growing competition.
Trichoderma has strong vitality and rapid reproduction. The ability to compete for living space and nutritional resources is extremely high, and it can reject and inhibit Fusarium oxysporum. Trichoderma hyphae re-parasitizes on the hyphae of Fusarium oxysporum by winding, interspersing, clinging, etc., and invade the hyphae of Fusarium oxysporum to absorb nutrients.
It dissolves the cell wall and enters the parasitic hyphae and grows in it, deforming the hyphae of Fusarium oxysporum and shortening the cells. Finally, the pathogenic bacteria broke and disintegrated. The anti-biomass produced by Trichoderma during the growth process can effectively inhibit the growth and spore germination of Fusarium oxysporum, so that the cytoplasm of Fusarium oxysporum hyphae is decomposed, the protoplasm is condensed, and it gradually decays and inactivates and disintegrates.
At present, banana wilt disease has entered a rapid expansion stage, and banana production is facing a huge threat. When chemical control is ineffective, it is imperative to strengthen biological control.
Therefore, a large number of repeated field applications of bacteria with antagonistic effects on banana fusarium wilt has become an urgent problem to be solved.
The soil is a symbiosis place of multiple microorganisms. It may be more effective to choose a strain that can symbiotically and antagonizes banana Fusarium wilt to jointly control banana Fusarium wilt.