The present invention relates to a method of introducing a symbiotic fungus into a plant. More particularly, the present invention relates to a method of introducing an endophyte whose final metabolic product is a chanoclavine to a plant.
Japanese Patent Publication (Kokai) No. 05-317092 has disclosed a method of artificially introducing an endophyte to perennial rye grass. In the method, a test is first performed to confirm whether the endophyte is living in a plant tissue such as callus derived from perennial rye grass. After the callus is confirmed to contain no endophyte, the endophyte is introduced into the callus and the plant tissue is reproduced.
A symbiotic fungus, i.e. the endophyte, is a filamentous fungus living in a plant tissue. It is know that a plant infected by such a filamentous fungus has improved resistance to pests and diseases, better growth rate, and resistance to environmental stresses such as heat and dryness, as compared with a plant with no infection. Thus, it is possible to improve plant characteristics through artificial infection of the endophyte.
A symbiotic fungus capable of infecting and living in a plant successively biosynthesizes metabolic products as shown in FIG. 1. An end product of the biosynthesis is an ergopeptine such as ergovaline or ergotamine.
It is known that a grass symbiotically infected by the endophyte shows toxicity due to the presence of ergoto alkaloids. The toxicity is considered to be a problem in husbandry as it affects livestock. In the case of pasture, for example, grasses infected with the endophyte such as perennial rye grass and tall fescue are very commonly distributed, and cases of poisoning have been reported due to the ergoto alkaloids.
Rye grass slugger was first reported in New Zealand in 1906, and has occurred mainly in two countries in Oceania, i.e. New Zealand and Australia. The rye grass slugger occurs when the endophyte infects perennial rye grass withered in a severe dry condition from summer to autumn, and livestock such as sheep eat the grass.
In the rye grass slugger, when livestock eat the grass, the livestock show various symptoms, i.e. stiffen limbs and shaking neck, shoulder and flank. In other words, a kind of spasm occurs, and if the symptom continues, the animals become weaker. In the worst case, they are no longer able to move and may starve to death. It has now become clear that the substance responsible for the rye grass slugger is Lolitrum B, a Lolitrum alkaloid.
Fescue toxicosis mainly occurred in the southeast of the U.S. Cows consumed tall fescue, and suffered serious weight loss, and did not eat sufficient fodder. Their milk production declined, and their birth rate also fell. The cows had eaten grasses infected by endophytes, and ergovaline, i.e. an ergoto alkaloid, was specifically detected in the endophyte-infected grasses. It thus became clear that the ergovaline causes fescue toxicosis.
As described above, when a plant, especially pasture, is infected by the endophyte, resistance to pests and disease, a growth rate and resistance to environmental factors such as heat and dryness are improved. However, the biosynthesized substances of the endophyte are poisonous to livestock, and give rise to the problems of the rye grass slugger, fescue toxicosis, etc.
In view of the problems described above, an object of the invention is to provide a plant into which the symbiotic fungus is artificially introduced, and a method of artificially introducing the symbiotic fungus into a plant. According to the present invention, the plant does not show toxicity against livestock and has strong resistance to pest.
Further objects and advantages of the invention will be apparent from the following description of the invention.