Preliminary Study On The Isolation, Culture And Inoculation Techniques Of Ustilaginodea Virens Causing Rice False Smut

Rice false smut is a worldwide fungal disease in rice caused by Ustilaginodea virens (Cooke) Takahashi,which infected the panicles of rice and produced rice false balls.Is was all long ignored before 1980s' .However,with the change of rice cultivars and increasing of fertilization in the paddyfield, rice false smut in China has being more and more serious,which influences greatly on the yild and quality of rice,produced to poison human and animals.Up to now, the disease has become one of the major rice diseases in all the major rice production areas in China..The stdudy was focused mainly on the pathogen isolation, artifical culture, inoculation technique and infection cycle to find out the possible infection and growth process of the pathogen in nature,and to optimize an artifical inoculation method.The main results are gained as follows:1,Improvement of the method of isolation . To the contrast of the traditional method, two effective separation method had been constructed, There are improvement tissue and improvement rice fasle ball isolation method.The strongpoint of these two new method were that the pathogen cultivated was easy to grow,and take less time than traditional method.2,The biological characteristics and basis identification of pathogen. There are two methods of reproduction of the chlamycladospores of rise false smut under water: single germination, double germination, and the later is generally common. There are two development type of the chlamycladospores. One is to produce primary conidia on the top of hypha after the spore bourgeon, and then produce lots of secondary conidias beside the primary conidia. The other one is not to produce conidia during the later prophase. The first one is more common. The conidia can automatically desquamate from the hypha and a distinct spoor is left. however, some of the conidias can' t desquamate and can produce new mycelial, leaving a bulge.The growth of pathogen is slow in the PSA culture medium, so only after 7 days can we see megascopic colonies. The classic colonies ishillock white during the primary phase, then turned yellow gradually. There are too many chlamycladospores balls around the colonies after 60 days in the PSA. The phenotype of chlamycladospores is very similar to rice false balls. Round or elliptical, with thorn, yellow, with verruca on the surface, can produce conidia easily under water. The reproduction ability gradually weakened with the increasing generation of strain. And the strain generally can't produce chlamycladospores after subculture 2 generation. With the microscope observation,we could see the yellow hypha of the colonies have many characteristics: the volume ampliate, the septum obvious, the number increased, the shape is moniliform. These mycelial can produce conidia under proper condition. We confer these mycelium is the forebody of chlamycladospores, but to some reason, they can't produce mature chlamycladospores. All the above can be used as the judgement evidence of Ustilaginodea virens.3. Study of inoculation technique of Ustilaginodea virens .Preliminary studied on the cycle of infection and the optimum phases of inoculation of the Ustilaginodea virens from the field experiment and potted plant experiment. results are that the rice can be infect by the Rise false smut more easily at the 2～3 d and 11～12 d before emergence of panicle, the conidia is the primary infection and 2% tomato juice make the infect more easily.4.The acquirement and its characteristics of albino stock. A albino mutant of Ustilaginodea virens have gained under manual condition. The albino mutant can't produce any spores under PSA or PS. The color of the mutant depigmented and finally became water-soaking after 30 days under PSA. The white colonies could be also gained through cultivating the water-soaking mycelial. This is the classic figure of the albino mutant. The mutant couldn't infect rice. So we confer that the pathogenicity of the mutant was lost. The ITS homology of the mutant with the normal strain is 100%. The result showed that the mutant belongs to Ustilaginodea virens.5. The observation of the process of infection :through field and laboratory slice up observation.Rice false smut can infect rice before flowering.