Research On Amorphous And Growth Characteristics Of Four Phytsiological Races Of Pyricularia Grisea

Rice blast was recognized as one of the most serious disease in China. As a result of different races of Pyricularia grisea and vulnerable to variation,the control of this disease posed a great problem. Four races of P. grisea which had strong virulence found in Heilongjiang province,was used for the investigation of amorphous and biological characteristics. The influences of temperature,pH and nutritive medium on the growth of races of P. grisea were examined. The discussion of the impact of environment conditions gave information for the research and control of this disease of rice.Four races of P. grisea, named 42-7, 54-5, 67-9 and 69-2, were purified. The effects of temperature, pH and mediums on the growth and multiplication were discussed.The study on the temperature of cultivation showed that the optimum temperature was 28℃. On the condition of 37℃, the growth of the four races was inhibited, though the virility was retained. On the condition of 16℃, a long time was needed for the adoption of all the four races to environment. After preparation period, the growth rate of races of 54-5, 67-9 and 69-2 was equal to that at the temperature of 28℃. However, the race named 42-7 showed a notable influence of temperature was observed.The study on pH exhibited that a less notable influence of pH on the four races of P. grisea was found in contrast to temperature. The shape of colony was greatly affected by pH. At the acidic condition, the small amount of aerial hypha was big; at the based condition, aerial hypha was thin, and rare.The study on mediums showed that a fast growth rate was obtained on PDA medium while a low growth was found on oat-agar medium. In term of colony shape, P. grisea grew best in PDA medium; the growth rate was not high enough, but the shape of colony was very thick, the four races only produced thin aerial hypha in classical rice-bran-agar medium and oat-agar medium.Hypha of the four races was found colorless and transparent; septum was found between two cells in the hypha. Spores all showed pear-like shape which contains two septum's; Germ tube of race 69-2 germinated at both pole of spores while the other three races only had germ tubes germinated at the small poll of spores.The appearance and biological characteristics was studied on the four races of P. grisea, which provided useful information on the precaution and control of rice blast in Heilongjiang province. The influence of environmental factors on the growth of P. grisea was systematically examined with an emphasis on the impact of pH. This study provided useful information on the mechanism and control of rice disease.