Breeding Of Rice Resistance To Sheath Blight By Gene Engeneering

In the past studies on sheath blight resistance of transgenic rice, there was an obvious shortcoming of identification, in which the materials used to screening belonged to early separation generation, or were tissue separated from plant. This study was conducted with homozygous rice lines transferred with chitinase gene (RC24) and -1,3-glucanse gene ( -1,3-Glu), and the sheath blight ratings were investigated. The main results were as following.(1) RC24 and -1,3-Glu were simultaneously transferred into an susceptible indica rice variety- "Qisiruanzhan" grown in south China. Several independent lines co-harboring RC24 and -1,3-Glu were obtained. There were extremely significant differences of resistance among transgenic lines, which could be divided into 4 types of resistance, medium resistance, medium susceptible and susceptible. The fact that 92.1% of lines were medium resistance or medium susceptible showed that target gene might only play partly role in sheath blight resistance. There were resistance differences between lines derived from the same transformant, suggesting that transgenic plant might be gomphosis .(2) Most transgenic lines had no mutation of agronomical traits, but a handful of lines had mutations of lately mature, higher plant height and bigger grain, suggesting that tissue culture could induce abundant variations, which were beneficial to selection and agronomical trait improvement.(3) In order to induce the expression of chitinase gene, transgenic lines were infected with Rhizoctonia solani strain RH-9, and the chitinase activities were measured. The results showed that resistance was significant correlated with the chitinase activity. Susceptible varieties Qisiruanzhan and Lemont transferred with exogenous chitinase gene had little change in the chitinase activity after inoculation, which might be due to the constitutive expression of exogenous chitinase gene. Resistance variety Qimiaoxiang had asignificant enhancement of expression of endogenous chitinase gene, but the amount of expression induced was equal to that of medium resistance transgenic lines of Qisiruanzhan. This fact suggested that chitinase gene was only one factor responsible for resistance, and the high levels expression of whole protection system genes was the key reason that Qimiaoxiang's resistance was excellent.(4) The chitinase activities of transgenic lines measured at different growth stage or with different leaf were alike, which suggested the expression of chitinase gene was constitutive. Check varieties of resistance and susceptible had changes in chitinase activity after inoculation, and both reached the peak of the chitinase activity 72 hours later. The fact that there was no differences of chitinase activity among different leaves also showed that the infection signals could be transmitted quickly, which activated the protection system. Thus, all parts of the whole plant were resistant to disease.