Genetic transformation of NERICA,interspecific hybrid rice between <Emphasis Type="Italic">Oryza glaberrima</Emphasis> and <Emphasis Type="Italic">O. sativa</Emphasis>, mediated by <Emphasis Type="Italic">Agrobacterium tumefaciens</Emphasis>

We developed an efficient gene transfer method mediated by Agrobacterium tumefaciens for introgression of new rice for Africa (NERICA) cultivars, which are derivatives of interspecific hybrids between Oryza glaberrima Steud. and O. sativa L. Freshly isolated immature embryos were inoculated with A. tumefaciens LBA4404 that harbored binary vector pBIG-ubi::GUS or pIG121Hm, which each carried a hygromycin-resistance gene and a GUS gene. Growth medium supplemented with 500 mg/l cefotaxime and 20 mg/l hygromycin was suitable for elimination of bacteria and selection of transformed cells. Shoots regenerated from the selected cells on MS medium containing 20 g/l sucrose, 30 g/l sorbitol, 2 g/l casamino acids, 0.25 mg/l naphthaleneacetic acid, 2.5 mg/l kinetin, 250 mg/l cefotaxime, and 20 mg/l hygromycin. The shoots developed roots on hormone-free MS medium containing 30 mg/l hygromycin. Integration and expression of the transgenes were confirmed by PCR, Southern blot analysis, and histochemical GUS assay. Stable integration, expression, inheritance, and segregation of the transgenes were demonstrated by molecular and genetic analyses in the T₀ and T₁ generations. Most plants were normal in morphology and fertile. The transformation protocol produced stable transformants from 16 NERICA cultivars. We also obtained transformed plants by inoculation of calluses derived from mature seeds, but the frequency of transformation was lower and sterility was more frequent.     

非洲新稻(NERICA)品种在武汉生态条件下的生育期、白叶枯病抗性和稻米品质的初步评价

从非洲水稻研究中心引进了78份非洲新稻品种资源,2009年在武汉大田条件下种植,对生育期、水稻白叶枯抗性和稻米品质进行了初步评价。观察表明,生育期可以分为4个类型:短生育期品种13份,中生育期品种37份,长生育期11份,生育期特长在武汉不能安全抽穗的品种17份。白叶枯抗性鉴定表明,57.7%的品种高抗或抗长江中下游籼稻区的优势白叶枯病菌株ZHE173,76.9%的品种高抗或抗来自云南稻区的菌株YN18,对中国新发现的强致病力菌株FuJ能达到抗级水平的仅有3个品种,而达到中抗水平的有5个品种,凡是对FuJ达到中抗以上的品种,均高抗或抗ZHE173和YN18。对50个品种的米质分析表明,非洲新稻品种的稻米加工品质和粒型品质特别优良。非洲新稻品种资源可以用于改良国内新品种的白叶枯病抗性和稻米加工品质。     

Nonglandular silicified trichomes are essential for rice defense against chewing herbivores

Interspecific New Rice for Africa (NERICA) varieties have been recently developed and used in Sub-Saharan Africa but herbivore resistance properties of these plants remain poorly understood. Here we report that, compared to a local Japanese cultivar Nipponbare, NERICA 1, 4 and 10 are significantly more damaged by insect herbivores in the paddy fields. In contrast to high levels of leaf damage from rice skippers and grasshoppers, constitutive and induced volatile organic compounds for indirect plant defense were higher or similar in NERICAs and Nipponbare. Accumulation of direct defense secondary metabolites, momilactones A and B, and p-coumaroylputrescine (CoP) was reduced in NERICAs, while feruloylputrescine accumulated at similar levels in all varieties. Finally, we found that Nipponbare leaves were covered with sharp nonglandular trichomes impregnated with silicon but comparable defense structures were virtually absent in herbivory-prone NERICA plants. As damage to the larval gut membranes by Nipponbare silicified trichomes that pass intact through the insect digestive system, occurs, and larval performance is enhanced by trichome removal from otherwise chemically defended Nipponbare plants, we propose that silicified trichomes work as an important defense mechanism of rice against chewing insect herbivores.     

Flash flooding resistance of rice genotypes of Oryza sativa L., O. glaberrima Steud., and Interspecific hybridization progeny

In the costal area and inland valleys of Guinea, flash floods occur frequently following heavy rain during the rainy season. Young rice seedlings are particularly vulnerable to submergence stress due to insufficient height and carbohydrate reserves. In an attempt to characterize the physiological responses of young seedlings to flash flood, a wide genetic base including O. sativa, O. glaberrima, and interspecific hybridization progenies (IHP) was used.

Twelve day-old seedlings were submerged for 7 days, and plant height, dry matter accumulation (DMA), and lodging were measured. Upland rice (O. sativa) showed greater shoot elongation, larger reduction in DMA during submergence, and higher lodging, which lead to low flash flooding resistance (FFR). The physiological traits of most O. glaberrima and upland rice (O. sativa) to flash flood were opposite to those of submergence tolerant cultivars, as evidenced from the results of a principal component analysis. The physiological response of Saligbeli was different to other O. glaberrima genotypes in terms of FFR. Saligbeli exhibited enhanced shoot elongation with the increase in DMA during submergence. These features seemed to be a unique way to cope with submergence. Some IHP adapted to lowland cultivation showed traits similar to Saligbeli. The vigorous growth of Saligbeli and IHP underwater should be further investigated for improving FFR in rice.