Molecular progress on the mapping and cloning of functional genes for blast disease in rice (Oryza sativa L.): current status and future considerations.

Rice blast disease, which is caused by the fungal pathogen Magnaporthe oryzae, is a recurring problem in all rice-growing regions of the world. The use of resistance (R) genes in rice improvement breeding programmes has been considered to be one of the best options for crop protection and blast management. Alternatively, quantitative resistance conferred by quantitative trait loci (QTLs) is also a valuable resource for the improvement of rice disease resistance. In the past, intensive efforts have been made to identify major R-genes as well as QTLs for blast disease using molecular techniques. A review of bibliographic references shows over 100 blast resistance genes and a larger number of QTLs (∼500) that were mapped to the rice genome. Of the blast resistance genes, identified in different genotypes of rice, ∼22 have been cloned and characterized at the molecular level. In this review, we have summarized the reported rice blast resistance genes and QTLs for utilization in future molecular breeding programmes to introgress high-degree resistance or to pyramid R-genes in commercial cultivars that are susceptible to M. oryzae. The goal of this review is to provide an overview of the significant studies in order to update our understanding of the molecular progress on rice and M. oryzae. This information will assist rice breeders to improve the resistance to rice blast using marker-assisted selection which continues to be a priority for rice-breeding programmes.

Optimization of MR-Relaxometry for BMD-measurements and its Correlation with DEXA.

The aim of this study was to optimize MRI conventional protocols for BMD measurements using MR-Relaxometry in systems not facilitated with special multi echo protocols. Since, cortical and trabecular bone separation can not be performed in DEXA, so the results might lead to erroneous interpretation of BMD values. One method for bone quality determination is MR relaxometry that derives R2(=1/T2), R2*(=1/T2*) and R2'(=R2*-R2). This study was performed by 1.5T MRI system(Picker Vista-Q800), an uniformity phantom(1.25gr/l CuSO4, with T2=200ms for calibration), a body RF-Coil, 7 normal, 7 osteopenia, 7 osteoporosis volunteers and Lunar DEXA system(DPX-MD). To determine R2*and R2, multi GE and SE protocols with different TE/TR were used. Then in phantom and in coronal section of femoral-neck, relaxation rates were compared with BMD. The slope of neperian-logarithm of signal vs. TE in GE as -R2*used for protocol optimization. Therefore, for phantom calibration, optimized GE parameters of TE=13.42/18/26.8 ms, TR=800ms and ST=8mm used for the measurement of R2*, while, the measurement of R2 required the optimized SE parameters of TE=30/60/90/120ms, TR=800ms and ST=8mm, with CV(R2*)=2.96%, CV(R2)=3%, respectively. In volunteers for SE, TE of 36/54/63/72ms and TR=800ms were used, while, for GE the TEs/TR were the same as those of phantom study. R2*and R2' showed a significant positive correlation with BMD, r=0.62(p<0.05) & r=0.62(p<0.05) respectively. Finally, in accordance with DEXA values, the results showed that MR-Relaxometry is a proper tool for BMD-measurements in femoral-neck. Also it may be used as a complement method for DEXA failure in BMD-assessments.