Rice tungro disease (RTD) is a serious constraint to rice production in South and Southeast Asia. RTD is caused by Rice tungro spherical virus (RTSV) and Rice tungro bacilliform virus. Rice cv. Utri Merah is resistant to RTSV. To identify the gene or genes involved in RTSV resistance, the association of genotypic and phenotypic variations for RTSV resistance was examined in backcross populations derived from Utri Merah and rice germplasm with known RTSV resistance. Genetic analysis revealed that resistance to RTSV in Utri Merah was controlled by a single recessive gene (tsv1) mapped within an approximately 200-kb region between 22.05 and 22.25 Mb of chromosome 7. A gene for putative translation initiation factor 4G (eIF4G(tsv1)) was found in the tsv1 region. Comparison of eIF4G(tsv1) gene sequences among susceptible and resistant plants suggested the association of RTSV resistance with one of the single nucleotide polymorphism (SNP) sites found in exon 9 of the gene. Examination of the SNP site in the eIF4G(tsv1) gene among various rice plants resistant and susceptible to RTSV corroborated the association of SNP or deletions in codons for Val(1060-1061) of the predicted eIF4G(tsv1) with RTSV resistance in rice.
W heat is a major grain crop and primary staple food of Pakistan and it is a major source of carbohydrates and energy (Chattha et al., 2017a(Chattha et al., , 2018. The seed of wheat contains 2.11% minerals, 68% carbohydrate, 2.9% fat, 15.4% proteins and an important source of calories and micro-nutrients Abstract | Delayed wheat sowing is the main factor responsible for the lower yield of wheat owing to low temperature during emergence and early growth. Seed size has an appreciable potential to improve stand establishment, growth, and yield under late sowing conditions. Therefore, the present study was performed to assess the impact of diverse seed sizes (SS) on the growth and yield of wheat crop under late sowing conditions. The study was comprised of different sowing dates (SD), SD 1 : 15 th December, SD 2 : and 30 th December and different seed size classes i.e. bold (having a diameter of > 2.7 mm), medium (having a diameter of > 2.3 mm to 2.7 mm), small (having a diameter of ≤ 2.3 mm) and mixed seeds. The results indicated that different sowing dates and seed size classes had a significant effect on germination, growth, and yield of wheat crop. The crop sown on 15 th December took less time to start emergence (7.8 days) and resulted in maximum plant height (81 cm), grains per spike (44.5), productive tillers (321.5), spike length (10.2 cm), 1000 grain weight (37.2 g), and grain yield (3.83 t ha -1 ) and maximum time to start emergence (11 days) and minimum plant height (60 cm), grains per spike (35.7), productive tillers (273), spike length (8.6 cm), 1000 grain weight (32 g), and grain yield (2.7 t ha -1 ) was recorded in the crop sown on 30 th December. In the case of seed size classes, bold seed performed appreciably well and took less time to start emergence (8.5 days) and had more plant height (74.7 cm), productive tillers (326), spike length (10.1 cm), grains per spike (45), 1000 grain weight (37 g), and grain yield (3.67 t ha -1 ) compared to other seed size classes. In conclusion, bold seed size can significantly improve the wheat production under late sown conditions due to better stand establishment, vigorous germination, and increase in yield related traits.
The two adjacent genes of coat protein 1 and 2 of rice tungro spherical virus (RTSV) were amplified from total RNA extracts of serologically indistinguishable field isolates from the Philippines and Indonesia, using reverse transcriptase polymerase chain reaction (RT-PCR). Digestion with HindIII and BstYI restriction endonucleases differentiated the amplified DNA products into eight distinct coat protein genotypes. These genotypes were then used as indicators of virus diversity in the field. Inter- and intra-site diversities were determined over three cropping seasons. At each of the sites surveyed, one or two main genotypes prevailed together with other related minor or mixed genotypes that did not replace the main genotype over the sampling time. The cluster of genotypes found at the Philippines sites was significantly different from the one at the Indonesia sites, suggesting geographic isolation for virus populations. Phylogenetic studies based on the nucleotide sequences of 38 selected isolates confirm the spatial distribution of RTSV virus populations but show that gene flow may occur between populations. Under the present conditions, rice varieties do not seem to exert selective pressure on the virus populations. Based on the selective constraints in the coat protein amino acid sequences and the virus genetic composition per site, a negative selection model followed by random-sampling events due to vector transmissions is proposed to explain the inter-site diversity observed.
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