Rice Aroma: Biochemical, Genetics and Molecular Aspects and Its Extraction and Quantification Methods

Aroma in rice is unique and a superior grain quality trait, varieties especially Basmati and Jasmine-type are fetching a high export price in the International markets. Among the identified volatile aroma compounds, 2AP (2 acetyl-1-pyrroline) is believed to be the distinctive biochemical compound contributing the flavor in rice. Genetically, aroma in rice arises by the phenotypic expression of spontaneous recessive mutations of the OsBadh2 gene (also known as fgr/badh2 /osbadh2/os2AP gene) which was mapped on chromosome 8. An 8-bp deletion in the exon 7 of this gene was reported to result in truncation of betaine aldehyde dehydrogenease enzyme whose loss-of-function lead to the accumulation of a major aromatic compound (2AP) in fragrant rice. Among the different sampling methods and analytical techniques for the extraction and quantification of scentedness, simultaneous distillation extraction (SDE) is traditional and normalized, whereas solid-phase micro extraction (SPME) and supercritical fluid extraction (SFE) are new, very simple, rapid, efficient and most importantly solvent-free methods. These methods are coupled with Gas Chromatography–Mass Spectrometry (GC–MS), Gas Chromatography-Flame Ionization Detector (GC-FID) and/or Gas chromatography olfactometry (GC-O) and also with sensory evaluation for readily examining 2AP compound found in rice. The major factor affecting the aroma in rice was their genetic makeup. However, the aroma quality may be differed due to different planting, pre-harvest and postharvest handling and storage. For a more extensive elucidation of all effective and fundamental factors contributing to fragrance, it is essential to explore target quantitative trait loci (QTLs) and their inheritance and locations

Genetic variability of early flowering and yield contributing traits in Barnyard Millet [Echinochloa frumentacea (Roxb). Link] grown at different altitudes

131-136Barnyard millet is an important up surging minor millet in Asia countries for food and nutritional security. Being a minor crop, the genetics and inheritance of the traits need to understand, for effective utilization in the crop improvement programmes. Here, we investigated the genetic background and inheritance of different traits in barnyard millet genotypes. Forty germplasm accessions were evaluated in different ecological environments of southern India for 17 quantitative traits. Genetic variability analysis using GENSTAT and the pooled REML mean data results revealed that Phenotypic Co-efficient of Variation (PCV) was greater than the Genotypic Co-efficient of Variation (GCV) over the diverged ecological locations indicating the existence of environmental influence on all the biometric traits studied. In the Western Ghats region (E1), high heritability coupled with high genetic advance was exhibited for traits like days to flowering, plant height, days to maturity, number of nodes, length of nodes, number of basal tillers, stem diameter, flag leaf length, flag leaf width, inflorescence length, inflorescence width, length of peduncle, number of racemes, single ear head weight and grain yield per plant. Traits like thousand grain weight expressed moderate genetic advance with high heritability while, length of lower racemes expressed moderate heritability with high genetic advance. Similarly, high heritability coupled with high genetic advance was recorded for all the characters in valley region (E2) except thousand grain weight that showed high heritability but moderate genetic advance. In contrast, in the area of plains (E3), all the traits exhibited high heritability coupled with high genetic advance. Since, majority of the traits have shown high heritability with high genetic advance, selection might be effective in these traits irrespective of the environment

Comparative Metabolomic Profiling of Horse Gram (Macrotyloma uniflorum (Lam.) Verdc.) Genotypes for Horse Gram Yellow Mosaic Virus Resistance

Horse gram (Macrotyloma uniflorum (Lam.) Verdc.) is an under-utilized legume grown in India. It is a good source of protein, carbohydrates, dietary fiber, minerals, and vitamins. We screened 252 horse gram germplasm accessions for horse gram yellow mosaic virus resistance using the percent disease index and scaling techniques. The percentage values of highly resistant, moderately resistant, moderately susceptible, susceptible, and highly susceptible were 0.34, 13.89, 38.89, 46.43, and 0.34, respectively. Repetitive trials confirmed the host-plant resistance levels, and yield loss was assessed. The present disease index ranged from 1.2 to 72.0 and 1.2 to 73.0 during the kharif and rabi seasons of 2018, respectively. The maximum percent yield loss was noticed in the HS (75.0 -89.4), while HR possessed the minimum (1.2-2.0). The methanolic leaf extracts of highly resistant and highly susceptible genotypes with essential controls were subjected to gas chromatography-mass spectrometry analysis. Differential accumulation of metabolites was noticed, and a total of 81 metabolites representing 26 functional groups were identified. Both highly resistant and susceptible genotypes harbored eight unique classes, while ten biomolecules were common. The hierarchical cluster analysis indicated a distinct metabolite profile. Fold change in the common metabolites revealed an enhanced accumulation of sugars, alkanes, and carboxylic acids in the highly resistant genotype. The principal component analysis plots explained 93.7% of the variation. The metabolite profile showed a significant accumulation of three anti-viral (octadecanoic acid, diphenyl sulfone, and 2-Aminooxazole), one insecticidal (9,10-Secocholesta-5,7,10(19)-triene-3,24,25-triol), one antifeedant (cucurbitacin B), and six metabolites with unknown biological function in the highly resistant genotype

Breeding Mechanisms for High Temperature Tolerance in Crop Plants

Increase in global warming poses a severe threat on agricultural production thereby affecting food security. A drastic reduction in yield at elevated temperature is a resultant of several agro-morphological, physiological and biochemical modifications in plants. Heat tolerance is a complex mechanism under polygenic inheritance. Development of tolerant genotypes suited to heat extremes will be more advantageous to tropical and sub tropical regimes. A clear understanding on heat tolerance mechanism is needed for bringing trait based improvement in a crop species. Heat tolerance is often correlated with undesirable traits which limits the economic yield. In addition, high environmental interactions coupled with poor phenotyping techniques limit the progress of breeding programme. Recent advances in molecular technique led to precise introgression of thermo-tolerant genes into elite genetic background which has been reviewed briefly in this chapter

An Overview of the Bionomics, Host Plant Resistance and Molecular Perspectives of Sesamia inferens Walker in Cereals and Millets

There is an urgent need to enhance agricultural production as well as productivity to meet the food demand of the growing population, estimated to be 10 billion by 2050, using a holistic and sustainable approach. The daily food sources for almost three-fourth of the global population, cereals and millets, are prone to several biotic factors and abiotic pressures. In particular, cereals and millet cultivation are limited by the polyphagous pink stem borer, Sesamia inferens Walker (Lepidoptera:Noctuidae) gaining national importance, since its larvae and pupae are concealed within the stem, none of the management measures have been found effective in controlling the menace. However, host plant resistance (HPR) is a reasonable and ecologically safe method wherein resistance mechanisms of crops could lower the stem borer infestation. The foremost challenge in understanding the mechanism would be to detecting the genes of interest in the crop using novel biotechnological approaches. The fundamental criterion for developing insect-resistant lines relies on recognizing the mechanism of plant resistance. The entire life cycle of this group of borers is completed or hidden within the stem, posing a hurdle in their management. Thus, molecular markers and Quantitative Trait Locus (QTL) mapping offer a more efficient approach to entomologists and plant breeders wherein they can work with traits like QTLs for stem borer resistance. In this review, an attempt has been made to provide an extensive summary of the host range and crop losses due to this borer, besides its taxonomic position, geographic distribution, bionomics, genetics of resistance, and molecular perspectives

Genetic variability of early flowering and yield contributing traits in Barnyard Millet [Echinochloa frumentacea (Roxb). Link] grown at different altitudes

Barnyard millet is an important up surging minor millet in Asia countries for food and nutritional security. Being a minorcrop, the genetics and inheritance of the traits need to understand, for effective utilization in the crop improvementprogrammes. Here, we investigated the genetic background and inheritance of different traits in barnyard millet genotypes.Forty germplasm accessions were evaluated in different ecological environments of southern India for 17 quantitative traits.Genetic variability analysis using GENSTAT and the pooled REML mean data results revealed that Phenotypic Co-efficientof Variation (PCV) was greater than the Genotypic Co-efficient of Variation (GCV) over the diverged ecological locationsindicating the existence of environmental influence on all the biometric traits studied. In the Western Ghats region (E1),high heritability coupled with high genetic advance was exhibited for traits like days to flowering, plant height, days tomaturity, number of nodes, length of nodes, number of basal tillers, stem diameter, flag leaf length, flag leaf width,inflorescence length, inflorescence width, length of peduncle, number of racemes, single ear head weight and grain yield perplant. Traits like thousand grain weight expressed moderate genetic advance with high heritability while, length of lowerracemes expressed moderate heritability with high genetic advance. Similarly, high heritability coupled with high geneticadvance was recorded for all the characters in valley region (E2) except thousand grain weight that showed high heritabilitybut moderate genetic advance. In contrast, in the area of plains (E3), all the traits exhibited high heritability coupled withhigh genetic advance. Since, majority of the traits have shown high heritability with high genetic advance, selection mightbe effective in these traits irrespective of the environment

Selection and validation of reliable reference genes for quantitative real-time PCR in Barnyard millet (Echinochloa spp.) under varied abiotic stress conditions

Abstract Quantitative real-time polymerase chain reaction (RT-qPCR) using a stable reference gene is widely used for gene expression research. Barnyard millet (Echinochloa spp.) is an ancient crop in Asia and Africa that is widely cultivated for food and fodder. It thrives well under drought, salinity, cold, and heat environmental conditions, besides adapting to any soil type. To date, there are no gene expression studies performed to identify the potential candidate gene responsible for stress response in barnyard millet, due to lack of reference gene. Here, 10 candidate reference genes, Actin (ACT), α-tubulin (α-TUB), β-tubulin (β-TUB), RNA pol II (RP II), elongation factor-1 alpha (EF-1α), adenine phosphoribosyltransferase (APRT), TATA-binding protein-like factor (TLF), ubiquitin-conjugating enzyme 2 (UBC2), ubiquitin-conjugating enzyme E2L5 (UBC5) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), were selected from mRNA sequences of E. crus-galli and E. colona var frumentacea. Five statistical algorithms (geNorm, NormFinder, BestKeeper, ΔCt, and RefFinder) were applied to determine the expression stabilities of these genes in barnyard millet grown under four different abiotic stress (drought, salinity, cold and heat) exposed at different time points. The UBC5 and ɑ-TUB in drought, GAPDH in salinity, GAPDH and APRT in cold, and EF-1α and RP II in heat were the most stable reference genes, whereas ß-TUB was the least stable irrespective of stress conditions applied. Further Vn/Vn + 1 analysis revealed two reference genes were sufficient to normalize gene expression across all sample sets. The suitability of identified reference genes was validated with Cu-ZnSOD (SOD1) in the plants exposed to different abiotic stress conditions. The results revealed that the relative quantification of the SOD1 gene varied according to reference genes and the number of reference genes used, thus highlighting the importance of the choice of a reference gene in such experiments. This study provides a foundational framework for standardizing RT-qPCR analyses, enabling accurate gene expression profiling in barnyard millet

Development and Metabolic Characterization of Horse Gram (<i>Macrotyloma uniflorum</i> Lam. (Verdc.)) Mutants for Powdery Mildew Resistance

Horse gram is one of the lesser-known beans widely grown in India. One hundred and twenty-three homozygous horse gram mutants were screened for powdery mildew (PM) disease resistance using the grade 0 to 4. The mutants were grouped based on the disease level of 0 to 2 (resistant) and susceptible (3 to 4). The PM altered the chlorophyll fluorescence (a/b ratio), maturity duration, and yield attributing traits. The yield loss ranged from 4.55% to 72.66%. After affirming the resistance level, the resistant mutant (RM) with minimum yield loss (scale:0) and the susceptible mutant (SM) with maximum loss (scale:4) were used for metabolomic analysis through GC-MS. PM infection induced expression of 66 metabolites representing 32 functional classes. The number of unique classes in RM and SM was 13 and 11, respectively, while eight were common. A fold change in the common metabolites indicated an enhanced accumulation of amine, alcohol, and ester in RM. Along with pathogen-induced defensive metabolites, RM produced silane and fluorene, whose biological significance in disease resistance is unknown. Though SM expressed defence-related bio-molecules, it failed to yield better

Development and Metabolic Characterization of Horse Gram (Macrotyloma uniflorum Lam. (Verdc.)) Mutants for Powdery Mildew Resistance

Horse gram is one of the lesser-known beans widely grown in India. One hundred and twenty-three homozygous horse gram mutants were screened for powdery mildew (PM) disease resistance using the grade 0 to 4. The mutants were grouped based on the disease level of 0 to 2 (resistant) and susceptible (3 to 4). The PM altered the chlorophyll fluorescence (a/b ratio), maturity duration, and yield attributing traits. The yield loss ranged from 4.55% to 72.66%. After affirming the resistance level, the resistant mutant (RM) with minimum yield loss (scale:0) and the susceptible mutant (SM) with maximum loss (scale:4) were used for metabolomic analysis through GC-MS. PM infection induced expression of 66 metabolites representing 32 functional classes. The number of unique classes in RM and SM was 13 and 11, respectively, while eight were common. A fold change in the common metabolites indicated an enhanced accumulation of amine, alcohol, and ester in RM. Along with pathogen-induced defensive metabolites, RM produced silane and fluorene, whose biological significance in disease resistance is unknown. Though SM expressed defence-related bio-molecules, it failed to yield better

Development and Metabolic Characterization of Horse Gram (Macrotyloma uniflorum Lam. (Verdc.)) Mutants for Powdery Mildew Resistance

Horse gram is one of the lesser-known beans widely grown in India. One hundred and twenty-three homozygous horse gram mutants were screened for powdery mildew (PM) disease resistance using the grade 0 to 4. The mutants were grouped based on the disease level of 0 to 2 (resistant) and susceptible (3 to 4). The PM altered the chlorophyll fluorescence (a/b ratio), maturity duration, and yield attributing traits. The yield loss ranged from 4.55% to 72.66%. After affirming the resistance level, the resistant mutant (RM) with minimum yield loss (scale:0) and the susceptible mutant (SM) with maximum loss (scale:4) were used for metabolomic analysis through GC-MS. PM infection induced expression of 66 metabolites representing 32 functional classes. The number of unique classes in RM and SM was 13 and 11, respectively, while eight were common. A fold change in the common metabolites indicated an enhanced accumulation of amine, alcohol, and ester in RM. Along with pathogen-induced defensive metabolites, RM produced silane and fluorene, whose biological significance in disease resistance is unknown. Though SM expressed defence-related bio-molecules, it failed to yield better