1. CROP IMPROVEMENT
1.5 SEED SCIENCE AND TECHNOLOGY .1 Studies on seed quality traits
1.4.2.4 Testing seed viability through accelerated ageing
Seeds of good and poor storing soybean genotypes along with their F2:3 seeds were subjected to accelerated ageing test. Germination and vigour indices were considered to classify the seeds as good and poor in storability. The conditions of accelerated ageing were optimized at 41±10C in 100% relative humidity for 72 h.
Genotypes with high viability had good germination (%), more normal seedling and high vigour index I and II.
Genotypes with poor vigour index after accelerated ageing test
1.4.2.5 Inheritance of drought tolerance in soybean at seedling stage
Crosses were made between two tolerant (PK 1180 and SL 46) and two susceptible (UPSL 298 and PK 1169) germplasm lines. F1 plants were selfed to raise F2 progeny. F2 plants at V3 stage were screened for seedling survivability. Segregation analysis of F2 population derived from a cross PK 1180 x UPSL 298 has shown a goodness of fit to 3 tolerant: 1 susceptible with probability of 0.992 at χ2 (3:1) value of 0.015 under hydroponics. The results were confirmed in another F2 population derived from a cross PK 1169 x SL 46.
1.4.2.6 Mapping of drought tolerance in soybean at seedling stage
The results obtained from single marker analysis have shown that the marker Satt277 is linked to drought tolerance at seedling stage.The marker has
shown a goodness of fit to 3:1 ratio in the F2 population by χ2 tests. Linkage analysis indicated that marker Satt277 linked to drought tolerance was located on chromosome 6. The genetic distance between the marker (Satt277) and tolerance gene is 3.2 cM.
1.5 SEED SCIENCE AND TECHNOLOGY
parameters. However, the results of these tests often show poor correlation with long-term storage under dry conditions. This is mainly due to differences in the physiology of seeds at a different water activity (aw) under these two ageing conditions. Here, we investigated genetic variation in the seed subjected to dry elevated partial pressure of oxygen (EPPO) ageing (21 days at 35°C) for 300 Indica rice accessions.
A wide range of genotypic variation was observed for germination parameters after ageing. A 1M-SNP dataset was screened for marker-trait associations using a linear mixed model accounting for population structure. Association analysis yielded eleven unique loci across the genome for all measured longevity parameters by applying a significance threshold of P<0.00001. The significant SNP on the most reliable locus (L7) was located within the Rc gene, a bHLH transcription factor (TF), regulating pro-anthocyanidin (PAs) synthesis in seeds. Further, storage experiments using isogenic lines (SD7-1D and SD7-1d) with the same genetic background confirmed the functional role of Rc gene conferring tolerance to dry EPPO ageing.
Functional Rc gene results in accumulation of PAs in the pericarp of rice seeds, an important sub-class of flavonoids, have strong antioxidant activity, which may explain why genotypes with an allelic variation for this gene show variation in seed tolerance to dry EPPO ageing. In summary, our experiments with dry EPPO ageing and subsequent GWA analysis identified seed longevity loci which differ from loci previously identified in rice under moist deterioration conditions.
Comparison of survival curves obtained with seeds of isogenic lines (SD7-1D and SD7-1d) stored under dry-EPPO ageing conditions
1.5.1.3 Early seed vigour in rice
Microarray data obtained from dry mature rice seeds of three rice genotypes with the contrasting phenotype for speed of germination was subjected to MapMan analysis to better deduce the reasons for differential response of the rice genotypes for the speed of germination per se. It was found that early germinating genotype is well equipped with the transcripts of regulatory pathways like transcription factors, protein modification, protein degradation, hormonal balance, cell redox potential, calcium regulation, Map kinases, receptor kinases and G proteins.
1.5.1.4 Genetic purity evaluation in CMS line of pearl millet
SCAR markers (SCAR1, SCAR2 and SCAR3) were developed for evaluating the genetic purity of A-line against the B-line admixtures in pearl millet genotypes with A1 cytoplasm .
A-line specific SCAR markers developed for ensuring the purity of A-line against the B-line admixtures in pearl millet genotypes with A1 cytoplasm
1.5.1.5 Seed dormancy in mungbean
Studies were taken up to understand the resistance to pre-harvest sprouting in mungbean cultivars.
Initially 106 mungbean genotypes were characterized for pod and seed characters and then screened using standardized pod germination and standard seed germination methods. Correlation studies among pod characters revealed significant negative correlation between presence of hard seeds and pod germination (-0.77) and pod water absorption (-0.36). All the seed characters studied showed negative correlation with hardseededness except the roundness of seeds.
Significant negative correlation was observed between hardseededness and seed size characters as well as 100-seed weight (-0.37). Considering both pod and seed characters, six promising cultivars with
contrasting resistance to pre-harvest sprouting (seed dormancy) were identified and were further studied for their seed water absorption. A clear-cut variation in per cent increase in seed weight was noticed after 6 h of soaking. However, precise difference in the actual water content (g water g-1 dry weight) among dormant and non-dormant genotypes was observed only after 26 h of soaking, indicating more time and water is required for complete saturation of internal tissues across genotypes.
1.5.1.6 Biochemical assessment in relation to hard seed in mungbean
One dormant (D) (TM 96-25) and one non dormant (ND) (Pusa 1331) genotypes were selected for biochemical studies of dormancy development in four different stages of seed development. The seed viability at stage 3, i.e. approx. 26 days after anthesis (DAA) is similar in both D and ND genotypes but later the germination percentage was reduced in D type due to hardseededness. The proanthocynadin content and seed coat permeability were studied using different staining methods. No role of proanthocynadins in mungbean dormancy was found. There is an increase in the lignin content and peroxidase activity in the stage 4 of D type compared to ND, indicating the role of lignin in the mungbean dormancy.
1.5.1.7 Seed dormancy behavior in Indian mustard and storability potential of conventional and quality mustard genotypes
Seed dormancy behaviour was evaluated in conventional and quality Indian mustard and some of the quality genotypes showed dormancy. Among various dormancy breaking protocols prechilling was found to be more effective. The antioxidant enzymes involved in ascorbate-glutathione cycle viz., ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), and glutathione reductase (GR) were studied in conventional and quality Indian mustard.
Significant differences were found in different types of mustard with respect to these enzymes. Conventional and quality Indian mustard varieties were assessed for superoxide and hydrogen peroxide content in the seeds. It was found that double zero genotypes
had significant high content of superoxide radical compared to single zero and conventional genotypes.
The superoxide radical was found to be negatively correlated with seed vigour indices.
1.5.1.8 Morphological, physiological and molecular traits associated with seed vigour and longevity in soybean
Eighty eight soybean genotypes were characterized on the basis of 36 descriptors comprising various plant, leaf, flower and seed traits. Variability was observed for growth habit, 50% days to flowering, growth type, plant height and shattering behavior. Promising genotypes were selected on the basis of good plant vigour and disease resistance. Distinct classes could be made on the basis of plant and seed vigour; high vigour and low vigour groups were represented by EC 39098, IC 90755, PLSO 6A; and CAT 582, CAT 356, IC 317660, respectively. Range of germination was 83-95%
for high vigour genotypes and 75-85% for low vigour genotypes.
1.5.2 Studies on seed priming
1.5.2.1 Priming technologies for enhancing planting value in specialty maize under sub- optimal temperature conditions
Sub optimum temperatures had severe effect on seed germination and field performance of specialty maize. QPM and sweet corn genotypes were most sensitive to sub-optimum conditions. Among treatments seed hydropriming (17h/25OC) followed by dry dressing with Thiram, halopriming with KNO3 @ 0.3%, ZnSO4 @ 0.3% + MnSO4 @ 0.5%, bio-priming with T. harzianum and drought alleviating bacteria along with Bio phos were significantly better in improving seed germination, vigour and field stand under sub- optimum conditions in specialty maize.
1.5.2.2 Effect of priming treatments on pigeonpea under temperature stress conditions
Eight priming treatments standardized for sub- optimal conditions were given to seeds of two varieties of pigeonpea, i.e. Pusa 991 and Pusa 992 and sown in three different sowing dates. Significant differences for various seed quality, field emergence and yield
attributing traits among the varieties and sowing time were observed. Priming treatments had significant effect on first count (%), germination (%), vigour index II, mean emergence time, plant height (cm) and seed yield/plant (g) of pigeonpea varieties under different sowings dates/temperature conditions. Seed yield in both the varieties significantly decreased with delay of sowings, however, the exposure of seeds for 24 h at 40°C resulted in highest seed yield/plant under temperature stress conditions, which was at par with seed exposure for 6 h at 40°C treatment. Exposure of seeds for 24 h at 40°C enhanced seed yield/plant up to 2.8% in cv. Pusa 991 and 2.2% in Pusa 992 in comparison to control under different temperature conditions. Under laboratory conditions, haloprimed seeds when tested under salt stress conditions (6EC) resulted in significantly higher vigour index II over control.
1.5.2.3 Effect of priming treatments on soybean under temperature stress conditions
Five priming treatments: T1- Control (untreated), T2- Hydropriming (4 h at 25°C), T3- Exposure for 1 h at 40°C, T4- Osmopriming (6h at 25°C in 60% PEG 6000) and T5- Halopriming with Salt (4h in 4 EC solution) standardized for sub-optimal conditions were given to seeds of two soybean varieties i.e.; Pusa 9752 and JS 335 and sown in three different sowing dates. No plants were established, except few in T3, because of continuous rains during first two sowings. Data from the third sowing revealed significant differences between the varieties for plant height, numbers of pods/plant, and seed yield/plant. The planting value of soybean seeds was found significantly affected by the priming treatments when sown at 360C. Significant decrease in mean emergence time and improvement over control in field emergence (%), plant stand establishment (%) and plant height (cm) was observed in seeds exposed to 40°C for 1 h.
1.5.3 Technologies for mitigating biotic and abiotic stresses
1.5.3.1 Mitigating effect of elevated temperatures on seed set, yield and quality in wheat
Five mitigation treatments, viz. glycine betaine (600 ppm), salicylic acid (200 ppm), ascorbic acid (10
ppm), KCl (1%) and citric acid (1.5 %) were evaluated on two wheat varieties, viz. HD3117 (late sown) and HD 3171 (timely sown). Phenology of wheat crop was significantly affected by higher temperature. The overall trend across various sprays revealed that plant height and number of tillers showed a declining trend as the sowing was delayed from November to January, irrespective of the chemical sprayed. Two characters viz., 1000-seed weight and germination percentage were affected significantly due to heat stress. Glycine betaine (600 ppm) followed by salicylic acid (200 ppm) were most effective in mitigating adverse effects of heat stress.
1.5.3.2 Seed transmission of a distinct soybean yellow mottle mosaic virus strain in natural (Vigna radiata) and experimental (Phaseolus vulgaris) hosts As the modes of transmission of soybean yellow mottle mosaic virus (SYMMV) has not been described, we assessed the possibility of SYMMV to be transmitted through seed collected from field infected mungbean plants and mechanically sap inoculated French bean plants using serological and molecular techniques followed by progeny assays. Direct antigen coated enzyme linked immunosorbent assay (DAC-ELISA) and reverse transcription polymerase chain reaction (RT-PCR) results are inconsistent with field infected mungbean seed tissues to confirm seed transmissibility, irrespective of seed number used. Seed from mechanical sap inoculated French bean showed higher absorbance values in DAC-ELISA and amplification corresponding to replicase, movement and coat protein regions of SYMMV genome. The relative accumulation of SYMMV assessed through quantitative RT-PCR (qRT-PCR) was higher in pod walls, immature seed and stamens and stigma of mechanical sap inoculated French bean plants. Progeny assays with infected seed revealed the seed transmissibility of SYMMV at the rate of 63.33% in mungbean and 73.33% in French bean.
Mechanical sap inoculation of mungbean progeny seedlings on French bean cv. Pusa Parvati produced characteristic symptoms of SYMMV. The results obtained from this study demonstrate that SYMMV is seed borne in nature and can be transmitted to next generation seedlings.