Genetic Diversity and Population Structure Analysis in Early Generations Maize Inbreds Derived From Local Germplasm of Eastern Himalayan Regions Using Microsatellite Markers

North- Eastern parts of India fall under the Eastern Himalayan region and it is a diversity hotspot of many crops, including maize. Maize is an important traditional cereal crop grown in hill ecology of the region mainly for food, fodder and feed. To tap the potentiality of maize genetic resources in crop improvement programmes, assessment of genetic diversity is a basic requirement. Hence, in the present study, assessment of genetic diversity in thirty early generation maize inbreds developed from different germplasm of NE India was taken up using genome wide distributed fifty two microsatellite markers. The marker analysis revealed a large variation with a total of 189 alleles with an average of 3.63 alleles per marker locus. The allele size ranged from 50 bp ( phi 036 ) to 295 bp ( p 101049 ) which revealed a high level of genetic diversity among the loci. The PIC value ranged from 0.17 ( umc 1622 ) to 0.76 ( umc 1153 ) with an average value of 0.49. The value of expected Heterozygosity (H Exp ) ranged from 0.19 to 0.80 with an average of 0.57, whereas the Observed Heterozygosity (H Obs ) ranged from 0 to 0.89 with a mean of 0.14.The genetic dissimilarity between the genotype pairs ranged from 0.40 to 0.64 with a mean value of 0.57. Cluster analysis resolved the inbreds into three distinct sub-clusters. Similarly, population structure analysis also classified the inbred lines into three-subpopulations. Marker-trait associations showed a total of twelve SSR markers significantly associated with seven agronomic traits. From the present study, wide genetic variability was found among the maize inbreds with high potential to contribute new beneficial and unique alleles in genetic enhancement program of maize in India and particularly, in NE region.

Assessing antioxidant system and yield of maize (Zea mays L.) inbreds under elevated temperature condition

Maize (Zea mays L.) is the most important food and feed crop grown under diverse soil and climatic conditions. Among the cereals, demand for maize is increasing year after year, but fluctuation in climatic conditions especially the temperature extremes is the current and future threat in maize cultivation. Each degree Celsius increase in global mean temperature causes yield reduction up to 7.4 per cent in maize. The high temperature stress impact at the reproductive stage affects grain filling rate and duration. Adaptation of maize crop to future warmer climatic conditions requires a better understanding of physiological responses to elevated temperatures. With this view, a pot culture experiment was conducted at the Department of Crop Physiology, TNAU, Coimbatore during the summer season of 2020. Two maize inbreds viz., UMI 1230 and CBM-DL- 322 were taken for the study and exposed to high temperature stress treatments viz., T1 - ambient, T2 - ambient+4°C and T3 - ambient+6°C (44°C) for 10 days during the reproductive stage to assess the changes in biochemical and yield traits. The ambient+4ºC treatment revealed that the maize inbred line CBM-DL-322 recorded lower malondialdehyde content with over production of antioxidant enzyme activity (superoxide dismutase, catalase and ascorbate peroxidase). Cob weight and seed set parentage showed a negative correlation with both elevated temperatures. It is concluded that the maize inbreds line CBM-DL- 322 performed better at an elevated temperature at ambient+4°C and recorded more cob weight (57.09g) compared to UMI 1230 inbred (43.56g).

Oleic Acid Glycerides Content in the Oils of Maize Endospermic Mutants and Its Dependence on Temperature During Ripening

Identification of sources of increased content of oleic acid glycerides (oleates) and determination of the nature of its variability are prerequisites for improving oil quality. The purpose of this study was to establish the variability of the content of oleic acid glycerides (oleates) in maize oil depending on the genotype and ripening temperature. The experiments were carried out on a series of common maize inbreds and inbred-carriers of the su1, ae, and su2 mutations, which were grown for three years. The fatty acid composition of the oil was analysed by the Peisker gas chromatographic method. Genotype–environment interactions were assessed using the Eberhard– Russell algorithm. It was found that the carriers of the su1 and su2 mutations had the highest oleate content. The oleate content of maize oil generally increased with increasing ripening temperature. Unrelated inbreds based on one mutation significantly differed in the genetically determined level of oleate and showed non-identical responses to the ripening temperature. In inbreds of the first type, the content of oleates changed significantly with temperature fluctuation, while inbreds of the second type provided a fairly stable level of the trait under these conditions.

QTL Map of Early- and Late-Stage Perennial Regrowth in Zea diploperennis

Numerous climate change threats will necessitate a shift toward more sustainable agricultural practices during the 21st century. Conversion of annual crops to perennials that are capable of regrowing over multiple yearly growth cycles could help to facilitate this transition. Perennials can capture greater amounts of carbon and access more water and soil nutrients compared to annuals. In principle it should be possible to identify genes that confer perenniality from wild relatives and transfer them into existing breeding lines to create novel perennial crops. Two major loci controlling perennial regrowth in the maize relative Zea diploperennis were previously mapped to chromosome 2 (reg1) and chromosome 7 (reg2). Here we extend this work by mapping perennial regrowth in segregating populations involving Z. diploperennis and the maize inbreds P39 and Hp301 using QTL-seq and traditional QTL mapping approaches. The results confirmed the existence of a major perennial regrowth QTL on chromosome 2 (reg1). Although we did not observe the reg2 QTL in these populations, we discovered a third QTL on chromosome 8 which we named regrowth3 (reg3). The reg3 locus exerts its strongest effect late in the regrowth cycle. Neither reg1 nor reg3 overlapped with tiller number QTL scored in the same population, suggesting specific roles in the perennial phenotype. Our data, along with prior work, indicate that perennial regrowth in maize is conferred by relatively few major QTL.

Assessment of Genetic Diversity and Marker-Trait Associations Using Selected Early Maize Inbreds Derived From Local Landraces of Eastern Himalayan Regions

North- Eastern parts of India fall under Eastern Himalayan region and it is a diversity hotspot of many crops including maize. Evaluation of genetic diversity is required to tape the potentiality of genetic resources in any crop improvement programmes. In the present study, genetic diversity at fifty two microsatellite markers were conducted in 30 early maize inbreds developed from local landraces of NE India. Genetic diversity analysis revealed a total of 189 alleles with a mean of 3.63 alleles/ locus. The allele size ranged from 50 bp (phi 036) to 295 bp (p 101049) which revealed a high level of genetic diversity among the loci. The PIC among the 30 genotypes ranged from 0.17 (umc 1622) to 0.76 (umc 1153) with an average value of 0.49. The value of Expected Heterozygosity (HExp) ranged from 0.19 to 0.80 with an average of 0.57, whereas the Observed Heterozygosity (HObs) ranged from 0 to 0.89 with a mean of 0.14.The genetic dissimilarity between the genotype pairs ranged from 0.40 to 0.64 with a mean value of 0.57. Cluster analysis grouped the 30 inbreds into distinct three sub-clusters. Similarly, population structure and principal coordinate analysis) analysis also classified the 30 inbred lines into three-subpopulations. AMOVA revealed that 6% of total variance is due to differences among populations, while 94% of total molecular variance is accounted by within populations. Marker-trait associations showed a total of twelve SSR markers significantly associated with seven agronomic traits. From the present finding, these results show that the thirty maize inbreds have high genetic diversity which would be useful for choosing promising parents and for making cross combination based on genetic distance and clustering for genetic improvement programmes of maize.

Development of Extra-Early Provitamin A Quality Protein Maize Inbreds with Resistance/Tolerance to Striga hermonthica and Soil Nitrogen Stress

A hemiparasitic plant, Striga hermonthica (Del.) Benth and soil nitrogen stress are the key constraints to maize (Zea mays L.) productivity in sub-Saharan Africa, where commonly cultivated maize is the normal endosperm type that is deficient in provitamin A, tryptophan and lysine (PVATL). Seventy-six extra-early maize inbreds with provitamin A, tryptophan, and lysine qualities (TZEEIORQ) were developed to address these constraints, and four checks were assessed under Striga, low and high nitrogen conditions at three locations in Nigeria. The inbreds were further genotyped with two beta-carotene hydroxylase 1 (crtRB1) markers, and their seeds were quantified for provitamin A content. Significant (P < 0.01) genetic variations were observed for grain yield and other agronomic attributes of the inbreds under varying environmental conditions. Levels of PVATL for the inbreds ranged from 2.21–10.95 µg g−1, 0.04–0.08%, and 0.19–0.39%, respectively. Beta-carotene marker, crtRB1-3′TE, was polymorphic and grouped the inbreds into two. The marker was effective in identifying inbreds with moderate provitamin A content. Inbreds TZEEIORQ 5, TZEEIORQ 52, and TZEEIORQ 55 exhibited resistance to Striga, tolerance to nitrogen stress with moderate levels of PVATL and could be invaluable sources of favorable alleles for breeding nutritionally improved maize varieties with resistance/tolerance to Striga and soil nitrogen stress.