Molecular Breeding for Abiotic Stresses in Maize (Zea mays L.)

Abiotic constraints resulting from climate changes have widespread yield reducing effects on all field crops and therefore should receive high priority for crop breeding research. Conventional breeding has progressed a lot in building tolerant genotypes but abiotic stress tolerance breeding is limited by the complex nature of abiotic stress intensity, frequency, duration and timing, linkage drag of undesirable traits/genes with desirable traits; and transfer of favorable genes/alleles from diverse plant genetic resources limited by gene pool barriers giving molecular breeding a good option for breeding plant genotypes that can thrive in stress environments. Molecular breeding (MB) approaches viz., marker-assisted selection (MAS), marker-assisted backcrossing breeding (MABB), marker assisted recurrent selection (MARS) and genomic selection (GS) or genome wide selection (GWS) offer opportunities for plant breeders to develop high yielding maize cultivars with resilience to diseases in less time duration precisely. For complex traits (mainly abiotic stresses) where multiple QTLs control the expression, new strategies like marker assisted recurrent selection (MARS) and genomic selection (GS) are employed to increase precision and to reduce cost of phenotyping and time duration with disease resilience. This review discusses recent developments in molecular breeding for developing and improving abiotic stress resilience in field crops

Breeding climate change resilient maize and wheat for food security

Climate change is affecting agriculture directly or indirectly, worldwide and is an important challenge that threatens the long-term production growth of cereals. Fluctuating temperature, green-house gases, rainfall, and high humidity directly affect the crops, pathogens, insects, and weeds. Several new diseases, weeds, and insect pests have started appearing with the changing climate. Maize and wheat are the two of the most important food crops worldwide with too are getting affected. Predictions suggest that climate change will reduce maize and wheat production this will coincide with a substantial increase in demand for maize and wheat due to rising populations. Maize and wheat research has a crucial role to play in enhancing adaptation to and mitigation of climate change while also enhancing food security. The varieties of agricultural crops with increased tolerance to heat and drought stress and resistance to pests and diseases are serious for handling existing climatic variability and for adaptation to progressive climate change. Numerous climate resilient agricultural technologies such as zero tillage (no tillage), laser land leveling, happy seeder, raised-bed planting, tensiometer, and rotavator have been invented for the conservation of agricul-ture. Further, drip irrigation and fertigation, leaf color chart (LCC) for need-based application of nitrogen, integrated nutrient management (INM) systems, integrated pest management (IPM) systems, integrated disease management (IDM) systems, site-specific management systems using remote sensing, GPS, and GIS, and Web-based decision support systems for controlling diseases and insect pests are being commercialized to mitigate the climate change

Studies on drought tolerance in maize inbred lines using morphological and molecular approaches

A set of hundred homozygous maize inbred lines were analyzed for drought toleranceby studying twenty-four traits related to maturity, morphological, physiological, yield, quality and few root traits. Evaluation confirmed a wide range of variability revealing significant response of main effects (lines, irrigations and years and their respective digenic and trigenic interactions). These lines were subjected to different stress regimes over years leading to identification of fifteen elite lines which performed well under droughtstress showing inbuilt drought tolerance. A set of 32 SSR markers, having genome-wide coverage, were chosen for genotyping the inbred lines. These markers generated a total of 239 polymorphic alleles with an average of 7.47 alleles per locus. The minimum and maximum PIC value was 0.886 and 0.608 with a mean of 0.782. The coefficient of genetic dissimilarity ranged from 0.215 to 0.148. DARwin derived cluster analysis grouped 15 elite maize lines in three major clusters with five lines each in cluster-III and II and four lines in cluster-I with KDM-361A as root. Molecular diversity however, confirmed diverse genetic nature of six lines (KDM-372, KDM-343A, KDM-331, KDM-961, KDM-1051 and KDM-1156) showing drought tolerance. Exploitation of identified elite lines in a crossing program involving all possible combinations would help to develop hybrids with inbuilt mechanism to drought tolerance. Markers viz., umc -1766, umc-1478 and phi-061 recorded PIC >8 and alleles per locus more than 9 and therefore, discriminated the set of lines more efficiently. Genotyping data complemented by morpho- hysiological parameters were used to identify a number of pair-wise combinations for the development of mapping population segregating for drought tolerance and potential heterotic pairs for the development of drought tolerant hybrids.

Molecular breeding for resilience in maize - A review

Abiotic and biotic constraints have widespread yield reducing effects on maize and should receive high priority for maize breeding research. Molecular Breeding offers opportunities for plant breeders to develop cultivars with resilience to such diseases with precision and in less time duration. The term molecular breeding is used to describe several modern breeding strategies, including marker-assisted selection, marker-assisted backcrossing, marker-assisted recurrent selection and genomic selection. Recent advances in maize breeding research have made it possible to identify and map precisely many genes associated with DNA markers which include genes governing resistance to biotic stresses and genes responsible for tolerance to abiotic stresses. Marker assisted selection (MAS) allows monitoring the presence, absence of these genes in breeding populations whereas marker assisted backcross breeding effectively integrates major genes or quantitative trait loci (QTL) with large effect into widely grown adapted varieties. For complex traits where multiple QTLs control the expression, marker assisted recurrent selection (MARS) and genomic selection (GS) are employed to increase precision and to reduce cost of phenotyping and time duration. The biparental mapping populations used in QTL studies in MAS do not readily translate to breeding applications and the statistical methods used to identify target loci and implement MAS have been inadequate for improving polygenic traits controlled by many loci of small effect. Application of GS to breeding populations using high marker densities is emerging as a solution to both of these deficiencies. Hence, molecular breeding approaches offers ample opportunities for developing stress resilient and high-yielding maize cultivars

Trends in breeding oat for nutritional grain quality - An overview

Oat is an economically important crop and ranks sixth in world cereal production after maize, wheat, rice, barley and sorghum. It has been primarily utilized as livestock feed. However, the utilization of oats for human consumption has increased progressively, owing to its dietary and health benefits which relies mainly on the total dietary fibre and ?-glucan content, which significantly reduces postprandial blood glucose, insulin and blood lipids, especially serum total and low density lipoprotein cholesterol. Henceforth, enhancing Oat b-glucan content forhuman consumption is desirable. As it is a polygenic trait controlled mainly by genes with additive effects, phenotypic selection for greater b-glucan content would be effective for developing cultivars with elevated b-glucan contents. Oat b-glucan concentration has been found to be positively correlated with protein content and negatively correlated with oil content. ?-glucan yield (i.e., Product of grain yield and ?-glucan content) has been found to correlate positively with both grain yield (r = 0.92) and ?-glucan content (r = 0.66). Hence, this nutritional oat grain quality has been improved through selection for improved grain yield as they both increase simultaneously. Among wild accessions, A. atlantica genotypes have high ?-glucan content (2·2–11·3%) and have been used in breeding programmes for increasing the ?-glucan content of adapted elite local germplasm. Besides conventional breeding approaches, molecular breeding approaches have made possible to identify several molecular markers linked to ?-glucan rich regions across oat genome hence enabling mapping and dissection of ?-glucan rich genomic regions and accelerating the improvement in nutritional grain quality

Diversity analysis of maize inbred lines using DIVA-GIS under temperate ecologies

The vagaries of Climate Change variability need to be addressed and as climatic conditions change at particular experimental sites and maize producing regions, mega-environment assignments will need to be reassessed to guide breeders to appropriate new germplasm and target environments . The development of improved germplasm to meet the needs of future generations in light of climate change and population growth is of the upmost importance . Evaluation of the inbred lines from diverse ecosystems would be effective for production of lines with resilience towards climate variability. Hence, with this objective diverse set of inbred lines sourced from all over India were characterized and were evaluated with DIVA-GIS for diversity analysis of maize inbred lines. Grid maps generated for these maize inbred lines for eleven quantitative traits indicated that these lines can be sourced from North and South India. High Shannon diversity index with maximum range of 2.17-3.0, 2.25-3.0, 2.36-3.0, 2.4-4.0, 2.0-3.0, and 2.2-3.0 were recorded for the traits viz; plant height, ear height, grain weight, grain yield, kernel row and protein content respectively indicating the high response of these traits to ecosystem. However, inbred lines were found to be diverse for all the traits except for ears plant-1 (EPP) and they have been sourced from Northern and Southern parts of India while for EPP recorded less diversity index range of 0.4-1.0 indicating source from South India. Interestingly, less diverse inbred lines for all the eleven quantitative traits have been sourced from Indogangetic plains as indicated in diversity grid maps. Maximum diversity indices were recorded for anthesis silking interval (ASI), days to silking, days to tasseling, which are in the range of 0.97-2.0, 1.528-2.0, 1.516-2.0 and 1.528-2.0 respectively. Hence, DIVA-GIS enabled identification of diverse sources from varied ecosystems which can be used for developing improved lines/ cultivars with greater resilience towards climate change

Breeding Maize for Food and Nutritional Security

Maize occupies an important position in the world economy, and serves as an important source of food and feed. Together with rice and wheat, it provides at least 30 percent of the food calories to more than 4.5 billion people in 94 developing countries. Maize production is constrained by a wide range of biotic and abiotic stresses that keep afflicting maize production and productivity causing serious yield losses which bring yield levels below the potential levels. New innovations and trends in the areas of genomics, bioinformatics, and phenomics are enabling breeders with innovative tools, resources and technologies to breed superior resilient cultivars having the ability to resist the vagaries of climate and insect pest attacks. Maize has high nutritional value but is deficient in two amino acids viz. Lysine and Tryptophan. The various micronutrients present in maize are not sufficient to meet the nutritive demands of consumers, however the development of maize hybrids and composites with modifying nutritive value have proven to be good to meet the demands of consumers. Quality protein maize (QPM) developed by breeders have higher concentrations of lysine and tryptophan as compared to normal maize. Genetic level improvement has resulted in significant genetic gain, leading to increase in maize yield mainly on farmer’s fields. Molecular tools when collaborated with conventional and traditional methodologies help in accelerating these improvement programs and are expected to enhance genetic gains and impact on marginal farmer’s field. Genomic tools enable genetic dissections of complex QTL traits and promote an understanding of the physiological basis of key agronomic and stress adaptive and resistance traits. Marker-aided selection and genome-wide selection schemes are being implemented to accelerate genetic gain relating to yield, resilience, and nutritional quality. Efforts are being done worldwide by plant breeders to develop hybrids and composites of maize with high nutritive value to feed the people in future