Line x testers analysis of tropical maize inbred lines under heat stress for grain yield and secondary traits

The combining ability and mode of gene action in tropical maize germplasm is not extensively studied. In the present study, a line x tester analysis involving 290 test-cross hybrids developed by crossing 145 tropical maize inbred lines with two testers and four standard checks was conducted for grain yield and other agronomic traits under heat stress during summer 2013 at B gudi agriculture research station. The main objective of the investigation was to study mode of gene action governing the traits under heat stress along with identification of superior inbred lines based on combining ability to develop heat tolerant hybrids. Analysis of variance showed that mean squares for genotypes was highly significant for grain yield, days to anthesis and silking, anthesis silk interval, plant height and ear height under heat stress. The combining analysis for lines (GCA), tester (GCA) and line x tester (SCA) showed significant difference (P < 0.01) for all the traits under study except ASI for LXT interaction. This indicates that both additive and non additive gene action control the expression of these traits under heat stress. The low GCA variance to SCA variance ratio for all the traits showed preponderance of non-additive gene action in the inheritance of the traits. Among 145 inbred lines used for study, the inbreds L78, L73, and L37 showed good general combining ability for grain yield. The crosses L118 x L2 and L143 x L1 were having good specific combiners ability for grain yield under heat stress. These inbreds can be used in breeding program for development of heat tolerant hybrids through exploitation of dominant gene action

Genetic diversity, linkage disequilibrium and population structure among CIMMYT maize inbred lines, selected for heat tolerance study

Rising temperatures has led to reduced maize yields in tropical and sub tropical countries. This provides the necessity for identifying the diverse inbred lines that can produce high yielding hybrids under high temperature regimes. With this view, the present study was conducted to analyse the extent of genetic diversity and population structure among 64 CIMMYT maize inbred lines using SNP markers derived from GBS (Genotyping by sequencing) along with characterization of haplotype blocks and linkage disequilibrium. The average polymorphic information content (0.37) and gene diversity was very high (0.5) with mean kinship coefficients of 0.28 and genetic distance more than 0.4 between pair of two inbred lines. Clustering analysis based on ward’s method and euclid- ian distance showed presence of three sub groups. The population structure analysis using principle components showed three sub population. The average physical distance between pairs of markers was 27.7 kb with linkage disequilibrium (LD) estimation (r2) of 0.36 across all chromosomes, with rapid LD decay of 6.34 kb at r2 = 0.2. Haplotype analysis with 75,664 SNPs under confidence interval model revealed 616 haplotype blocks across all chromosomes with highest number of blocks on chromosome 5. The results clearly indicate the uniqueness of the majority of the inbred lines, which can contribute to new alleles in breeding programs for heat tolerance

Heat-tolerant maize for rainfed hot, dry environments in the lowland tropics: from breeding to improved seed delivery

Climate change-induced heat stress combines two challenges: high day- and nighttime temperatures, and physiological water deficit due to demand-side drought caused by increase in vapor-pressure deficit. It is one of the major factors in low productivity of maize in rainfed stress-prone environments in South Asia, affecting a large population of smallholder farmers who depend on maize for their sustenance and livelihoods. The International Maize and Wheat Improvement Center (CIMMYT) maize program in Asia, in partnership with public-sector maize research institutes and private-sector seed companies in South Asian countries, is implementing an intensive initiative for developing and deploying heat-tolerant maize that combines high yield potential with resilience to heat and drought stresses. With the integration of novel breeding tools and methods, including genomics-assisted breeding, doubled haploidy, field-based precision phenotyping, and trait-based selection, new maize germplasm with increased tolerance to heat stress is being developed for the South Asian tropics. Over a decade of concerted effort has resulted in the successful development and release of 20 high-yielding heat-tolerant maize hybrids in CIMMYT genetic backgrounds. Via public–private partnerships, eight hybrids are presently being deployed on over 50,000 ha in South Asian countries, including Bangladesh, Bhutan, India, Nepal, and Pakistan

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Not AvailablePapaya ringspot virus (PRSV) is one of the most devastating viruses which causes huge damage to papaya plantations across the globe. PRSV is a positive sense RNA virus encoding for a polyprotein that is processed into ten proteins. In this study for the first time we analyzed the variability for 15 PRSV isolates from a selected geographical region of a South Indian state Karnataka, which is under intensive papaya cultivation. Variability studies were done for two genes at the 5′ end of the viral genome, namely P1 and helper component proteinase (Hc-Pro) and towards the 3′ end, a 788 nt overlapping region of nuclear inclusion B (NIb, 692 nt) and of capsid protein (CP, 96 nt), referred as NIb-CP. Our studies indicate that the P1 is most variable region with a wider range of sequence identity, followed by Hc-Pro, while the 788 nt of NIb-CP was most conserved. P1 also showed maximum recombination events followed by Hc-Pro, whereas NIb-CP did not show any recombination. Further, the pattern and number of phylogenetic clusters was variable for each of the three genomic regions of PRSV isolates. Estimation of selection pressure for all the three PRSV genomic regions indicated negative and purifying selection.Not Availabl

Enhancing Legume Cultivars through Agronomy, Breeding, and Genetics

Legumes are a multipurpose crop species, with a great economic value, which, worldwide, are commonly cultivated for human food, livestock fodder, industrial raw materials, and soil health enhancement. Over the last few decades, numerous research projects have been conducted for the genetic improvements of legumes, in order to meet the Sustainable Development Goals of 2015–2030. Remarkable progress has been made in legume genetics, genomics, and breeding. The first references to the genome of legume plants were published in 2010, and these were the complete draft genome sequences of Glycine max. The chromosome scale high-quality genome assembly and annotations are available for many legume species today, including Glycine max; Lotus japonicus; Medicago ruthenica (L.); Medicago truncatula; Phaseolus lunatus; Mucuna pruriens; Vicia sativa; Trifolium pratense; Lupinus angustifolius; Cajanus cajan; Vigna radiata ssp.; and Cicer arietinum. Large-scale transcriptomic, genotyping, and phenotyping data have been generated from this diverse panel of legume cultivars for their varietal improvements. This Special Issue presents a collection of a variety of articles that cover the recent progress that has been made in legume genetics, genomics, and breeding. The authors have addressed the applications of phenotypic and genotypic diversity for the selection of the best cultivars; of morphological traits for the selection of the best local variety, the estimation of the agronomic performances of resistant and susceptible cultivars; the nutritional characteristics of the seed protein; genome-wide association studies on agronomic traits and isolation; and the characterization and function studies of many agronomically important genes

Introgression of Stay Green Quantitative Trait Locus (QTLS) into Elite Sorghum Variety by MABC

Sorghum is a major staple food crop for the people in semi-arid areas of Asia. Post-flowering drought is a global constraint of sorghum production. The study aimed to improve stay-green characteristics of GS-23 sorghum variety by transferring stg3A and stg3B QTL`s respectively from donor genotypes K260 and K359w of ICRISAT by using marker assisted backcrossing. The experimental material comprised of six basic generations P1, P2, F1, F2, BC1 and BC2 developed from crossing GS-23 × K260 and GS-23 × K359 were genotyped using a set of 133 SNPs and 79 SSR markers. Whereas, 53 polymorphic SNPs among parents and backcross F1s for stay green trait at maturity were used to track introgression of stay green trait. Similarly,10 SSR markers were found to be polymorphic were used to track introgression of stay green trait i.e., stay green trait QTL`s stg3A and stg3B from donor parent K260 and K359w respectively in GS-23 background across backcross population and to identify plants that were homozygous for the desired allele. In which 02 SNPs SnpSB0039 and SnpSB0093 were identified as polymorphic for both K260 and K359w. Whereas 17 SNPs identified polymorphic for K260 and 34 SNPs for K359w. These SNPs were validated in both F1 and BC1F1 populations of both the crosses. Similarly, out of 10 SSR markers utilized, 02 SSRs were identified polymorphic to K260 and 02 SSRs were identified for K359w. Whereas 06 SSRs were polymorphic to both the parents K260 and K359w. Prominent 02 SSRs viz., Xtxp 141_Fam and Xgap84_Vic found to be more reliable and polymorphic to both the parents. These SSRs were validated in both F1 and BC1F1 populations of both the crosses. The genotypic analysis revealed the presence of favorable alleles in homozygous conditions at markers loci associated with stg3A and stg3B&nbsp; QTL`s in BC populations, suggesting successful introgression of stay green QTLs from the donor parents to the recurrent parent. Therefore, our study demonstrated the utility of marker-assisted backcrossing for drought tolerance improvement of locally adapted sorghum variety

Assessing Combining Ability of Doubled Haploid Maize (Zea mays L.) Breeding Lines for Grain Yield and Yield Components under Heat Stress Condition

Maize (Zea mays L.), a leading cereal worldwide and staple food of many countries, is a multipurpose crop used for human food, animal feed and industry purposes. Maize has wider genetic adaptability to grow under different agro-ecological environments. 29 and 48 DH lines derived from MPS 1 and MPS 2, respectively, were crossed with more than one testers belonging to opposite heterotic in L x T fashion. The resultant double haploid testcrosses, and their parents were evaluated along with checks during kharif (in South Asia: the autumn crop sown at the beginning of the summer rains) 2019 at three locations. Among female lines of MPS1, DH line ZL19337 was identified as good general combiner and registered significant negative GCA effect for days to 50 per cent anthesis and days to 50 per cent silking. While, DH lines ZL19641 and ZL19357 recorded significantly positive GCA for plant height and grain yield, respectively. Among female lines of MPS 2, DH line ZL19492 was identified as good general combiner and recorded significant negative GCA effects for days to 50 per cent anthesis, and days to 50 per cent silking. Similarly, DH lines, ZL19534 and ZL19572 were identified as good general combiners for grain yield and ear position, respectively. Among testers of MPS1, ZL1840 was identified as the good general combiner for days to 50 per cent anthesis, days to 50 per cent silking and plant height and CAL14113 for ear height and grain yield.&nbsp; Similarly, VL1010996 was identified as the good general combiner for days to 50 per cent anthesis, days to 50 per cent silking, plant height, ear height, ear position and grain yield in MPS 2. Hybrid&nbsp; ZH2063 exhibited desired SCA effects for days to 50 per cent anthesis and days to 50 silking and&nbsp; ZH2010 was identified as a good specific combiner for days to 50 per cent anthesis and grain yield in MPS 1. Hybrid ZH20158 recorded desirable SCA effects for the trait days to 50 silking, While, ZH20251 and ZH20183 were identified as good specific combiners for plant height and&nbsp; grain yield in MPS 2

Character Association Study in Maize Hybrids Developed through Integration of Rapid Cycle Genomic Selection and Doubled Haploid Technology for Heat Stress Tolerance

Heat stress is becoming a major constraint for maize production; therefore heat stress resilience has emerged as an important aspect in maize hybrids targeted for post rainy spring season. Selection of genotypes based on high grain yield under heat stress condition is often misleading and the identification of secondary traits also associated with grain yield may help in development of heat tolerant cultivars. Hence, the present research work to study the association of traits was conducted during summer and kharif 2018 and rabi 2018-19 at Bheemarayanagudi and Raichur using 111 testcross progenies of doubled haploids derived from C1, C2 and C3 cycles of multi-parental synthetic population 1 and 2 improved through rapid cycle genomic selection for heat stress tolerance. The phenotypic correlation analysis under heat stress and optimal conditions, number of kernels per cob and cob girth exhibited the strong positive association with grain yield per plant. Further, under early spring condition number of kernels per cob, cob length, cob girth and 100 grain weight recorded the strong positive association with grain yield per plant. However, when considering across heat stress, early spring and optimal conditions, the grain yield per plant showed positive and significant strong to moderate association with the traits viz., number of kernels per cob, cob length and cob girth under all the seasons. In addition, days to 50% silking showed significant negative correlation with grain yield per plant under heat stress and optimal condition. Hence, the simultaneous selection criteria for the genotypes that exerts early silking, higher number of kernels per cob, higher cob girth and lengthy cob should be the priority of breeders to achieve higher grain yields in maize under heat stress condition as well as optimal conditions

Genotype-by-Environment Interaction Effects under Heat Stress in Tropical Maize

Spring maize area has emerged as a niche market in South Asia. Production of maize during this post-rainy season is often challenged due to heat stress. Therefore, incorporating heat stress resilience is an important trait for incorporation in maize hybrids selected for deployment in this season. However, due to the significant genotype &times; environment interaction (GEI) effects under heat stress, the major challenge lies in identifying maize genotypes with improved stable performance across locations and years. In the present study, we attempted to identify the key weather variables responsible for significant GEI effects, and identify maize hybrids with stable performance under heat stress across locations/years. The study details the evaluation of a set of prereleased advanced maize hybrids across heat stress vulnerable locations in South Asia during the spring seasons of 2015, 2016 and 2017. Using factorial regression, we identified that relative humidity (RH) and vapor pressure deficit (VPD) as the two most important environmental covariates contributing to the large GEI observed on grain yield under heat stress. The study also identified reproductive stage, starting from tassel emergence to early grain-filling stage, as the most critical crop stage highly susceptible to heat stress. Across-site/year evaluation resulted in identification of six high yielding heat stress resilient hybrids

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Not AvailableMost parts of the Asian tropics are hotspots of climate change effects and associated weather variabilities. One of the major challenges with climate change is the uncertainty and inter-annual variability in weather conditions as crops are frequently exposed to different weather extremes within the same season. Therefore, agricultural research must strive to develop new crop varieties with inbuilt resilience towards variable weather conditions rather than merely tolerance to individual stresses in a specific situation and/or at a specific crop stage. C4 crops are known for their wider adaptation to range of climatic conditions. However, recent climatic trends and associated variabilities seem to be challenging the threshold limit of wider adaptability of even C4 crops like maize. In collaboration with national programs and private sector partners in the region, CIMMYT-Asia maize program initiated research for development (R4D) projects largely focusing on saving achievable yields across range of variable environments by incorporating reasonable levels of tolerance/resistance to major abiotic and biotic stresses without compromising on grain yields under optimal growing conditions. By integrating novel breeding tools like - genomics, double haploid (DH) technology, precision phenotyping and reducing genotype × environment interaction effects, a new generation of maize germplasm with multiple stress tolerance that can grow well across variable weather conditions were developed. The new maize germplasm were targeted for stress-prone environments where maize is invariability exposed to a range of sub-optimal growing conditions, such as drought, heat, waterlogging and various virulent diseases. The overarching goal of the stress-resilient maize program has been to achieve yield potential with a downside risk reduction.Not Availabl