Conventional Breeding Strategies Research Articles

Revolutionizing Tomato Cultivation: CRISPR/Cas9 Mediated Biotic Stress Resistance.

Tomato (Solanum lycopersicon L.) is one of the most widely consumed and produced vegetable crops worldwide. It offers numerous health benefits due to its rich content of many therapeutic elements such as vitamins, carotenoids, and phenolic compounds. Biotic stressors such as bacteria, viruses, fungi, nematodes, and insects cause severe yield losses as well as decreasing fruit quality. Conventional breeding strategies have succeeded in developing resistant genotypes, but these approaches require significant time and effort. The advent of state-of-the-art genome editing technologies, particularly CRISPR/Cas9, provides a rapid and straightforward method for developing high-quality biotic stress-resistant tomato lines. The advantage of genome editing over other approaches is the ability to make precise, minute adjustments without leaving foreign DNA inside the transformed plant. The tomato genome has been precisely modified via CRISPR/Cas9 to induce resistance genes or knock out susceptibility genes, resulting in lines resistant to common bacterial, fungal, and viral diseases. This review provides the recent advances and application of CRISPR/Cas9 in developing tomato lines with resistance to biotic stress.

Establishment of an Efficient Sugarcane Transformation System via Herbicide-Resistant CP4-EPSPS Gene Selection

Sugarcane (Saccharum spp.), a major cash crop that is an important source of sugar and bioethanol, is strongly influenced by the impacts of biotic and abiotic stresses. The intricate polyploid and aneuploid genome of sugarcane has shown various limits for conventional breeding strategies. Nonetheless, biotechnological engineering currently offers the best chance of introducing commercially significant agronomic features. In this study, an efficient Agrobacterium-mediated transformation system that uses the herbicide-resistant CP4-EPSPS gene as a selection marker was developed. Notably, all of the plants that were identified by PCR as transformants showed significant herbicide resistance. Additionally, this transformation protocol also highlighted: (i) the high yield of transgenic lines from calli (each gram of calli generated six transgenic lines); (ii) improved selection; and (iii) a higher transformation efficiency. This protocol provides a reliable tool for a routine procedure for the generation of resilient sugarcane plants.

Direct Organogenesis of Citrus Cultivars from Shoot Tip Nodal Segments.

Citrus cultivar improvement via conventional breeding strategies is impeded by factors related to its reproductive biology. The orange is a hybrid between pomelo (Citrus maxima) and mandarin (Citrus reticulata). Among various orange cultivars, Valencia oranges have a bit of bitter tang mixed in with their sweetness, as Navel oranges are, the most widely cultivated citrus species, quite sweeter, and also don't contain any seeds. Tangelo mandarin orange cultivar is a hybrid of C. reticulata × C. maxima or × C. paradisi. The present study was undertaken to optimize the hormonal composition of the media with regard to plant growth regulators for in vitro propagation of sweet orange cultivars from nodal segment explants. The nodal segment explants were collected from three citrus cultivars, Washington Navel, Valencia and Tangelo. Murashige and Skoog (MS) medium supplemented with sucrose and different concentrations of growth regulators was used for shoot proliferation and root induction, and the optimum medium composition was assessed. The patent for Citrus Tissue Culture was obtained from the Office of Research Affairs, Haramaya University. The results indicate that the highest shoot response was recorded for Washington's navel with maximum shoot proliferation rate (99.75%), shoot number per explant (1.76), shoot length (10.70 cm), leaf number per explants (3.54) after three weeks of culture. In all experiments, no growth was observed for the basal MS medium. Phytohormone combinations of IAA (1.2 mg/L) and kinetin (2.0 mg/L) were found to be the best for shoot proliferation. Among the cultivars, there were significant differences for the highest rooting rate (81.255), root number (2.22), and root length (2.95 cm) variables for Washington Navel. The lowest rooting rate (48.45%), root number (1.47) and root length (2.26 cm) were observed for Valencia. The highest rooting rate (84.90%), root number per microshoot (2.22) and root length (3.05 cm) was on MS medium supplemented with 1.5 mg/L NAA. A comparison of different concentrations of IAA and NAA on root induction of microshoots from nodal segments of citrus cultivars demonstrated NAA was a more effective hormone than IAA.

Evaluation of breeding cost in the French maritime pine breeding program and perspectives for alternative strategies using molecular markers

The economic efficiency of conventional breeding strategies for forest trees based on biparental crosses is compared with that of alternative strategies based on pedigree reconstruction using molecular markers. Analyses of economic efficiency is based on comparisons of breeding scenarios corresponding to the same total investment. The first step is the description and cost evaluation of each basic operation, from crossing to genetic selection and clonal archive establishment. Breeding scenarios are then compared by stochastic sampling with a parametric genetic model (POPSIM), the comparison criteria in this case being genetic gain in the seed orchard for a given level of genetic diversity. Additionally, the economic gain resulting from the use of improved material is estimated for different levels of breeding investment. Our analysis shows that genotyping costs account for a much smaller proportion of total investment than phenotyping costs. We also show that, in comparisons of breeding scenarios corresponding to the same total investment, the three main breeding strategies (biparental crosses, polymix crosses, and open pollination) achieve similar genetic gains provided that sufficiently large numbers of parents are considered. These results open up promising perspectives for the wider integration of molecular markers into forest tree breeding strategies.

Breeding for Biotic Stress Resistance in Pea

Pea (Pisum sativum) stands out as one of the most significant and productive cool-season pulse crops cultivated worldwide. Dealing with biotic stresses remains a critical challenge in fully harnessing pea’s potential productivity. As such, dedicated research and developmental efforts are necessary to make use of omic resources and advanced breeding techniques. These approaches are crucial in facilitating the rapid and timely development of high-yielding varieties that can tolerate and resist multiple stresses. The availability of advanced genomic tools, such as comprehensive genetic maps and reliable DNA markers, holds immense promise for integrating resistance genes from diverse sources. This integration helps accelerate genetic gains in pea crops. This review provides an overview of recent accomplishments in the genetic and genomic resource development of peas. It also covers the inheritance of genes controlling various biotic stress responses, genes that control pathogenesis in disease-causing organisms, the mapping of genes/QTLs, as well as transcriptomic and proteomic advancements. By combining conventional and modern omics-enabled breeding strategies, genetic gains can be significantly enhanced.

Conventional and molecular breeding strategies for improvement of drought tolerance cultivars in rice: Recent approaches and outlooks

Rice is a vital staple food, especially in Asia, but it is highly susceptible to drought, leading to significant yield losses. To ensure food sustainability, drought-tolerant rice varieties are essential. Conventional breeding methods improve drought tolerance by focusing on biometric traits like root depth, avoidance, escape, and tolerance. This involves screening and crossing drought-tolerant varieties with high-yielding ones, followed by selection and evaluation. Techniques such as pedigree selection, recurrent selection, and backcrossing introduce desirable genes to enhance drought tolerance. Induced mutation through radiation exposure is also used. The molecular basis of drought tolerance involves identifying and manipulating genes responsible for rice's response to water stress. Techniques like QTL analysis, transcriptomics, genomics, and proteomics identify genes and QTLs associated with drought tolerance. Important genes involved in drought response include DREB, LEA, and ROS scavenging genes. Identifying QTLs enables the development of molecular markers for efficient screening of drought-tolerant rice genotypes. In conclusion, conventional breeding and molecular approaches are employed to develop drought-tolerant rice varieties. Conventional breeding improves biometric traits, while molecular techniques identify and manipulate specific genes associated with drought tolerance. This combination holds promise for high-yielding and drought-tolerant rice cultivars, contributing to global food security. However, further research is needed to understand the complex genetic mechanisms underlying drought tolerance in rice and enhance breeding precision and efficiency.

Genomic assisted breeding and holistic management of abiotic and biotic stress in silkworm host cultivation: A review

Silk is a high-value, low-volume product, produced by an important insect commonly known as the silkworm. Sericulture serves as a source of livelihood for farmers besides being an important source of economy for many countries including India. Sustainable production of premium silk depends on continuous production of quality foliage as feed for silkworms obtained from host plants. The production of silk is significantly hampered when host plants are subjected to biotic and abiotic stresses. The foliage harvest could be enhanced when these constraints are efficiently managed by the development of stress-resistant host cultivars. Improved stress-resistant cultivars have been developed using conventional breeding strategies and used in commercial cultivation. However, the highly heterozygous genetic nature of the hosts makes it difficult to understand the inheritance and expression of these quantitative traits. Adoption of appropriate conventional breeding strategies along with genomics tools such as genome-wide association studies, transcriptomics, proteomics, metabolomics and advanced OMICS approaches could prove handy in the development of improved and stress-resistant cultivars. Deeper understanding of the mechanism of tolerance to various stress is required in breeding for improved cultivars. The number of stress-tolerant cultivars is scanty and therefore, holistic management of these stresses through an inter-disciplinary approach could be the most suitable strategy. Adoption of appropriate cultural practices and control measures is necessary for sustainable production under stress regimes. This comprehensive review holds great importance in improving silkworm host cultivation and to researchers in the field of sericulture.

Drought stress in rice: morpho-physiological and molecular responses and marker-assisted breeding.

Rice (Oryza Sativa L.) is an essential constituent of the global food chain. Drought stress significantly diminished its productivity and threatened global food security. This review concisely discussed how drought stress negatively influenced the rice's optimal growth cycle and altered its morpho-physiological, biochemical, and molecular responses. To withstand adverse drought conditions, plants activate their inherent drought resistance mechanism (escape, avoidance, tolerance, and recovery). Drought acclimation response is characterized by many notable responses, including redox homeostasis, osmotic modifications, balanced water relations, and restored metabolic activity. Drought tolerance is a complicated phenomenon, and conventional breeding strategies have only shown limited success. The application of molecular markers is a pragmatic technique to accelerate the ongoing breeding process, known as marker-assisted breeding. This review study compiled information about quantitative trait loci (QTLs) and genes associated with agronomic yield-related traits (grain size, grain yield, harvest index, etc.) under drought stress. It emphasized the significance of modern breeding techniques and marker-assisted selection (MAS) tools for introgressing the known QTLs/genes into elite rice lines to develop drought-tolerant rice varieties. Hence, this study will provide a solid foundation for understanding the complex phenomenon of drought stress and its utilization in future crop development programs. Though modern genetic markers are expensive, future crop development programs combined with conventional and MAS tools will help the breeders produce high-yielding and drought-tolerant rice varieties.

Optimization of Hormonal Compositions of Media in In Vitro Propagation of Orange Cultivars from Shoot Tip Nodal Segments

Orange is one of the most horticulturally important and widely cultivated Citrus species. Citrus cultivar improvement via conventional breeding strategies is normally impeded by factors related to its reproductive biology. The present study was undertaken to investigate the optimization of growth regulators’ composition of media in in vitro propagation of orange cultivar from nodal segment explants. The nodal segment explants were collected from sweet orange cultivars. The MS medium supplemented with sucrose and different concentrations of growth regulators were used for shoot proliferation and root induction. The optimum compositions of growth regulators in MS medium were assessed. The result indicated that the highest shoot response was recorded for Washington naval orange with maximum shoot proliferation rate (99.75%), shoot number per explant (3.10), shoot length (10.70 cm), leaf number per explants (12.50) after three weeks of culture. In all experiments, no growth was observed for the basal MS medium. Phytohormones combinations of indole-3-acetic acid, IAA (1.2 mg/L), and kinetin (2.0 mg/L) were found to be the best for shoot proliferation. Among the cultivars, significantly, the highest rooting rate (81.25%), root number (4.95), and root length (2.95 cm) were recorded for Washington naval orange cultivar. The least rooting rate (48.45%), root number (3.55), and root length (2.26 cm) were observed from the Valencia cultivar. Significantly, the highest rooting rate (84.90%), root number per microshoot (5.20), and root length (3.05 cm) for MS medium supplemented with 1.5 mg/L 1-naphthalene acetic acid (NAA). The comparison of different concentrations of IAA and NAA on root induction of microshoots from nodal segments of sweet orange cultivars demonstrated NAA as the more effective hormone than IAA.

Breeding Strategies for Drought Tolerance in Crop Plant, A View

Drought is one of the most severe abiotic stresses in many regions of the world, and it is one of the most urgent issues in the current climate scenario. Drought-tolerant varieties are in high demand, which appears to be a challenging task for plant breeders. However, difficulties are complicated by crop production challenges on genetic and physiological bases. Drought is one of the most major environmental factors affecting crop productivity and quality around the world. Drought mostly impacts crops that thrive in wetland conditions, which account for 80% of all farmed land in the world. Climate change raises the likelihood of increased drought in many regions of the world in the next decades, causing crop damage as a result of abnormal metabolism and perhaps reducing crop growth, crop death, or crop development death. Drought resistance is defined as the mechanism(s) that cause the crop to lose the least amount of yield in a drought environment compared to the highest yield in a constant-free of optimal environment. Drought stress reduces the size of the leaves, stem extension, and root proliferation inside the soil; it also disrupts plant water relations and reduces water-use efficiency, reducing the plant’s yielding ability. Therefore, breeding for drought resistance is a good approach, combining both conventional and molecular approaches to develop a drought resistant variety. Root morphology research, proline estimates, and leaf rolling are all factors to take into account. Breeding improved drought-tolerant cultivars may be more effective if selection is based on a comprehensive approach to testing. Water stress also affects the crop’s physiological activity by inhibiting photosynthesis and assimilates consumption in the growing leaves. Plant hormones play a key role in transducing the stress signal, with abscisic acid (ABA) being the most important among them. To alleviate suitable crop productivity under environmental stresses, scientists developed various breeding strategies, such as conventional breeding, which works for both self-pollinated and cross-pollinated crops and is used to develop or improve cultivars using a basic conservative tool for manipulating plant genomes within the natural genetic boundaries of species. Pedigree, recurrent selection, back-crossing, and mutation breeding are among the conventional breeding strategies used to generate cultivars that can withstand drought stress.

Genotypic Yield Stability of Wild and Landrace Sorghum Species Under Drought Stress and Striga Infestation

Recurring drought stress cycles and widespread striga (Striga hermonthica (Del.) Benth) infestations are two of the major constraints of sorghum production in sub-Saharan Africa (SSA) where they cause a crop loss of about 60 billion US dollars and affect a population of about 100 M people annually. Plant breeders continue to employ conventional and molecular crop breeding strategies in the search for durable genetic resistance/tolerance mechanisms or for germplasm with genes against these two constraints. Crop wild relatives and landraces remain valuable resources of resistance/tolerance genes and have been utilized in the past to improve tolerance to drought stress and resistance to striga. The aim of this study was to assess the stability of performance of 64 sorghum wild relatives, landraces and progenies from some generation of crosses under striga infested and drought stress conditions in agroecological environments endemic for these two stresses. The performance of the genotypes under drought stress was assessed in well-watered and in water stressed conditions at the Kenya Agricultural Livestock Research Organization (KALRO) Kiboko Research Centre whereas the same set was evaluated under striga artificially infested field and potted trials at the KALRO Alupe Research Centre during 2018/2019 rainy seasons. Genotypes, B35 × ICSV III N, Macia, N13, ICSV 111 IN, F6YQ212 × B35, SRN39, GENO47293, ICSV 111 IN × B35, IS9830, Framida, GENO 45827, F6YQ212, B35 × AKUOR ACHOT were found to maintain stable high yields in both striga and drought conditions. The results here, showed that Genotype, Genotype × Environment (GGE) interaction partitioned genotypes in two of the four mega-environments according to their stability and mean grain yield (GY) and identified representative genotypes of the two traits that could be exploited to develop superior sorghum varieties adapted to drought and striga prone environments.

Genomics Enabled Breeding Strategies for Major Biotic Stresses in Pea (Pisum sativum L.).

Pea (Pisum sativum L.) is one of the most important and productive cool season pulse crops grown throughout the world. Biotic stresses are the crucial constraints in harnessing the potential productivity of pea and warrant dedicated research and developmental efforts to utilize omics resources and advanced breeding techniques to assist rapid and timely development of high-yielding multiple stress-tolerant–resistant varieties. Recently, the pea researcher’s community has made notable achievements in conventional and molecular breeding to accelerate its genetic gain. Several quantitative trait loci (QTLs) or markers associated with genes controlling resistance for fusarium wilt, fusarium root rot, powdery mildew, ascochyta blight, rust, common root rot, broomrape, pea enation, and pea seed borne mosaic virus are available for the marker-assisted breeding. The advanced genomic tools such as the availability of comprehensive genetic maps and linked reliable DNA markers hold great promise toward the introgression of resistance genes from different sources to speed up the genetic gain in pea. This review provides a brief account of the achievements made in the recent past regarding genetic and genomic resources’ development, inheritance of genes controlling various biotic stress responses and genes controlling pathogenesis in disease causing organisms, genes/QTLs mapping, and transcriptomic and proteomic advances. Moreover, the emerging new breeding approaches such as transgenics, genome editing, genomic selection, epigenetic breeding, and speed breeding hold great promise to transform pea breeding. Overall, the judicious amalgamation of conventional and modern omics-enabled breeding strategies will augment the genetic gain and could hasten the development of biotic stress-resistant cultivars to sustain pea production under changing climate. The present review encompasses at one platform the research accomplishment made so far in pea improvement with respect to major biotic stresses and the way forward to enhance pea productivity through advanced genomic tools and technologies.

Development of new wine‐, dried‐ and tablegrape scions and rootstocks for Australian viticulture: past, present and future

This review highlights the contributions of CSIRO to the development of new scions and rootstocks for the Australian winegrape, driedgrape and tablegrape industries. Initially, CSIRO played a pivotal role in the selection of high-yielding Sultana clones which contributed over half the total Australian grape crop in the 1970s used for wine- and driedgrape production. It was also responsible for importation and evaluation of the Salt Creek (syn. Ramsey) rootstock which provided tolerance to root-knot nematodes and salinity and became the most widely adopted rootstock for the emerging Australian wine industry in the 1980–1990s. The CSIRO has also successfully bred or released several new grape cultivars. While the adoption rate for the CSIRO wine cultivars has been limited, CSIRO-selected cultivars dominate the Australian driedgrape industry, while CSIRO-released cultivars continue to play an important role in the Australian tablegrape industry. In the 1990s, CSIRO commenced the application of molecular biology techniques for grapevine germplasm improvement. Researchers from CSIRO were some of the first in the world to successfully regenerate transgenic grapevines and demonstrate the potential of this technology to produce low-browning driedgrapes and mildew-resistant premium winegrapes. More recently, the focus has shifted to the mapping of resistance loci from wild grape species and their introgression into new winegrape scions to provide resistance to mildews and new rootstocks to provide durable resistance to rootknot nematodes and phylloxera. Finally, this review considers some future challenges faced by the Australian grape industries and how these might be addressed using conventional or molecular breeding strategies.

Discovery of potential protein biomarkers associated with sugarcane white leaf disease susceptibility using a comparative proteomic approach.

Sugarcane white leaf disease (SCWLD) is caused by phytoplasma, a serious sugarcane phytoplasma pathogen, which causes significant decreases in crop yield and sugar quality. The identification of proteins involved in the defense mechanism against SCWLD phytoplasma may help towards the development of varieties resistant to SCWLD. We investigated the proteomes of four sugarcane varieties with different levels of susceptibility to SCWLD phytoplasma infection, namely K88-92 and K95-84 (high), KK3 (moderate), and UT1 (low) by quantitative label-free nano-liquid chromatography-tandem mass spectrometry (nano LC-MS/MS). A total of 248 proteins were identified and compared among the four sugarcane varieties. Two potential candidate protein biomarkers for reduced susceptibility to SCWLD phytoplasma were identified as proteins detected only in UT1. The functions of these proteins are associated with protein folding, metal ion binding, and oxidoreductase. The candidate biomarkers could be useful for further study of the sugarcane defense mechanism against SCWLD phytoplasma, and in molecular and conventional breeding strategies for variety improvement.

Successful creation of seedless (sterile) leucaena germplasm developed from interspecific hybridisation for use as forage

Context The legume shrub/tree leucaena (Leucaena leucocephala (Lam.) de Wit.) is highly regarded as a cattle fodder, although it is considered an environmental weed in many parts of Australia. Aims We investigated the feasibility of developing a forage variety of triploid leucaena through interspecific hybridisation that is sterile (without seeds) as a strategy to mitigate its weed risk. Methods A conventional breeding strategy was used to create triploid hybrids from hand-crosses between tetraploid and diploid species of leucaena. Molecular markers were developed to confirm successful crosses and flow cytometry was used to confirm the ploidy level. The plants are being evaluated for flowering behaviour, seed and herbage production across two environmentally diverse sites at Carnarvon and Kununurra in northern Western Australia. Key results During 2018/19 and 2019/20, 2260 crosses between 45 different combinations of diploid females by tetraploid males and their reciprocals have created over 3000 putative triploid hybrid plants. This is the first time that triploids have successfully been created in Australia and 10 new parental combinations were created as a world-first. Conclusions A cohort of sterile triploid plants has been identified and selections will be made based on their edible biomass productivity, insect tolerance, capacity for regrowth after cutting, nutritive value and plant chemistry (including anti-methanogenic responses). A sterile leucaena variety will have application not only in Australian grazing systems but also in other tropical regions of the world. Implications A cost-effective technology for mass vegetative propagation of leucaena will be required for commercialisation of a sterile variety.

Genetics and Genomics of Fusarium Wilt of Chilies: A Review

Hot pepper (Capsicum annum L.) is a major spice crop and is used worldwide for its nutritional value. In the field, its plant is susceptible to various fungal diseases, including fusarium wilt, caused by soil-borne fungus Fusarium oxysporum f. sp. capsici, which can survive in the soil for several years. The infected plant can be recognized by the yellowing of older leaves and downward curling of apical shoots, followed by plant wilting and ultimately the death of the plant. The resistance mechanism in plants is controlled by a single dominant gene, and conventional plant breeding techniques are used to develop a wilt-resistant germplasm. Non-conventional techniques such as gene pyramiding and expression enhancement of antifungal genes could be used to shorten the time to develop resistance against fusarium wilt in hot peppers. In this review, we discuss different aspects of the disease and the molecular basis of resistance in chili/hot pepper plants. Furthermore, this review covers the scope of conventional and non-conventional breeding strategies and different management approaches used to tackle the disease.

Breeding maize (Zea mays) for Striga resistance: Past, current and prospects in sub-saharan africa.

Striga hermonthica, causes up to 100% yield loss in maize production in Sub‐Saharan Africa. Developing Striga‐resistant maize cultivars could be a major component of integrated Striga management strategies. This paper presents a comprehensive overview of maize breeding activities related to Striga resistance and its management. Scientific surveys have revealed that conventional breeding strategies have been used more than molecular breeding strategies in maize improvement for Striga resistance. Striga resistance genes are still under study in the International Institute for Tropical Agriculture (IITA) maize breeding programme. There is also a need to discover QTL and molecular markers associated with such genes to improve Striga resistance in maize. Marker Assistance Breeding is expected to increase maize breeding efficiency with complex traits such as resistance towards Striga because of the complex nature of the host‐parasite relationship and its intersection with other environmental factors. Conventional alongside molecular tools and technical controls are promising methods to effectively assess Striga in Sub‐Saharan Africa.

Genetic dissection of physiological traits over trait based breeding in bread wheat conferring terminal heat tolerance

Breeding of heat-tolerant cultivars requires knowledge of the genetic behavior of morpho-physiological traits. Gene action was investigated using wide phenotypic segregation ranging across six generations (P1, P2, F1, BC1, BC2 and F2) of four different tolerant × sensitive crosses for grain filling duration, GFD (40.14–46.20); canopy temperature depression, CTD (2.42–5.97); normalized difference vegetation index, NDVI (0.35–0.61); membrane thermostability index, MSI (31.40–40.93); no. of grains/spike, GN/SP (26.29–54.80); thousand-grain weight, TGW (31.70–44.45); and grain yield/plant, GY (15.37–24.89) under terminal heat stress. Scaling results indicated an absence of epistasis for MSI and TGW in cross PBN51 × HUW510. The prominence of Dominance × dominance interaction over additive × additive and additive × dominance interactions along with significant dominant gene effect [h] for all traits except MSI was observed. For MSI, similar signs of [d] and [i] along with significant [j] showed the possibility of exploitation of additive gene effect. CTD, NDVI and GN/SP were controlled by duplicated epistasis, whereas both complementary and duplicate epistasis was found for GFD. Digenic interactions with prominent duplicate epistasis indicate that biparental mating or diallel selective mating might be efficiently utilized for their improvement. The present investigation indicated a preponderance of non-additive gene action for studied traits, thus, implying toward delaying of selection to the later generations to exploit transgressive segregants. Any conventional breeding strategy would be followed for generating the cultivars with low CTD, reduced cell membrane injury, with higher NDVI, TGW, GFD, no. of grains/spike and grain yield/plant.

Root endophyte induced plant thermotolerance by constitutive chromatin modification at heat stress memory gene loci.

Global warming has become a critical challenge to food security, causing severe yield losses of major crops worldwide. Conventional and transgenic breeding strategies to enhance plant thermotolerance are laborious and expensive. Therefore, the use of beneficial microbes could be an alternative approach. Here, we report that the root endophyte Enterobacter sp. SA187 induces thermotolerance in wheat in the laboratory as well as in open‐field agriculture. To unravel the molecular mechanisms, we used Arabidopsis thaliana as model plant. SA187 reprogramed the Arabidopsis transcriptome via HSFA2‐dependent enhancement of H3K4me3 levels at heat stress memory gene loci. Unlike thermopriming, SA187‐induced thermotolerance is mediated by ethylene signaling via the transcription factor EIN3. In contrast to the transient chromatin modification by thermopriming, SA187 induces constitutive H3K4me3 modification of heat stress memory genes, generating robust thermotolerance in plants. Importantly, microbial community composition of wheat plants in open‐field agriculture is not influenced by SA187, indicating that beneficial microbes can be a powerful tool to enhance thermotolerance of crops in a sustainable manner.

Challenges and Progresses of Molecular Plant Breeding in Crop Improvement

Molecular marker is applicable to many aspects of plant improvement and crop production. The main objective of plant breeding to produce crops with improved characteristics with the utilization of the available genetic variability and producing sufficient genetic variability of crops by different breeding techniques. There are possibilities to improve the desired traits through conventional breeding methods in the presence of genetic diversities. However, there are several challenges to make the significant improvement on the crop through conventional breeding. Conventional breeding is almost always based on phenotypic variation of the crops, which is affected by environments (non-heritable components) and crop improvement cycle takes long time. However, molecular marker is designed to meet this challenges regardless of its cost and it’s not affected by environment where ever the experiment is conducted either in laboratory or field condition. Molecular marker procedures are playing a significant role to increase the effectiveness in breeding and shorten the development crop improvement stages. Molecular markers also used develop resistant crop to pests and diseases, develop tolerant crop to environmental conditions and improve the crop in required quality. In facing the challenge of improving several lines for quantitative traits, marker assisted selection strategies use DNA markers in one key selection step to maximize their impact. With the development of molecular marker technology, the fate of plant breeding has changed. Different types of molecular markers have been developed in identification and characterization germplasm, DNA sequences in identification of the genomic regions involved in the expression of the target traits, to analysis the genetic variation, cytogenetic, quantitative genetics, biotechnology and genomics and it’s applied in genetic diversity analysis in crop improvement. It is possible to increase agricultural productivity through addressing the problems of yield reduction and its links with pest management and climate change using advanced breeding technologies. There are several major challenges in the application of molecular markers to agronomically important traits. Some of them are: economic factors, lack of grants to researchers, lack of adequately trained personnel. Generally, the integrating molecular marker technologies with the conventional breeding strategies are increasingly important to realize genetic gains with greater speed and precision. Keywords: Molecular marker; Marker assisted breeding; quantitative traits; Plant breeding DOI: 10.7176/JNSR/11-21-04 Publication date: November 30 th 2020