Crop yield reduction as a consequence of increasingly severe climatic events threatens global food security. Genetic loci that ensure productivity in challenging environments exist within the germplasm of crops, their wild relatives and species that are adapted to extreme environments. Selective breeding for the combination of beneficial loci in germplasm has improved yields in diverse environments throughout the history of agriculture. An effective new paradigm is the targeted identification of specific genetic determinants of stress adaptation that have evolved in nature and their precise introgression into elite varieties. These loci are often associated with distinct regulation or function, duplication and/or neofunctionalization of genes that maintain plant homeostasis.

Genetic mechanisms of abiotic stress tolerance that translate to crop yield stability.

The first haploid angiosperm, a dwarf form of cotton with half the normal chromosome complement, was discovered in 1920, and in the ninety years since then such plants have been identified in many other species. They can occur either spontaneously or can be induced by modified pollination methods in vivo, or by in vitro culture of immature male or female gametophytes. Haploids represent an immediate, one-stage route to homozygous diploids and thence to F(1) hybrid production. The commercial exploitation of heterosis in such F(1) hybrids leads to the development of hybrid seed companies and subsequently to the GM revolution in agriculture. This review describes the range of techniques available for the isolation or induction of haploids and discusses their value in a range of areas, from fundamental research on mutant isolation and transformation, through to applied aspects of quantitative genetics and plant breeding. It will also focus on how molecular methods have been used recently to explore some of the underlying aspects of this fascinating developmental phenomenon.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1467-7652.2009.00498.x

Haploids in flowering plants: origins and exploitation.

Deleterious effects of climate change and human activities, as well as diverse environmental stresses, present critical challenges to food production and the maintenance of natural diversity. These challenges may be met by the development of novel crop varieties with increased biotic or abiotic resistance that enables them to thrive in marginal lands. However, considering the diverse interactions between crops and environmental factors, it is surprising that evolutionary principles have been underexploited in addressing these food and environmental challenges. Compared with domesticated cultivars, crop wild relatives (CWRs) have been challenged in natural environments for thousands of years and maintain a much higher level of genetic diversity. In this review, we highlight the significance of CWRs for crop improvement by providing examples of CWRs that have been used to increase biotic and abiotic stress resistance/tolerance and overall yield in various crop species. We also discuss the surge of advanced biotechnologies, such as next-generation sequencing technologies and omics, with particular emphasis on how they have facilitated gene discovery in CWRs. We end the review by discussing the available resources and conservation of CWRs, including the urgent need for CWR prioritization and collection to ensure continuous crop improvement for food sustainability.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/eva.12434

Back into the Wild – Apply Untapped Genetic Diversity of Wild Relatives for Crop Improvement

Rice is semi-aquatic, adapted to a wide range of hydrologies, from aerobic soils in uplands to anaerobic and flooded fields in waterlogged lowlands, to even deeply submerged soils in flood-prone areas. Considerable diversity is present in native rice landraces selected by farmers over centuries. Our understanding of the adaptive features of these landraces to native ecosystems has improved considerably over the recent past. In some cases, major genes associated with tolerance have been cloned, such as SUB1A that confers tolerance of complete submergence and SNORKEL genes that control plant elongation to escape deepwater. Modern rice varieties are sensitive to flooding during germination and early growth, a problem commonly encountered in rainfed areas, but few landraces capable of germination under these conditions have recently been identified, enabling research into tolerance mechanisms. Major QTLs were also identified, and are being targeted for molecular breeding and for cloning. Nevertheless, limited progress has been made in identifying regulatory processes for traits that are unique to tolerant genotypes, including faster germination and coleoptile elongation, formation of roots and leaves under hypoxia, ability to catabolize starch into simple sugars for subsequent use in glycolysis and fermentative pathways to generate energy. Here we discuss the state of knowledge on the role of the PDC-ALDH-ACS bypass and the ALDH enzyme as the likely candidates effective in tolerant rice genotypes. Potential involvement of factors such as cytoplasmic pH regulation, phytohormones, reactive oxygen species scavenging and other metabolites is also discussed. Further characterization of contrasting genotypes would help in elucidating the genetic and biochemical regulatory and signaling mechanisms associated with tolerance. This could facilitate breeding rice varieties suitable for direct seeding systems and guide efforts for improving waterlogging tolerance in other crops.

/pdf/tolerance-of-anaerobic-conditions-caused-by-flooding-during-1dgxduyppc.pdf

Tolerance of anaerobic conditions caused by flooding during germination and early growth in rice (Oryza sativa L.).

Flooding tolerance: O2 sensing and survival strategies.

Effect of Genotype and Callus Induction Medium on Green Plant Regeneration from Anther of Nepalese Rice Cultivars

2 Abstract: The use of gamete based dihaploid technology greatly enhances the production of complete homozygous wheat lines in a single generation and increases the precision and efficacy of selection process in crop breeding. It is a useful tool to reduce the time in attaining homozygosity not only for wheat breeding, but also for various aspects of its genetical studies. Anther culture and wide hybridization are most commonly used method for wheat polyhaploid induction. However, in the recent years it has commonly been experienced that wheat x maize system of crosses following chromosome elimination is an effective and handy tool among available methods for haploid induction in wheat. Its superiority over other techniques includes higher efficacy (2-3 times more efficient for green plant production than the anther culture), simple, less genotype dependent response, less gametoclonal variation and less time consuming. In this paper we try to elucidate several aspects of this system to be used for the production of dihaploid lines in wheat improvement programme.

Overview of Wheat X Maize System of Crosses for Dihaploid Induction in Wheat

This study was under taken to elucidate the effect of genotypes and media compositions on callus induction from mature rice seeds. Three different callus induction media, designated as A (N6 mineral salts + N6 vitamins, 2 mg/l each + myoinositol, 100 mg/l + 2,4-D, 2.5 mg/l + kinetin, 0.5mg/l + AgNO 3 , 10 mg/l + maltose, 50 gm/l); B (MS organic salts + N6 mineral salts + NAA, 4 mg/l + kinetin, 2 mg/l + AgNO 3 , 5mg/l and sucrose, 60 gm/l); and C (B media without AgNO 3 ), and six rice genotypes viz. Jumlimarshi, Tilki, Jethobudo, Manshara, Masuli and Pahenle were evaluated. The modified N6 medium supplemented with 2, 4-D, 2.5 mg/l and AgNO 3 , 10 mg/l exhibited better performance in callus induction. Among genotypes, callus induction frequency was higher (100%) in Masuli, Tilki and Jumlimarshi regardless of media tested. The positive effect of AgNO 3 was only observed in medium A for quality callus induction and subsequent plant regeneration. The genotype Tilki performed better regarding plant regeneration (27.77%). Therefore, it is suggested that application of medium A is advantageous to accomplish overall efficiency of callus induction and plant regeneration from seeds of various rice genotypes. Key words: 2, 4-D; AgNO 3 ; dehulled rice; in vitro; regeneration 
J. Inst. Agric. Anim. Sci. 26:21-26 (2005)

/pdf/effect-of-genotype-and-culture-media-on-callus-induction-and-4sjppj71s7.pdf

Effect of Genotype and Culture Media on Callus Induction and Plant Regeneration from Matured Rice Grain Culture

The present study was carried out taking single F 1 wheat and four maize varieties, viz. Arun-1, Arun-2, Khumal Yellow and Rampur Composite, to determine the efficiency and influence of maize genotypes on various parameters of haploid formation. Wheat spikelets were hand pollinated with freshly collected maize pollen, and 1 ml of 100 ppm 2,4-D was immediately injected on the uppermost internode. Twenty-four hours after 2,4- D injection, the cups of the florets were filled with the same solution of 2,4-D for two more consecutive days. Seventeen days after pollination, the embryos were excised and cultured in half-strength MS basal medium supplemented with 30 g/l sucrose, and 7 g/l agar. The cultured embryos were maintained at 25°C with 16/8 hours light/darkness after treating in the dark for seven days at 4°C and incubation in the dark for seven days at 25°C. Application of 2,4-D after pollination was found to be essential to the recovery of culturable size of embryos. The significant effect of maize genotypes on frequency of ovary development, embryo formation and haploid plant per pollinated floret was observed. The mean percentages of embryo formation and haploid plants per pollinated floret varied from 5.17 to 21.45 and 0.96 to 10.15, respectively, depending upon the maize varieties used. The highest frequency of embryo recovery and plant per floret was found when wheat F 1 was pollinated with Arun-2 followed by Arun-1 and Khumal Yellow. It is suggested that the production of dihaploids (DHs) in wheat can be enhanced by using more responsive maize genotypes as pollinators. Key words: 2,4-D, caryopsis, floret, haploid embryo, wheat x maize cross Himalayan Journal of Sciences Vol.4(6) 2007 p.65-69

/pdf/production-of-haploid-wheat-plants-from-wheat-triticum-157z1umsrz.pdf

Production of haploid wheat plants from wheat ( Triticum aestivum L.) x maize ( Zea mays L.) cross system

2 Abstract: Polyhaploid induction response was studied taking 23 F wheat genotypes derived from diverse 1 sources of germplasm using maize variety, Khumal Yellow, as a pollen parent. Wheat spikelets were hand pollinated with freshly collected maize pollen. Hand pollinated wheat spikes were immediately injected with 1 ml of 100 ppm 2, 4-Dichlorophenoxyacetic acid (2, 4-D) at uppermost internode. On the following two days, the cups of the florets were filled with the same solution of 2, 4-D. After 17 days of pollination, developed embryos were aseptically excised and cultured in ½ MS basal medium. Cultures were kept for 7 day at 4°C in dark and then grown at 25°C with 16/8 hours light/dark regime. The highly differential response of wheat genotypes on percentages of seed set, embryo formation and plant per pollinated floret was enunciated. The percentages of embryos formation and polyhaploid plants per floret varied from 0-56.0 and 0-10.1, respectively. The highest percentage of embryo recovery and plant per floret was found in F wheat in 1 crosses involving Bezostaya-1/Ghiling and E#06/Bez-1//WK962. Altogether, 42 polyhaploid plants were successfully produced by pollinating 2120 florets from fourteen hybrid combinations. This study indicated that the efficiency of polyhaploid induction in wheat through wheat x maize system is also determined by wheat genotypes under study.

/pdf/response-of-wheat-genotypes-to-maize-mediated-polyhaploid-2e2jkcep0o.pdf

Response of Wheat Genotypes to Maize Mediated Polyhaploid Production

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