ABSTRACT
Intraspecific hybrids of Arabidopsis sometimes display heterosis. However, allelic variation of flowering repressor genes causes late flowering in F1, which might distort the potential ...heterosis effect due to prolonged vegetative growth. Here, overexpression of flowering gene FT synchronized flowering and eliminated growth differentials between parental and F1. These findings indicate the possibility of quantitatively demonstrating the inherent heterosis caused by heterozygosity.
Gadam cultivar of sorghum has been characterized by low yields compared to the international yield levels of sorghum. In this research, Gadam was crossed with Serena, Seredo, and Kari/Mtama-1 in an ...attempt to increase yield through heterosis. The objective of this study was to determine the level of compatibility and heterosis in crosses between Gadam and the three sorghum lines in a reciprocal crossing. Gadam was crossed with the three lines and their reciprocals to make six treatments that were subjected to compatibility and heterosis tests. The F1 hybrid lines and their parental controls were sown in a randomized complete block design in three replicates. Compatibility and heterosis data variances were analyzed using R statistical software. The cross between Gadam x Serena, Serena x Gadam and the parent Gadam exhibited moderate mean plant height ranging from 99.5 cm to 120.5 cm. The cross Gadam x Serena recorded a desirable negative mid-parent heterosis of -19.89 and -16.16 for plant height and days to maturity respectively. All F1 hybrids recorded positive mid-parent heterosis for the panicle length, the number of reproductive tillers, a thousand seed weight, and the number of tillers per plant. The crosses Gadam x Seredo, Seredo x Gadam, Gadam x Serena and Kari/Mtama-1 x Gadam recorded significantly lower grain filling percentages compared to their parents. In conclusion, the F1 hybrids differed significantly from their reciprocal crosses especially in days of heading, flowering, and maturity indicating a significant maternal influence in these traits. Also, the mid-parent and better parent heterosis had a nonsignificant difference in quantitative traits assessed except for the plant height and grain filling percentage.
Population genomic analysis of hybrid zones is instrumental to our understanding of the evolution of reproductive isolation. Many temperate hybrid zones are formed by the secondary contact between ...two parental populations that have undergone postglacial range expansion. Here, we show that explicitly accounting for historical parental isolation followed by range expansion prior to secondary contact is fundamental to explaining genetic and fitness patterns in these hybrid zones. Specifically, ancestral population expansion can result in allele surfing, where neutral or slightly deleterious mutations drift to high frequency at the expansion front. If these surfed deleterious alleles are recessive, they can contribute to substantial heterosis in hybrids produced at secondary contact, counteracting negative effects of Bateson-Dobzhansky-Muller incompatibilities (BDMIs) and hence weakening reproductive isolation. When BDMIs are linked to such recessive deleterious alleles, the fitness benefit of introgression at these loci can facilitate introgression at the BDMIs. The extent to which this occurs depends on the strength of selection against the linked deleterious alleles and the distribution of recombination across the chromosome. Finally, surfing of neutral loci can alter the expected pattern of population ancestry; thus, accounting for historical population expansion is necessary to develop accurate null genomic models of secondary contact hybrid zones.
Rice is the foremost food crop among cereals and it is staple food crop providing high calories for the people of South East Asia. The Objectives of the study was the extent of heterosis components ...of grain yield in F1 hybrids. The Materials for this study considered of parents and thirty F1 hybrids derived from crossing of three cross lines viz., IR58025A, IR62829A and PUSA3A and ten testers. Pollen and spikelet fertility revealed the identification of ten testers. For heterosis studies majority of the crosses showed positive heterosis for the characters viz., productive tillers, filled grains per panicle, spikelet fertility, thousand grain weight, grain yield per plant, grain length, grain breadth, grain L/B ratio, kernel L/B ratio, milling recovery, head rice recovery, and amylose content. Negative heterosis were recorded for the characters namely days to first flowering, plant height, panicle length, kernel length, kernel breadth and alkali digestion value. Hybrids IR58025A ´ ASD19, IR62829A ´ ASD16, PUSA3A ´ IR42 were found to record high per se performance, higher percentage of standard heterosis for majority of the traits.
Self-incompatibility (SI) systems prevent self-fertilization in several species of Poaceae, many of which are economically important forage, bioenergy and turf grasses. Self-incompatibility ensures ...cross-pollination and genetic diversity but restricts the ability to fix useful genetic variation. In most inbred crops it is possible to develop high-performing homozygous parental lines by self-pollination, which then enables the creation of F1 hybrid varieties with higher performance, a phenomenon known as heterosis. The inability to fully exploit heterosis in outcrossing grasses is partially responsible for lower levels of improvement in breeding programmes compared with inbred crops. However, SI can be overcome in forage grasses to create self-compatible populations. This is generating interest in understanding the genetical basis of self-compatibility (SC), its significance for reproductive strategies and its exploitation for crop improvement, especially in the context of F1 hybrid breeding.
We review the literature on SI and SC in outcrossing grass species. We review the currently available genomic tools and approaches used to discover and characterize novel SC sources. We discuss opportunities barely explored for outcrossing grasses that SC facilitates. Specifically, we discuss strategies for wide SC introgression in the context of the Lolium-Festuca complex and the use of SC to develop immortalized mapping populations for the dissection of a wide range of agronomically important traits. The germplasm available is a valuable practical resource and will aid understanding the basis of inbreeding depression and hybrid vigour in key temperate forage grass species.
A better understanding of the genetic control of additional SC loci offers new insight into SI systems, their evolutionary origins and their reproductive significance. Heterozygous outcrossing grass species that can be readily selfed facilitate studies of heterosis. Moreover, SC introduction into a range of grass species will enable heterosis to be exploited in innovative ways in genetic improvement programmes.
In the ovules of most sexual flowering plants female gametogenesis is initiated from a single surviving gametic cell, the functional megaspore, formed after meiosis of the somatically derived ...megaspore mother cell (MMC). Because some mutants and certain sexual species exhibit more than one MMC, and many others are able to form gametes without meiosis (by apomixis), it has been suggested that somatic cells in the ovule are competent to respond to a local signal likely to have an important function in determination. Here we show that the Arabidopsis protein ARGONAUTE 9 (AGO9) controls female gamete formation by restricting the specification of gametophyte precursors in a dosage-dependent, non-cell-autonomous manner. Mutations in AGO9 lead to the differentiation of multiple gametic cells that are able to initiate gametogenesis. The AGO9 protein is not expressed in the gamete lineage; instead, it is expressed in cytoplasmic foci of somatic companion cells. Mutations in SUPPRESSOR OF GENE SILENCING 3 and RNA-DEPENDENT RNA POLYMERASE 6 exhibit an identical defect to ago9 mutants, indicating that the movement of small RNA (sRNAs) silencing out of somatic companion cells is necessary for controlling the specification of gametic cells. AGO9 preferentially interacts with 24-nucleotide sRNAs derived from transposable elements (TEs), and its activity is necessary to silence TEs in female gametes and their accessory cells. Our results show that AGO9-dependent sRNA silencing is crucial to specify cell fate in the Arabidopsis ovule, and that epigenetic reprogramming in companion cells is necessary for sRNA-dependent silencing in plant gametes.
The experiment consists of thirty hybrids generated in a Line x Tester mating design by crossing six lines with five male parents and studied along with two checks (BPT5204 and DRR dhan-45) for 16 ...characters contributing to yield and grain Zn content in rice. Analysis of variance exhibited significant differences among the genotypes for all the traits under investigation indicating the presence of sufficient variability in material and can be exploited. Among all the crosses, the hybrid, HUR-3022 x Dudhkander exhibited the highest significant positive heterobeltiosis for the number of effective tillers (91.94%), the number of grains per panicle (16.44%), 1000 grain weight (26.28%), grain yield per plant (214.03%) and biomass (225.12 %). HUR-3022 x Sathi exhibited the highest positive better parent heterosis for grain Zn content (38.37%). Standard heterosis over checks BPT-5204 and DRR dhan-45 of 214.03 and 40.07 per cent respectively, were exhibited by the cross, HUR-3022 x Dudhkander for yield plant per plant HUR-3022 x Sathi exhibited the highest positive economic heterosis of 69.42 and 60.26 per cent over BPT-5204 and DRR dhan-45 for grain Zn, respectively. Hence, these two hybrids viz., HUR-3022 x Dudhkander and HUR-3022 x Sathi can be exploited in breeding hybrids for high yield and high grain Zinc with further evaluation in multiple locations.
Key message
The review outlines advances in pigeonpea genomics, breeding and seed delivery systems to achieve yield gains at farmers’ field.
Pigeonpea is a nutritious and stress-tolerant grain legume ...crop of tropical and subtropical regions. Decades of breeding efforts in pigeonpea have resulted in development of a number of high-yielding cultivars. Of late, the development of CMS-based hybrid technology has allowed the exploitation of heterosis for yield enhancement in this crop. Despite these positive developments, the actual on-farm yield of pigeonpea is still well below its potential productivity. Growing needs for high and sustainable pigeonpea yields motivate scientists to improve the breeding efficiency to deliver a steady stream of cultivars that will provide yield benefits under both ideal and stressed environments. To achieve this objective in the shortest possible time, it is imperative that various crop breeding activities are integrated with appropriate new genomics technologies. In this context, the last decade has seen a remarkable rise in the generation of important genomic resources such as genome-wide markers, high-throughput genotyping assays, saturated genome maps, marker/gene–trait associations, whole-genome sequence and germplasm resequencing data. In some cases, marker/gene–trait associations are being employed in pigeonpea breeding programs to improve the valuable yield and market-preferred traits. Embracing new breeding tools like genomic selection and speed breeding is likely to improve genetic gains. Breeding high-yielding pigeonpea cultivars with key adaptation traits also calls for a renewed focus on systematic selection and utilization of targeted genetic resources. Of equal importance is to overcome the difficulties being faced by seed industry to take the new cultivars to the doorstep of farmers.
A research study was conducted involving four high yielding rice varieties viz., CO 51, MDU 6, ADT (R) 45 and ASD 16 as lines and five drought tolerant genotypes viz., CR Dhan 201, CR Dhan 203, DRR ...DHAN 42, Apo and GP 239 as testers to understand the nature of gene action, combining ability of parents and hybrids, the extent of heterosis for drought tolerance and yield traits. The ratio of GCA and SCA were less than unity revealed the predominance of dominance gene action for all the drought tolerant and yield traits. Based on both per se performance and gca, the lines viz., MDU 6, ADT (R) 45 and the tester viz., DRR DHAN 42 were identified as the best general combiners for yield and drought related traits. Hence, these parental genotypes could be used in developing cross combinations to produce desirable segregants with various mechanisms of drought tolerance and grain yield. Among the 20 hybrids, CO 51 x CR Dhan 203 and MDU 6 x CR Dhan 201 were good specific combiners, which had significant sca effects for many yield and drought tolerant traits. The crosses MDU 6 x DRR DHAN 42 and ADT (R) 45 x DRR DHAN 42 exhibited significantly positive heterosis for panicle length, productive tillers, chlorophyll stability index, relative water content, filled grains per panicle, grain yield, root length, dry root weight, root volume, root thickness and root/shoot ratio. Combining per se performance, sca and standard heterosis, the hybrids MDU 6 × DRR DHAN 42, ADT (R) 45 ×DRR DHAN 42, ASD 16 × DRR DHAN 42 and MDU 6 × CR Dhan 201 were identified as superior hybrids since they possessed good performance for many drought tolerant traits.
Heterosis for days to flowering,days to maturity, plant height, number of primary branches per plant, number of capsules per plant, number of seeds per capsule,chlorophyll content,oil per ...cent,protein per cent and single plant yield were evaluated in 36 crosses derived from a 9 x 9 diallel mating design in sesame. Heterosis was worked out over midparent and better parent.Combinations Priya X Vianyak, PBTil-1 X TMV-6 and TC-25 X Vinayak showed a highly significant relative heterosis and heterobeltiosis for single plant yield and some of its yield components and hence could be exploited for developing superior varieties.
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