Efficient Breeding Strategies Research Articles

Molecular Mapping of QTLs Associated with Lodging Resistance in Dry Direct-Seeded Rice (Oryza sativa L.).

Dry direct-seeded rice (DSR) is an alternative crop establishment method with less water and labor requirement through mechanization. It provides better opportunities for a second crop during the cropping season and therefore, a feasible alternative system to transplanted lowland rice. However, lodging is one of the major constraints in attaining high yield in DSR. Identification of QTLs for lodging resistance and their subsequent use in improving varieties under DSR will be an efficient breeding strategy to address the problem. In order to map the QTLs associated with lodging resistance, a set of 253 BC3F4 lines derived from a backcross between Swarna and Moroberekan were evaluated in two consecutive years. A total of 12 QTLs associated with lodging resistance traits [culm length (qCL), culm diameter (qCD), and culm strength (qCS)] were mapped on chromosomes 1, 2, 6, and 7 using 193 polymorphic SNP markers. Two major and consistent effect QTLs, namely qCD1.1 (with R2 of 10%) and qCS1.1 (with R2 of 14%) on chromosome 1 with id1003559 being the peak SNP marker (flanking markers; id1001973-id1006772) were identified as a common genomic region associated with important lodging resistance traits. In silico analysis revealed the presence of Gibberellic Acid 3 beta-hydroxylase along with 34 other putative candidate genes in the marker interval region of id1001973-id1006772. The positive alleles for culm length, culm diameter, and culm strength were contributed by the upland adaptive parent Moroberekan. Our results identified significant positive correlation between lodging related traits (culm length diameter and strength) and grain yield under DSR, indicating the role of lodging resistant traits in grain yield improvement under DSR. Deployment of the identified alleles influencing the culm strength and culm diameter in marker assisted introgression program may facilitate the lodging resistance under DSR.

Differential DNA methylation and gene expression in reciprocal hybrids between Solanum lycopersicum and S. pimpinellifolium.

Wide hybridization is a common and efficient breeding strategy for enhancing crop yield and quality. An interesting phenomenon is that the reciprocal hybrids usually show different phenotypes, and its underlying mechanism is not well understood. Here, we reported our comparative analysis of the DNA methylation patterns in Solanum lycopersicum, Solanum pimpinellifolium and their reciprocal hybrids by methylated DNA immunoprecipitation sequencing. The reciprocal hybrids had lower levels of DNA methylation in CpG islands and LTR retroelements when compared with those of their parents. Importantly, remarkable differences in DNA methylation patterns, mainly in introns and CDS regions, were revealed between the reciprocal hybrids. These different methylated regions were mapped to 79 genes, 14 of which were selected for analysis of gene expression levels. While there was an inverse correlation between DNA methylation and gene expression in promoter regions, the relationship was complicated in gene body regions. Further association analysis revealed that there were 15 differentially methylated genes associated with siRNAs, and that the methylation levels of these genes were inversely correlated with respective siRNAs. All these data raised the possibility that the direction of hybridization induced the divergent epigenomes leading to changes in the transcription levels of reciprocal hybrids.

RNA-guided Cas9 as an invivo desired-target mutator in maize.

SummaryThe RNA‐guided Cas9 system is a versatile tool for genome editing. Here, we established a RNA‐guided endonuclease (RGEN) system as an in vivo desired‐target mutator (DTM) in maize to reduce the linkage drag during breeding procedure, using the LIGULELESS1 (LG1) locus as a proof‐of‐concept. Our system showed 51.5%–91.2% mutation frequency in T0 transgenic plants. We then crossed the T1 plants stably expressing DTM with six diverse recipient maize lines and found that 11.79%–28.71% of the plants tested were mutants induced by the DTM effect. Analysis of successive F2 plants indicated that the mutations induced by the DTM effect were largely heritable. Moreover, DTM‐generated hybrids had significantly smaller leaf angles that were reduced more than 50% when compared with that of the wild type. Planting experiments showed that DTM‐generated maize plants can be grown with significantly higher density and hence greater yield potential. Our work demonstrate that stably expressed RGEN could be implemented as an in vivo DTM to rapidly generate and spread desired mutations in maize through hybridization and subsequent backcrossing, and hence bypassing the linkage drag effect in convention introgression methodology. This proof‐of‐concept experiment can be a potentially much more efficient breeding strategy in crops employing the RNA‐guided Cas9 genome editing.

Genetics, Physiological Mechanisms and Breeding of Flood-Tolerant Rice (Oryza sativa L.).

Flooding of rice fields is a serious problem in the river basins of South and South-East Asia where about 15 Mha of lowland rice cultivation is regularly affected. Flooding creates hypoxic conditions resulting in poor germination and seedling establishment. Flash flooding, where rice plants are completely submerged for 10-15 d during their vegetative stage, causes huge losses. Water stagnation for weeks to months also leads to substantial yield losses when large parts of rice aerial tissues are inundated. The low-yielding traditional varieties and landraces of rice adapted to these flooding conditions have been replaced by flood-sensitive high-yielding rice varieties. The 'FR13A' rice variety and the Submergence 1A (SUB1A) gene were identified for flash flooding and subsequently introgressed to high-yielding rice varieties. The challenge is to find superior alleles of the SUB1A gene, or even new genes that may confer greater tolerance to submergence. Similarly, genes have been identified in tolerant landraces of rice for their ability to survive by rapid stem elongation (SNORKEL1 and SNORKEL2) during deep-water flooding, and for anaerobic germination ability (TPP7). Research on rice genotypes and novel genes that are tolerant to prolonged water stagnation is in progress. These studies will greatly assist in devising more efficient and precise molecular breeding strategies for developing climate-resilient high-yielding rice varieties for flood-prone regions. Here we review the state of our knowledge of flooding tolerance in rice and its application in varietal improvement.

Overcoming self-incompatibility in grasses: a pathway to hybrid breeding.

Allogamous grasses exhibit an effective two-locus gametophytic self-incompatibility (SI) system, limiting the range of breeding techniques applicable for cultivar development. Current breeding methods based on populations are characterized by comparably low genetic gains for important traits such as biomass yield. To implement more efficient breeding schemes, the overall understanding of the SI system is crucial as are the mechanisms involved in the breakdown of SI. Self-fertile variants in outcrossing grasses have been studied, and the current level of knowledge includes approximate gene locations, linked molecular markers and first hypotheses on their mode of action. Environmental conditions increasing seed set upon self-pollination have also been described. Even though some strategies were proposed to take advantage of self-fertility, there have, so far, not been changes in the methods applied in cultivar development for allogamous grasses. In this review, we describe the current knowledge about self-fertility in allogamous grasses and outline strategies to incorporate this trait for implementation in synthetic and hybrid breeding schemes.

Dissection of combining ability for yield and related traits using introgression lines in the background of a key restorer line in rice (Oryza sativa L.)

Combining ability analysis is commonly used to obtain information for designing more efficient hybrid breeding strategies in rice. However, genetic basis of combining ability is less studied. Two hundred and twenty eight testcross combinations developed by crossing 57 introgression lines derived from two donor parents with four types of widely used male sterile lines were used to conduct combining ability analysis and dissect the genetic basis of combining ability for grain yield and eight related traits. The variances of general combining ability (GCA) and special combining ability (SCA) for all nine traits were highly significant in both years. A total of 32 and 45 main effect QTL controlling GCA and SCA for the nine traits were identified across the two years, respectively. Only six QTL were commonly identified for GCA and SCA. Twenty one of the GCA QTL had the positive alleles from the recurrent parent, Shuhui527. Only 11 and six QTL were commonly detected in the two years, and in the two populations classified by the donor parents, respectively. As for SCA, 22 out of the 45 QTL were commonly identified in the two years and 25 QTL had positive effects. A total of 92 epistatic QTL pairs for GCA were identified. The Shuhui527 alleles at the markers RM508 and RM587 on chromosome 6 had the largest effects on GCA for GY and thus played important roles in making Shuhui527 a key parent in hybrid rice breeding. The ZDZ057 alleles at markers RM4584 on chromosome 7 and RM224 on chromosome 11 could be used to further improve GY GCA of Shuhui527.

Variability studies for needle and wood traits of different half sib progenies of Pinus roxburghii Sargent.

Genetic variability studies for needle and wood traits were carried out for the different half sib progenies of Chir pine, raised in 1985 at the main campus of University. There existed a significant variation for these traits among the different half sib progenies, viz., needle length (18.1-24.6cm), needle thickness (0.53-0.71mm), number of stomata per mm of a row (7.3-12.0), specific gravity of wood (0.36-0.46), tracheid length (1.51-1.85) and moisture content of wood (47.76-58.81). This variability was found under genetic control, as all these progenies are growing under same environment, and are of same age. Traits having high heritability and genetic gain like, needle thickness, wood specific gravity, tracheid length and others, indicate high genetic control. This variability can be exploited in tree improvement programs through selection and breeding approaches for development of advanced generations. Correlation studies for different traits at genotypic and phenotypic levels provided the basic knowledge of association to chalk out efficient breeding strategy for higher productivity through indirect selection.

Gene-based SNP discovery in tepary bean (Phaseolus acutifolius) and common bean (P. vulgaris) for diversity analysis and comparative mapping.

BackgroundCommon bean (Phaseolus vulgaris) is an important grain legume and there has been a recent resurgence in interest in its relative, tepary bean (P. acutifolius), owing to this species’ ability to better withstand abiotic stresses. Genomic resources are scarce for this minor crop species and a better knowledge of the genome-level relationship between these two species would facilitate improvement in both. High-throughput genotyping has facilitated large-scale single nucleotide polymorphism (SNP) identification leading to the development of molecular markers with associated sequence information that can be used to place them in the context of a full genome assembly.ResultsTranscript-based SNPs were identified from six common bean and two tepary bean accessions and a subset were used to generate a 768-SNP Illumina GoldenGate assay for each species. The tepary bean assay was used to assess diversity in wild and cultivated tepary bean and to generate the first gene-based map of the tepary bean genome. Genotypic analyses of the diversity panel showed a clear separation between domesticated and cultivated tepary beans, two distinct groups within the domesticated types, and P. parvifolius was confirmed to be distinct. The genetic map of tepary bean was compared to the common bean genome assembly to demonstrate high levels of collinearity between the two species with differences limited to a few intra-chromosomal rearrangements.ConclusionsThe development of the first set of genomic resources specifically for tepary bean has allowed for greater insight into the structure of this species and its relationship to its agriculturally more prominent relative, common bean. These resources will be helpful in the development of efficient breeding strategies for both species and will facilitate the introgression of agriculturally important traits from one crop into the other.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2499-3) contains supplementary material, which is available to authorized users.

Advanced Analytics for Agricultural Product Development

Syngenta, a leading developer of crop varieties (seeds) that provide food for human and livestock consumption, is committed to bringing greater food security to an increasingly populous world by creating a transformational shift in farm productivity. Syngenta Soybean Research and Development (R&D) is leading Syngenta’s corporate plant-breeding strategy by developing and implementing a new product development model that is enabling the creation of an efficient and effective soybean breeding strategy. Key to the new strategy is the combination of advanced analytics and plant-breeding knowledge to find opportunities to increase crop productivity and optimize plant-breeding processes. Syngenta uses discrete-event and Monte Carlo simulation models to codify Syngenta Soybean R&D best practices, and uses stochastic optimization to create the best soybean breeding plans and strategically align its research efforts. As a result of using these new analytical tools, Syngenta estimates that it will save more than $287 million between 2012 and 2016.

An Insight into the Glycemic Index of Rice

Glycemic index of rice is a highly complex trait. Rice varieties possessing slowly digestible starch (high amylose) are potentially characterized to have low glycemic index and can be useful for management of type II diabetes. Understanding genetic mechanisms underlying starch biosynthesis and metabolism of cooked rice can pave the way for developing efficient breeding and selection strategy for combining high grain yield with low glycemic index. In this context, reverse genetics can prove useful. Available rice genome sequence information encoding key enzymes involved in biosynthesis of amylose component of starch can unravel novel alleles involving single nucleotide polymorphisms (SNPs). A multi-allelic waxygene (Wx) encoding Granule-Bound Starch Synthase I (GBSS I) enzyme is known to determine amylose content in rice endosperm. Potential molecular markers are now available to detect GBSS I alleles (SNPs) associated with five classes of amylose (waxy: 0–5%, very low: 5–12%, low: 12–20%, intermediate: 20–25%, and high:25–33%). These can be routinely used to assist breeding programme. Besides, the presence of intra-class variations in amylose content could be attributed to additional regulatory elements or environmental conditions.

Genetic variability of Sweet Potato on yield and yield related traits at werer Agricultural Research Center, Ethiopia

Muluken Demelie 1 and Abiyot Aragaw 2 Ethiopian Institute of Agricultural Research (Werer Center), P.O. Box: 2003, Addis Ababa Ethiopia 1 International Potato Center – Ethiopia (CIP), .PO Box 10059 Addis Ababa, Ethiopia 2 ABSTRACT Sweet potato [ Ipomoea batatas (L.) Lam.] is important food security root crop in tropical and subtropical regions. It can tolerant of a wide range of edaphic and climatic conditions and grown with limited inputs. Genetic analysis reveals the genetic nature of the inheritance of tuber yield and yield components which is required to design efficient sweet potato improvement breeding strategy. Therefore, the objectives to determine genetic variability and to estimate the association of agro-morphological trait in sweet potato genotypes. Filed experiment was conducted at Were Agricultural Research Center using three varieties and eight accessions in Randomize Complete Block Design (RCBD) with three replications. Data were collected from twelve agro-morphological traits. This analysis of variance revealed significant (p<0.05) among sweet potato genotypes for all traits except stand count at sprout which showed non significant among sweet potato genotypes. Genotypes showed total tuber yield ranged from 123.67 to 370.04 with mean of 231.04 qt/ha while root weight 100 to 263 with mean of 168.04 gm. Newly released variety Ma’e gave highest yield. Genotypic coefficients of variation lower in magnitude than phenotypic coefficient of variation all agro-morphological traits. Genotypic coefficient of variation ranged from 0.77 (stand count at sprout) to 33.93 (unmarketable tuber yield) while phenotypic coefficient variation ranged between 3.47 (stand count at sprout) to 39.36 (unmarketable tuber yield). Heritability in broad sense was recorded for twelve traits ranged between 4.99% (stand count at sprout) to 86.45% (vine internode length). Genetic advance as percent mean ranged from 7.42% (stand count at harvest) to 60.27 (unmarketable tuber yield). Genotypic correlation higher in magnitude than corresponding phenotypic correlation for most of the traits. Genotypic correlation ranged from -0.56 (unmarketable and vine inter node length) to 0.98 (marketable and total tuber yield) while phenotypic correlation ranged from -0.56 (unmarketable and vine inter node length) to 0.97 (marketable and total tuber yield). This result suggested the importance of further collection to exploit the genetic variability between varieties and accessions for variety development of sweet potato in the country. Key words: phenotypic and genotypic coefficient of variation, heritability, genetic advance

Graphic Analysis of Trait Relations of Spinach (Spinacia oleracea L.) Landraces Using the Biplot Method

Interest in growing spinach (Spinacia oleracea L.) in Iran is increasing due to its potential returns relative to other leafy vegetable crops. An experiment was conducted to examine the influencing characters on spinach by using 54 spinach landraces with application of the biplot methodology in visualizing research data. The study revealed that genotype by trait (GT) biplot can graphically display the interrelationships among traits and facilitate visual comparison of genotypes. The first two principal components (PC1 and PC2) of the site regression model accounted for 66% of the total variation in 54 landraces and accounted for 78% of the total variation in 16 clusters which are generated from cluster analysis of above landraces. The polygon view of GT biplot suggested seven sections for the 54 landraces and suggested four sections for the 16 clusters. The vertex landrace G38 had longest days to flowering and the vertex landrace G20 had most values for the other measured traits. The other vertex genotypes were not good in any traits. The vertex clusters were C1, C4, C8, and C14 which cluster C8 had the highest values of flowering period, leaf length and petiole diameter while, cluster C14 had the highest values for the other traits. The results can be used to design efficient breeding strategies in spinach.

Co-evolution in a landrace meta-population: two closely related pathogens interacting with the same host can lead to different adaptive outcomes.

We examined the local adaptation patterns in a system comprising several interconnected heterogeneous plant populations from which populations of two phylogenetically closely related pathogens were also sampled. The host is Hordeum vulgare (cultivated barley); the pathogens are Pyrenophora teres f. teres (net form) and Pyrenophora teres f. maculata (spot form), the causal agents of barley net blotch. We integrated two approaches, the comparison between the population structures of the host and the pathogens, and a cross-inoculation test. We demonstrated that two closely related pathogens with very similar niche specialisation and life-styles can give rise to different co-evolutionary outcomes on the same host. Indeed, we detected local adaptation for the net form of the pathogen but not for the spot form. We also provided evidence that an a-priori well-known resistance quantitative-trait-locus on barley chromosome 6H is involved in the co-evolutionary ‘arms race’ between the plant and the net-form pathogen. Moreover, data suggested latitudinal clines of host resistance and that different ecological conditions can result in differential selective pressures at different sites. Our data are of interest for on-farm conservation of plant genetic resources, as also in establishing efficient breeding programs and strategies for deployment of resistance genes of P. teres.

English

Weeds are the most widespread biotic production constraint of rice in Africa and one of the major factors limiting grain yield. An efficient breeding strategy could be particularly important for improving weed management in sub-Saharan Africa (SSA) because most smallholder rice farmers use few external inputs. To understand rice weed competitiveness, experiments on reciprocal interspecific crosses derived from FKR19 (Oryza sativa) and CG20 (Oryza glaberrima) were carried out to estimate gene effects and heritability of traits: plant height at five leaves, plant height 30 days after transplanting, plant height at maturity, number of tillers at 30 and 60 DAT, number of fertile tillers, width of leaves at 80 DAT and at maturity, and length of leaves at 80 DAT and at maturity for rice–weed competitiveness. Six generations – P1, P2, F1, F2, BC1F1 and BC2F1 – were raised and subjected to generation mean analysis. The lowest heterosis of F1 was obtained in both crosses (CG20/FKR19 and FKR19/CG20), except for plant height at 30 days after transplanting and leaf width at maturity in the CG20/FKR19 cross. The majority of traits displayed higher dominance gene effects (H5_L, H30 and L_80 for CG20/FKR19; W_mat and L_mat for FKR19/CG20) than additive gene effects; the latter were slight and non-significant for the majority of traits. Duplicate epistasis was observed for the number of tillers 30 days after transplanting and leaf length at maturity and plant height at maturity. Additive genetic variance values were higher in CG20/FKR19, revealing that the CG20 variety can be used as a donor parent. Plant height at maturity, length of leaves at 80 DAT and at maturity showed high narrow-sense heritability (hn2>0.70), influencing weed competitiveness. Key words: Additive, dominance, heritability, rice, variance components, weed competitiveness.

Genomic selection in wheat: optimum allocation of test resources and comparison of breeding strategies for line and hybrid breeding.

The implementation of genomic selection in breeding programs can be recommended for hybrid and line breeding in wheat. High prediction accuracies from genomic selection (GS) were reported for grain yield in wheat asking for the elaboration of efficient breeding strategies applying GS. Our objectives were therefore, (1) to optimize the number of lines, locations and testers in different multi-stage breeding strategies with and without GS, (2) to elaborate the most efficient breeding strategy based on the selection gain and its standard deviation, and (3) to investigate the potential of GS to improve the relative efficiency of hybrid versus line breeding in wheat. We used the open source software package "selectiongain" to optimize the allocation of resources in different breeding strategies by predicting the expected selection gain for a fixed budget. Classical two-stage phenotypic selection was compared with three GS breeding strategies for line and hybrid breeding in wheat. The ranking of the alternative breeding strategies varied largely in dependence of the GS prediction accuracy. Fast-track breeding strategies based solely on GS were only advantageous for high GS prediction accuracies that is >0.50 and >0.65 for hybrid and line breeding, respectively. However, a GS prediction accuracy across breeding cycles of 0.3 or even less must be assumed as realistic for grain yield in wheat. For this low GS prediction accuracy, the use of GS is advantageous for line but especially for hybrid breeding in wheat. Furthermore, the use of GS in hybrid wheat breeding increased the relative efficiency of hybrid versus line breeding and, thus, might be an important pillar for the establishment of hybrid wheat.

A linkage map of chickpea (Cicer arietinum L.) based on population from ILC3279×ILC588 crosses: Location of genes for time to flowering, seed size and plant height

Quantitative traits of seed size, plant height and days to flowering were studied in a chickpea intraspecific F3:4 lines population derived from a ILC3279?ILC588 cross. The lines were genotyped with random amplified polymorphic DNA (RAPD), universal rice primer (URP) and sequence tagged microsatellite site (STMS) markers, and a genetic map composed of 7 linkage groups (LGs) covering 285.3 cM was constructed. Quantitative trait loci (QTLs) for the three characters were detected in LG2, LG3 and LG4. Two QTLs for days to flowering were detected on LG2 and LG3. These two QTLs accounted for 58% of the total phenotypic variation for days to flowering. A QTL for plant height was located in LG3 explaining around 42% of the variation. This trait was shown to be under a major gene control. For 100-seed weight, a QTL located in LG4 explained around 37% of the phenotypic variations. This information can be used to formulate the an efficient breeding strategy for improvement of time to flowering in short-season temperate environments, plant height with more reproductive biomass and improved yield with bigger seed size in chickpea.

Factor analytic and reduced animal models for the investigation of additive genotype-by-environment interaction in outcrossing plant species with application to a Pinus radiata breeding programme

Modelling additive genotype-by-environment interaction is best achieved with the use of factor analytic models. With numerous environments and for outcrossing plant species, computation is facilitated using reduced animal models. The development of efficient plant breeding strategies requires a knowledge of the magnitude and structure of genotype-by-environment interaction. This information can be obtained from appropriate linear mixed model analyses of phenotypic data from multi-environment trials. The use of factor analytic models for genotype-by-environment effects is known to provide a reliable, parsimonious and holistic approach for obtaining estimates of genetic correlations between all pairs of trials. When breeding for outcrossing species the focus is on estimating additive genetic correlations and effects which is achieved by including pedigree information in the analysis. The use of factor analytic models in this setting may be computationally prohibitive when the number of environments is moderate to large. In this paper, we present an approach that uses an approximate reduced animal model to overcome the computational issues associated with factor analytic models for additive genotype-by-environment effects. The approach is illustrated using a Pinus radiata breeding dataset involving 77 trials, located in environments across New Zealand and south eastern Australia, and with pedigree information on 315,581 trees. Using this approach we demonstrate the existence of substantial additive genotype-by-environment interaction for the trait of stem diameter measured at breast height. This finding has potentially significant implications for both breeding and deployment strategies. Although our approach has been developed for forest tree breeding programmes, it is directly applicable for other outcrossing plant species, including sugarcane, maize and numerous horticultural crops.

Inheritance of Decay of Fresh-cut Lettuce in a Recombinant Inbred Line Population from ‘Salinas 88’ × ‘La Brillante’

Fresh-cut lettuce (Lactuca sativa) packaged as salad mixes are increasingly popular to consumers but are highly perishable. Cultivars bred with extended shelf life could increase overall production efficiency by reducing the frequency of product replacement in the marketplace. Understanding the inheritance of shelf life is needed to develop efficient breeding strategies for this trait. A population of 95 recombinant inbred lines (RILs) from slow-decaying ‘Salinas 88’ × rapidly decaying ‘La Brillante’ was grown in four field experiments. Cut lettuce was evaluated for decay in modified atmosphere (MA) packages flushed with N2 or air (control). Correlations between field experiments ranged from 0.47 to 0.84 (P &lt; 0.01). Three quantitative trait loci (QTL) for decay of cut lettuce were detected on linkage groups (LGs) 1, 4, and 9 with ‘Salinas 88’ alleles associated with slower decay. The QTL on LG 4 (qSL4) was a major determinant of decay explaining 40% to 74% of the total phenotypic variance of the trait. The greatest effect of this QTL was observed between 29 and 50 days after harvest. QTL × environment interactions contributed less than 14% to the total variation. RILs with the ‘Salinas 88’ allele of qSL4 had slower decay when packaged in air compared with N2, whereas no difference between air and N2 packaging was detected with the ‘La Brillante’ allele. A subset of RILs with either the ‘Salinas 88’ or ‘La Brillante’ allele of qSL4 was grown in two field experiments and evaluated for decay of whole heads. Genetic variation among RILs for whole-head decay was found but could not be attributed to qSL4. Decay of cut lettuce in ‘Salinas 88’ × ‘La Brillante’ is a highly heritable trait conditioned by a few QTL and phenotypic selection is likely to be effective. However, shelf life evaluations are time-consuming, destructive, and require large amounts of field-grown lettuce. Therefore, qSL4 is a good QTL to develop molecular markers for marker-assisted selection. The mechanism of decay controlled by qSL4 is unknown but appears to be specific to cut lettuce and may have allele specific interactions with packaging atmospheric compositions.

Construction of a High-Density Simple Sequence Repeat Consensus Genetic Map for Pear (Pyrus spp.)

As an important fruit crop that is widely grown commercially in temperate regions of the world, pear (Pyrus) is a target for pursuing efficient breeding strategies. Construction of a reliable and dense genetic linkage map is critical for undertaking marker-assisted breeding. In this study, a population of 56 F1 seedlings of ‘Bayuehong’ × ‘Dangshansuli’ was used to construct a high-density simple sequence repeat (SSR)-based genetic linkage map. A total of 1,756 SSR markers, including 1,341 newly designed SSRs based on whole-genome sequencing of an Asiatic pear along with 415 previously reported SSRs, were first evaluated for polymorphism. Based on 894 SSRs demonstrating polymorphism, a consensus genetic map consisting of 734 loci distributed along all 17 linkage groups (LG) was constructed, with a total length of 1,661.4 cM and with an average marker interval of 2.26 cM. Comparisons among different maps of pear and apple were then made based on positions of previously mapped SSR markers on the consensus map. As a result, homologous linkage groups LG3 and LG11, LG5 and LG10, LG9 and LG17, LG13 and LG16, LG8 and LG15 have been identified. This high-density SSR map along with a set of SSR markers covering the whole genome of pear will greatly facilitate integration of independent maps, aid in pursuing comparative genome studies, and in evaluation of different germplasm in future genetic and breeding studies.

Breeding Strategy of Acacia Hybrid (Acacia mangium × A. auriculiformis) to Increase Forest Plantation Productivity in Indonesia

Acacia hybrid (Acacia mangium× A.auriculiformis) shows better growth and wood properties, and tolerance to pest and disease. Currently, acacia hybrid breeding strategy was developed through naturally hybrid selected from trees grown in plantation. However, mass propagation of acacia hybrid using such kind of strategy was not satisfied due to ageing effect. This study was aimed to develop a new acacia hybrid breeding strategy using controlled pollination hybridization technique. The strategy was developed through a series of research: flowering, crossing, hybrid identification, clone multiplication, and clonal test. The results of study showed that the series of research for developing acacia hybrid breeding strategy was achieved. Flowering time synchronization provided a high probability for the success of controlled pollination hybridization. Leaves taxonomy at seedling stage revealed to be an efective way to identify acacia hybrid with acuracy of 92.2%. The acacia hybrid was succesfully propagated using shoot cutting at rate of 78.1%. The best selected clones of acacia hybrid outperformed in height growth at rates of 17.28% over to superior pure parents, which is equivalent to the estimated stand productivity at around 48 m3 ha-1 y-1. The series of research provided a new effective and efficient breeding strategy for acacia hybrid.