Breeding opportunities for early,free-threshing and semi-dwarf <Emphasis Type="Italic">Triticum monococcum</Emphasis> L.

Einkorn wheat, Triticum monococcum L. (2n = 2x = 14, A^mA^m genome), is a primitive, cultivated form of diploid wheat. The shortcoming of einkorn is that it lacks the free-threshing habit. Early heading and semi-dwarf traits are also required to fit modern agricultural practice. In the present study we developed T. monococcum pre-breeding germplasm having early, free threshing traits by utilizing an early heading source, two sources of soft glume (spike) and three sources of semi-dwarfism to combine their phenotypes into pre-breeding materials. We found two different genes determined free threshing of einkorn wheat. One of them was the sog (soft glume) gene from Triticum sinskajae Filat. et Kurkiev (2n = 2x = 14, A^mA^m genome) and another was the sos (soft spike) gene, which was completely linked or pleiotropic with the gene for semi-dwarfism. The genes sos, spd (short peduncle) and sd17654 (semi-dwarf CItr 17654) were utilized to develop semi-dwarf T. monococcum lines. Field performance of 6 early and free-threshing pre-breeding materials with sos and spd genes were tested over three crop seasons. Five semi-dwarf pre-breeding materials (PBMs) were obtained. However, these materials had slightly less grain yield than #252 (tall and hulled check) and PBM-1 (tall free-threshing check). Harvest index of the pre-breeding materials was improved due to the presence of sos and spd genes. If optimized cultivation practice is performed, these pre-breeding materials can be utilized as sources of early, free-threshing and semi-dwarf traits to produce modern T. monococcum varieties.     

Genetic dissection of rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) tiller,plant height,and grain yield based on QTL mapping and metaanalysis

Tiller number per plant (TN) and plant height (PH) are important agronomic traits related to grain yield (GY) in rice (Oryza sativa L.). A total of 30 additive quantitative trait loci (A-QTL) and 9 significant additive × environment interaction QTLs (AE-QTL) were detected, while the phenotypic and QTL correlations confirmed the intrinsic relationship of the three traits. These QTLs were integrated with 986 QTLs from previous studies by metaanalysis. Consensus maps contained 7156 markers for a total map length of 1112.71 cM, onto which 863 QTLs were projected; 78 meta-QTLs (MQTLs) covering 11 of the 30 QTLs were detected from the cross between Dongnong422 and Kongyu131 in this study. A total of 705 predicted genes were distributed over the 21 MQTL intervals with physical length <0.3 Mb; 13 of the 21 MQTLs, and 34 candidate genes related to grain yield and plant development, were screened. Five major QTLs, viz. qGY6-2, qPH7-2, qPH6-3, qTN6-1, and qTN7-1, were not detected in the MQTL intervals and could be used as newly discovered QTLs. Candidate genes within these QTL intervals will play a meaningful role in molecular marker-assisted selection and map-based cloning of rice TN, PH, and GY.     

Evaluation of morpho-physiological traits of MRQ74 pyramided lines with drought yield QTLs

Drought regularly affects rainfed lowland and upland rice ecosystems in Malaysia. Three drought yield QTLs, viz qDTY _2.2 , qDTY _3.1 and qDTY _12.1 successfully pyramided into MRQ74 to increase its yield under reproductive stage drought stress (RS). Forty-eight genotypes comprising 39 pyramided lines (PLs) with different qDTYs combinations, four parents including MRQ74 (recipient) and five checks were evaluated for morpho-physiological traits under RS and non-stress (NS). This study aims to determine which traits influenced by individual qDTY and qDTY combinations and to gain better understanding of QTL interactions in enhancing grain yield (GY) under RS. Results showed plant height, number of panicles, root length, root weight, relative water content and 100-grain weight increased while chlorophyll content and GY decreased under RS compared to NS. No significant difference was observed in days to flowering, leaf rolling and grain length between selected PLs and MRQ74 under RS. Six PLs with yield advantage (YA) of 208.17–1751.63 kg ha^?1 compared to MRQ74 in RS but yielded similar to MRQ74 under NS were further selected. Under RS, qDTY class analysis showed qDTY _12.1 individually and combination qDTY _12.1  + ?qDTY _2.2 produced the highest yield of 1521.77 and 1092.30 kg ha^?1 respectively. qDTY _12.1 as single or combination with other qDTY is the best qDTY in stabilizing GY under RS. PL-77 with qDTY _12.1 is the best PL with YA of more than 1100 kg ha^?1 compared to MRQ74 in both RS and NS conditions can be recommended for cultivation in normal and drought-prone areas.     

Relationship between hybrid performance and genetic variation in self-fertile and self-sterile sugar beet pollinators as estimated by SSR markers

Sugar beet hybrid varieties are produced through the crosses between male sterile lines and the multigerm pollinators. The uniformity of pollinators used for hybrid crosses depends on the presence of self-sterility (S ^s ) and self-fertility (S ^f ) genes. The aim of the study was to analyze correlation between hybrid performance and genetic distance or heterozygosity of the sugar beet pollinators. Twelve diploid pollinators classified as self-sterile (S ^s ) or self-fertile (S ^f ) and two cytoplasmic male sterile (CMS) lines were crossed in line × tester scheme, producing 24 F₁ hybrids. The parents and the hybrids were evaluated for root yield and quality traits, from which F₁ performance, combining abilities, mid-parent and high-parent heterosis were calculated. Parental genetic distance and diversity of the pollinators were estimated by SSR markers and, together with GCA and F₁ performance, correlated with the heterosis effects. The S ^f hybrids had better GCA and higher values of root yield, root weight, and root circumference than the S ^s hybrids. Heterosis was recorded in more combinations with the S ^f than with the S ^s pollinators. Parameters of genetic diversity were higher in the S ^s (Na = 3.125; Ne = 2.341; He = 0.555) than in the S ^f pollinators (Na = 3.000; Ne = 2.188; He = 0.510). Genetic distance between the tested pollinators and the CMS lines was low (0.072–0.224) indicating that the genetic base of the investigated germplasm was narrow. Correlation of the heterosis effects with GD and heterozygosity was detected only for the root yield traits.     

Variance components and heritability of traits related to root: shoot biomass allocation and drought tolerance in wheat

Enhanced root growth in plants is fundamental to improve soil water exploration and drought tolerance. Understanding of the variance components and heritability of root biomass allocation is key to design suitable breeding strategies and to enhance the response to selection. This study aimed to determine variance components and heritability of biomass allocation and related traits in 99 genotypes of wheat (Triticum aestivum L.) and one triticale (X. Triticosecale Wittmack) under drought-stressed and non-stressed conditions in the field and greenhouse using a 10?×?10 alpha lattice design. Days to heading (DTH), days to maturity (DTM), number of tillers (NPT), plant height (PH), spike length (SL), shoot and root biomass (SB, RB), root to shoot ratio (RS), thousand kernel weight (TKW) and yield (GY) were recorded. Analyses of variance, variance components, heritability and genetic correlations were computed. Significant (p?<?0.05) genetic and environmental variation were observed for all the traits except for spike length. Drought stress decreased heritability of RS from 47 to 28% and GY from 55 to 17%. The correlations between RS with PH, NPT, SL, SB and GY were weaker under drought-stress (r?≤???0.50; p?<?0.05) compared to non-stressed conditions, suggesting that lower root biomass allocation under drought stress compromises wheat productivity. The negative association between GY and RS (r?=???0.41 and ??0.33; p?<?0.05), low heritability (<?42%) and high environmental variance (>?70%) for RS observed in this population constitute several bottlenecks for improving yield and root mass simultaneously. However, indirect selection for DTH, PH, RB, and TKW, could help optimize RS and simultaneously improve drought tolerance and yield under drought-stressed conditions.     

Effects of introgressions from <Emphasis Type="Italic">Festuca pratensis</Emphasis> on winter hardiness of <Emphasis Type="Italic">Lolium perenne</Emphasis>

Previous studies reported that some genotypes with introgressed Festuca chromosome segment(s) in Lolium genome showed enhanced winter hardiness compared to Lolium. The aim of this study was to search comprehensively for the Festuca pratensis chromosome regions affecting winter hardiness-related traits when introgressed into the Lolium perenne genome. Association between F. pratensis introgression and winter hardiness-related traits (fall and winter hardiness indexes, early-spring dry matter yield, and freezing tolerance) were screened in the diploid introgression populations (n = 203) that had some F. pratensis chromosome segments introgressed. Eighty-four intron markers corresponding to unique rice genes randomly distributed across the genome were used for genotyping. Winter hardiness of almost all plants in the introgression populations was lower than that of the F. pratensis and triploid hybrid parents, but the average was higher than that of L. perenne. A significant positive effect of F. pratensis introgression on early-spring dry matter yield was detected on chromosome 7. This quantitative trait locus (QTL) was confirmed by linkage analysis using a backcross population with F. pratensis introgression in the target region of chromosome 7. However, the contribution of the newly identified QTL was rather small (6.7–9.6%), suggesting that superior winter hardiness of F. pratensis compared to L. perenne is conferred by multiple small-effect QTLs. We also detected a previously unreported negative effect of Festuca introgression on winter hardiness. Newly obtained QTL information in this study would contribute to the design of Festuca/Lolium hybrid breeding.     

Mapping QTLs with epistatic effects and QTL × treatment interactions for salt tolerance at seedling stage of wheat

Quantitative trait loci (QTLs) with additive (a), additive × additive (aa) epistatic effects, and their treatmental interactions (at and aat) were studied under salt stress and normal conditions at seedling stage of wheat (Triticum aestivum L.). A set of 182 recombinant inbred lines (RILs) derived from cross Xiaoyan 54 × Jing 411 were used. A total of 29 additive QTLs and 17 epistasis were detected for 12 traits examined, among which eight and seven, respectively, were identified to have QTL × treatment effects. Physiological traits rather than biomass traits were more likely to be involved in QTL × treatment interactions. Ten intervals on chromosomes 1A, 1D, 2A (two), 2D, 3B, 4B, 5A, 5B and 7D showed overlapping QTLs for different traits; some of them represent a single locus affecting different traits and/or the same trait under both treatments. Eleven pairs of QTLs were detected on seemingly homoeologous positions of six chromosome groups of wheat, showing synteny among the A, B and D genomes. Ten pairs were detected in which each pair was contributed by the same parent, indicating a strong genetic plasticity of the QTLs. The results are helpful for understanding the genetic basis of salt tolerance in wheat and provide useful information for genetic improvement of salt tolerance in wheat by marker-assisted selection.     

Creating cold resistant strawberry via interploidy hybridization between octoploid and dodecaploid

Strawberry cultivars showed limited cold resistance in the Northeast of China, while we obtained a synthetic dodecaploid strawberry hybrid ‘YH15-10’ (2n = 12x = 84) which showed sufficient cold resistance in this area. The reciprocal crosses between F. × ananassa cv. ‘Allstar’ (2n = 8x = 56) and ‘YH15-10’ (2n = 12x = 84) were carried out to select cold resistant strawberry in this study. The 134 seedlings were obtained from the cross of Allstar × YH15-10, while failed in its reciprocal cross. The 30 randomly selected seedlings were examined in terms of morphological characters, chromosome numbers and cold resistance. Most morphological characters were widely separated among F1 progeny with a high broad-sense heritability, which showed that these variations mainly resulted from genetic effect. Some hybrids exhibited heterosis, especially in growth vigor and runner production. Among the 30 tested hybrids, 28 decaploids (2n = 10x = 70), one octoploid (2n = 8x = 56) and one enneaploid (2n = 9x = 63) were observed. The 63.3% hybrids demonstrated higher cold resistance than that of ‘Allstar’ at P < 0.05. These high polyploidy strawberries have potential values in commercial production and modern cultivar improvement.     

A SNP mutation affects rhizomania-virus content of sugar beets grown on resistance-breaking soils

Rhizomania is one of the most devastating biotic stresses affecting sugar beet (Beta vulgaris L.). It is caused by Beet necrotic yellow vein virus (BNYVV) vectored by the plasmodiophorid Polymyxa betae K. The only means available to control the disease is the use of genetically resistant varieties. “Rizor” or “Holly” (Rz1) and WB42 (Rz2) have been the most widely used resistance sources in the commercial varieties. Recently, naturally occurring resistance-breaking (RB) rhizomania strains have been identified causing major concerns. The aim of this study was to identify SNP mutations that show associations with resistance to rhizomania in sugar beet plants grown under resistance-breaking (RB)-BNYVV soils. Rhizomania virus content was evaluated by indirect triple-antibody sandwich-ELISA within two F ₂ segregating populations respectively grown on an AYPR and IV-BNYVV strain infected soils. Bulked segregant analysis (BSA) was performed. The resistant and susceptible plants were genotyped with a 384-SNPs panel. Of the 384 SNPs, SNP249 was found to associate with the resistance both to the AYPR strain (R ² = 0.37; P = 0.0004) and to the IV-BNYVV (R ² = 0.09; P = 0.0074). Our results suggested that the SNP249 could be readily applicable for marker-assisted breeding of resistance to AYPR strain of rhizomania.     

Mapping of new resistance (<Emphasis Type="Italic">Vr2</Emphasis>, <Emphasis Type="Italic">Rm1</Emphasis>) and ornamental (<Emphasis Type="Italic">Di2</Emphasis>, <Emphasis Type="Italic">pl</Emphasis>) Mendelian trait loci in peach

Peach powdery mildew is one of the major diseases of the peach. Various sources of resistance to PPM have thus been identified, including the single dominant locus Vr2 carried by the peach rootstock ‘Pamirskij 5’. To map Vr2, a linkage map based on microsatellite markers was constructed from the F₂ progeny (WP²) derived from the cross ‘Weeping Flower Peach’ × ‘Pamirskij 5’. Self-pollinations of the parents were also performed. Under greenhouse conditions, all progenies were scored after artificial inoculations in two classes of reactions to PPM (resistant/susceptible). In addition to Vr2, WP² segregated for three other traits from ‘Weeping Flower Peach’: Rm1 for green peach aphid resistance, Di2 for double-flower and pl for weeping-growth habit. With their genomic locations unknown or underdocumented, all were phenotyped as Mendelian characters and mapped: Vr2 mapped at the top of LG8, at 3.3 cM, close to the CPSCT018 marker; Rm1 mapped at the bottom of LG1, at a position of 116.5 cM, cosegregating with the UDAp-467 marker and in the same region as Rm2 from ‘Rubira’^®; Di2 mapped at 28.8 cM on LG6, close to the MA027a marker; and pl mapped at 44.1 cM on LG3 between the MA039a and SSRLG3_16m46 markers. Furthermore, this study revealed, for the first time, a pseudo-linkage between two traits of the peach: Vr2 and the Gr locus, which controls the red/green color of foliage. The present work therefore constitutes a significant preliminary step for implementing marker-assisted selection for the four major traits targeted in this study.     

Genome-wide association study of yield components and fibre quality traits in a cotton germplasm diversity panel

A genome-wide association study (GWAS) was conducted on a diversity panel of 103 cotton accessions over three seasons to determine genetic contributions to a range of cotton yield components including fibre quality, plant architecture and stomatal conductance traits. The accessions covered breeding lines, released cultivars and some obsolete cultivars that contributed significantly to modern breeding pools. They were genotyped with Illumina’s CottonSNP63 K single nucleotide polymorphism (SNP) assay. Broad-sense heritability was low for yield component traits (\(h_{B}^{2}\) = 0.14–0.43), except for gin turnout and boll weight (\(h_{B}^{2}\)) = 0.74 and 0.59, respectively), and low to high for fibre quality traits (\(h_{B}^{2}\) = 0.26–0.89). Population structure analysis revealed extensive admixture and cryptic relatedness amongst the accessions. Genome-wide linkage disequilibrium (LD) analyses showed LD decayed, on average, within a physical distance of 5 Mbp and reduced to 2 Mbp at r ² ≥ 0.2, suggesting that few markers are necessary for association mapping in cotton. A mixed linear model accounting for population structure and cryptic relatedness identified 17 and 50 significant SNP associations for fibre length and micronaire, respectively. GWAS failed to detect significant associations in other traits, with the contribution of any single SNP to the phenotypic falling below 5%. This may be due to the low level of DNA polymorphism in cotton and/or insufficient resolution provided by the cotton SNP chip. Whole genome sequencing combined with whole genomic selection approaches that do not require prior knowledge about the effect or function of individual SNPs may be better suited than GWAS for trait dissection and prediction in cotton breeding.     

Identification of QTLs for agronomic traits using association mapping in lentil

A diverse panel of 96 genotypes of lentil was used in this study to identify QTL for nine agronomic traits through marker-trait association analysis. This study showed significant genetic variability among the lentil genotypes for nine agronomic traits and had medium to large broad sense heritability estimates (h² =?0.58–0.95). Screening of 534 SSR markers resulted in 266 polymorphic loci that generated 697 alleles ranging from 2 to 16 alleles per locus across the genotypes. The model-based population structure analysis identified two distinct subpopulations among lentil genotypes and each subpopulation did not show any admixture. Marker trait association (MTA) analysis following ML model resulted in the identification of 24 MTAs for nine traits at P?<?0.01. The per cent of phenotypic variation explained by each associated marker with particular agronomic trait ranged from 7.3 to 25.8%. The highest proportion of total phenotypic variation (23.1–25.8%) was explained by the QTLs controlling the primary branches/per plant. In the present study, few EST-SSR markers showed significant association with days to maturity, pods/plant, secondary branches/plant, 100 seed weight, yield/plant and reproductive duration and explained large phenotypic variation (7.3–23.8%). Hence, these markers can be used as functional markers in lentil breeding program for developing improved cultivars.     

Estimating gene action,combining ability and heterosis for grain yield and agronomic traits in extra-early maturing yellow maize single-crosses under three agro-ecologies of Ghana

Maize (Zea mays L.) is the most important cereal crop produced in Ghana. However, yield of the crop is generally low, producing just about 1.7 t/ha. The low yield is attributed to continuous use of local/unimproved varieties. Generally, hybrid varieties have proven to out-yield the local/unimproved varieties due to improved vigour. Development of hybrid varieties depend on good understanding of combining ability and inheritance of important quantitative traits such as grain yield (GY). 45 half-diallel crosses generated from 10 extra-early maturing yellow inbred lines were evaluated in 2015 under rain-fed conditions. The objectives were to determine the genetic control, breeding value and estimate heritability for GY and agronomic traits of the inbred lines under contrasting growing environments in Ghana. General combining ability (GCA) and specific combining ability (SCA) were important in the inheritance of GY and agronomic traits of the inbred lines. However, GCA was more important than SCA across environments to suggest that additive gene action was more important than non-additive gene action in the inheritance of GY and agronomic traits in the inbred lines. High broad-sense heritability, for GY and other agronomic traits indicated preponderance of additive gene action in trait expression, thus, selection based on phenotypic expression could be feasible. Inbred lines P1, P4 and P8 were good combiners for high GY. The genotype, P4 × P8, was identified as the ideal and most yielding single-cross hybrid across research environments and should be further tested on-farm before commercialization.     

Phenotypic variation in root architecture traits and their relationship with eco-geographical and agronomic features in a core collection of tetraploid wheat landraces (<Emphasis Type="Italic">Triticum turgidum</Emphasis> L.)

To obtain varieties with root systems adapted to marginal environments it is necessary to search for new genotypes in genetically diverse materials, such as landraces that are more likely to carry novel alleles for different root features. A core collection of ‘durum’ wheat, including three subspecies (dicoccon, turgidum and durum) from contrasting eco-geographical zones, was evaluated for root traits and shoot weight at the seminal root stage. Distinctive rooting phenotypes were characterized within each subspecies, mainly in subsp. durum. Contrasting rooting types, including large roots with shallow distributions, and others with high root numbers were identified. Correlations with climatic traits showed that root shape is more relevant in adaptation to eco-geographical zones in subsp. dicoccon, whereas in subsp. turgidum and durum, which come from warmer and drier areas, both size and shape of roots could have adaptive roles. Root traits with the largest positive effects on certain yield components under limited water conditions included root diameter in subsp. dicoccon, root size in turgidum, and root number in durum. Additionally, shoot weight at the seedling stage had important effects in subsp. turgidum and durum. Twenty-eight marker–trait associations (MTAs) previously identified in this collection for agronomic or quality traits were associated with seminal root traits. Some markers were associated with only one root trait, but others were associated with up to six traits. These MTAs and the genetic variability characterized for root traits in this collection can be exploited in further work to improve drought tolerance and resource capture in wheat.     

Evaluating the contribution of Yr genes to stripe rust resistance breeding through marker-assisted detection in wheat

Numerous stripe rust resistance genes have been identified from wheat, and new virulent races of Puccinia striiformis f. sp. tritici have also emerged in recent years. Deployment of diverse combinations of resistance genes is an efficient way to combat virulent evolution of strip rust pathogen. In this study, publically available molecular markers were used to identify the distribution of 36 Yr genes in 672 wheat accessions. The effectiveness of Yr genes individually and in combinations was also evaluated in field conditions. The result showed effective resistance of some recently applied genes, such as Yr15 and Yr65. It also showed the lost efficacy of some once widely used genes, such as Yr9 and Yr10. Moreover, significant additive effects were observed in some gene combinations, such as Yr9 + Yr18 and Yr30 + Yr46. Proper deploying of Yr genes and utilizing the positive interactions will be helpful for durable resistance breeding in wheat.     

Stability of <Emphasis Type="Italic">Solanum aethiopicum</Emphasis> Shum accessions under varied water deficit stress levels and identification of pertinent breeding traits for resistance to water shortage

Drought is a major constraint to productivity of Solanum aethiopicum ‘Shum’ group due to loss in market and nutrient value of stressed plants. This study evaluated S. aethiopicum Shum group accessions to identify genotypes (G) that excel across moisture deficit stress levels (WLs). A split-plot arrangement composed of four WLs and twenty accessions of S. aethiopicum as main plot and sub-plot factors, respectively, was implemented in a screenhouse, and repeated for two experiments. In each experiment, there was a highly significant effect of at least two WLs on mean performance among at least two accessions for most of the traits at p < 0.05. Further, very highly significant WL × G interactions were obtained for leaf relative water content (LRWC), leaves per plant (LPP) and plant height (PH), and non-significant for leaf blade length and leaf blade width. The order of priority as breeding traits for stability superiority across WLs was suggested as LRWC > PH > LPP. Consequently, based on LRWC, the most superiorly stable accessions were identified as accession 160 followed by accessions 145, 137, 108P and 184G while the least stable ones were identified as accessions 163G, 141, 163 and 108. The broad sense heritability (H ²) for each of the three recommended traits for drought resistance breeding was above 0.9 thus supportive for a good response to selection. Drought stress negatively affected the performance of S. aethiopicum Shum group but the exhibited variation allowed for selection of superiorly stable genotypes.     

Genetic effect of <Emphasis Type="Italic">Striga</Emphasis> resistance in sorghum genotypes

Striga is an important parasitic weed causing substantial economic losses in cereal and legume crop production in sub-Saharan Africa. Integrated Striga management approaches such as a combined use of Striga resistant varieties and Fusarium oxysporum f.sp. strigae (FOS), a biocontrol agent of Striga, are an option to control the parasite and to boost sorghum productivity. Understanding host gene action influencing Striga resistance, with or without FOS treatment, is key to developing improved sorghum varieties with durable resistance and high yield. The objective of this study was to determine the gene action and inheritance of Striga resistance using genetically diverse populations of sorghum involving FOS treatment. Twelve sorghum parents selected for Striga resistance, FOS compatibility or superior agronomic performances were crossed using a bi-parental mating scheme. The selected male and female parents and their F₁ progenies, backcross derivatives and the F₂ segregants were field evaluated at three locations in Tanzania known for their severe Striga infestations using a lattice experimental design with two replications. The following data were collected and subjected to generation mean analysis (GMA): days-to-50% flowering (DFL), seed yield per plant (SYP) and number of Striga per plant (SN). GMA showed the preponderance of additive genetic action contributing to the total genetic variation in the evaluated sorghum populations. The additive genetic effect for DFL, SYP and SN, with and without FOS treatments, ranged from 72.02 to 86.65% and 41.49 to 95.44%, 75.62 to 91.42% and 71.83 to 91.89%, and 77.35 to 93.56% and 72.86 to 95.84%, in that order. The contribution of non-additive genetic effects was minimal and varied among generations. FOS application reduced DFL and SN and improved SYP in most of the tested sorghum populations. DFL of sorghum populations was reduced by a mean of 8 days under FOS treatment compared to the untreated control in families such as 675 × 654, AS435 × AS426 and 1563 × AS436. FOS treatment improved SYP with a mean of 6.44 g plant^?1 in 3424 × 3993 and 3984 × 672. The numbers of Striga plants were reduced with a mean of 16 plants due to FOS treatment in the crosses of 675 × 654, 1563 × AS436, 4567 × AS424, and 3984 × 672. The study demonstrated that additive genes were predominantly responsible for the inheritance of Striga resistance in sorghum. Pure line cultivar development targeting reduced DFL, SN and high SYP in the selected populations may provide enhanced response to selection for integrated Striga management (ISM) programme.     

Identification and validation of root length QTLs for water stress resistance in hexaploid wheat (<Emphasis Type="Italic">Titicum aestivum</Emphasis> L.)

Thorough understanding of the genetic mechanisms governing drought adaptive traits can facilitate drought resistance improvement. This study was conducted to identify chromosome regions harbouring QTLs contributing for water stress resistance in wheat. A RIL mapping population derived from a cross between W7984 (Synthetic) and Opata 85 was phenotyped for root length and root dry weight under water stress and non-stress growing conditions. ANOVA showed highly significant (p ≤ 0.01) variation among the RILs for both traits. Root length and root dry weight showed positive and significant (p ≤ 0.01) phenotypic correlation. Broad sense heritability was 86% for root length under stress and 65% for root dry weight under non-stress conditions. A total of eight root length and five root dry weight QTLs were identified under both water conditions. Root length QTLs Qrln.uwa.1BL, Qrln.uwa.2DS, Qrln.uwa.5AL and Qrln.uwa.6AL combined explained 43% of phenotypic variation under non-stress condition. Opata was the source of favourable alleles for root length QTLs under non-stress condition except for Qrln.uwa.6AL. Four stress specific root length QTLs, Qrls.uwa.1AS, Qrls.uwa.3AL, Qrls.uwa.7BL.1 and Qrls.uwa.7BL.2 jointly explained 47% of phenotypic variation. Synthetic wheat contributed favourable alleles for Qrls.uwa.1AS and Qrls.uwa.3AL. Two stable root dry weight QTLs on chromosomes 4AL and 5AL were consistently found in both water conditions. Three validation populations were developed by crossing cultivars Lang, Yitpi, and Chara with Synthetic W7984 to transfer two of the QTLs identified under stress condition. The F_2.3 and F_3.4 validation lines were phenotyped under the same level of water stress as RILs to examine the effect of these QTLs. There were 13.5 and 14.5% increases in average root length due to the inheritance of Qrls.uwa.1AS and Qrls.uwa.3AL, respectively. The result indicated that closely linked SSR markers Xbarc148 (Qrls.uwa.1AS) and Xgwm391 (Qrls.uwa.3AL) can be incorporated into MAS for water stress improvement in wheat.     

Morphological and molecular characterization of the second backcross progenies of Ogu-CMS Chinese kale and rapeseed

Ogura cytoplasmic male sterility (Ogu-CMS) is widely used in the production of commercial hybrids of Brassica oleracea. However, the widespread application of the Ogu-CMS system in B. oleracea has hindered the germplasm innovation of Ogu-CMS resources due to the lack of a natural restorer line. Previously, the Ogu-CMS fertility-restored interspecific hybrids between rapeseed 15Y403 (2n = 38, AACC) and Chinese kale JL1 (2n = 18, CC) have been successfully produced. However, these progenies, which still contained a large proportion of rapeseed genomic components, showed poor fertility and a low seed setting rate under natural pollination. To improve fertility and seed setting, a successive backcross with JL1 was performed to produce BC₂ progenies. Screening with the Rfo-specific marker, five individuals harboring the Rfo gene were identified among 98 BC₂ progenies. These five individuals underwent background marker screening and an evaluation of agronomic traits and fertility. One individual (code: 15Q23) was identified with higher pollen viability, better seed setting under natural pollination, and a closer genetic background to the parent Chinese kale JL1. Many morphological traits showed no significant differences (P < 0.05) between 15Q23 and the backcross parent JL1. However, the average seed setting of 15Q23 under natural pollination was 0.72 seeds per pod, which was 50 times higher than that of BC₁ progenies, and the average pollen viability was 87.07%, which was significantly better than that of the F₁ and BC₁ plants (P < 0.01). The genetic background of 15Q23 was more closer to the parent JL1 than that of BC₁ plants and another BC₂ fertility-restored individual, with 82% of the polymorphic alleles being the same as those of the parent Chinese kale JL1. Thus, the individual 15Q23 could be used as a donor plant for further backcrosses. This study lays the foundation for the development of Ogu-CMS restorer material in B. oleracea.     

Morph-physiological responses of cotton interspecific chromosome substitution lines to low temperature and drought stresses

Limited knowledge about genetic and physiological traits associated with drought and low temperature stresses and narrow genetic diversity in Upland cotton (Gossypium hirsutum L.) are serious impediments in its genetic improvement. The objectives of this research were to determine the genetic and physiological traits associated with drought and low temperature effects and to identify chromosomal effects on these traits using chromosome substitution (CS) lines from three alien species of Gossypium, G. barbadense, G. tomentosum, and G. mustelinum, respectively. Two experiments were conducted to study low temperature and drought stress effects during seedling emergence and early growth stages in 21 cotton CS-lines with parent, Texas Marker (TM)-1. In Experiment I, plants were grown at optimum (30/22 °C) and low (22/14 °C) temperature conditions under optimum water and nutrient conditions. In Experiment II, plants were grown at optimum water (soil moisture content of 0.167 m³ m^?3) and in drought (soil moisture content 0.105 m³ m^?3) conditions under optimum temperature conditions. Above- and below-ground growth traits including several root traits of the CS lines were assessed at 25 days after sowing. The findings suggest which substituted chromosome or chromosome segment from the alien species likely harbors one or more genes for higher and lower tolerance to low temperature, respectively. CS-T04 and CSB08sh showed higher and lower tolerance to low temperature, respectively and CS-T04 and CS-B22sh showed higher and lower tolerance, respectively, to drought. CS lines are valuable analytical tool and useful genetic resources for targeted exploitation of beneficial genes for drought and low temperature stresses in Upland cotton.