GENETIC ANALYSIS OF QUALITATIVE AND QUANTITATIVE TRAITS AMONG PROGENIES OF ENSET CLONES ORIGINATED FROM SOUTHERN ETHIOPIA

<p>The present cultivated enset (<em>Ensete ventricosum</em>) clonal landraces in Ethiopia originated from few wild progenitors. However, enset has a mixed mode of reproduction in which, the wild enset reproduces sexually through seeds, while cultivated enset is generally propagated vegetatively. The objectives of this study were to determine the genetic structure of enset cultivars through genetic analysis of qualitative morphological traits and estimate their genetic variability by evaluating the quantitative agronomic traits data generated from progenies of cultivated and wild enset genotypes. Hence, seeds collected from six cultivated and four wild enset genotypes were used for this study. Data on four qualitative and six quantitative morphological traits were recorded from the progenies of the 10 enset genotypes. Progenies of seven enset genotypes segregated in a 3:1 segregation ratio while progenies of the remaining genotypes segregated differently for the qualitative traits considered. With regard to the quantitative traits, the progenies of the 10 enset genotypes differed significantly for five of the six traits except pseudostem length. The cultivated clones, in general performed better than that of the wild types. Moderate heritability (h2b) estimates and high genetic advances were obtained for leaf length (0.38, 62.0%), pseudostem circumference (0.35, 78.5%), and plant height (0.30, 19.1%) indicating selection for these traits indirectly improves economic yield of enset clones. This study demonstrated the possibility of creating genetic variation through selfing the existing enset genotypes for traits of interest and making improvements either through selection or crossing the elite types to develop novel enset cultivars.</p>

Improvement of the submergence stress tolerance of local South Sumatran rice through the introgression of the Sub1 gene by using marker-assisted selection

Submergence stress due to unpredictable soil flooding is one of the main constraints encountered in rainfed growing areas, especially in Southern Sumatran riparian swamps. The development of submergence-stress-tolerant cultivars through the introgression of Sub1 via marker-assisted backcrossing (MABC) is an ideal solution. This study was carried out during 2020 at Sriwijaya University, Palembang, Indonesia, with the aim to select Sub1-introgressed lines in BC3F1 generations on the basis of MABC and to screen out the SSR markers that were unlinked to the target gene for application in subsequent background selection studies. Results revealed that almost all the backcrossed progenies segregated from the rice parental cultivars ‘FR13A’ and ‘Pegagan’. The backcrossed lines showed significantly improved submergence stress tolerance and recovery rates compared with their parents. Sub1 introgression into the BC3F1 generation was confirmed by the tightly linked Sub1 marker SUB1C173, and marker RM23915 was used for recombinant selection. These markers followed the expected marker segregation ratio in accordance with the Mendelian single gene model. In the parental polymorphism survey, 84 out of 237 SSR markers that were unlinked to the target loci were found to be available for background study. Twenty-seven backcrossed lines were selected on the basis of foreground selection. Seven plants were selected on the basis of the recombinant marker RM23915. Five backcrossed lines were further selected on the basis of submergence stress tolerance and agronomic performance.

Numerical Investigation of Segregation Evolution during the Vacuum Arc Remelting Process of Ni-Based Superalloy Ingots

Segregation defects greatly affect the service performance and working life of castings during the vacuum arc remelting (VAR) process. However, the corresponding research on the prediction of segregation defects is still not comprehensive. Through considering the influence of water-cooled crucible on the electromagnetic field inside an ingot, a full-scale model for the comprehensive prediction of freckles and macrosegregation defects during the VAR process is developed in this paper. The macroscopic solute transport phenomenon and the segregation behavior of Ni-5.8 wt% Al-15.2 wt% Ta alloy are predicted. The results indicate that the freckles are mainly concentrated in the lower region of the ingot. With the growth of the ingot, the solute enrichment channels gradually develop into solute enrichment regions, and the channel segregation evolves into macrosegregation. The Lorentz force mainly affects the flow pattern at the top of the molten pool, while the complex flow of multiple vortices is dominated by thermosolutal buoyancy. The maximum and minimum relative segregation ratio inside the ingot can reach 290% and −90%, respectively, and the positive segregation region accounts for about 79% of the total volume. This paper provides a new perspective for understanding the segregation behavior inside the ingot by studying the segregation evolution during the VAR process.

Genetic Resistance of Lactuca spp. against Fusarium oxysporum f. sp. lactucae Race 1

Fusarium wilt of lettuce is caused by the pathogen Fusarium oxysporum f. sp. lactucae (Fol) and is a growing threat to global lettuce production. Fol was first detected in Florida in 2017 and was subsequently confirmed as race 1. Management strategies for this long-persisting soil pathogen are limited, time-consuming and expensive, and they may lack efficacy. Identifying diverse sources of genetic resistance is imperative for breeding adapted cultivars with durable resistance. The objectives of this study were to identify sources of resistance against a race 1 isolate of Fol in Florida, delineate the relationship between foliar and taproot symptoms, and investigate the inheritance of resistance and partial resistance in two F2 populations. Thirteen experiments were conducted in greenhouse and field locations to characterize the diversity of genetic resistance in the genus Lactuca. Leaf cultivars Dark Lollo Rossa and Galactic; romaine breeding lines 43007, 60182, and C1145; and iceberg breeding line 47083 consistently exhibited low foliar and taproot disease symptoms. Resistance was not identified among the wildtype Lactuca or primitive plant introductions (PI) in this study based on taproot symptoms. An additional test was conducted to study the segregation pattern of Fol resistance between one resistant and one susceptible accession (R × S) and one partial resistant and one susceptible accession (PR × S). The F2 population from ‘60182 × PI 358001-1’ fit the expected segregation ratio for a single recessive locus model, whereas the ratio for ‘Dark Lollo Rossa × PI 358001-1’ did not fit either recessive or dominant single locus models. These sources of resistance are potential candidates for developing commercial cultivars with multiple resistance loci against Fol race 1, especially for the Florida lettuce production system.

Genetic Mapping and Identification of the Candidate Genes for Mottled Rind in Cucumis melo L.

The rind appearance of melon is one of the most vital commercial quality traits which determines the preferences and behavior of consumers toward the consumption of melon. In this study, we constructed an F2 population derived from SC (mottled rind) and MG (non-mottled rind) lines for mapping the mottled rind gene(s) in melon. Genetic analysis showed that there were two dominant genes (CmMt1 and CmMt2) with evidence of epistasis controlling the mottled rind. Meanwhile, the phenotypic segregation ratio implied that the immature rind color had an epistatic effect on the mottled rind, which was regulated by CmAPRR2. A Kompetitive Allele-Specific PCR (KASP) DNA marker (CmAPRR2SNP(G/T)) was developed and shown to co-segregate with rind color, confirming that CmAPRR2 was CmMt1. Using bulked segregant analysis sequencing and KASP assays, CmMt2 was fine-mapped to an interval of 40.6 kb with six predicted genes. Functional annotation, expression analysis, and sequence variation analyses confirmed that AtCPSFL1 homolog, MELO3C026282, was the most likely candidate gene for CmMt2. Moreover, pigment content measurement and transmission electron microscopy analysis demonstrated that CmMt2 might participate in the development of chloroplast, which, in turn, decreases the accumulation of chlorophyll. These results provide insight into the molecular mechanism underlying rind appearance and reveal valuable information for marker-assisted selection breeding in melon.

Analysis of the Segregation Distortion of FcRAN1 Genotypes Based on Whole-Genome Resequencing of Fig (Ficus carica L.) Breeding Parents

The common fig (Ficus carica L.) has a gynodioecious breeding system, and its sex phenotype is an important trait for breeding because only female plant fruits are edible. During breeding to select for female plants, we analyzed the FcRAN1 genotype, which is strongly associated with the sex phenotype. In 12 F1 populations derived from 13 cross combinations, the FcRAN1 genotype segregation ratio was 1:1, whereas the M119-226 × H238-107 hybridization resulted in an extremely male-biased segregation ratio (178:7 = male:female). This finding suggests that the segregation distortion was caused by some genetic factor(s). A whole-genome resequencing of breeding parents (paternal and maternal lines) identified 9,061 high-impact SNPs in the parents. A genome-wide linkage analysis exploring the gene(s) responsible for the distortion revealed 194 high-impact SNPs specific to Caprifig6085 (i.e., seed parent ancestor) and 215 high-impact SNPs specific to H238-107 (i.e., pollen parent) in 201 annotated genes. A comparison between the annotated genes and the genes required for normal embryo or gametophyte development and function identified several candidate genes possibly responsible for the segregation distortion. This is the first report describing segregation distortion in F. carica.

Identification of Gray Leaf Spot Disease Candidate Gene in Narrow-Leafed Lupin (Lupinus angustifolius L.)

Selection for resistance against gray leaf spot (GLS) is a major objective in the lupin breeding programs. A segregation ratio of 1:1 (resistant:susceptible) in F8 recombinant inbred lines (RIL8) derived from a cross between a breeding line 83A:476 (resistant to GLS) and a wild accession P27255 (susceptible to GLS) indicated that GLS was controlled by a single major gene. To develop molecular markers linked to GLS, in the beginning, only 11 resistant lines and six susceptible lines from the 83A:476 and P27255 population were genotyped with MFLP markers, and three MFLP markers were identified to be co-segregated with GLS. This method was very efficient, but the markers were located outside of the gene, and could not be used in other germplasms. Then QTL analysis and fine mapping were conducted to identify the gene. Finally, the gene was narrowed down to a 241-kb region containing two disease resistance genes. To further identify the candidate gene, DNA variants between accessions Tanjil (resistant to GLS) and Unicrop (susceptible to GLS) were analyzed. The results indicated that only one SNP was detected in the 241 kb region. This SNP was located in the TMV resistance protein N-like gene region and also identified between 83A:476 and P27255. Genotyping the Tanjil/Unicrop RIL8 population showed that this SNP co-segregated with GLS resistance. The phylogenetic tree analysis of this gene among 18 lupin accessions indicates that Australian resistant breeding line/varieties were clustered into one group and carry two resistant alleles, while susceptible accessions were clustered into different groups.

Identification and Fine-mapping of a New Bacterial Blight Resistance Gene, Xa47(t), in G252, an Introgression Line of Yuanjiang Common Wild Rice (Oryza rufipogon)

Bacterial blight (BB) disease caused by Xanthomonas oryzae pv. oryzae (Xoo) is a common, widespread, and highly devastating disease that affects rice yield. Breeding resistant cultivars is considered the most effective measure for controlling this disease. The introgression line G252 derived from Yuanjiang common wild rice (Oryza rufipogon) was highly resistant to all tested Xoo strains, including C5, C9, PXO99, PB, T7147Y8, Hzhj19, YM1, YM187, YJdp-2, and YJws-2. To identify the BB resistance gene(s) of G252, we developed an F2 population from the cross between G252 and 02428. A linkage analysis was carried out between the phenotype and genotype in the population. A segregation ratio of 3:1 was observed between the resistant and susceptible individuals in F2 progeny, indicating a dominant resistance gene, Xa47(t), in G252. The resistance gene was mapped within an approximately 26.24 kb physical region on chromosome 11 between two InDel markers, R13I14 and 13rbq-71; and moreover, one InDel marker, Hxjy-1, co-segregated with Xa47(t). Three genes were predicted within the target region, including a promising candidate gene encoding a nucleotide-binding domain and leucine-rich repeat (NLR) protein (LOC_Os11g46200) by combining the structure and expression analysis. Physical mapping data suggested that Xa47(t) was a new broad-spectrum BB resistance gene.

Genome sequencing identified novel mechanisms underlying virescent mutation in upland cotton Gossypiuma hirsutum

Background Virescent mutation broadly exists in plants and is an ideal experimental material to investigate regulatory mechanisms underlying chlorophyll synthesis, photosynthesis and plant growth. Up to date, the molecular mechanisms in two virescent mutations have been clarified in cottons (Gossypiuma hirsutum). A virescent mutation has been found in the cotton strain Sumian 22, and the underlying molecular mechanisms have been studied. Methods The virescent mutant and wild type (WT) of Sumian 22 were cross-bred, and the F1 population were self-pollinated to calculate the segregation ratio. Green and yellow leaves from F2 populations were subjected to genome sequencing and bulked-segregant analysis was performed to screen mutations. Real-time quantitative PCR (RT-qPCR) were performed to identify genes in relations to chlorophyll synthesis. Intermediate products for chlorophyll synthesis were determined to validate the RT-qPCR results. Results The segregation ratio of green and virescent plants in F2 population complied with 3:1. Compared with WT, a 0.34 Mb highly mutated interval was identified on the chromosome D10 in mutant, which contained 31 genes. Among them, only ABCI1 displayed significantly lower levels in mutant than in WT. Meanwhile, the contents of Mg-protoporphyrin IX, protochlorophyllide, chlorophyll a and b were all significantly lower in mutant than in WT, which were consistent with the inhibited levels of ABCI1. In addition, a mutation from A to T at the -317 bp position from the start codon of ABCI1 was observed in the genome sequence of mutant. Conclusions Inhibited transcription of ABCI1 might be the mechanism causing virescent mutation in Sumian 22 cotton, which reduced the transportation of protoporphyrin IX to plastid, and then inhibited Mg-protoporphyrin IX, Protochlorophyllide and finally chlorophyll synthesis. These results provided novel insights into the molecular mechanisms underlying virescent mutation in cotton.