Floral and Fruit Development
View abstracts in the conference PDF booklet.
Flowering, Yield and Fruit Quality of Three Organically Grown Zucchini Cultivars Evaluated in two Different Cropping Seasons
Elisabeth Abele¹, Jens Hartung², Michael Fleck3, Sabine Zikeli4, Simone Graeff-Hönninger¹
¹Department of Agronomy, Institute of Crop Science, University of Hohenheim, Stuttgart, 70599, Germany. ²Department of Agronomy, Institute of Biostatistics, University of Hohenheim, Stuttgart, 70599, Germany. 3Kultursaat e. V., Echzell, Germany. 4Department of Agronomy, Co- ordination for Organic Farming and Consumer Protection, University of Hohenheim, Stuttgart, 70599, Germany
In Germany the demand for organically produced zucchini is increasing. The usual cultivation period is from mid-May to mid/end-September. Temperature and growing-degree-days (GDD) influence plant development, they differ within this cultivation period. In this research it was hypothesized that the temperature affects the time from planting to flowering and the production of the first fruit in zucchini. Further, the needed temperature sum to build up the first flower is genetically driven and differs between cultivars. Hence, the objectives of this study were to evaluate the impact of temperature in different cultivation periods within a year on days to flowering and first fruit production for various zucchini cultivars and on overall marketable yield. For this purpose, three open pollinating cultivars were grown in 2017 in an organic field trial in Kleinhohenheim (Stuttgart, Baden-Württemberg, Germany). One green (cv. Leila), one yellow (KSZ-KB-Gelb.1) and one striped cultivar (cv. Cocozelle) were planted on 23.05.2017 and on 27.07.2017. The results showed that a minimum of 314 GDD in the first set and 291 GDD in the last set was necessary to induce the first flower. In both cultivation-sets, cv. Leila was the earliest cultivar showing the first female flower 16 and 19 days after planting with a GDD of 265 and 224, followed by the flowering of cv. Cococelle 22 and 28 days after planting and a GDD of 327 and 318. The last cultivar KSZ-KB-Gelb.1 flowered 24 and 29 after planting with a GDD of 351 and332. To produce the first fruit within the first planting date a higher GDD of 328 on average was needed when compared to the last planting date with 312. Cv. Leila had the first fruits 20 days after planting in comparison to 23 days at the later planting date, followed by cv. Cocozelle and KSZ-KB-Gelb.1. Overall the study indicated that a lower requirement of GDD results in earlier flowering, thus earlier fruiting and finally higher yields. In addition, cultivars with a lower GDD requirement might be more suitable also for planting dates in the later season of a year, when temperatures start to decrease.
Genetic Analysis of Trimonoecy in Watermelon
Encarnación Aguado, Alicia García, Susana Manzano, Jonathan Romero, Gustavo Cebrian, Manuel Jamilena
Dept. of Biology and Geology, Agrifood Campus of International Excellence (CeiA3) and Research Center in Agri-food Biotechnology (BITAL), Almería, Spain
Sex expression and sex determination are both regulated by the plant hormone ethylene in watermelon. The arrest of stamen development in female flowers of monoecious cultivars depend on the ethylene biosynthesis gene CitACS4. A single missense mutation in the coding region of this gene (m) promotes the conversion of female into hermaphrodite flowers, and therefore of monoecy (MM) into trimonoecy (Mm) or andromonoecy (mm). Andromonoecy and trimonoecy are undesirable traits in watermelon, since hermaphrodite flowers need to be emasculated when acting as female parents in hybrid seed production, and also because the traits are usually associated with a reduction in fruit set and fruit quality under greenhouse conditions. Trimonoecy occurs in heterozygous plants for the mutant m allele (Mm), but also in certain cultivars that are homozygous for the CitACS4 WT allele (MM). 48 Spanish traditional cultivars and 4 commercial inbred lines (P84, P85, P86 and P87) were phenotyped for sex associated traits, and then genotyped for M and m alleles of CitACS4. Most of the MM cultivars were monoecious, but two MM cultivars (BG24 and BG31) and two MM lines (P84 and P85) were phenotyped as trimonoecious, which suggests the existence of additional mutant CitACS4 alleles or genes regulating sex determination in watermelon. The sequencing of CitACS4 in MM lines and cultivars demonstrated that the trimonoecious phenotype was not caused by a new CitACS4 allele. By contrast, the segregation ratio between monoecious and trimonoecious plants in the F2 derived from the cross between P86 (monoecious) and P84 (trimonoecious) indicated that trimonoecy is regulated by a recessive gene other than CitACS4.
Sex Determinism Genes in Cucurbit Crops: Evolutionary History and Domestication
Catherine Dogimont¹, Vincent Rittener-Ruff¹, Vérane Sarnette¹, Nathalie Giovinazzo¹, Ilknur Solmaz², Nebahat Sari², Adnane Boualem³, Abdelhafid Bendahmane³
¹INRA UR 1052 Génétique et Amélioration des Fruits et Légumes, Montfavet, 84 143, France. ²Department of Horticulture, Faculty of Agriculture, University of Cukurova, Adana, Turkey. ³INRA, Institute of Plant Sciences Paris-Saclay, Orsay, 91405, France
Whereas most angiosperms plants are hermaphrodite, a diversity of type of flowers (male, female, or bisexual) on separate or on the same plants are present in Cucurbitaceae. Our previous works have shown that the genes CmWIP1, CmACS7 and CmACS11, associated with three loci (G, M, A), control sex expression in melon. The ethylene biosynthesis enzyme ACC synthase-7 is responsible for the sex transition from monoecious (female and male flowers) to andromonoecious (hermaphrodite and male flowers). We demonstrated that syntenic orthologous genes encode for the ethylene rate limiting enzyme in C. melo, C. sativus, and Citrullus lanatus and that the inactivation of the enzyme leads to the development of stamens in female flowers in these plant species. These results clearly indicate that the ACS7 gene and the ethylene pathway was recruited for sex determinism across Cucurbitaceae before Cucumis and Citrullus divergence, which was estimated to 20 Myago. Interestingly, in cucurbit crops, functional alleles were lost in some landraces (in andromonoecious and androecious plants) but were maintained in some others (monoecious landraces). This made it possible to use genetic approaches, positional mapping and TILLING, to elucidate key components of the mechanisms that contribute to sexual type in cucurbit crops. This also highlights that andromonoecy was selected several times during the domestication processes of cucurbit crops.
Quantitative Trait Loci for Parthenocarpic Fruit Set in Cucumber Identified from Biparental and Natural populations
Ronald Dymerski, Jr.¹, Yiqun Weng²
¹University of Wisconsin, Madison, WI, USA. ²U.S. Department of Agriculture, Agricultural Research Service, Vegetable Crops Research Unit, Madison, WI, USA
Parthenocarpy is a horticulturally important trait in cucumber that is required for production in protected environments. It is also a desirable trait with potential for increasing yield and quality in processing cucumber production. Although many successful parthenocarpic cucumber varieties have been developed, the genetic and molecular mechanisms behind parthenocarpic fruit set (PFS) in cucumber are still not well understood. In our previous study, we identified several PFS QTL using an F2:3 population derived from a cross between highly parthenocarpic inbred line 2A and low parthenocarpic line Gy8. In this study, we conducted QTL mapping for PFS in cucumber using a double haploid segregating population derived from 2A×Gy8, and validated the QTL, parth7.1 for early PFS. We also conducted a genome-wide association analysis (GWA) of this trait using a diverse panel of 129 cucumber lines. Genotyping of lines was performed through genotyped by sequencing (GBS) and resequencing data resulting in ~6,700 high quality SNPs. Phenotypic data for PFS were collected in multiple pollen exclusion environments. Six regions in cucumber chromosomes 1, 2, 3, 6, and 7 of the cucumber genome were detected with significant association of PFS between the environments. These regions included the parth7.1 identified in the 2A with biparental populations. This study will provide meaningful insight for future genetic investigations of loci associated with PFS from this natural and biparental populations. National Institute of Food and Agriculture, U.S. Department of Agriculture, under award numbers 2015-51181-24285 and 2017-67013-26195. Partial Funding provided by the Specialty Crop Block Grant Program at the U.S. Department of Agriculture (USDA) through Grant 14-SCBGP-CA-0006 (The CucCAP Project).
Genetic Interactions between EIN1, EIN2 and EIN3 in the Regulation of Sex Expression and sex Determination in Squash
Alicia García¹, Encarnación Aguado¹, Susana Manzano1, Jonathan Romero¹, Gustavo Cebrián¹, Dolores Garrido², Manuel Jamilena¹
¹Dept. of Biology and Geology, Agrifood Campus of International Excellence (CeiA3) and Research Center in Agri-food Biotechnology (BITAL). University of Almería, Almería, Spain. ²Department of Plant Physiology, University of Granada, Granada, Spain
The plant hormone ethylene regulates different developmental processes, including sex determination and sex expression in the species of the Cucurbitaceae family. We have developed an EMS collection consisting on 3,751 mutant families in zucchini squash (Cucurbita pepo L.). The high throughput screening of the collection for ethylene triple response resulted in the identification of three ethylene insensitive mutants: ein1, ein2, ein3. Mutant were backcrossed with the background line MUC16, and sex expression and sex determination traits compared in WT and mutant plants of BC2S1 or BC3S1 segregating populations. The mutations ein1, ein2 and ein3 promoted the conversion of female into bisexual or hermaphrodite flowers, and therefore of monoecy into andromonoecy, but they also delayed the transition to female flowering and reduced the number of pistillate flowers per plant. The ein2 and ein3 mutations segregated as semi-dominant for ethylene triple response and sex expression, but andromonoecy only occurred in homozygous mutant plants. Homozygous plants for ein1 were completely blocked in female flowering transition, but heterozygous Ein/ein1 plants produced some hermaphrodite flowers. Since the three mutations were female sterile in homozygous condition, the genetic interactions between these three loci were studied in double heterozygous plants for each two mutant alleles. The loci did not complement each other, but they were found to be dose-dependent under certain mutant combinations. The additive or synergistic effects ein mutations on female flowering transition and sex determination suggests functional redundancy of genes regulating ethylene sensitivity, and sex expression and sex determination in C. pepo. The molecular homology between EIN2 and EIN3 genes also supports this conclusion.
Fine-mapping of a Major Quantitative Trait Locus Qdff3-1 Controlling Flowering Time in Watermelon
Winnie Gimode¹, Josh Clevenger¹, Cecilia McGregor²
¹Institute of Plant Breeding, Genetics and Genomics, University of Georgia, Athens, GA, USA.
²Department of Horticulture, University of Georgia, Athens, GA, USA
Flowering time is crucial in watermelon (Citrullus lanatus) production as it determines time of fruit set. Early flowering is desirable because it enables crops to escape biotic and abiotic stresses that are intensified by long production cycles. Production of seedless watermelon is also reliant on synchronized flowering of diploid pollenizers and the triploid watermelon cultivars. Incorporation of single nucleotide polymorphisms (SNPs) for marker assisted selection (MAS) of flowering time in watermelon breeding would potentially aid in selection for the early flowering trait, which would shorten the production time. Moreover, seedless watermelon breeding would be enhanced through appropriate triploid-diploid pairings. A major quantitative trait locus (Qdff3-1: 12Mbp-17Mbp) associated with days to female flower was previously identified on chromosome 3 of watermelon. This QTL contributes approximately 50% of the phenotypic variance. The objective of this study was to determine more precisely the interval of Qdff3-1 and the gene controlling flowering time in watermelon. A combination of QTL-seq and candidate gene sequencing was used to identify SNP markers in the region. Validation and fine mapping through QTL-seq identified three candidate genes underlying Qdff3-1: FT, TEMPRANILLO and PIP-kinase. Kompetitive Allele Specific PCR (KASPTM) assays were developed for the SNP markers identified. Potential markers for selection were tested on the recombinant inbred line (RIL) mapping population and a panel of cultivars to establish marker-trait association and determine their applicability in MAS for flowering time in watermelon. SNPs that represent potential tools for the refinement of the QTL have been identified and may be applicable in MAS of this trait in watermelon. To further delineate the QTL, recombinants were identified in the RIL and an F2 population of 372 lines. Six recombinants were selected following genotyping, and F3 populations developed from them for flowering time evaluation in summer 2018. Fine-mapping is currently ongoing and preliminary data indicates FT as the most likely candidate gene. Partial Funding provided by the Specialty Crop Block Grant Program at the U.S. Department of Agriculture (USDA) through Grant 14-SCBGP-CA-0006 (The CucCAP Project)
Genetic Characterization of a Key Regulator of Pigment Accumulation in Melon and Watermelon
Elad Oren1, Galil Tzuri¹, Lea Vexler1, Ayala Meir¹, Asaf Dafna¹, Uzi Sa’ar¹, Arthur Schaffer², Nurit Katzir¹, Joseph Burger¹, Yaakov Tadmor¹, Amit Gur¹
¹Newe-Yaar research Center, ARO, Ramat Yishay, 3009500, Israel. ²Agricultural Research Organization, Volcani Center, Rishon LeZiyyon, 7505101, Israel
Color and pigment content are important aspects of fruit quality and consumer acceptance of cucurbits. Here, we describe the independent mapping and cloning of a common causative gene regulating pigment accumulation in melon and watermelon. We initially show that this gene is causative for the qualitative difference between dark and light green rind in both crops. Further analyses demonstrate the link between sequence or expression level variations at this gene and pigment content in rind and flesh of mature melon fruits. GWAS of young fruit rind color in a panel composed of 177 diverse melon accessions did not result in any significant association, leading to an earlier assumption that multiple genes are involved in shaping phenotypic variation of this trait. Through sequencing of 25 representative accessions and allelism tests between light rind accessions, we show that multiple independent SNPs in the gene are causative for the light rind phenotype. The multi-haplotypic nature of this gene explains the lack of detection power obtained through GBS-based GWAS and confirms the pivotal role of this gene in shaping fruit color variation in melon. This study demonstrates the power of combining bi- and multi-allelic designs with deep sequencing to resolve lack of power due to high haplotypic diversity and low allele frequencies. Due to its central role and broad effect on pigment accumulation, this gene is an attractive target for bio-fortification of cucurbit crops.
Towards Understanding and Predicting Fruit Quality in Winter Squash
Christopher Hernandez
Cornell University, Ithaca, NY, USA
Fruit quality in winter squash is a complex trait made up of many components. To better understand fruit quality, we used RNA-Seq to obtain gene expression profiles in four squash cultivars from C. moschata and C. maxima that cover the spectrum of fruit quality. Through comparison of gene expression across key fruit developmental time points within and between cultivars, we are identifying gene expression differences that may underlie variation in important fruit quality components such as Brix, dry matter, starch, sugar, and carotenoid content. Results from this study along with the application of genomic prediction to improve fruit quality in squash will be discussed.
Chemical Characterization of Cucurbita ficifolia Bouché During its Development and its Hypoglycemic Effect
Araceli Moya-Hernández, Elsa Bosquez-Molina, José Verde-Calvo, Gerardo Blancas-Flores
Universidad Autónoma Metropolitana, Ciudad De México, 09340, Mexico
Cucurbita ficifolia is known in Mexico as chilacayote and is consumed mainly in the Valley of Mexico. Recent studies have shown that the extract of this fruit has important hypoglycemic properties similar to the drugs used for the treatment of diabetes mellitus type 2 (DM 2) such as glibenclamide and tolbutamide. However, it is still unknown which compounds attribute this property to the chilacayote as well as its state of development in which this effect is greater.
The objectives of this study were: 1) to characterize the main chemical compounds of chilacayote during its development and 2) to determine its hypoglycemic effect during its development. In order to achieve these objectives, seeds of C. ficifolia were sown and the flowers were marked with the date of anthesis, from this date samples were taken at 10, 15, 25, 30, 40 and 45 days for further analysis. The chemical characterization was by means of high performance liquid chromatography (HPLC) Agilent. For the determination of the hypoglycemic effect, male mice of strain CD-1 were used, groups were formed to which the different extracts were administered, and a positive control was used administered with glibenclamide and a control with isotonic saline solution. The compounds found were gallic acid, quercetin, catechin, kaempferol and myristicin in different concentrations throughout their development. The hypoglycemic effect showed significant differences in its early stages (P<0.05) of development, however this effect is in all stages of the development. So it can be concluded that this fruit is a good alternative for the treatment of DM 2.
Use of Grafting to Promote Flowering in Late and Short-day Flowering Cultigens of Squash
Andrew Ogden, James Loy
University of New Hampshire, Durham, NH, USA
Wild species and landraces of Cucurbita are important resources for plant breeders as they often contain novel genes for economically important traits. Utilizing such germplasm presents challenges to breeders in temperate climates because wild species and landraces from tropical and subtropical regions may flower late in development or only under short days. Although previous researchers have induced flowering in recalcitrant flowering cucurbit cultigens by grafting them to early flowering rootstocks, details of methodology and floral development are scant, and there has been no confirmation of fruit set and seed production from these efforts. We sought to develop a grafting method that would reliably induce flowering and fruit set in a short-day flowering landrace of C. moschata and the short-day flowering species, C. ficifolia. Initial experiments revealed leaf removal from the scion is necessary, presumably to prevent synthesis of an inhibitor molecule. Grafts performed at the one and two leaf stage of rootstocks failed to induce flowering of scions. Scion insertion into rootstock by a cleft graft at or above the 4th node together with leaf removal from the main stem of the scion for 20 nodes was effective in causing floral induction. Vigorous shoot development in a lateral branch of the rootstock between nodes 0-4 also proved to be necessary as a source of photosynthate for the scion. In a greenhouse study, once floral induction occurred, flowering continued even with renewed leaf growth along the scion main stem; however, flowers aborted prior to fruit set. Without leaf removal, flower buds were initiated at early nodes on scions, but aborted early in development. In field studies conducted in 2018, flowering was again induced with grafting and leaf removal for 20 nodes, and in the C. moschata accession, fruit set and growth was obtained. Self-grafted plants with and without leaf removal, un-grafted plants with and without leaf removal, and grafted plants without leaf removal all failed to flower. This method should be a useful tool for plant breeders and curators of Cucurbita germplasm.
CsERF31 and CsERF39 Play Key Roles in Cucumber Female Flower Differentiation by Activating M (CsACS2)
Jian Pan, Haifan Wen, Huanle He, Junsong Pan, Gang Wang, Run Cai
School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, 200240, China
In cucumber (Cucumis sativus L.), the differentiation and development of female flowers are important processes that directly affect the fruit yield and quality. Sex differentiation is mainly controlled by three ethylene synthase genes, F (CsACS1G), M (CsACS2), and A (CsACS11). Thus, ethylene plays a key role in the sex differentiation in cucumber. The “one-hormone hypothesis” posits that F and M regulate the ethylene levels and initiate female flower development in cucumber. Nonetheless, the precise molecular mechanism of this process remains elusive. The functional analysis of the M gene suggested that the activation of M was essential to accumulation of ethylene signal. To investigate the ethylene-mediated sex differentiation process and the interplay mechanism between F and M, three cucumber chromosome segment substitution lines with different F and M loci were generated. According to the transcriptome analysis of the three lines, we identified two ERF1-like genes, CsERF31 and CsERF39, as the key players in female flower initiation. CsERF31 and CsERF39 had especially high expression levels in FFMMAA lines. Both of genes showed high expression in 1-2 mm female bud, declining with the development of female flower, which is similar to M. In addition, the expression of CsERF31 and CsERF39 were significantly induced by ethephon and suppressed by AgNO3 and Aminoethoxyvinyl Glycine (AVG). These results indicated that CsERF31 and CsERF39 were involved in female flower differentiation through response to the ethylene signal. The biochemical experiments further demonstrated that CsERF31 and CsERF39 bind directly the ERE-box in the promoter of M and activate its expression. Thus, we suggest in female flower initiation, CsERF31 and CsERF39 responded to the ethylene signal derived from F and mediated the positive feedback regulation of ethylene by activating M; M amplifies the ethylene signal via CsERF31 and CsERF39, which form a “Ethylene-CsERF31/39–M-Ethylene” positive feedback regulation. Then, the genes, activated by the high-level ethylene signal promote female flower initiation. In conclusion, our research offers an extended “one-hormone hypothesis” of sex differentiation in cucumber.