Rootstock Cultivars Research Articles

Intricate genetic variation networks control the adventitious root growth angle in apple

BackgroundThe root growth angle (RGA) typically determines plant rooting depth, which is significant for plant anchorage and abiotic stress tolerance. Several quantitative trait loci (QTLs) for RGA have been identified in crops. However, the underlying mechanisms of the RGA remain poorly understood, especially in apple rootstocks. The objective of this study was to identify QTLs, validate genetic variation networks, and develop molecular markers for the RGA in apple rootstock.ResultsBulked segregant analysis by sequencing (BSA-seq) identified 25 QTLs for RGA using 1955 hybrids of the apple rootstock cultivars ‘Baleng Crab’ (Malus robusta Rehd., large RGA) and ‘M9’ (M. pumila Mill., small RGA). With RNA sequencing (RNA-seq) and parental resequencing, six major functional genes were identified and constituted two genetic variation networks for the RGA. Two single nucleotide polymorphisms (SNPs) of the MdLAZY1 promoter damaged the binding sites of MdDREB2A and MdHSFB3, while one SNP of MdDREB2A and MdIAA1 affected the interactions of MdDREB2A/MdHSFB3 and MdIAA1/MdLAZY1, respectively. A SNP within the MdNPR5 promoter damaged the interaction between MdNPR5 and MdLBD41, while one SNP of MdLBD41 interrupted the MdLBD41/MdbHLH48 interaction that affected the binding ability of MdLBD41 on the MdNPR5 promoter. Twenty six SNP markers were designed on candidate genes in each QTL interval, and the marker effects varied from 0.22°-26.11°.ConclusionsSix diagnostic markers, SNP592, G122, b13, Z312, S1272, and S1288, were used to identify two intricate genetic variation networks that control the RGA and may provide new insights into the accuracy of the molecular markers. The QTLs and SNP markers can potentially be used to select deep-rooted apple rootstocks.

Determining leaf stomatal properties in citrus trees utilizing machine vision and artificial intelligence

Identifying and quantifying the number and size of stomata on leaf surfaces is useful for a wide range of plant ecophysiological studies, specifically those related to water-use efficiency of different plant species or agricultural crops. The time-consuming nature of manually counting and measuring stomata have limited the utility of manual methods for large-scale precision agriculture applications. A deep learning segmentation network was developed to automate the analysis of stomatal density and size and to distinguish between open and closed stomata using citrus trees grafted on different rootstocks as a model system. A novel method was developed utilizing the Mask-RCNN algorithm, which allows identification, quantification, and characterization of stomata from leaf epidermal peel microscopic images with an accuracy of up to 99%. Moreover, this method permits the differentiation of open and closed stomata with 98% precision and measurement of individual stomata size. In the citrus model system, significant differences in the size and density of stomata and diurnal regulation patterns were detected that were associated with the rootstock cultivar on which the trees were grafted. Nearly 9000 individual stomata were analyzed, which would have been impractical using manual methods. The novel automated method presented here is not only accurate, but also rapid and low-cost, and can be applied to a variety of crop and non-crop plant species.

Efficient Micropropagation of Chestnut Hybrids (Castanea spp.) Using Modified Woody Plant Medium and Zeatin Riboside

The chestnuts genus (Castanea spp.) is comprised of economically important trees native to the Northern hemisphere that are used as food and hardwood timber. Here, a very efficient method for micropropagation of European × Japanese chestnut hybrids (Castanea sativa × C. crenata) is described. Woody Plant Medium was used as the basal medium. In vitro shoots of four rootstock cultivars were micropropagated without shoot-tip necrosis on multiplication medium containing 5.7 or 11.4 µmol·L−1 zeatin riboside, and were rooted on rooting medium containing 2.46 µmol·L−1 indolebutyric acid. Monthly shoot multiplication rates for each cultivar were 2–5 folds. In vitro rooting percentages for four cultivars were 87% for ‘Maraval’, 67% for ‘Marigoule’, 93% for ‘Marsol’, and 97% for ‘Précoce Migoule’. Within a 5 week period, 80%–95% of rooted shoots were successfully acclimated under high humidity conditions after they were planted in either soil or rockwool.

Simultaneous selection of peach rootstocks by mixed models

The term adaptability refers to the ability of a genotype to respond favorably to environmental spur, while stability is the predictability of genotypic behavior. Therefore, the objective was to select Prunus rootstock cultivars with greater adaptability and genotypic stability for subtropical environmental conditions using the HMPRVG method. The experiment was conducted in Chapecó, Santa Catarina State, Brazil. Twenty-one rootstock genotypes were evaluated under the ‘BRS-Libra’ canopy cultivar and one genotype from self-rooted seedlings. The 22 genotypes were evaluated for canopy volume, yield, fruit diameter and fruit set in the growing seasons 2015/16, 2016/17, 2017/18 and 2018/19. Adaptability and stability were measured by means of the harmonic mean relative performance of genotypic values (HMRPGV). In addition, genetic parameters for heritability and ratio test were measured. According to the results, the self-rooted, ‘De Guia’, ‘I-67-52-4’, ‘Mexico Row 1’ and ‘Rosaflor’ genotypes coincided most frequently in the ranking of the three most adaptable and stable genotypes. On the other hand, the ‘P. mandshurica’, ‘Rigitano’ and ‘Santa Rosa’ genotypes corresponded to the lowest adaptability and stability values, thus constituting low quality genetic materials for cultivation. It can be concluded that under the tested conditions the HMPRVG method is efficient for the Prunus rootstock selection cultivars and the ‘BRS-Libra’ grafted on ‘Mexico Row 1’, ‘Rosaflor’ rootstocks and trees from self-rooted seedlings have greater adaptability and phenotypic stability under the subtropical cultivation conditions.

Effect of arbuscular mycorrhizal fungi, glomus mosseae and G. intraradices and antagonistic fungi pochonia chlamydosporia var. chlamydosporia and purpureocillium lilacinum on disease indices and reproduction rate of Meloidogyne javanica in three peach rootstocks under greenhouse conditions.

Biocontrol is one of the methods widely studied to reduce nematode damage. The biological control efficacy of two arbuscular mycorrhizal fungi, Glomus mosseae and G. intraradices and two antagonistic fungi, Pochonia chlamydosporia var. chlamydosporia and Purpureocillium lilacinum on disease indices and reproduction rate of root-knot nematode, Meloidogyne javanica were studied on three local cultivars of peach rootstocks namely Helendri, Shorabi3 and Gf677. The experiment was conducted as a factorial experiment in a completely randomized design with 30 treatments and five replications under greenhouse conditions. Evaluations were performed 90 days after nematode inoculation by measuring the plant growth parameters and growth and reproduction rate of M. javanica. Results of nematode reproduction indices showed more effect of P. chlamydosporia var. chlamydosporia on reduction of nematode biological activity than other biocontrol fungi. The number of galls, egg masses, second stage juveniles and reproduction factor in GF677 treated with this fungus decreased comparing to control, as 42.2, 41.8, 39 and 6.36 percent, respectively. Although the fungus was effective on all stages of nematode development, but the number of egg masses and number of eggs per egg mass were more affected.

Nutritional efficiency for nitrogen, phosphorus and potassium in peach rootstocks

The aim of this study was to determine nutritional efficiency for macronutrients (NPK) in three peach rootstock cultivars, as well as relate these indices to growth variables. The experimental design was completely randomized, with four replications of five plants each and treatments consisting of the Capdeboscq, Flordaguard and Okinawa Roxo cultivars. The experiment was conducted between April and August of 2017, at the Federal University of Pelotas (31°52′00″S and 52°21′24″W, and altitude of 13.1 m), with the plants grown in 1-L bags containing commercial substrate to which a dose of 8 g L−1 slow-release fertilizer in an NPK formulation of 14–14–14. Eighty days after transplanting, the growth characteristics were measured, and the macronutrient content was determined. From this data, efficiency indices were calculated for nutrient uptake, transport and use. The cultivars under evaluation differ in growth characteristics as well as nutritional efficiency for the evaluated macronutrients. The Flordaguard cultivar showed greater efficiency in the transport and use of nitrogen (N), and in the use of phosphorus (P) and potassium (K), which was reflected in superior growth parameters, suggesting that the cultivar is the most suitable for use in places with restrictions on the availability of these nutrients.

Vegetative development of vine rootstock cultivars in brazilian cerrado conditions

In the State of Goiás, studies related to the vine's responses to the region's edaphoclimaticconditions are scarce. Therefore, the objective of this work was to evaluate the growth of three vine rootstock cultivars, IAC 572 'Jales', IAC313 'Tropical' and IAC766 'Campinas', in the region of Goiânia, GO, after drastic pruning for uniformity. To evaluate the growth of rootstocks, the experiment was carried out in random blocks, in a double factorial scheme (3x7), with five replications, each repetition formed by a plant. The first factor consisted of three rootstocks: IAC313 ‘Tropical’, IAC572 ‘Jales’ and IAC766 ‘Campinas’. The plants were evaluated after 45 days after a drastic uniformization pruning, totaling seven evaluations (45, 60, 75, 90, 105, 120, 135 days after pruning), this being the second factor. The diameter of the main branch at the height of grafting (80 cm) and length of the main branch were evaluated. With the data on the diameter and length of the main branch, the absolute growth rate in diameter and length was calculated.The IAC572 'Jales' rootstock cultivar has greater vigor for branch growth, being 69% and 47.3% longer in length, and 49.8% and 18.8% longer in diameter than the IACrootstock. IAC 313 'Tropical' 'and' IAC766 'Campinas', respectively. The IAC766 ‘Campinas’ rootstock cultivar, although it has low vigor in branch growth, presents satisfactory development.

Genomics-assisted prediction of salt and alkali tolerances and functional marker development in apple rootstocks

BackgroundSaline, alkaline, and saline-alkaline stress severely affect plant growth and development. The tolerance of plants to these stressors has long been important breeding objectives, especially for woody perennials like apple. The aims of this study were to identify quantitative trait loci (QTLs) and to develop genomics-assisted prediction models for salt, alkali, and salt-alkali tolerance in apple rootstock.ResultsA total of 3258 hybrids derived from the apple rootstock cultivars ‘Baleng Crab’ (Malus robusta Rehd., tolerant) × ‘M9’ (M. pumila Mill., sensitive) were used to identify 17, 13, and two QTLs for injury indices of salt, alkali, and salt–alkali stress via bulked segregant analysis. The genotype effects of single nucleotide polymorphism (SNP) markers designed on candidate genes in each QTL interval were estimated. The genomic predicted value of an individual hybrid was calculated by adding the sum of all marker genotype effects to the mean phenotype value of the population. The prediction accuracy was 0.6569, 0.6695, and 0.5834 for injury indices of salt, alkali, and salt–alkali stress, respectively. SNP182G on MdRGLG3, which changes a leucine to an arginine at the vWFA-domain, conferred tolerance to salt, alkali, and salt-alkali stress. SNP761A on MdKCAB, affecting the Kv_beta domain that cooperated with the linked allelic variation SNP11, contributed to salt, alkali, and salt–alkali tolerance in apple rootstock.ConclusionsThe genomics-assisted prediction models can potentially be used in breeding saline, alkaline, and saline-alkaline tolerant apple rootstocks. The QTLs and the functional markers may provide insight for future studies into the genetic variation of plant abiotic stress tolerance.

Influence of Citrus Scion/Rootstock Genotypes on Arbuscular Mycorrhizal Community Composition under Controlled Environment Condition.

Citrus is vegetatively propagated by grafting for commercial production, and most rootstock cultivars of citrus have scarce root hairs, thus heavily relying on mutualistic symbiosis with arbuscular mycorrhizal fungi (AMF) for mineral nutrient uptake. However, the AMF community composition, and its differences under different citrus scion/rootstock genotypes, were largely unknown. In this study, we investigated the citrus root-associated AMF diversity and richness, and assessed the influence of citrus scion/rootstock genotypes on the AMF community composition in a controlled condition, in order to exclude interferences from environmental factors and agricultural practices. As a result, a total of 613,408 Glomeromycota tags were detected in the citrus roots, and 46 AMF species were annotated against the MAARJAM database. Of these, 39 species belonged to Glomus, indicating a dominant role of the Glomus AMF in the symbiosis with citrus. PCoA analysis indicated that the AMF community’s composition was significantly impacted by both citrus scion and rootstock genotypes, but total samples were clustered according to rootstock genotype rather than scion genotype. In addition, AMF α diversity was significantly affected merely by rootstock genotype. Thus, rootstock genotype might exert a greater impact on the AMF community than scion genotype. Taken together, this study provides a comprehensive insight into the AMF community in juvenile citrus plants, and reveals the important effects of citrus genotype on AMF community composition.

Stable and efficient transformation of apple

Apple is one of precious fruit crop grown in temperate zone. In the post genomic era, the analysis of gene functions in horticultural crops such as apple is required for agricultural utilization. For analysis of such crops, the protocol establishment of tissue culture and transformation is essential. Although transformation efficiency in family Rosaceae is generally very low, some cultivars of Malus species have high transformation ability. Apple cultivars are usually clonally propagated by grafting on rootstocks, which can affect fruit quality and maturity and scion productivity. Apple rootstock cultivar Japan Morioka 2 (JM2) was produced at the Division of Apple Research, Institute of Fruit and Tea Science, NARO, in Japan. JM2, which was developed for dwarfing scions and improving disease resistance, is easily propagated by hardwood cutting. Furthermore, JM2 can be stably transformed at a high efficiency, which is better than other JM series rootstocks derived from the same parent. Leaflets of cultured shoots of JM2 have been transformed using Agrobacterium (Rhizobium) with a transducing gene. In this article, the JM2 transformation protocol is introduced in detail. Various genes and promoters have been confirmed to function as expected, with the resultant transformants exhibiting specific staining and fluorescent signals, and modified floral organ shapes, precious blooming and other characteristics. JM2 is thus a useful rootstock material for the enhancement of genetic research on apple and its relatives.

The influence of rootstocks on the scions’ aromatic profiles of Vitis vinifera L. cv. Chardonnay

In modern horticulture, grafting is widely used to confer biotic and abiotic stress tolerance, which can also affect many scion phenotypes, such as the physiochemical, phenolic and aroma compositions of grape berries. In this study, the effects of five rootstocks (101-14, 1103P, Beta, 5BB and SO4) on the berry ripening and aromatic profiles of Chardonnay (CH) grape berries over two years (2016 and 2017) were evaluated and some differences were observed. Compared to the own-rooted vines, berry weight was increased by the rootstocks to varying extents and the berries from all the five grafted vines accumulated significantly lower total soluble solids (TSS). CH/101-14 increased the berries’ titratable acid (TA) to varying degree, showing decreased TSS/TA ratio in CH/101-14 and suggesting tendency for retarding maturation. All the rootstocks except SO4 could enhance both the total amounts of free- and bound-form volatile compounds, especially CH/1103P. Five volatile compounds, free-benzeneacetaldehyde, bound-1-octen-3-ol, bound-(E)-2-nonenal, bound-1,2,4-trimethyl-benzene and bound-1,2,3,4-tetramethyl-benzene were identified to have significant contribution to distinguish the grafted rootstock cultivar of the Chardonnay grape berries. Furthermore, characteristic volatile compounds for each rootstock were also screened out. Combined with the characteristics and concentrations of volatile compounds, rootstock 1103P could significantly improve the free and bound volatile compounds in Chardonnay berries under our experimental conditions.

No detection of seed transmission of citrus tatter leaf virus in ‘Meyer’ lemon

Citrus tatter leaf virus (CTLV), a strain of apple stem grooving virus, is a virus of citrus that is of commercial importance for trifoliate orange (Poncirus trifoliata) and trifoliate hybrid rootstocks. Bud-union crease is a CTLV-induced incompatibly symptom observed with these rootstocks and citrus scions which results in stunted tree growth. CTLV is a regulated pathogen for most citrus budwood certification programs worldwide. Due to the requisite virus testing, commercially supplied scion budwood would therefore seldom be a point of contamination. However, citrus rootstocks are primarily propagated by seed and the potential for seed transmission of CTLV in citrus is unclear and remains a potential source of infection. A single, unconfirmed report of seed transmission of CTLV in ‘Eureka’ lemon (Citrus × limon) exists, and although this report was not of a rootstock cultivar, it does point to the risk of seed transmission in citrus and close relatives in the family Rutaceae. CTLV-positive ‘Meyer’ lemon (C. × limon) trees in an experimental plot in the Eastern Cape Province of South Africa presented an opportunity to again test seed transmission in citrus. Seed was obtained from the infected ‘Meyer’ lemon trees, and 1164 seedlings were grown in an insect-secure greenhouse and screened for CTLV in pooled batches by conventional and real-time RT-PCR. No positive samples were detected and results indicated a lack of virus seed transmission in ‘Meyer’ lemon. Findings of this study are therefore not supportive of CTLV seed transmission in citrus.

Influence of Rootstock Propagation Method on Traits of Grafted Sweet Orange Trees

The rootstock plays a large role in modern citrus production because of its influence on tolerance to adverse abiotic and biotic soil-borne stresses, and on the general horticultural characteristics of the grafted scion. In recent years, rootstock has received increased attention as a management strategy to alleviate the devastating effects of the bacterial disease huanglongbing (HLB), also known as “citrus greening.” In commercial citrus nursery production, rootstocks are typically propagated by seed. Because of the increased demand for HLB-tolerant rootstocks, seed supply is often inadequate for the most popular cultivars. Cuttings and tissue culture (TC) propagation are alternative methods to supply adequate quantities of genetically identical rootstocks to be used as liners for grafting. However, there are concerns among nursery owners and citrus growers regarding the possible inferiority of rootstocks that are not propagated by seed. This study investigates the influence of rootstock propagation method on traits of sweet orange trees grafted on four commercially important rootstock cultivars during the nursery stage and during the first year of growth in a commercial citrus orchard. Several of the measured traits during the nursery stage, including rootstock sprouting, grafted tree growth, and root mass distribution were significantly influenced by the rootstock propagation method, but traits were also influenced by the rootstock cultivar. Our results also suggest that for tissue culture-propagated plants, differences in the starting material and the culturing method can affect the grafted tree behavior. Except for canopy spread and scion to rootstock trunk diameter ratio, tree growth during the orchard stage was determined by the combination of propagation method and rootstock, rather than by propagation method alone.

Genome Sequences of Both Organelles of the Grapevine Rootstock Cultivar 'Börner'.

Genomic long reads of the interspecific grapevine rootstock cultivar 'Börner' (Vitis riparia GM183 × Vitis cinerea Arnold) were used to assemble its chloroplast and mitochondrion genome sequences. We annotated 133 chloroplast and 172 mitochondrial genes, including the RNA editing sites. The organelle genomes in 'Börner' were maternally inherited from Vitis riparia.

Seed and Seedling Nursery Characteristics for 10 USDA Citrus Rootstocks

Six new hybrid rootstocks, ‘US-1279’, ‘US-1281’, ‘US-1282’, ‘US-1283’, ‘US-1284’, and ‘US-1516’, were released from the U.S. Department of Agriculture (USDA) citrus breeding program to provide improved tree tolerance to huanglongbing (HLB), the most destructive disease facing the citrus industry in the United States and many other parts of the world. Five of these new rootstocks were released based on field performance in trials with the rootstocks propagated by stem cuttings, rather than the traditional propagation using nucellar seedlings. In this study, we evaluated the fruit, seed, and seedling characteristics of these new rootstocks, along with four other USDA rootstocks of commercial importance. The study included a determination of the percentage of true-to-type and off-type seedlings by both plant morphology and simple sequence repeat (SSR) markers. All 10 rootstocks produced an acceptable number of seeds and good seedling emergence from those seeds. The rootstocks ‘Swingle’, ‘US-802’, ‘US-812’, ‘US-1283’, ‘US-1284’, and ‘US-1516’ had a high percentage of true-to-type seedlings and correspondingly good potential to be propagated by seeds. However, no true-to-type plants were observed among seedlings from the rootstocks ‘US-1279’, ‘US-1281’, and ‘US-1282’, indicating that economical seed propagation will be impossible for these cultivars. The 10 SSR marker sets used in this study were observed to easily differentiate the 10 rootstocks studied, and readily distinguished true-to-type and off-type seedlings among progeny from all 10 rootstock clones. This study presents information of significant value for commercial nurseries involved in propagation of citrus rootstocks, and those involved in citrus rootstock breeding and development around the world. We propose the use of these 10 SSR marker sets as readily applicable for accurate identification of most citrus rootstock cultivars and their true-to-type seedlings.

A Partially Phase-Separated Genome Sequence Assembly of the Vitis Rootstock 'Börner' (Vitis riparia × Vitis cinerea) and Its Exploitation for Marker Development and Targeted Mapping.

Grapevine breeding has become highly relevant due to upcoming challenges like climate change, a decrease in the number of available fungicides, increasing public concern about plant protection, and the demand for a sustainable production. Downy mildew caused by Plasmopara viticola is one of the most devastating diseases worldwide of cultivated Vitis vinifera. In modern breeding programs, therefore, genetic marker technologies and genomic data are used to develop new cultivars with defined and stacked resistance loci. Potential sources of resistance are wild species of American or Asian origin. The interspecific hybrid of Vitis riparia Gm 183 x Vitis cinerea Arnold, available as the rootstock cultivar ‘Börner,’ carries several relevant resistance loci. We applied next-generation sequencing to enable the reliable identification of simple sequence repeats (SSR), and we also generated a draft genome sequence assembly of ‘Börner’ to access genome-wide sequence variations in a comprehensive and highly reliable way. These data were used to cover the ‘Börner’ genome with genetic marker positions. A subset of these marker positions was used for targeted mapping of the P. viticola resistance locus, Rpv14, to validate the marker position list. Based on the reference genome sequence PN40024, the position of this resistance locus can be narrowed down to less than 0.5 Mbp on chromosome 5.

Photosynthetic performance is determined by scion/rootstock combination in mango seedling propagation

This study aimed to identify the most promising rootstock for the development of ‘Uba’ mango seedlings. We used three polyembryonic Mangifera indica L. rootstock cultivars (‘Oleo’, ‘Uba’ and ‘Imbu’) and one ‘Uba’ scion cultivar, 'Uba Clone 2′ ('UC2′). The chlorophyll a fluorescence, gas exchange, proline content and growth of the rootstocks and their respective scion/rootstock combinations (UC2/Oleo, UC2/Uba and UC2/Imbu) were analyzed. The parameters selected for the PSII photochemical system by chlorophyll a fluorescence kinetics (F2, F3, dV/dt0, DI0/RC, DFABS and DFTOTAL) were suggested as physiological indicators and the leaf proline content was suggested as a biochemical indicator for identifying the higher PSII quantum efficiency, increased water use efficiency and greater vegetative growth in UC2/Oleo. With these results, it was possible to better understand the potential effects of ‘Oleo’, ‘Uba’ and ‘Imbu’ rootstocks on ‘Uba’ mango scion performance, distinguish the grafted plants on the ‘Oleo’ rootstock and confirm the superiority of this rootstock in the production of ‘Uba’ mango seedlings under optimal environmental conditions. Thus, measuring chlorophyll a fluorescence, a fast and nondestructive method, can be highly useful for identifying the most promising rootstock for the production of 'Uba' mango seedlings, replacing time-consuming methods in crop management.

Cucurbitaceae Germplasm Resistance to Verticillium Wilt and Grafting Compatibility with Watermelon

Grafting is used in watermelon [Citrullus lanatus (Thunb.) Matsum and Nakai] production as a means to combat soilborne diseases. To support the development of new rootstock cultivars in the United States, we screened cucurbit germplasm accessions for resistance to verticillium wilt (caused by Verticillium dahliae Kleb.) and for compatibility as watermelon rootstocks. Screening was done using a field naturally infested with V. dahliae [5 and 7.5 colony-forming units (cfu)·g−1 soil in 2017 and 2018, respectively], and plants were inoculated at transplanting (1.5 and 104 cfu of V. dahliae per plant in 2017 and 2018, respectively). In 2017, 56 germplasm accessions from three genera commonly used as rootstocks, Cucurbita, Lagenaria, and Benincasa, were sourced from the U.S. Department of Agriculture (USDA) National Plant Germplasm System and area under the verticillium wilt (disease) progress curve (AUDPC) values ranged from 16 to 397. The 14 accessions with the lowest AUDPC values and good germination (>40%) were used as rootstocks along with the commercial rootstock cv. Tetsukabuto (control), and all were grafted with watermelon cv. Secretariat as the scion in 2018. Grafted plant survival rate was greatest for ‘Tetsukabuto’ (90%) and the accession PI 381840 (L. siceraria) (89%), and ranged from 22% to 85% for all other accessions. All grafted treatments that produced mature fruit in 2018 tended to flower at the same time as nongrafted ‘Secretariat’, with first male and female flowers occurring in 45 to 50 days and 44 to 51 days after transplanting, respectively. There were no significant differences in AUDPC values due to grafting or when accessions were compared with ‘Tetsukabuto’. Only six accessions produced mature fruit when grafted with ‘Secretariat’, indicating they were compatible for watermelon grafting. Fruit weight and number as well as total soluble solids, pH, lycopene content, rind firmness and thickness, and dry matter content were similar for all accessions and ‘Tetsukabuto’ grafted on ‘Secretariat’. Only fruit flesh firmness differed and was highest for ‘Secretariat’ grafted on ‘PI 491316’ and lowest for ‘Secretariat’ grafted on ‘PI 49174’. The six verticillium wilt-tolerant accessions that were compatible with watermelon could potentially be used as rootstocks or as sources of genetic resistance in rootstock breeding programs.

Tomato production in hydroponic system using different agrofilms as greenhouse cover

ABSTRACT Protected cultivation has increased over the years. More studies on the benefits of using photoselective agrofilms are necessary. The choice of material to cover the greenhouse is a decisive factor for crop development and production. The aim of this study was to evaluate the effect of diffuser and blue-colored agrofilms on the production of different tomato cultivars of indeterminate growth habit under NFT hydroponic system. A completely randomized design in a 2x3 factorial scheme (two environments and three cultivars) was used: two agrofilm types (blue and diffuser) and 3 cultivars (Monterrey, Arendell and Totalle). Each plot consisted of 30 plants per treatment, with four replicates. Commercial tomato seedlings of indeterminate growth habit grafted on rootstock cultivar (Shincheonggang) were used. During the experiment, the electrical conductivity, intensity of radiation inside the greenhouse, gas exchange, soluble solids, lycopene content, pH and fruit production were evaluated. We concluded that the amount of radiation transmitted through the diffuser favors an increase of about 18% in gas exchange, 12% in lycopene content and 9.4% in tomato crop production.

Uptake of cadmium (Cd) by selected citrus rootstock cultivars

Cadmium (Cd) is a primary heavy metal causing crops toxicity, however, Cd uptake by citrus is little studied and largely unknown. In this study, nine (9) citrus rootstock cultivars were selected and grown under Cd stress at concentrations of 0, 2.5, 10, 20, 50, and 100 mg L−1 (Cd0, Cd2.5, Cd10, Cd20, Cd50 and Cd100, respectively) for 30 d, and citrus growth, Cd concentration, Cd transport ratio (TR%), and Cd uptake factor (PUF%) were measured. Results showed that after 30 d treatments, all selected citrus rootstocks remained alive under a relatively low Cd concentrations (Cd0, Cd2.5 and Cd10), but the mortality rate increased with increasing Cd concentrations beyond Cd20, and all citrus completely died at Cd100. Cd exposure significantly suppressed seedling growth. At 20 % growth reduction, tissue Cd concentrations were Cleopatra mandarin (C. reticulate Blanco) < Brazil sour orange (C. aurantium) < ‘Swingle’ citrumelo (C. paradisi × Poncirus. trifoliate Raf.) < Ziyang Xiangcheng (C. junos Sieb. ex Tanaka) < Carrizo citrange (C. sinensis Osb. × P. trifoliate Raf.) < Goutou sour orange (C. aurantium) < Yichang Cheng (C. ichangensis Swingle) < Red tangerine (C. tangerine) < Trifoliate orange (P. trifoliata Raf.). Moreover, the Cd accumulation in the roots was much higher than in the leaves, and the accumulation was elevated with increasing Cd concentration. Principal component analysis (PCA), including fresh weight growth rate of root and shoot, Cd concentration in root and shoot, transport ratio (TR%), plant uptake factor (PUF%), indicated that selected 9 cultivars could be classified into 4 categories: (1) Trifoliate orange possessed a weak capacity for Cd uptake and accumulation, and its growth was less affected, (2) Goutou sour orange had a weak Cd uptake capacity, but a strong capacity for Cd accumulation and translocation, (3) Ziyang Xiangcheng and Cleopatra mandarin exhibited relatively a strong capacity for both Cd uptake and translocation, (4) The others did not clearly show changes in physiological Cd transport features. This comprehensive evaluation showed that Trifoliate orange was high tolerance to Cd, and Goutou sour orange was low tolerance to Cd, whereas Ziyang Xiangcheng and Cleopatra mandarin were intolerant of Cd.