Rootstock Breeding Programs Research Articles

Comparative metabolomics and transcriptomics analyses provide insights into branching changes induced by heterografting in Pinus massoniana seedlings

The investigation of dwarfing rootstocks for the establishment of high-generation seed orchards is a prospective avenue of research. In this investigation, Pinus massoniana, Pinus yunnanensis var. pygmaea (P. pygmaea), and P. elliottii seedlings were used as rootstocks for grafting with P. massoniana scions. Grafting P. massoniana onto P. pygmaea rootstock resulted in observable phenotypic alterations in lateral branches, apical buds, and needle length. Certain characteristic metabolites of rootstocks, such as fatty acyls, pregnenolones, steroids, and steroid derivatives, were found to be highly expressed in scions after grafting. RNA-seq analysis revealed MYB-related, SBP, and bHLH demonstrating a significant positive correlation, while C2H2 and Orphans exhibited negative correlations with the differential intensity of metabolites related to lipids and lipid-like molecules. This study offers valuable insights for the establishment of rootstock breeding programs.

Guiding principles in the Geneva® apple rootstock breeding program

The Geneva® apple rootstock breeding program has been operating for more than 50 years and through a rigorous breeding and selection process has released several rootstocks that have provided solutions for some of the major rootstock related problems faced by the apple industry worldwide. Research and development for new apple rootstocks encompasses diverse disciplines and research areas including plant physiology, genetics, genomics, transcriptomics, horticulture, and economics. The process of developing the plan for developing new apple rootstocks and related knowledge base is guided by grower-advised principles and distilled into priorities including disease and insect resistance (fire blight, replant disease, wooly apple aphids, viruses, and viroids), productivity, and sustainability (dwarfing, early bearing, yield efficiency, nutrient absorption efficiency, improved fruit size and quality and winter hardiness). The project continues to develop new breeding populations to address these priorities and discover new germplasm sources to increase resilience of the germplasm to future challenges

“Extreme hybrids” from the Australian citrus rootstock breeding program

Citrus is one of the most genetically diverse fruit trees used by humans, and yet few rootstock breeders have ventured beyond a narrow range of parents. For the last 25 years we have explored wider graft and sexual compatibility within the citrus subfamily (Aurantioideae) than any previous attempts, and have identified new genera and species for rootstock breeding. Whilst the vast majority of this work has met with failure, it has identified factors such as sexual incompatibility, late-acting lethality and poor field adaptation as the reasons why many citrus relatives are not currently amenable to rootstock breeding. A major breakthrough early in the program was the discovery that Oceania citrus species are extremely sensitive to Citrus tristeza virus (CTV) when used as rootstocks, and the realisation that resistance must be introgressed if we are to ever discover useful traits masked by this disease sensitivity. Bridging hybrids were required to transfer this virus resistance and a newly discovered species (Citrus wakonai) was employed to speed-up the process. After three generations of crossing, our “extreme hybrids” with Oceania parentage now show commercial performance equivalent to industry standards. By providing citrus growers with a range of high-performance rootstocks from extremely complex genetic backgrounds we can increase the biological diversity of orchards without compromising production. Our hope is that these “extreme hybrids” may help in the battle against Huanglongbing (HLB) disease.

Rootstocks for the Mediterranean citrus industry: current choices and new releases

Modern citriculture relies on the use of rootstocks to guarantee adaptability to environmental and biotic constraints and to speed up the establishment of a potentially unlimited number of homogeneous plants of a specific clone, which in turn ensures uniformity in the production of high-quality fruit. In this contribution, the status of rootstock availability for the Mediterranean citrus industry is described along with its evolution during the last decades. The major turning points in rootstock choice were caused by the spread of new diseases, such as Citrus Tristeza Virus (CTV), that hastened the use of resistant or tolerant rootstocks. In Italy, the growers decisions on rootstock replacement were facilitated by information from rootstock trials performed for more than 70 years in several areas of southern Italy, as well as information from other countries. However, there is still the need to find alternatives to sour orange (which was the most commonly used rootstock before the CTV outbreak), especially for cultivation under suboptimal growing conditions. Nowadays, the process of replacing standard rootstocks with new ones with better performance should be assisted by a long-term evaluation strategy, since negative characteristics can become evident after many years of evaluation in combination with specific scion varieties. Ongoing rootstock breeding programs in different parts of the world and in Italy are critically described.

Citrus rootstock breeding in an HLB-endemic environment with an industry in crisis

The arrival (2005) and rapid establishment in Florida of the most devastating disease known to citriculture, namely Huanglongbing or Citrus Greening Disease, has caused dramatic changes to the long-term citrus rootstock breeding program at the University of Florida’s Citrus Research and Education Center (UF-CREC). Since all commercial scion/rootstock combinations have proven to be susceptible to the disease, there is an urgent need to quickly develop improved rootstocks with good horticultural attributes that can mitigate the disease in trees grafted with commercial scions. This report describes our efforts to achieve this goal. Our approach is to rapidly develop and screen a large population of genetically-diverse hybrid rootstock candidates. Multiple available sources of potential rootstock germplasm are being exploited in our efforts. We have identified several good rootstock candidates that are showing improved HLB tolerance. These are now being propagated either by seed or micropropagation as needed for advanced multi-site trials with multiple scions. This research offers potential for the ultimate solution to HLB, leading to sustainable and profitable citriculture in HLB-endemic areas

Comprehensive Assessment of Morphological Diversity in Bottle Gourd (Lagenaria siceraria) Accessions: A Focus on Roots and Morpho-Agronomic Traits

Phenotypic characterization of the variability present within bottle gourd has been limited to morpho-agronomic traits, and this evaluation is a prerequisite for a bottle gourd breeding program. Despite playing an important role in the phenotypic variation in plants, the root system has limited use in studies of morphological diversity. Thus, the objective of this study was to characterize the morphological diversity present in bottle gourd accessions of different countries based on roots and morpho-agronomic traits. The magnitude of morphological diversity and divergence among nineteen bottle gourd accessions that represent nine different countries of origin were evaluated with analysis of variance, principal component analysis, and an agglomerative hierarchical clustering (AHC) analysis. ANOVA for morpho-agronomic and root traits revealed significant morphological effects among the accessions, suggesting substantial differences among the bottle gourd accessions. The nineteen accessions were grouped into three clusters, and while these were not grouped according to the country of origin, clear differences among the roots and flowering traits were observed between the L. siceraria var. hispida with L. siceraria var. siceraria accessions, which were confirmed with the AHC analysis, revealing the divergence between these varieties and the opportunities for rootstock breeding programs.

Combining Genetic and Transcriptomic Approaches to Identify Transporter-Coding Genes as Likely Responsible for a Repeatable Salt Tolerance QTL in Citrus

The excessive accumulation of chloride (Cl−) in leaves due to salinity is frequently related to decreased yield in citrus. Two salt tolerance experiments to detect quantitative trait loci (QTLs) for leaf concentrations of Cl−, Na+, and other traits using the same reference progeny derived from the salt-tolerant Cleopatra mandarin (Citrus reshni) and the disease-resistant donor Poncirus trifoliata were performed with the aim to identify repeatable QTLs that regulate leaf Cl− (and/or Na+) exclusion across independent experiments in citrus, as well as potential candidate genes involved. A repeatable QTL controlling leaf Cl− was detected in chromosome 6 (LCl-6), where 23 potential candidate genes coding for transporters were identified using the C. clementina genome as reference. Transcriptomic analysis revealed two important candidate genes coding for a member of the nitrate transporter 1/peptide transporter family (NPF5.9) and a major facilitator superfamily (MFS) protein. Cell wall biosynthesis- and secondary metabolism-related processes appeared to play a significant role in differential gene expression in LCl-6. Six likely gene candidates were mapped in LCl-6, showing conserved synteny in C. reshni. In conclusion, markers to select beneficial Cleopatra mandarin alleles of likely candidate genes in LCl-6 to improve salt tolerance in citrus rootstock breeding programs are provided.

Molecular, phenotypic and histological analysis reveals a multi-tiered immune response and callose deposition in stone fruit rootstocks (Prunus spp.) against Pseudomonas syringae pv. syringae (Pss) infection

Bacterial canker, caused by Pseudomonas syringae pv syringae (Pss), is a serious disease of stone fruit orchards causing severe yield reductions and the death of entire trees. To analyze the response and to identify novel sources of Pss resistance in our rootstock breeding program, we used a novel, rapid and reliable leaf disk pathogenicity test to screen pre-breeding material constituted by interspecific hybrids of plum/peach/almond (‘AGAF’/‘ADAGAF’) or sweet cherry (‘PACIR’) species and commercial rootstocks with two Pss strains. Some ‘AGAF’/ ‘ADAGAF’ and all ‘PACIR’ rootstocks showed lower susceptibility than commercial rootstocks to Pss strains used. The reduced symptoms displayed by the ‘PACIR’ hybrids with Prunus lannesiana and P. incisa as genomic background suggest that these species could be novel sources of genetic resistance to Pss within the Cerasus subgenus. Histological and candidate gene expression analysis suggest a multi-tiered immune response of Prunus species to Pss attack with a higher callose deposition and activation of molecular mechanisms that would restrict the bacteria infection and help to maintain a better redox homeostasis and performance of ‘Marianna 2624′, a plum resistant genotype. Identification of Prunus species with resistance to Pss and the analysis of their immune response are the first step towards characterizing the underlying genetic mechanisms of resistance and introducing these traits into commercial germplasm.

Dissecting the genetic architecture of root-related traits in a grafted wild Vitis berlandieri population for grapevine rootstock breeding

In woody perennial plants, quantitative genetics and association studies remain scarce for root-related traits, due to the time required to obtain mature plants and the complexity of phenotyping. In grapevine, a grafted cultivated plant, most of the rootstocks used are hybrids between American Vitis species (V. rupestris, V. riparia, and V. berlandieri). In this study, we used a wild population of an American Vitis species (V. berlandieri) to analyze the genetic architecture of the root-related traits of rootstocks in a grafted context. We studied a population consisting of 211 genotypes, with one to five replicates each (n = 846 individuals), plus four commercial rootstocks as control genotypes (110R, 5BB, Börner, and SO4). After two independent years of experimentation, the best linear unbiased estimates method revealed root-related traits with a moderate-to-high heritability (0.36–0.82) and coefficient of genetic variation (0.15–0.45). A genome-wide association study was performed with the BLINK model, leading to the detection of 11 QTL associated with four root-related traits (one QTL was associated with the total number of roots, four were associated with the number of small roots (< 1 mm in diameter), two were associated with the number of medium-sized roots (1 mm < diameter < 2 mm), and four were associated with mean diameter) accounting for up to 25.1% of the variance. Three genotypes were found to have better root-related trait performances than the commercial rootstocks and therefore constitute possible new candidates for use in grapevine rootstock breeding programs.

A tale of three vines: current and future threats to wild Eurasian grapevine by vineyards and invasive rootstocks

AbstractAimEurasian grapevine (Vitis vinifera), one of the most important fruit crops worldwide, diverged from its wild and currently endangered relative (V. vinifera ssp. sylvestris) about 11,000 years ago. In the 19th century, detrimental phylloxera and disease outbreaks in Europe forced grapevine cultivation to use American Vitis species as rootstocks, which have now become naturalized in Europe and are starting to colonize similar habitats to the wild grapevine. Accordingly, wild grapevine now faces two additional threats: the expansion of vineyards and invasive rootstocks. Furthermore, climate change is expected to have significant impacts on the distribution of all grapevines in Europe. In this study, we quantified the distributional and bioclimatic overlap between grapewine's wild relative and the taxa associated with viticulture, under current and future climate.LocationEurope, North America.MethodsThe distributions of wild Eurasian grapevine, cultivated Eurasian grapevine and five American grapevine species used in rootstock breeding programs were linked to climate variables to model their bioclimatic niches. These ecological niche models were used to quantify the spatial and bioclimatic overlap between these seven Vitis taxa in Europe.ResultsNiche and spatial overlap is high between the wild, cultivated and rootstock grapevines, suggesting that existing conflicts between vineyards and wild grapevine conservation may be further complicated by naturalized rootstocks outcompeting the wild grapevine, especially under future scenarios of climate change. In the hottest scenario, only 76.1% of the current distribution of the Eurasian grapevine remains in suitable area.Main ConclusionsAs wild grapevine may ultimately provide a valuable gene pool for adapting viticulture to a changing world, these findings demonstrate the need for improved management of the wild grapevine and its natural habitat, to counteract the harmful effects of global change on the wild relatives of viticulture.

The selection of intra-inter specific Cucurbita rootstocks for grafted melon seedlings

This study was conducted to select promising Turkish local Cucurbita rootstocks among intraspecific and interspecific hybrids for grafted melon seedling based on hybrid success rate, hypocotyl traits and graft compatibility. Rooting potentials, root system architecture and plant growth parameters of the rootstocks grafted with melon were also evaluated. Two lines of C. maxima (male parent) and eleven lines of C. moschata (female parent) at S5 generation were used. In addition, six winter squash lines were used as male parent and six pumpkin lines were used as female parent in intraspecific hybridization program. Intraspecific hybrid combinations had quite high number of seeds per fruit as compared to interspecific hybrid combinations. The highest number of seeds per fruit was obtained from HMO2 × OMO2 (359) and OMO5 × HMO8 (314) hybrid combinations. Hypocotyl lengths of all hybrid cucurbit rootstock combinations ranged from 32.96 mm (RS17) to 73.35 mm (RS8) and hypocotyl thicknesses ranged from 2.71 mm (RS2) to 3.55 mm (RS8). Graft success rates varied between 96.6 – 100% in winter squash and pumpkin intraspecific hybrids and between 87.1 – 100% in interspecific hybrids. Significant differences were seen in root architecture parameters (root length, root volume, mean root diameter, root surface area and root dry matter weight) of intraspecific and interspecies hybrid Cucurbita lines. The findings of the study indicated that the intraspecific and interspecific local cucurbit rootstock candidates developed within the rootstock breeding program showed promise as viable options for commercial use as rootstocks for grafted melon seedlings. Research about the effects of selected intraspecific and interspecific hybrid Cucurbita rootstock candidates on earliness, fruit quality and yield parameters of grafted melon will continue.&#x0D; Keywords: Cucurbita maxima; Cucurbita moschata; Rootstock breeding; Root system architecture; Melon&#x0D;

Genetic Diversity of Apple Clonal Rootstocks from the Collection of the Michurinsk State Agrarian University Based on SSR Markers.

The Michurinsk State Agrarian University (Michurinsk SAU) is one of the leading centers for breeding apple clonal rootstocks. A diverse collection of apple rootstocks, founded in 1930s by V.I. Budagovsky, is maintained at the Michurinsk SAU. In the present study, 87 rootstocks from this collection were analyzed using 18 SSR markers to assess their genetic diversity and relatedness. The detected polymorphism level was rather high compared to the previous estimates of apple rootstock genetic variability. A total of 199 alleles were detected with an average of 11.1 alleles per locus. Among the detected alleles, 67 (33.67%) were rare and 43 (21.61%) were unique. The average PIC value was 0.73, and the expected and observed heterozygosity averaged 0.76 and 0.69, respectively. All the studied accessions except two could be identified with the used marker set. Cluster analysis revealed several groups according to the rootstocks' pedigrees and genetic origin. Furthermore, Structure analysis revealed two main groups of the studied rootstock accessions. No significant differentiation of the studied sample according to dwarfing ability was detected, while weak differentiation was detected according to leaf color. SSR genotyping data can be used for rootstock fingerprinting and pedigree verification and will facilitate collection management. In addition, data on the genetic diversity and structure of the studied collection may be useful for further development of the Michurinsk SAU rootstock breeding program.

Real-Time PCR to Phenotype Resistance to the Citrus Nematode Tylenchulus semipenetrans Cobb.

As pest management options, such as nematicides, become more restrictive, developing rootstocks resistant to the citrus nematode is fundamental for citrus production. This study provides an updated methodology to screen for citrus nematode resistance in rootstock-breeding programs. We developed a novel method to extract female citrus nematodes from roots that is suitable for molecular work and a real-time-PCR-based nematode quantification method for Tylenchulus semipenetrans. These procedures allow scaling up screening to high-throughput workflows, increasing the chances of finding rootstock candidates that combine all the desired traits. Our results contribute to the growing literature supporting quantification of nematodes with molecular methods.

Using float hydroculture for acclimatization of in vitro plantlets in some pyrus genotypes

In this study, the potential of float hydroculture for the acclimatization of in vitro plantlets of two wild pear types (Pyrus elaeagrifolia Pall.) and Old Home x Farmingdale 333 (OHxF 333) pear rootstock (P. communis L.) was investigated. The wild pear types are obtained from our dwarf clone rootstock breeding program and are resistant to drought and chlorosis stresses. In vitro plantlets were generated by rooting micro cuttings with 250 mg L– 1 IBA by quick-dip method for 10 s under aseptic conditions. After this treatment, the micro cuttings were cultured on MS basal medium with ½ strength of macro and micro elements without growth regulators for 4 weeks. The cultures were incubated in the dark for the first 5 days. For acclimatization by float hydroculture, in vitro plantlets were placed in the cells of a styrofoam tray on plastic tubs (25 cm x 25 cm x 12 cm) filled with tap water. The water was not replaced during acclimatization. The float hydrocultures were incubated for 4 weeks in a climate room at 25±2 °C with 16 h light (35 μmol∙m– 2∙s– 1) and 8 h dark photoperiod for 4 weeks. At the end of this period, the percentage of viable plantlets removed from float hydroculture was 84.0%, 62.7% and 64.7% in OHxF 333, AH-32 and AH-75, respectively. These percentages are quite high in wild pear types that could not acclimatize to external conditions with known methods. There was no significant difference between leaf mesophyll thickness of Pyrus plantlets removed from float hydroculture and the mature plants in the orchard. These values varied between 153.0 ± 18.2 µm and 202.4 ± 4.8 µm. In conclusion, float hydroculture is identified as an easy and successful acclimatization technique for genotypes that are particularly difficult to acclimatize in vitro plantlets such as wild pear types.

Transcription factors MhDREB2A/MhZAT10 play a role in drought and cold stress response crosstalk in apple.

Drought and cold stresses seriously affect tree growth and fruit yield during apple (Malus domestica) production, with combined stress causing injury such as shoot shriveling. However, the molecular mechanism underlying crosstalk between responses to drought and cold stress remains to be clarified. In this study, we characterized the zinc finger transcription factor ZINC FINGER OF ARABIDOPSIS THALIANA 10 (ZAT10) through comparative analysis of shoot-shriveling tolerance between tolerant and sensitive apple rootstocks. MhZAT10 responded to both drought and cold stresses. Heterologous expression of MhZAT10 in the sensitive rootstock 'G935' from domesticated apple (Malus domestica) promoted shoot-shriveling tolerance, while silencing of MhZAT10 expression in the tolerant rootstock 'SH6' of Malus honanensis reduced stress tolerance. We determined that the apple transcription factor DEHYDRATION RESPONSE ELEMENT-BINDING PROTEIN 2A (DREB2A) is a direct regulator activating the expression of MhZAT10 in response to drought stress. Apple plants overexpressing both MhDREB2A and MhZAT10 genes exhibited enhanced tolerance to drought and cold stress, while plants overexpressing MhDREB2A but with silenced expression of MhZAT10 showed reduced tolerance, suggesting a critical role of MhDREB2A-MhZAT10 in the crosstalk between drought and cold stress responses. We further identified drought-tolerant MhWRKY31 and cold-tolerant MhMYB88 and MhMYB124 as downstream regulatory target genes of MhZAT10. Our findings reveal a MhDREB2A-MhZAT10 module involved in crosstalk between drought and cold stress responses, which may have applications in apple rootstock breeding programs aimed at developing shoot-shriveling tolerance.

HiFi chromosome-scale diploid assemblies of the grape rootstocks 110R, Kober 5BB, and 101–14 Mgt

Cultivated grapevines are commonly grafted on closely related species to cope with specific biotic and abiotic stress conditions. The three North American Vitis species V. riparia, V. rupestris, and V. berlandieri, are the main species used for breeding grape rootstocks. Here, we report the diploid chromosome-scale assembly of three widely used rootstocks derived from these species: Richter 110 (110R), Kober 5BB, and 101–14 Millardet et de Grasset (Mgt). Draft genomes of the three hybrids were assembled using PacBio HiFi sequences at an average coverage of 53.1 X-fold. Using the tool suite HaploSync, we reconstructed the two sets of nineteen chromosome-scale pseudomolecules for each genome with an average haploid genome size of 494.5 Mbp. Residual haplotype switches were resolved using shared-haplotype information. These three reference genomes represent a valuable resource for studying the genetic basis of grape adaption to biotic and abiotic stresses, and designing trait-associated markers for rootstock breeding programs.

Agronomic evaluation of eight 41 B × 110 richter grapevine genotypes as rootstock candidates for mediterranean viticulture

Choosing the most appropriate rootstock(s) is a key decision for the profitability of vineyards; therefore, there must be a sufficient range of rootstocks in the market adapted to different environmental conditions and production objectives. However, rootstock-breeding programs have been scarce in recent decades, and most of the rootstocks used today were bred a century ago, when the needs of the sector were very different from today. In this work, we aimed to evaluate new rootstock candidates before their introduction in the market. An agronomic evaluation was conducted on eight novel rootstock genotypes obtained from the first generation of the cross-pollination of 41 B Millardet et de Grasset (41 B) and 110 Richter (110 R) grafted with ‘Syrah’ and ‘Tempranillo’ and planted in a typical vineyard of the Ebro Valley in Spain. During the four consecutive growing seasons (2016–2019), growth, yield and berry composition parameters at harvest were collected. A linear mixed-effects model was constructed, considering year and block as random effects. Multiple factor analysis and hierarchical clustering on principal components were performed to establish clusters of genotypes with similar behaviour. The rootstock candidates showed a very wide performance range compared to their parents. The trial allowed us to identify two very promising candidates (RG8 and RG10), whose registration as commercial rootstocks is already in progress.

QTLs Identification for Iron Chlorosis in a Segregating Peach-Almond Progeny Through Double-Digest Sequence-Based Genotyping (SBG).

Linkage maps are highly appreciated tools for cultivar and rootstock breeding programs because they are suitable for genetic and genomic studies. In this study, we report on using sequence-based genotyping (SBG) approach to simultaneously discover and genotype SNPs from two peach-based rootstocks (“Adafuel” and “Flordaguard”) and their progeny (n = 118): from a initial mapping population composed of 131 seedlings. The plant material was developed at the EEAD–CSIC Prunus rootstocks breeding program, aiming to obtain a segregating progeny for a range of characters of agronomical interest to rootstock breeding (iron-chlorosis and root-asphyxia tolerance, nematode resistance, vigor traits, and other effects on scion cultivars). Sequence reads obtained from double-digest SBG were aligned to the P. persica reference genome (Peach v2.0). While eight linkage groups were constructed for “Adafuel,” only four linkage groups were constructed for “Flordaguard,” given the low heterozygosity of this last genotype. High synteny and co-linearity were observed between obtained maps and Peach v2.0. On the other hand, this work aimed to elucidate the genetic basis of leaf chlorosis tolerance using the phenotypic segregation of the progeny to iron-chlorosis tolerance, along with the QTLs responsible for leaf chlorosis. The F1 mapping population, composed initially of 131 seedlings, was growing in four field trials established on calcareous soils at the experimental field of the EEAD-CSIC in Zaragoza, Spain. From the initial mapping population, 131 individuals were selected for their phenotypical characterization with SPAD measurements of plants grown in the field, exhibiting a great variability. Significant QTLs associated with tolerance to iron chlorosis were found in LG1, LG5, LG7, and LG8. The significant QTLs detected in LG5 and LG7 have not been associated with this abiotic stress before in Prunus. Several candidate genes such as Prupe.1G541100, predicted as glutamyl-tRNA reductase 1, Prupe.1G468200, encoding a 2-oxoglutarate (2OG), and Fe(II)-dependent oxygenase superfamily protein or Prupe.1G577000 (ppa011050.m), a NIFU-like protein 2 (NIFU2) were detected. The exact biological function of some of these genes should be verified for the future development of marker-assisted selection for peach iron chlorosis tolerance.

Inheritance of Yield Components and Morphological Traits in Avocado cv. Hass From "Criollo" "Elite Trees" via Half-Sib Seedling Rootstocks.

Grafting induces precocity and maintains clonal integrity in fruit tree crops. However, the complex rootstock × scion interaction often precludes understanding how the tree phenotype is shaped, limiting the potential to select optimum rootstocks. Therefore, it is necessary to assess (1) how seedling progenies inherit trait variation from elite ‘plus trees’, and (2) whether such family superiority may be transferred after grafting to the clonal scion. To bridge this gap, we quantified additive genetic parameters (i.e., narrow sense heritability—h2, and genetic-estimated breeding values—GEBVs) across landraces, “criollo”, “plus trees” of the super-food fruit tree crop avocado (Persea americana Mill.), and their open-pollinated (OP) half-sib seedling families. Specifically, we used a genomic best linear unbiased prediction (G-BLUP) model to merge phenotypic characterization of 17 morpho-agronomic traits with genetic screening of 13 highly polymorphic SSR markers in a diverse panel of 104 avocado “criollo” “plus trees.” Estimated additive genetic parameters were validated at a 5-year-old common garden trial (i.e., provenance test), in which 22 OP half-sib seedlings from 82 elite “plus trees” served as rootstocks for the cv. Hass clone. Heritability (h2) scores in the “criollo” “plus trees” ranged from 0.28 to 0.51. The highest h2 values were observed for ribbed petiole and adaxial veins with 0.47 (CI 95%0.2–0.8) and 0.51 (CI 0.2–0.8), respectively. The h2 scores for the agronomic traits ranged from 0.34 (CI 0.2–0.6) to 0.39 (CI 0.2–0.6) for seed weight, fruit weight, and total volume, respectively. When inspecting yield variation across 5-year-old grafted avocado cv. Hass trees with elite OP half-sib seedling rootstocks, the traits total number of fruits and fruits’ weight, respectively, exhibited h2 scores of 0.36 (± 0.23) and 0.11 (± 0.09). Our results indicate that elite “criollo” “plus trees” may serve as promissory donors of seedling rootstocks for avocado cv. Hass orchards due to the inheritance of their outstanding trait values. This reinforces the feasibility to leverage natural variation from “plus trees” via OP half-sib seedling rootstock families. By jointly estimating half-sib family effects and rootstock-mediated heritability, this study promises boosting seedling rootstock breeding programs, while better discerning the consequences of grafting in fruit tree crops.

Molecular diversity estimates of Pakistani citrus rootstocks

Quality rootstocks are mandatory to fortify and boost up the citrus industry. Traditionally, Pakistani citrus industry is based on two rootstocks (rough lemon and sour orange), and consequently facing many biotic and abiotic constraints. Characterization and evaluation of new rootstocks is also essential to expand the citrus genetic resources for better utilization and to improve future breeding programmes. In this study thirteen rootstocks were assessed based on twenty-five morphological traits (quantitative and qualitative) whereas genetic diversity was evaluated by using forty RAPD markers. Results manifested huge morphological diversity in Sachian Citromello, Citromello 1452, Yuma citrange and Benton rootstocks. Thirteen RAPD markers proved reliable and effective tool and showed significant amplification, producing a total of 286 fragments with 61.53% polymorphism. Moreover, RAPD markers showed the individuality of all the studied rootstocks and highlighted the similarities and dissimilarities among them. Findings of this study will provide basis for further investigations looking to the improvement of citrus rootstocks. Results are also valuable for future rootstock breeding programs, particularly in release of superior and trustworthy new rootstocks for Pakistani citrus industry. The combination of such kinds of morphological and molecular markers is highly powerful tool in accomplishing detailed analysis of Citrus phylogeny and origin.