Search Results (20)

Macadamia (Macadamia spp.) is an economically important nut crop whose severe recalcitrance to genetic transformation substantially hinders progress in functional genomics and molecular breeding. To overcome this critical technical bottleneck, this study established a highly efficient and broadly applicable in planta hairy root genetic transformation system with integrated visual screening. This system utilizes an Agrobacterium rhizogenes-mediated transformation method, employing multiple visual reporter gene systems (DsRed2, eGFP, RUBY, and AtPAP2) to achieve antibiotic-independent and non-destructive screening of transgenic roots. Notably, the system innovatively incorporates the air layering (marcotting) technique to extend in planta genetic transformation to branches of mature trees in the field. By circumventing the stringent sterile conditions required for conventional in vitro tissue culture, this approach achieves a largely genotype-independent transformation across open-pollinated seedlings with diverse genetic backgrounds (A4, GR1, HAES900, and O.C.). The transgenic hairy root induction frequencies ranged from 39.25% to 47.38%, although the GR1 genotype exhibited a notable developmental stage-dependent decline in transformation efficiency. Furthermore, transgenic hairy roots were successfully induced on mature tree branches, with a maximum induction rate of 28.2%. Gene expression analyses confirmed the stable, high-level expression of the target transgenes in all the transgenic hairy root lines. This in planta transformation system provides a reliable in vivo experimental platform for the rapid functional validation of candidate genes and the investigation of root biology in Macadamia. Moreover, it establishes a novel strategy for plant regeneration via root-to-shoot organogenesis, offering a promising avenue for the genetic improvement of recalcitrant woody plants. Full article

China’s macadamia industry has expanded remarkably; however, a comprehensive understanding of the interaction between cultivar and geographical origin in shaping oil quality remains limited. This gap constrains the development of high-value products. To address this, we conducted a systematic and comparative evaluation of macadamia nuts and their pressed oils from 15 representative cultivars across Yunnan, Guangxi, and Guangdong. Our analysis encompassed physicochemical properties, fatty acid profiles, key minor components (tocopherols, squalene, and polyphenols), and antioxidant activities. Oleic acid (56.66–62.75%) and palmitoleic acid (12.24–18.73%) were the dominant fatty acids, with Yunnan oils exhibiting the highest unsaturated fatty acid content (80.86%). Multivariate analyses revealed that geographical origin was a more dominant factor than cultivar in shaping the overall compositional profile, particularly for the minor bioactive components. A strong positive correlation was established between antioxidant capacity and the contents of polyphenols, squalene, and tocopherols. The Guangxi A4 cultivar emerged as the premier material due to its superior fatty acid profile, high bioactive content (squalene: 329.01 mg/kg; tocopherols: 64.10 mg/kg), and potent antioxidant capacity. Our findings provide a scientific foundation for the selective breeding and origin-based standardization of premium macadamia oils in China. Full article

Fruit endocarp and seed coat are essential protective structures that influence key agronomic and mechanical traits in species with lignified protective tissues, yet their regulatory mechanisms remain incompletely understood. Here, we conducted a comprehensive genome-wide analysis of the MADS-box gene family in four angiosperm species: Juglans sigillata, Carya illinoinensis, Macadamia integrifolia, and Ricinus communis. A total of 58, 55, 57, and 57 MADS-box genes were identified, respectively, and systematically characterized through phylogenetic, structural, and evolutionary analyses. Comparative results revealed that MIKCc-type genes are highly conserved and primarily expanded via segmental duplication under strong purifying selection. Co-expression network analysis identified MADS-box genes as high-connectivity hub candidates that are strongly associated with genes involved in tissue specification, hormone signaling, and secondary cell wall biosynthesis. Promoters analysis indicated that these genes contain diverse cis-regulatory elements; however, these results are based on sequence prediction and do not demonstrate functional regulatory interactions. Across species, MADS-box genes exhibited analogous temporal expression dynamics during lignified endocarp and seed coat development, consistent with a potentially conserved transcriptional framework. Collectively, this study provides new insights into the evolutionary diversification and putative functions of MADS-box genes, and proposes a putative hierarchical regulatory framework for lignified endocarp and seed coat development. These findings supply valuable candidate target genes for future molecular breeding aimed at improving shell thickness, hardness, and related agronomic traits in woody nut and oilseed species. Full article

Macadamia (Macadamia spp.), as a high-value cash crop, relies on varietal adaptability screening and quality optimization for enhanced industrial benefits. However, existing research has predominantly focused on the mature tree stage. Systematic studies on the physiological characteristics during the seedling stage and comprehensive multi-indicator evaluations remain insufficient, limiting improved variety selection and industrial development. This study investigated three macadamia varieties (A4, A16, A203). We systematically measured leaf morphology, photosynthetic parameters, antioxidant enzyme activities, and free amino acid content at the seedling stage, combined with a comprehensive analysis of mature fruit morphology, mineral elements, amino acid composition, and pericarp phenolic compounds. The results indicated that at the seedling stage: A4 exhibited the highest SPAD value and CAT activity, significantly exceeding A16 and A203 by 137.14% and 139.82%, respectively, alongside the lowest MDA content, highlighting its superior stress resistance; A16 showed the highest Pn, Cleaf, and WUE, with total amino acid content being 38.09% and 18.79% higher than A4 and A203, respectively; A203 demonstrated the highest light energy utilization efficiency, significantly higher SOD activity compared to A16 and A203, and the lowest O²⁻ content. Regarding fruit quality: A16 kernels contained the highest total amino acids and umami amino acids, with sweet and aromatic amino acids also being significantly higher than in other varieties; A203 performed notably well in K, Mg, and Mn content, with medicinal amino acids accounting for over 70% of the total; A4 pericarp contained significantly higher levels of phenolic compounds, such as p-hydroxybenzoic acid, compared to A16 and A203, some exceeding 80%. Correlation analysis revealed a complex regulatory network among fruit traits, mineral elements, amino acids, and phenolics. In summary, A4, A16, and A203 possess respective advantages in high stress resistance, superior flavor quality, and high nutritional functionality. This study establishes a comprehensive “morphology–photosynthesis–antioxidant activity–amino acids–quality” evaluation system, providing a scientific basis for targeted breeding and whole-industry-chain development of macadamia. Full article

Color serves as a crucial visual signal for attracting pollinating insects and directly affects the fruit set rate in woody crops. This study investigated the molecular mechanisms underlying flower color formation in macadamia. The results demonstrated that darker flower colors were associated with higher fruit set rates: the rates for purple, pink, pinkish-white, and white flowers were 2.78, 1.99, 1.35, and 1.31, respectively. High-throughput sequencing identified 1359 differentially accumulated metabolites, including benzoic acid, 4-hydroxybenzaldehyde, and isorhamnetin. Transcriptional regulators such as ERF, MYB, and WRKY were significantly up-regulated in darker flowers. KEGG analysis revealed two key metabolic pathways, in which genes including HCT (shikimate hydroxycinnamoyl transferase) and F3GalTase (flavonol 3-O-galactosyltransferase), as well as related metabolites such as p-coumaric acid, chlorogenic acid, and myricetin, showed higher expression levels in darker flowers. Anthocyanin content was highest in pink and pinkish-purple varieties (462.79 and 446.35 μg/g, respectively), and lower in white and light pink varieties (140.52 and 167.97 μg/g). In conclusion, flower color intensity is positively correlated with both fruit set rate and anthocyanin content. Genes involved in the flavonoid and phenylpropanoid pathways, along with transcription factors such as WRKY and MYB, collectively regulate flower color formation. This study provides a theoretical basis for macadamia flower color breeding. Full article

Background/Objectives: Macadamia integrifolia is a valuable subtropical fruit tree, yet genomic studies on its cultivars are limited. This study aims to elucidate the chloroplast genome features, variations, and phylogenetic relationships of three main cultivars (‘Guilin No. 1’, ‘Nanya No. 1’, ‘Qian’ao No. 1’) to support germplasm identification and breeding. Methods: chloroplast genomes of three M. integrifolia cultivars from Guangxi, Guangdong, and Guizhou were sequenced using Illumina technology, followed by assembly, annotation, and comparative analyses of structure, repeats, and codon usage. Phylogenetic relationships were reconstructed using complete genome sequences. Results: The three chloroplast genomes displayed typical quadripartite structures, with lengths of 159,714 bp, 159,195 bp, and 159,508 bp, and GC contents of 38.12%, 38.16%, and 38.14%, respectively. Each encoded 135 genes. Codon usage was biased towards A/U-ending codons. We identified 81, 87, and 80 SSRs and 26, 21, and 20 long repeats, respectively. IR boundary regions were highly conserved. Phylogenetically, the cultivars showed close relationships with M. integrifolia, Macadamia tetraphylla, and Macadamiaternifolia, forming a sister clade to Platanus occidentalis. Conclusions: This study provides essential chloroplast genomic resources for three M. integrifolia cultivars, revealing conserved structures and specific variations. The findings offer crucial insights for the genus's genetic diversity, supporting future germplasm evaluation and phylogenetic research. Full article

Nuts, including tree nuts such as almonds, walnuts, cashews, and macadamias, as well as peanuts, are widely consumed for their health benefits owing to their high-quality protein content. Globally, the nut industry represents a multi-billion-dollar sector, with increasing demand driven by consumer interest in nutrition, functional foods, and plant-based diets. Recent advances in proteomic technologies have enabled comprehensive analyses of nut seed proteins, shedding light on their roles in nutrition, allergenicity, stress responses, and food functionality. Seed storage proteins such as 2S albumins, 7S vicilins, and 11S legumins, are central to nutrition and allergenicity. Their behavior during processing has important implications for food safety. Proteomic studies have also identified proteins involved in lipid and carbohydrate metabolism, stress tolerance, and defense against pathogens. Despite technical challenges such as high lipid content and limited genomic resources for many nut species, progress in both extraction methods and mass spectrometry has expanded the scope of nut proteomics. This review underscores the central role of proteomics in improving nut quality, enhancing food safety, guiding allergen risk management, and supporting breeding strategies for sustainable crop improvement. Full article

Nut set is an important determinant of yield and plays a pivotal role in orchard profitability. The complex process of nut setting is governed by numerous factors, with pollination being a critical mechanism. Macadamia cultivars exhibit both self- and cross-pollination. Self-pollination may increase nut set, so it is a trait of interest in breeding. This study investigated nut setting and nutlet abscission on four cultivars, ‘HAES 791’, ‘HAES 741’, ‘HAES 344’, and ‘A16’, using three controlled self-pollination methods: (i) autogamy (AG), entailing bagging before anthesis with no hand-pollination; (ii) geitonogamy 1 (GG1), bagging following hand-pollination using pollen from the same raceme; and (iii) geitonogamy 2 (GG2), bagging following hand-pollination using pollen from different racemes of the same cultivar. These self-pollination methods were compared against open-pollination (OP). ‘HAES 741’ and ‘HAES 791’ were partially self-fertile, while ‘HAES 344’ and ‘A16’ were self-infertile. Final nut sets per raceme for ‘HAES 741’ were 0.43 by AG, 0.65 by GG1, and 0.5 by GG2, and for ‘HAES 791’, they were 0.90 by AG, 1.25 by GG1, and 1.0 by GG2. Final nut set per raceme with OP was higher compared to self-pollination methods and ranged between 3.5–6.5. In self-fertile cultivars, nut set following the three self-pollination methods accounted for 6.5–3.7% of the nut set following OP, and nutlet abscission following self-pollination methods accounted for 20–50% of nutlet abscission following OP. No significant differences in nut set and nutlet abscission were observed among AG, GG1, and GG2. Results suggest that macadamia orchards planted with self-fertile cultivars would be less reliant on external pollinators or artificial pollination to achieve adequate yields. Full article

Macadamia nut plantings in China are expanding year by year. In order to breed and promote superior varieties, this study analyzed the effects of different rootstocks and scions on the survival rate of grafted seedlings, and then selected the best substrate composition for plant growth. The results showed that the survival rate of the HAES788 variety as rootstock and Guire No. 1 as scion was the highest, reaching 96%. The optimal grafting time in December was better than that in March. Furthermore, among 16 substrate formulations, T12, T13, T15, and T16 had advantages of agglomerated soil and more well-developed root systems compared to the CK made of loess. The plant height, stem diameter, leaf length, leaf width, and dry weight of the aboveground and underground parts of the grafted seedlings planted in these substrate formulations were significantly higher than those plants planted in the CK. In addition, the substrate formulations T12, T13, T15, and T16 significantly improved the organic matter, total nitrogen, and total potassium content of the substrate soils, but little improvement was observed for total phosphorus content after 13 months. Overall, macadamia grafting times are best in December, with HAES788 and Guire No. 1 being the best rootstock and scion. The optimal substrate formulations are T12, T13, T15, and T16. This study provides a solid foundation for the production of high-quality macadamia plants. Full article

Global fruit and nut yields are affected by shortfalls in pollinator populations, and pollen limitation is most prevalent among tropical, bee-pollinated and self-incompatible plants. Macadamia is a subtropical, bee-pollinated crop in which some cultivars have been found to be highly outcrossing. We aimed to determine the extent of outcrossing and its effects on nut quality across a wide range of international macadamia cultivars in three countries. We sampled fruit from 19 macadamia cultivars across 23 sites in Australia, Brazil and South Africa. We used genotype-by-sequencing and MassARRAY methods to assign paternity to individual fruit and we assessed pollen-parent effects on nut quality. Macadamia was highly outcrossing, producing 80–100% of fruit by cross-pollination, at 17 of the 23 sites. Mixed mating (41–72% outcrossing) was identified at five sites, and low outcrossing (10%) was identified in one cultivar at one site where it was isolated from other flowering macadamia trees. Outcrossed fruit often had significantly better quality than selfed fruit, with 1.61–3.39 g higher nut-in-shell mass, 0.53–1.55 g higher kernel mass, 3.3–6.4% higher kernel recovery, and 3.0–3.5% higher oil concentration. The differences in kernel recovery equated to differences in value of USD 433–841 per ton of nut-in-shell at prices of USD 3000 per ton. In summary, macadamia cultivars were mostly highly outcrossing, and outcrossed nuts often had higher quality than selfed nuts. Growers should consider interplanting different cultivars more closely and distributing bee hives more widely to maximise cross-pollination, produce high yields, and optimise nut quality. Full article

Vigor control in tree crops plays an important role in increasing orchard efficiency and sustainability. It has enabled high-density plantations to maximize yield efficiency while reducing production costs. Although traditional methods such as frequent hedging and pruning are still used, dwarfing rootstocks and low-vigor cultivars are the most effective and sustainable means of vigor control, as these methods reduce labor and management costs while maintaining yield efficiency. Considerable variation among cultivars and rootstocks for vigor has been identified; however, mechanisms by which rootstocks affect scion vigor in slow-maturing tree crops remain unclear. With the lack of adequate information required for early and rapid selection, breeding programs in tree crops such as macadamia still utilize manual phenotyping, which is laborious, time-consuming, and expensive. Providing insights on emerging technologies that enhance breeding programs via rapid selection, this review summarizes the current state of vigor management and underlying mechanisms of vigor control in tree crops. It provides further understanding of the prospects of applying those techniques in rootstock and scion breeding for low-vigor and yield-efficient cultivars in tree crops, with specific reference to macadamia. Full article

Edible Macadamia is one of the most important commercial nut trees cultivated in many countries, but its large tree size and long juvenile period pose barriers to commercial cultivation. The short domestication period and well-annotated genome of Macadamia integrifolia create great opportunities to breed commercial varieties with superior traits. Recent studies have shown that members of the phosphatidylethanolamine binding protein (PEBP) family play pivotal roles in regulating plant architecture and flowering time in various plants. In this study, thirteen members of MiPEBP were identified in the genome of M. integrifolia, and they are highly similarity in both motif and gene structure. A phylogenetic analysis divided the MiPEBP genes into three subfamilies: MFT-like, FT-like and TFL1-like. We subsequently identified two TERMINAL FLOWER 1 homologues from the TFL1-like subfamily, MiTFL1 and MiTFL1-like, both of which were highly expressed in stems and vegetative shoots, while MiTFL1-like was highly expressed in young leaves and early flowers. A subcellular location analysis revealed that both MiTFL1 and MiTFL1-like are localized in the cytoplasm and nucleus. The ectopic expression of MiTFL1 can rescue the early-flowering and terminal-flower phenotypes in the tfl1–14 mutant of Arabidopsis thaliana, and it indicates the conserved functions in controlling the inflorescence architecture and flowering time. This study will provide insight into the isolation of PEBP family members and the key targets for breeding M. integrifolia with improved traits in plant architecture and flowering time. Full article

Macadamia pericarps that fail to abscise (‘stick-tights’) are an important trait to select against in breeding as they can harbour pests and diseases. Traditional macadamia breeding cycles are lengthy and expensive due to long juvenilities and large tree sizes. Thus, genome-wide association studies (GWAS) are an important investigative tool to identify candidate trait-linked markers to enable potential reductions in evaluation and selection cycles via marker-assisted selection (MAS) in young seedlings. This study assessed 199 wild macadamia germplasm accessions for stick-tight prevalence across two years. As the number of stick-tights per tree is limited by the number of nuts per tree, we conducted association analyses to identify SNPs linked with the number of stick-tights per tree, and examined whether such SNPs were also associated with, and thus confounded with, the number of nuts per tree. We also assessed associations with the proportion of stick-tights per total number of nuts. Thirty-two SNPs were associated with at least one of the stick-tight traits in one year (p < 0.001). Of all such SNPs, only one was associated with the number of nuts per tree (p < 0.001), indicating that most associations were not confounded with yield. Full article

Phenotyping in macadamia breeding programs is laborious, time-consuming and costly. Developing rapid and cost-effective phenotyping technologies can reduce costs and increase breeding efficiency. The aim of this project is to develop an image-based phenotyping tool for rapid, cost-effective and accurate assessment of kernel recovery (KR) in macadamia. Nut samples were collected from second-generation macadamia breeding progenies grown in Bundaberg research station, Queensland, Australia, and were measured for nut traits. Nuts were cracked at the suture line to measure nutshell thickness. A digital slide caliper was used for manual phenotyping, and a digital camera was used for image-based phenotyping of shell thickness. Pictures of the cracked nut samples were processed with Image J to extract phenotypic information. Correlations between shell thickness and kernel recovery were negative in both manual and image-based approaches. Correlations were low in manual measurements (−0.54 to −0.59) but very high with image-based measurements (−0.87). The outcomes indicate that shell thicknesses can be used as a predictor for KR in macadamia breeding programs, and more importantly, image-based measurements offer higher prediction accuracy of KR than manual measurements. Full article

Macadamia is a recently domesticated Australian native nut crop, and a large proportion of its wild germplasm is unexploited. Aiming to explore the existing diversity, 247 wild accessions from four species and inter-specific hybrids were phenotyped. A wide range of variation was found in growth and nut traits. Broad-sense heritability of traits were moderate (0.43–0.64), which suggested that both genetic and environmental factors are equally important for the variability of the traits. Correlations among the growth traits were significantly positive (0.49–0.76). There were significant positive correlations among the nut traits except for kernel recovery. The association between kernel recovery and shell thickness was highly significant and negative. Principal component analysis of the traits separated representative species groups. Accessions from Macadamia integrifolia Maiden and Betche, M. tetraphylla L.A.S. Johnson, and admixtures were clustered into one group and those of M. ternifolia F. Muell were separated into another group. In both M. integrifolia and M. tetraphylla groups, variation within site was greater than across sites, which suggested that the conservation strategies should concentrate on increased sampling within sites to capture wide genetic diversity. This study provides a background on the utilisation of wild germplasm as a genetic resource to be used in breeding programs and the direction for gene pool conservation. Full article