Ilex × attenuata ‘Sunny Foster’ represents a yellow leaf mutant originating from I. × attenuata ‘Foster#2’, a popular ornamental woody cultivar. However, the molecular mechanisms underlying this leaf color mutation remain unclear. Using a comprehensive approach encompassing cytological, physiological, and transcriptomic methodologies, notable distinctions were discerned between the mutant specimen and its wild type. The mutant phenotype displayed aberrant chloroplast morphology, diminished chlorophyll content, heightened carotenoid/chlorophyll ratios, and a decelerated rate of plant development. Transcriptome analysis identified differentially expressed genes (DEGs) related to chlorophyll metabolism, carotenoid biosynthesis and photosynthesis. The up-regulation of CHLD and CHLI subunits leads to decreased magnesium chelatase activity, while the up-regulation of COX10 increases heme biosynthesis—both impair chlorophyll synthesis. Conversely, the down-regulation of HEMD hindered chlorophyll synthesis, and the up-regulation of SGR enhanced chlorophyll degradation, resulting in reduced chlorophyll content. Additionally, genes linked to carotenoid biosynthesis, flavonoid metabolism, and photosynthesis were significantly down-regulated. We also identified 311 putative differentially expressed transcription factors, including bHLHs and GLKs. These findings shed light on the molecular mechanisms underlying leaf color mutation in I. × attenuata ‘Sunny Foster’ and provide a substantial gene reservoir for enhancing leaf color through breeding techniques.

Ilex verticillata (L.) A. Gray (Winter Red) is a deciduous shrub and native to North America with high ornamental value, which was introduced into China in 2006. In Oct. 2020, leaf spots occurred on I. verticillata at the nursery of Baima Base for Teaching and Scientific Research of Nanjing Forestry University (31°36'51"N, 119°11'8"E). In the early stage, there were small black spots occurred on the leaves. Then, these spots enlarged and coalesced into regular or irregular gray necrotic lesions with dark margins (Fig. S1A). The incidence of this disease was ca. 93%. Infected leaves were collected and surface-sterilized with 75% ethanol. Pieces cut from the margin of the lesions of ca. 5×5 mm were placed on potato dextrose agar (PDA) Petri plates and incubated at 25±2°C for 7 days. Ten Alternaria fungal isolates were single-spore isolated. Since these isolates shared similar morphological characters, isolates 9-1 and 15-2-2 were randomly chosen for further experiments. 2-yr-old potted I. verticillata were used for pathogenicity test in vivo. Leaves were surface-sterilized using 75% ethanol and wounded using a sterilized needle and inoculated with mycelial plugs or 10 μL of conidial suspensions (105 spores mL-1), respectively. The inoculated plants were kept in a growth chamber at 25°C and 85% RH under a 12-h photoperiod. PDA plugs without fungus or sterilized H2O were used as controls, respectively. The experiment was repeated 2 times. Each treatment had 3 replicates. By day 7, necrotic lesions were observed on the leaves inoculated with the fungal isolates 9-1 or 15-2-2. No lesions were found on the plants inoculated with PDA discs or dH2O (Fig. S1). To complete Koch’s postulates, the pathogen was re-isolated from the infected leaves and shared similar morphological characteristics of colonies and conidia with the original inoculated isolates. Conidiophores of the 2 isolates were pale brown, erect or curved, (20.1-)21.4–29.9(-39.9) × (8.4-)10.6–14.9(-18.3) μm, (n = 30). Conidia were dictyospores, nearly ovoid or clubbed, brown or grayish brown, (25.2-)27.5–42.8(-47.9) × (5.7-)6–7.7(-8.7) μm, (n = 30), in branched or unbranched chains (Fig. S1). These morphological characteristics matched A. alternata (Woudenberg et al. 2013). The internal transcribed spacer (ITS), glyceraldehyde-3-phosphate dehydrogenase gene (GAPDH), endopolygalacturonase gene (endoPG), anonymous noncoding region (OPA10-2), small subunit gene (SSU), and large subunit gene (LSU) of isolates 9-1 and 15-2-2 were amplified using primer sets of Woudenberg et al. (2013). The SSU (OK428540, OK428541), LSU (OK428538, OK428539), ITS (OK316966, OK316967), GAPDH (OK428542, OK428543), endoPG (OK428544, OK428545), and OPA10-2 (OK428536, OK428537) of isolates 9-1 and 15-2-2 showed 99, 99, 99, 99, 100, and 100% similarity to the sequences of A. alternata ex-type CBS 916.96, respectively. Phylogenetic analyses using concatenated sequences of ITS, GAPDH, OPA10-2, LSU, SSU, and endOPG also showed that the isolates of 9-1 and 15-2-2 clustered with A. alternata ex-type and was supported with a 100% bootstrap value (Fig. S2). Based on the morphological and phylogenetic results, these fungal isolates were identified as A. alternata. A. alternata was reported as the pathogen of leaf spot and other diseases on more than 380 hosts (Farr & Rossman, 2022). To our knowledge, this was the first report of A. alternata causing leaf spot on I. verticillata in China. This report is important because the discovery is related to the management strategies of the new pathogen on I. verticillata. The monitoring and control of the disease needs to be emphasized in the future.

"Peace Time: A New Yellow-fruit Holly Cultivar" published on Feb 2022 by American Society for Horticultural Science.

"‘Jingshan Princess’: A New Ilex ×attenuata Cultivar with Entire Leaf Margin and Yellow Foliage" published on Sep 2024 by American Society for Horticultural Science.

The mechanisms underlying leaf variegation in the ornamental Ilex × ‘Solar Flare’ remain poorly understood. To investigate this phenomenon, we conducted a comprehensive characterization of its variegated leaves. Compared to green sectors, yellow sectors exhibited severe chloroplast structural abnormalities, including swollen chloroplasts, damaged thylakoid membranes, and reduced chloroplast numbers. These yellow sectors also showed significantly lower chlorophyll and carotenoid levels, along with a depletion of key chlorophyll precursors—protoporphyrin IX (Proto IX), magnesium protoporphyrin IX (Mg-Proto IX), and protochlorophyllide (Pchlide). Photosynthetic efficiency was significantly impaired. Comparative transcriptome analysis identified 3510 differentially expressed genes (DEGs) between yellow and green sectors. Key disruptions in chlorophyll biosynthesis included upregulated CHLD expression and downregulated CHLH and CHLG expression, leading to impaired chlorophyll synthesis. Additionally, chlorophyll degradation was accelerated by PAO upregulation. Defective chloroplast development in yellow sectors was associated with the downregulation of GLK1, GLK2, and thylakoid membrane-related genes (PsbC, PsbO, PsbR, PsaD, and PsaH). These molecular alterations likely drive the variegated phenotype of I. × ‘Solar Flare’. These observations advance our understanding of the genetic and physiological mechanisms regulating leaf variegation in this cultivar.

Holly (Ilex L.) is a genus of woody dioecious plants with substantial ecological and economic value. However, its high species diversity and morphological similarity make accurate identification challenging. To address this, we constructed a multi-taxon Ilex leaf image dataset. We then trained six deep learning models—GoogLeNet, ResNet50, ResNet101, DenseNet121, DenseNet169, and EfficientNet-B3—using a unified PyTorch framework on cloud computing resources. Leaf images were preprocessed by background removal, resizing, cropping, and normalization. Model performance was evaluated using accuracy, F1-score, and Grad-CAM visualizations. Under an image-level data split that may overestimate generalization, all six models achieved over 99% classification accuracy on preprocessed leaf images under controlled laboratory conditions. DenseNet121 and DenseNet169 performed best, reaching 99.65% accuracy. Because images of the same leaf or same plant could appear in both training and test sets under this split, plant-level cross-validation is required to assess real-world generalizability. The reported accuracies represent an upper-bound estimate under image-level splitting. The framework offers a rapid and accurate tool for preliminary screening under controlled conditions, but its performance on raw field photographs and across different collection sites remains to be validated.