Plastome Phylogenomics of Aucuba (Garryaceae)

On Pattern-Cladistic Analyses Based on Complete Plastid Genome Sequences

The fundamental Hennigian principle, grouping solely on synapomorphy, is seldom used in modern phylogenetics. In the submitted paper, we apply this principle in reanalyzing five datasets comprising 197 complete plastid genomes (plastomes). We focused on the latter because plastome-based DNA sequence data gained dramatic popularity in molecular systematics during the last decade. We show that pattern-cladistic analyses based on complete plastid genome sequences can successfully resolve affinities between plant taxa, simultaneously simplifying both the genomic and analytical frameworks of phylogenetic studies. We developed "Matrix to Newick" (M2N), a program to represent the standard molecular alignment of plastid genomes in the form of trees or relationships directly. Thus, massive plastome-based DNA sequence data can be successfully represented in a relational form rather than as a standard molecular alignment. Application of methods of median supertree construction (the Average Consensus method has been used as an example in this study) or Maximum Parsimony analysis to relational representations of plastome sequence data may help systematist to avoid the complicated assumption-based frameworks of Maximum Likelihood or Bayesian phylogenetics that are most used today in massive plastid sequence data analyses. We also found that significant amounts of pure genomic information that typically accommodate the majority of current plastid phylogenomic studies can be effectively dropped by systematists if they focus on the pattern-cladistics or relational analyses of plastome-based molecular data. The proposed pattern-cladistic approach is a powerful and straightforward heuristic alternative to modern plastome-based phylogenetics.

Identification of Colletotrichum aenigma as the new causal agent of leaf blight disease on Aucuba japonica Thunb., and screenings of effective fungicides for its sustainable management

Aucuba japonica Thunb is an evergreen woody ornamental plant with significant economic and ecological values. It also produces aucubin, showing a variety of biological activities. It is widely planted in the southwest region of China, including karst landscape areas in Guizhou Province. In January 2022, a serious leaf blight disease was observed on the leaves of A. japonica in the outdoor gardens of Guizhou University, Guiyang, Guizhou, China. The causal agent was identified as Colletotrichum aenigma through amplification and sequencing of the internal transcribed spacer (ITS) region, translation of the chitin synthase (CHS) and actin (ACT) genes, and morphological characterizations. Koch's postulates were confirmed by its pathogenicity on healthy leaves, including re-isolation and identification. To our knowledge, this is the first report of C. aenigma causing leaf blight on A. japonica worldwide. To identify pathogen characteristics that could be utilized for future disease management, the effects of temperature and light on mycelial growth, conidia production, and conidial germination, and the effects of humidity on conidial germination were studied. Optimal temperatures for mycelial growth of C. aenigma BY827 were 25-30°C, while 15°C and 35°C were favorable for conidia production. Concurrently, alternating 10-h light and 14-h dark, proved to be beneficial for mycelial growth and conidial germination. Additionally, conidial germination was enhanced at 90% humidity. In vitro screenings of ten chemical pesticides to assess their efficacy in suppressing C. aenigma representative strain BY827. Among them, difenoconazole showed the best inhibition rate, with an EC50 (concentration for 50% of maximal effect) value of 0.0148 μg/ml. Subsequently, field experiment results showed that difenoconazole had the highest control efficiency on A. japonica leaf blight (the decreasing rate of disease incidence and decreasing rate of disease index were 44.60 and 47.75%, respectively). Interestingly, we discovered that C. aenigma BY827 may develop resistance to mancozeb, which is not reported yet among Colletotrichum spp. strains. In conclusion, our study provided new insights into the causal agent of A. japonica leaf blight, and the effective fungicides evaluated provided an important basis and potential resource for the sustainable control of A. japonica leaf blight caused by C. aenigma in the field.

The Phylogenetic Significance of Fruit Structures in the Family Cornaceae of China and Related Taxa

The fruit morphological structures of the Cornaceae of China and related taxa were studied using the wax GMA semi-thin section method and other methods to identify characters useful in delimiting clades circumscribed in previous molecular phylogenetic studies. Maximum parsimony analyses of 27 fruit structural characters resulted in a generally poorly resolved strict consensus tree, yet one whose major clades matched those revealed previously. Cornaceae of China and related taxa are recognized in four significant clades with the following fruit structural features: (1) Helwingia, fruits lack trichome, the abdominal vascular bundles are close to the endocarp, and the endocarp sclereid is elongated; (2) Aucuba, single-cell lanceolate trichomes, pericarp without secretory structure; (3) Torricellia, polygon and elongated sclereids in the endocarp, pericarp without crystal and tannin; and (4) Cornus sensu lato, the trichome is T-shaped, the abdominal ventral bundle is absent, and the endocarp sclereid is nearly round. In Cornus sensu lato, this document supported that the cornelian cherries (CC, subg. Cornus) and the big-bracted dogwoods (BB, subg. Syncarpea) are sister groups. The dwarf dogwoods (DW, subg. Arctocrania) are sister to them, and the blue- or white-fruited dogwoods (BW, subg. Kraniopsis, subg. Yinquania, and subg. Mesomora) are the base of the Cornus sensu lato clade. The number of cell layers of endocarps and the types of crystals afford sound evidence for identifying their relationship. This study indicated that the fruit structures of Cornaceae might provide morphological and anatomical evidence for molecular phylogeny.