Assessing sequence heterogeneity in Chlorellaceae DNA barcode markers for phylogenetic inference

Phylogenetic inference is an important approach that allows the recovery of the evolutionary history and the origin of the Chlorellaceae species. Despite the species' potential for biofuel feedstock production, their high phenotypic plasticity and similar morphological structures among the species have muddled the taxonomy and identification of the Chlorellaceae species. This study aimed to decipher Chlorellaceae DNA barcode marker heterogeneity by examining the sequence divergence and genomic properties of 18S rRNA, ITS (ITS1-5.8S rRNA-ITS2-28S rRNA), and rbcL from 655 orthologous sequences of 64 species across 31 genera in the Chlorellaceae family. The study assessed the distinct evolutionary properties of the DNA markers that may have caused the discordance between individual trees in the phylogenetic inference using the Robinson-Foulds distance and the Shimodaira-Hasegawa test. Our findings suggest that using the supermatrix approach improves the congruency between trees by reducing stochastic error and increasing the confidence of the inferred Chlorellaceae phylogenetic tree. This study also found that the phylogenies inferred through the supermatrix approach might not always be well supported by all markers. The study highlights that assessing sequence heterogeneity prior to the phylogenetic inference could allow the approach to accommodate sequence evolutionary properties and support species identification from the most congruent phylogeny, which can better represent the evolution of Chlorellaceae species.

Frequent Association of Colletotrichum Species with Citrus Fruit and Leaf Spot Disease Symptoms and their Genetic Diversity in Ethiopia

Citrus leaf and fruit spot is one of the most important biotic constraints of citrus production in Ethiopia. The symptomatic leaf and fruit samples were collected from 29 orchards of 15 major citrus growing districts of Ethiopia. One hundred sixty-seven fungal isolates were recovered and identified to species level through DNA barcoding; and their relationships were established using multigene phylogeny. The internal transcribed spacers, long subunit and actin gene sequences revealed that those 167 isolates belonged to either Collectotrichum gloeosporioides or Collectotrichum boninense species complexes (sensu lato), but no recovery of Pseudocercospora angolensis, the primary causal agent of the citrus leaf and fruit spot disease. Detached leaf assays confirmed pathogenicity of isolates of both C. gloeosporioides and C. boninense species complexes on citrus. They reproduced disease symptoms and the pathogens were re-isolated from symptomatic tissues. This study reports frequent association of C. gloeosporioides and C. boninense species complexes with citrus fruit and leaf spot disease in Ethiopia. This finding suggests the need for in-depth studies to determine the roles of C. gloeosporioides and C. boninense species complexes in citrus fruit and leaf spot disease epidemiology.