Ramulosis of cotton, caused by Colletotrichum gossypii var. cephalosporioides (CGC), is an important disease of cotton in Brazil. The main objective of this work was to test whether CGC is a phylogenetic species inside the Colletotrichum gloeosporioides species complex. A Bayesian inference phylogenetic analysis of a combined ITS and TUB2 dataset was conducted with 21 strains identified as CGC and five strains of Colletotrichum gossypii (CG), associated with cotton anthracnose, obtained from diseased plants from different regions of Brazil. All CGC strains formed a highly supported lineage inside the clade of Colletotrichum theobromicola, a member of the C. gloeosporioides species complex. CG strains formed another lineage in the same clade. These findings were supported by a second analysis conducted with three genes (ITS+TUB2+GAPDH) and a subset of five CGC and three CG strains. During pathogenicity tests, all five CGC strains tested induced typical symptoms of ramulosis on inoculated plants, including foliar necrosis, death of apical meristems and over sprouting. Plants inoculated with CG strains exhibited foliar necrotic spots two months after inoculation. These results give phylogenetic support for the placement of CGC in the C. gloeosporioides species complex, and the distinction between the ramulosis and anthracnose pathogens of cotton in Brazil.

Corynespora cassiicola C.T. Wei is a widespread plant pathogenic fungus that causes target-shaped necrotic spots on plant leaves and on stems, roots, flowers, and fruits and has been recorded worldwide on up to 400 plant species. The disease is known as Corynespora leaf spot or target spot on cotton and soybean. A single DNA fragment (600 bp) was amplified using described primers, and based on cytb nucleotide sequences, four out of 12 isolates of C. cassiicola were found to have a mutation that replaces the codon for amino acid 143 from GGT to GCT, resulting in an amino acid change from glycine to alanine (G143A). All four isolates were sampled from soybean plants located in north (LIM14) and central (ELM04, ELM06, and ELM07) Alabama. No other point mutation on cytb was found for six C. cassiicola isolates sampled on cotton (BRW03, MAC01, FHP01, FHP22, HSV01, and HSV12) or on other two isolates sampled on soybean (LIM02 and LIM13). Other known mutations were found in our isolates. According to the Fungicide Resistance Action Committee, C. cassiicola rapidly developed resistance to fungicides and is an example of a pathogen that must be classified as a high risk of developing resistance to a different fungicide class. To the best of our knowledge, the present study is the first to report a G143A mutant in C. cassiicola from field populations in the United States.

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

No abstract

No abstract

No abstract