Species diversity, novel interactions and absence of well‐supported host‐guided phylogenetic groupings of Neotropical Alternaria isolates causing foliar lesions in Solanaceae

Abstract

Aim: To report the characterization of 120 Alternaria isolates inducing early blight-like foliar lesions in nine species of five Solanaceae genera collected across all macrogeographical Brazilian regions. Material and Results: Phylogenetic relationships were assessed via analyses of the Alternaria alternata allergenic protein-coding, glyceraldehyde-3-phosphate dehydrogenase and the calmodulin gene sequences. Most of the tomato isolates were placed into the Alternaria linariae cluster, whereas most of the potato isolates were grouped with Alternaria grandis. Novel host-pathogen interactions were also reported. Seventeen isolates were selected for morphometrical characterization, and a subsample of 13 isolates was employed in pathogenicity assays on tomato, potato, eggplant, scarlet eggplant, Capsicum annuum, Datura stramonium, Physalis angulata and Nicotiana tabacum. Eleven isolates were able to induce foliar lesions in tomatoes but none in C. annuum. Potato was susceptible to a subgroup of isolates but displayed a subset of isolate-specific interactions. Morphological traits were in overall agreement with molecular and host range data. Conclusion: Alternaria linariae and A. grandis were confirmed as the major causal agents of tomato and potato early blight, respectively. However other Alternaria species are also involved with early blight in solanaceous hosts in Brazil.Significance and Impact of the Study: The diversity and host-specific patterns of the Alternaria isolates from Solanaceae may have practical implications in establishing effective early blight genetic resistance and cultural management strategies especially for tomato and potato crops.

Phenotypic and genetic variability of fungal isolates associated with the Septoria leaf spot disease of lettuce (Lactuca sativa) in Brazil

“…Nevertheless, this nucleotide dataset allowed for the establishment of more precise phylogenetic relationships among the S. lactucae isolates. Low genetic diversity is consistent with predominantly asexual reproduction as also inferred for Alternaria species in Brazil (Lourenço Jr. et al 2009;Peixoto et al 2021). In the study of Lourenço Jr. et al (2009) were detected low number of mutations (n = 16), nucleotide diversity (0.007), and nucleotide differences (3.20) for Alt a1 gene.…”

Small‐spored Alternaria spp. (section Alternaria) are common pathogens on wild tomato species

“…Most of our collected isolates are small‐spored and belong to the Alternaria section Alternaria . The fact that only two isolates belong to section Porri is surprising because large spored species like A. linariae are reported as major problems on tomatoes (e.g., Peixoto et al, 2021). According to Adhikari et al (2020), A. alternata on tomato is neglected and poorly understood in comparison to A. linariae (Adhikari et al, 2020).…”

Small-sporedAlternariaspp. (sectionAlternaria) are common pathogens on wild tomato species

“…The fact that only two isolates belong to section Porri is surprising, because large spored species like A. linariae are reported as major problems on tomato (e.g. Peixoto et al ., 2021). According to Adhikari et al 2020, A. alternata on tomato is neglected and poorly understood in comparison to A. linariae (Adhikari et al ., 2020).…”

“…The fact that hardly any A. solani was found on the wild tomatoes might indicate that there is no cross-contamination from crops to the wild. Peixoto et al 2021 found several Alternaria pathogens from different solanaceous plants in Brazil to cause early blight symptoms on tomato. As these had originally been collected from persistent weeds, they claim it is likely that these plants can act as alternative hosts and might become a source of inoculum to important crops (Peixoto et al ., 2021).…”

“…Peixoto et al 2021 found several Alternaria pathogens from different solanaceous plants in Brazil to cause early blight symptoms on tomato. As these had originally been collected from persistent weeds, they claim it is likely that these plants can act as alternative hosts and might become a source of inoculum to important crops (Peixoto et al ., 2021). Interestingly, our collected pathogens from wild tomato plants did not infect cultivated tomato in an infection assay.…”