Identification and characterization of Alternaria species causing leaf spot on cabbage, cauliflower, wild and cultivated rocket by using molecular and morphological features and mycotoxin production

Abstract

Alternaria species are common pathogens of fruit and vegetables able to produce secondary metabolites potentially affecting human health. Twenty-nine isolates obtained from cabbage, cauliflower, wild and cultivated rocket were characterized and identified based on sporulation pattern and virulence; the phylogenetic analysis was based on the β-tubulin gene. Isolates were identified as A. alternata, A. tenuissima, A. arborescens, A. brassicicola and A. japonica. Pathogenicity was evaluated on plants under greenhouse conditions. Two isolates showed low level of virulence on cultivated rocket while the other isolates showed medium or high level of virulence. Isolates were also characterized for their mycotoxin production on a modified Czapek-Dox medium.Production of the five Alternaria toxins, tenuazonic acid, alternariol, alternariol monomethyl ether, altenuene and tentoxin were evaluated. Under these conditions, about 80% of the isolates showed the ability to produce at least one mycotoxin.

Incidence, pathogenicity and diversity of Alternaria spp. associated with alternaria leaf spot of canola (Brassica napus) in Australia

“…All 12 Alternaria spp. ( A. alternata , A. arborescens , A. brassicae , A. conjuncta , A. ethzedia , A. eureka , A. hordeicola , A. infectoria , A. japonica , A. malvae , A. metachromatica and A. tenuissima ) reported in the current study have been associated with alternaria leaf spot either within or outside Australia on one or more Brassicaceae or non‐Brassicaceae hosts (Sampson & Walker, ; Shivas, ; Fisher et al ., ; You et al ., , ; Mułenko et al ., ; Garibaldi et al ., ; Sharma et al ., ; Bassimba et al ., ; Harteveld et al ., ; Lee et al ., ; Bashir et al ., ; Barkat et al ., ; Taj et al ., ; Van de Wouw et al ., ; Atlas of Living Australia, ; APPD, ; Farr & Rossman, ; Moslemi et al ., ; Siciliano et al ., ). It is evident that leaf spotting on canola in Australia is not soley caused by a single widely recognized Alternaria species such as A. brassicae , but that a range of up to nine other Alternaria spp.…”

“…In addition, Siciliano et al . () found that all tested isolates of A. alternata , A. arborescens , A. brassicicola , A. japonica and A. tenuissima were pathogenic across different hosts in the family of Brassicaceae; while Farr & Rossman () reported A. ethzedia on B. napus in Switzerland, A. hordeicola on Hordeum vulgare in Norway and A. malvae on Malva sinensis in China. Furthermore, alternaria leaf spotting caused by A. conjuncta has been recorded on Daucus carota in Poland (Mułenko et al ., ), A. infectoria on Malus domestica in South Africa (Farr & Rossman, ), A. metachromatica on Solanum lycopersicum in Pakistan (Bashir et al ., ), A. tenuissima on Farfugium japonicum in Korea (Lee et al ., ), and Cajanus cajan in India (Sharma et al ., ).…”

“…For example, A. arborescens has been recorded on cabbage and cultivated rocket ( Eruca spp.) in Italy (Siciliano et al ., ), A. japonica on Diplotaxis tenuifolia in Italy (Garibaldi et al ., ) and Brassica rapa subsp. rapa in Spain (Bassimba et al ., ), and for A. ethzedia on B. napus in Switzerland (Farr & Rossman, ).…”

“…For example, in WA, Shivas (1989) While Alternaria blight symptoms can exhibit on any host plant component and at all growing stages, it is the leaf spotting/blight that is of most concern. Symptoms can vary; for example, while leaf spotting produced by A. brassicae usually appears as grey-coloured lesions (Meena et al, 2010), these may or may not be surrounded by a distinct yellow halo (Siciliano et al, 2017). Furthermore, McDonald (1959) described A. brassicae leaf spot symptoms on canola in the field as completely grey under humid conditions but grey with black margins or totally black under less favourable conditions and can show chlorotic and defoliation effects.…”

Virulence variability across the Alternaria spp. population determines incidence and severity of alternaria leaf spot on rapeseed

“…Furthermore, Siciliano et al . () found three distinct virulences for A. alternata on cultivated rocket (high, moderate, and low virulence) and two distinct of virulences for A. japonica on wild rocket (high and moderate virulence). Finally, variability in virulence has also been demonstrated in A. alternata , A. brassicicola , and A. raphani on Brassicaceae in other studies (Atkinson, ; Stoll, ; Czyżewska, ; Nowakowska et al .…”