Survey and prevalence of species causing Alternaria leaf spots on brassica species in Pernambuco

Abstract

Brassicaceae family comprises plant species that are very important as vegetable crops, such as the species complex Brassica oleracea and Brassica rapa. Alternaria brassicicola and A. brassicae are among the most important pathogens of Brassicaceae causing Alternaria leaf spot disease. The occurrence and prevalence of Alternaria species causing leaf spots in brassica crops in Pernambuco was acessed, as well as the existence of a possible preference by vegetable host for these pathogens. Twenty-eight fields were surveyed in the Agreste region of Pernambuco state, in the 2005 and 2006 growing seasons. In each year, 10 Chinese cabbage, six cabbage, six cauliflower and six broccoli fields were visited. In each field, 50 leaves showing at least five lesions were randomly collected. Species identification was performed taking into account morphology of the conidia that was compared with literature data. Among the two Alternaria species found, A. brassicae was found in all Chinese cabbage fields while A. brassicicola was found in all fields of cabbage, cauliflower and broccoli. Overall, A. brassicicola was more prevalent than A. brassicae. In Chinese cabbage there was predominance of A. brassicae, with mean prevalence of 91. 0% and 96.5% in 2005 and 2006. On the other hand, in broccoli and cabbage there was high predominance of A. brassicicola, with mean prevalence between 95.1% and 99.8%. In cauliflower, although the prevalence has been of A. brassicicola, high frequency of A. brassicae was noted. The frequency of co-occurrence of both Alternaria species was very low. The results of this study reinforce the hypothesis of existence of host preference within species of Alternaria that cause leaf spots in brassica crops, especially when Chinese cabbage, broccoli and cabbage are considered. This information is critical to developing strategies for managing Alternaria leaf spots in Brassicaceae species.

Morphological, molecular and pathogenic characterization of Alternaria longipes, the fungal pathogen causing leaf spot on Atractylodes macrocephala

“…And among those pathogens, Alternaria account for the most. For instance, leaf spot on Atractylodes is caused by A. tenuissima (Wang et al, 2007), and A. brassicae caused leaf spot on Chinese cabbage (Michereff et al, 2012). Diseases caused by Alternaria species are common and these diseases occur worldwide.…”

Alternaria brassicicola – Brassicaceae pathosystem: insights into the infection process and resistance mechanisms under optimized artificial bio-assay

“…On the other hand, the cultigen PGH05I performed better under artificial inoculation, manifested by the marginally higher DSI under natural epidemiological conditions. This might indicate the presence of other stress factors: Local differences in growing conditions or climate (Hong and Fitt 1995;Scholze 2002;Shrestha et al 2005), suboptimal developmental stage upon pathogen incidence, or presence of other pathogens under natural epidemiological conditions, in particular the opportunistic ones such as A. alternata (Kubota et al 2006;Michereff et al 2012;Tohyama & Tsuda 1995). Under natural infection in the field, the conidia concentration may be low, and plants may escape infection (Sharma et al 2002), hence the need to repeatedly test the resistance of the established breeding materials in the field to prevent escapes.…”

“…It leads to 15 to 70% losses, mainly by infection of seeds and seedlings, but also of the edible produce (Kumar et al 2014;Nowicki et al 2012b;Shrestha et al 2005). Production of the vegetable brassicas is mainly affected by A. brassicicola and A. brassicae, whereas the oleiferous seed crops are mainly affected by A. brassicae (Kumar et al 2014;Michereff et al 2012;Nowicki et al 2012b). The dark leaf spot disease is particularly common in tropical or subtropical regions, but also threatens the Brassicaceae production in areas with high humidity and frequent rainfall (Humpherson-Jones and Phelps 1989).…”

The occurrence of Alternaria species on cabbage in Iran

“…During the study aimed to identify causal agents of dark leaf spot disease of the four brassica crops grown in Thailand, A. brassicicola was the only identified species based on morphological and molecular characteristics (Pattanamahakul, Strange, 1999). In a survey of species causing Alternaria leaf spots on Brassica species in Pernambuco, A. brassicae was found in all Chinese cabbage fields, while A. brassicicola was found in all fields of cabbage, cauliflower and broccoli, an indication of host preferences (Michereff et al, 2012). In a recent study to determine pathogen species diversity on oilseed Brassicas, Alternaria brassicae, A. brassicicola and A. alternata were isolated from infected samples and A. brassicae was the dominant species (Aneja et al, 2014).…”