Analysis of phylogeny, distribution, and pathogenicity of Botryosphaeriaceae species associated with gummosis of Anacardium in Brazil, with a new species of Lasiodiplodia

Abstract

Netto, M. S. B., Lima, W. G., Correia, K. C., da Silva, C. F. B., Thon, M., Martins, R. B., Miller, R. N. G., Michereff, S. J., and Câmara, M. P. S. 2016. Analysis of phylogeny, distribution, and pathogenicity of Botryosphaeriaceae species associated with gummosis of Anacardium in Brazil, with a new species of Lasiodiplodia. We identified Botryosphaeriaceae species associated with gummosis on Anacardium in Brazil. Isolates were sampled and identified on the basis morphology and phylogeny, through analysis of a partial translation elongation factor 1-α sequence, ribosomal DNA internal transcribed spacers, and β-tubulin gene sequence. Ten taxa were identified, namely, Lasiodiplodia brasiliense, L. euphorbicola, L. gonubiensis, L. iraniensis, L. jatrophicola, L. gravistriata sp. nov., L. pseudotheobromae, L. theobromae, Neofusicoccum batangarum, and Pseudofusicoccum stromaticum. Lasiodiplodia theobromae has been previously reported in cashew and is the most prevalent species observed. All the other species are reported here for the first time on this host. All species of Botryosphaeriaceae were pathogenic on detached green cashew shoots. Differences in aggressiveness were observed among the species, with N. batangarum, L. iraniensis, L. jatrophicola, and L. gravistriata characterized as the most aggressive species, whilst L. euphorbicola and L. pseudotheobromae were identified as the least aggressive.

Introduction

Cashew (Anacardium occidentale) is a tropical evergreen crop cultivated worldwide with a centre of origin in the Amazonian forest of Brazil. In contrast to the other seven species within the genus Anacardium, only cashew (A. occidentale) is an economically important nut crop, with both an edible hypo carp (apple) and nutritious kernel arising from a drupe (Aliyu 2012). It is important as an export commodity, with considerable consumption in Europe and the USA. Brazilian production in 2013 reached 259 900 t, from a production area of 708 430 ha. In 2016, 12 165 t of cashew nuts were exported generating about US$ 79 M. The north-eastern region of Brazil is responsible for 99 % of the country's production (Agrianual 2015), with the cashew industry in rural areas recognized to be of considerable socio-economic importance (Moreira et al. 2013).

Of the numerous diseases that compromise cashew production, cashew gummosis, which is caused by Lasiodiplodia theobromae, is considered one of the most important diseases for the cashew industry (Cysne et al. 2010). This fungal species was first reported on cashew in 1990 (Freire 1991), and was soon recognized as one of the most important diseases of the crop in north-eastern Brazil (Freire et al., 2002, Moreira et al., 2013). The main symptoms of this disease comprise the appearance of cankers along the trunk or branches, which develop over time and release a characteristic resin-like gum. Gummosis subsequently results in reduced water and nutrient transport, branch dieback, inflorescence blight, reduction in photosynthesis, and eventual plant death (Freire et al., 2002, Moreira et al., 2013).

To date only L. theobromae has been found associated with cashew gummosis (Freire et al., 2002, Cardoso et al., 2004, Muniz et al., 2012, Moreira et al., 2013). However, identification of causal agents was based on analysis of fungal morphology and cultural characteristics, which are today considered insufficient for species identification in the genus Lasiodiplodia (Phillips et al. 2013).

Lasiodiplodia is a member genus of the Botryosphaeriaceae, a family in the Dothideomycetes. This family contains numerous fungal species which occur as saprophytes, parasites or endophytes on a diverse range of plant hosts (Slippers and Wingfield, 2007, Phillips et al., 2013). In addition to cashew in Brazil, genera of Botryosphaeriaceae such as Botryosphaeria, Fusicoccum, Macrophomina, Neofusicoccum, Neoscytalidium, and Pseudofusicoccum (Marques et al., 2013b, Machado et al., 2014) have been reported to cause disease in several other economically important crops including avocado (Persea americana), banana (Musa spp.), barbados cherry (Malpighia glabra), cacao (Theobromae cacao), castor bean (Ricinus communis), citrus (Citrus spp.), coconut palm (Cocos nucifera), custard apple (Annona squamosa), grapevine and table grape (Vitis spp.), guaraná (Paullinia cupana), guava (Psidium guajava), mango (Mangifera indica), muskmelon (Cucumis melo), papaya (Carica papaya), passion fruit (Passiflora edulis), physic nut (Jatropha curcas), sour sop (Annona muricata), and watermelon (Citrullus lanatus) (Costa et al., 2010, Marques et al., 2013a, Machado et al., 2014, Netto et al., 2014, Correia et al., 2016).

Although the taxonomy of the Botryosphaeriaceae has until recently been based upon morphology of asexual morphs, more recent phylogenetic inference based upon analysis of sequence data for target DNA loci has had considerable impact on the systematics of the Botryosphaeriaceae, with increased resolution enabling discrimination of species with overlapping morphological characteristics (De Wet et al., 2008, Phillips et al., 2013).

Despite the pathogenic importance attributed to Botryosphaeriaceae on diverse host plants, there have been no phylogenetic analyses of this family on cashew. Given the increasing economic importance of cashew gummosis and the recent reports of new species of Botryosphaeriaceae occurring on tropical plants, it is possible that a number of species of this family may be associated with cashew gummosis in Brazil. For effective disease management, a clear understanding of disease aetiology is essential for determination of the distribution of individual species and their disease epidemiology. In this context, the objectives of this study were (i) to identify species of Botryosphaeriaceae associated with cashew gummosis in Brazil, (ii) to determine the prevalence and distribution of each species, and (iii) to characterize isolates in terms pathogenicity and virulence using excised cashew green shoots.