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Coconut palm (Cocos nucifera L.) is one of the most important perennial tropical crops. Stem-end rot is the major postharvest disease of coconut in Brazil. The fungus Lasiodiplodia theobromae is the only species that has been reported to be associated with this disease. However, a comprehensive study elucidating the true identity of this pathogen with molecular tools has never been conducted. In recent years, new species of Lasiodiplodia have been proposed after molecular studies were performed, indicating the existence of a species complex. The aims of this research were to study the etiology of the postharvest stem-end rot of immature coconut based on a combination of morphological and phylogenetic analyses, to establish the phylogenetic position of such taxa, and to assess the pathogenicity of each taxon. Four species were identified: L. brasiliense, L. egyptiacae, L. pseudotheobromae, and L. theobromae. All of the species were distinguished morphologically and phylogenetically and were proven to be pathogenic to coconut following artificial inoculation. L. theobromae was the most common and the most aggressive species. This study represents the first report of three additional species of Lasiodiplodia as causal agents of postharvest stem-end rot of immature coconut in Brazil.

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Three field experiments were carried out to assess the level of resistance of several cultivars to early blight (EB) and to examine the association between host resistance and either foliage maturity or tuber skin types. A total of 26 cultivars were used in Exps. 1 and 2, and 24 in Exp. 3. Plants were inoculated with isolates of Alternaria grandis at 31 days after planting. EB severity was quantified in each plot every seven days. The approach to determine the resistance levels of potato cultivars was based on multivariate analysis techniques. The tested cultivars responded as either resistant, moderately resistant, moderately susceptible or susceptible to EB. Most of the cultivars were classified as susceptible or moderately susceptible to EB. Resistant cultivars were mid-season, mid-late or late maturity. None of the susceptible cultivars were later maturity (mid-late or late maturity). In most cases, susceptible cultivars were earlier maturity (early or mid-early maturity). Most resistant cultivars had rough, mid-rough or smooth skin. None of the susceptible cultivars had rough skin. In most cases, susceptible or moderately susceptible cultivars had smooth skin. Obtaining potato cultivars that are resistant to this destructive disease will help reduce production costs and the need for costly fungicides.