Scientia Horticulturae 99 (2004) 143–152 Pre-harvest rindstain of ‘Encore’ mandarin: initial histological signs of epicarp disturbance and extent of the disorder M.I. Maia a,∗ , M.C. Medeira a , M.J. Pinto b , A.M. Duarte b a Departmento de Fisiologia Vegetal, Estação Agronómica Nacional, Quinta do Marquˆ es, 2780-505 Oeiras, Portugal b Universidade do Algarve, UCTA, Gambelas, 8000-117 Faro, Portugal Accepted 26 May 2003 Abstract Pre-harvest rindstain in ‘Encore’ mandarin starts by the injury of a few epidermal cells. The con- nection between the damaged epidermis and the collapsed layers of flavedo, extending in parallel with rind surface was only visible on cross-sections containing the narrow zone of injured epidermal cells. The individual cell alteration including loss of membrane integrity and the accumulation of large amounts of osmiophilic materials in the cytoplasm are the result of a degrading process. Minute disruptions in the cuticle may provide shelters for resting forms of amoeboid or plasmodial-like or- ganisms living on the rind. Our results suggest that these organisms could be involved in the disorder expression. © 2003 Elsevier B.V. All rights reserved. Keywords: Citrus; Histology; Plasmodial organisms; Pre-harvest; Peel-pitting; Rind blemish; Rind injury; Ultrastructure 1. Introduction Rindstain in ‘Encore’ mandarin (Citrus nobilis Lour. × Citrus deliciosa Ten.) is a rind disorder that arises as chlorotic spots. This disorder decreases the commercial value al- though the fruit palatability is not impaired (Vitor et al., 1999). Externally this disorder resembles other rindstains caused by climate, mechanical injury, chemical treatments or post-harvest chilling (Freeman, 1976; Agust´ ı and Almela, 1989; Arpaia et al., 1991; Duarte and Guardiola, 1995). ∗ Corresponding author. Tel.: +351-21-4403500; fax: +351-21-4416011. E-mail address: fisiologiavegetal@vizzavi.pt (M.I. Maia). 0304-4238/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0304-4238(03)00088-8