Crop load related deformity of developing Pistacia vera cv `Kerman' nuts A. Fabbri a,* , L. Ferguson b , V.S. Polito b a Istituto di Coltivazioni Arboree, Universita Á di Catania I-43100, Parma, Italy b Department of Pomology, University of California, Davis, CA 95616, USA Accepted 2 June 1998 Abstract Pistachio nut (cv `Kerman') development was examined on light-bearing and heavy-bearing trees during the 1993 and 1994 growing seasons to characterize fruit development. The highest incidence of damage by other means (DBOM) occurred during May when fruit thinning was occurring and shells were developing. Disease, insects, and mechanical damage were eliminated as causing DBOM. Dormant spraying of calcium, manganese, and boron resulted in no significant mitigation of DBOM. However, the incidence of DBOM appeared to increase with increasing crop load. From an anatomical study it appeared that the process leading to tissue degeneration in pistachio fruit pericarp may start as early as the second week after bloom, although in some cases its onset is later. The most affected tissue is the endocarp parenchyma, whose cells become necrotic and collapse, thus causing shrinkage and fracture in the shell. In the worst cases only the mesocarp (hull) remains functional, providing thin protection for the embryo, as no shell is present in the affected areas. The degeneration may also involve the mesocarp, at times with hypertrophy. The localized curly aspect of the nuts occurs when the degeneration is not simultaneous, or equal, on the entire wall. The macroscopic degeneration ranges from dramatic to barely noticeable. # 1998 Elsevier Science B.V. All rights reserved. Keywords: Pistachio; Fruit development; Fruit histology; Alternate bearing 1. Introduction A pistachio shell deformity designated as `damage by other means' (DBOM) by California pistachio processors appeared in California's San Joaquin Valley in Scientia Horticulturae 77 (1998) 219±234 * Corresponding author. Present address: Dipartimento di Biologia Evolutiva e Funzionale, Viale delle Scienze, 43100 Parma, Italy. Tel.: +39 521 905966; fax: +39 521 905965; e-mail: fabbri@ipruniv.cce.unipr.it 0304-4238/98/$ ± see front matter # 1998 Elsevier Science B.V. All rights reserved. PII:S0304-4238(98)00155-1