Cytological modi®cations in maize plants infected by barley yellow dwarf virus and maize dwarf mosaic virus R. Musetti a, * , L. Bruni a , M.A. Favali b a Dipartimento di Biologia Applicata alla Difesa delle Piante, Universita Á di Udine, via delle Scienze, 208, 33100 Udine, Italy b Dipartimento di Biologia Evolutiva e Funzionale, Universita Á di Parma, viale delle Scienze, 43100 Parma, Italy Received 30 November 2001; revised 6 March 2002; accepted 7 March 2002 Abstract Three inbred lines of maize (33-16, MO17 and B73) differing in their susceptibility to Barley yellow dwarf virus and Maize dwarf mosaic virus were studied to compare the ultrastructural modi®cations induced by the two viruses in leaf tissues of different age. The results demonstrate that the alterations induced by the two viruses in the different maize lines could depend on the particular line tested. q 2002 Elsevier Science Ltd. All rights reserved. Keywords: Maize; Barley yellow dwarf virus; Maize dwarf mosaic virus; Mixed infection; Transmission electron microscopy 1. Introduction Barley yellow dwarf virus (BYDV) a member of the Luteoviridae, and maize dwarf mosaic virus (MDMV), belonging to the Potyviridae, are two of the most wide- spread viruses that affect maize and other Gramineae world- wide, causing serious economical losses (Toler, 1985; Lister and Ranieri, 1995; Rubies-Autonell et al., 1995). In nature, they can occur as mixed infections; in this case it has been observed that in maize, an increase in the damage reduced production by nearly 100%, especially in inbred lines, that are particularly susceptible to infection (Loi et al., 1990; Osler et al., 1990; Shukla et al., 1994). Regarding the ultrastructural characteristics and the cellular alterations caused by BYDV or MDMV in infected plants, numerous articles and reviews have been published (Brakke et al., 1986; Favali et al., 1987; Eweida et al., 1988; Calder and Ingerfeld, 1990; Favali et al., 1990, 1995), but few of them described mixed infections (Knox et al., 1987; Langenberg, 1991; Almasi et al., 1996). In the case of single infection, both viruses cause cyto- pathic alterations in the tissues of host plants (Amai and Kojima, 1990; Favali et al., 1990; Baunoch et al., 1991). In particular, it is well known, that MDMV and all the other Potyviruses are localized in the cytoplasm of the mesophyll cells where they are associated with characteristic and diag- nostic cytoplasmic inclusions (CIs) (Shukla et al., 1994). BYDV is localized in the phloem of the infected plants and also for this virus (as well as for others), the presence intheinfectedcells,ofinclusionbodies,crystallineoramor- phous of different size and shape has been reported but these are not useful for the diagnosis (Favali et al., 1987). The aim of this work was to study and compare the ultra- structural alterations caused by mixed infection of BYDV and MDMV in leaf tissues of different age of three inbred lines of maize (33-16, MO17 and B73) different for their susceptibility to the two viruses (Osler et al., 1990). 2. Materials and methods 2.1. Plant material Maize plants of different inbred lines, 33-16, B73 and MO17, were grown in a greenhouse and arti®cially infected with MDMV-A strain and BYDV-PAV strain according to the method described by Osler et al. (1990). A second group of uninfected plants of the same lines was kept as healthy controls. The three lines, all important for making commercial hybrid lines, were chosen for their different susceptibility to MDMV and BYDV: 3316 is particularly susceptible to BYDV, MO17 to MDMV and B73 is intermediate, showing characteristic symptoms of the two viruses (Loi et al., 1990; Osler et al., 1990; Ivanovich et al., 1992). Before preparation for microscopic analysis, all the plants were tested with ELISA using antisera against BYDV-PAV strain and MDMV-A strain (Loi et al., 1990). Micron 33 (2002) 681±686 PERGAMON 0968±4328/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S0968-4328(02)00020-3 www.elsevier.com/locate/micron * Corresponding author.