Note BREAKDOWN OF RESISTANCE IN SWEET PEPPER AGAINST Pepper yellow mosaic virus IN BRAZIL

Plants of Capsicum annuum cv. Magali R, resistant to Pepper yellow mosaic virus (PepYMV), which showed severe yellow mosaic, leaf malformation and stunting were observed during the 2003/04 growing season in Lins, São Paulo State, Brazil. Potyvirus-like particles observed in leaf sap from infected plants under the electron microscope reacted with an antiserum against PepYMV in PTA-ELISA. In addition to C. annuum cv. Magali R, this potyvirus also infected systemically the resistant C. annuum cv. Rubia R. The nucleotide sequence of part of the CP gene of this potyvirus shared 96–98% identity with that of other PepYMV isolates. The partial nucleotide sequence of the 3' NTR showed 94–96% identity with that of PepYMV. These data indicate that this potyvirus is a resistance-breaking isolate of PepYMV.


INTRODUCTION
During the 1960s, Potato virus Y (PVY) was the most prevalent and economically important virus on sweet pepper (Capsicum annuum L.) crops in Brazil (Nagai, 1983).The disease caused by this potyvirus was controlled after the introduction of several PVYresistant cultivars in the 1970s (Kurosawa et al., 2005).However, during the early 1990s, the occurrence of a PVY isolate that was able to overcome the resistance of those cultivars was reported.This iso-late, then referred to as PVY m or PVY 1,2 (Boiteux et al., 1996) was recognized as a new species of potyvirus, named Pepper yellow mosaic virus (PepYMV) (Inoue-Nagata et al., 2002).
As this virus became prevalent in sweet pepper crops in Brazil, the introduction of virus-resistant hybrids such as Magali R and Rubia R were landmarks for the sweet pepper crop because of their resistance to PVY strains 0, 1, and 1,2, and PepYMV.('SCM 334'), which also confers resistance to Pepper mottle virus (PepMoV) (Palloix & Kyle, 1995;Dogimont et al., 1996;Andrés et al., 1998;Echer & Costa, 2002), it is supposed that the same gene might be responsible for the resistance to PepYMV.
During the 2003/04 growing season, 80% of Magali R plants from a greenhouse planting in São Paulo State, Brazil were found exhibiting severe mosaic.Preliminary electron microscopic analysis of extracts from diseased plants showed the presence of potyvirus-like particles, which were further characterized as a strain of PepYMV, hereby designated as PepYMV-Lins.

MATERIAL AND METHODS
Leaf samples from C. annuum cv.Magali R, which exhibited stunting, severe yellow mosaic, and malformed leaves, were collected from a commercial crop in Lins, São Paulo State, Brazil, for virus isolation.Leaf extracts of these plants, prepared in 0.02 M phosphate buffer, pH 7.0, were rub-inoculated on leaves of five C. annuum cultivars, and other species listed in Table 1.The original isolate of PepYMV used by Inoue-Nagata et al. (2002) to describe this species of potyvirus was also inoculated as control.
Aphid transmission tests of PepYMV-Lins were carried out with Aphis gossypii and Myzus persicae raised on Nicotiana tabacum and Raphanus raphanistrum, respectively.Aphids were fasted for 1 h and then transferred onto C. annuum cv.Magali infected with PepYMV-Lins, for a ten min acquisition access period and were transferred to healthy Magali R plants (20 aphids per plant) for a 24 h inoculation access period.Ten and 15 plants were inoculated with M. persicae and A. gossypii, respectively.
All test-plants were maintained in a greenhouse for evaluations based on disease expression and virus detection in inoculated and newly emerged leaves by PTA-ELISA (Mowat & Dawson, 1987).Diluted (1:1000) polyclonal antiserum against PepYMV (Inoue-Nagata et al., 2002) was used.Leaf extracts from healthy and PepYMV (original isolate) infected pepper plants were used as negative and positive controls, respectively.

RESULTS AND DISCUSSION
PepYMV and PepYMV-Lins induced the same reaction in the majority of the inoculated test-plants, except on C. annuum cvs.Magali R and Rubia R, in which PepYMV-Lins caused mosaic, leaf malformation, necrosis on apical leaves and plant stunting (

Table 1 )
. A. gossypii and M. persicae transmitted PepYMV-Lins to 80% and 100% of the inoculated plants, respectively.Infection of all test-plants was confirmed by PTA-ELISA.