Viral determinants associated with the distinct biological properties of two isolates of Lettuce mosaic virus (LMV): Kinetics of viral infection and infection of the embrionary tissues / Determinantes virais associados às diferentes propriedades biológicas de dois isolados de Lettuce mosaic virus (LMV): cinética da infecção viral e infecção dos tecidos embrionários

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Lettuce mosaic, caused by the potyvirus Lettuce mosaic virus (LMV), is one of the main diseases of lettuce. The type strain of the virus includes isolates which are seed borne in lettuce, but which cannot infect lettuce cultivars harboring the recessive resistance aleles mo11 e mo12. The Most strain includes isolates which are also seed borne and can infect cultivars with the recessive resistance genes. The Brazilian isolate AF199 belongs to the Most strain. Its seed transmission rate can be as high as 16,5%. This isolate induces severe symptoms in Nicotiana benthamiana and has a shorter latent period in comparison to isolate E, collected in Spain. Furthermore, this isolate induces systemic necrosis in some lettuce cultivars. Isolate E can infect cultivars with the recessive resistance genes, but it is not seed borne in these cultivars. The objectives of this work were: (i) to analyze the tissues of ovules and embryos from lettuce plants infected by isolates AF199 and E; (ii) to study the fitness mechanisms of isolates AF199 and E, and of three recombinants obtained between these two isolates, in lettuce Salinas 88 and N. benthamiana. Isolate AF199 was detected in all tissues of ovules collected before and after fertilization. Conversely, isolate E was not detected in any ovule tissues, before or after fertilization. These results suggest that the absence of seed transmission of isolate E is due to the inability of viral particles in reaching the reproductive tissues, and that viral factors related to movement within the plant could be involved in seed transmission. The kinetics of systemic infection was analyzed in plants in which the inoculated leaf was removed after different periods of time. Viral RNA accumulation was analyzed in inoculated and non-inoculated leaves. The results indicate that isolate AF199 reaches a higher concentration in both inoculated and non-inoculated leaves, earlier than isolate E, in both hosts. The recombinant Rec1 induced distinct symptoms and reached a higher titer in N. benthamiana compared to the parental isolates. Rec4 reached the lowest concentration among the isolates/recombinants tested in N. benthamiana. In lettuce, the relative concentrations of the recombinants Rec3 and Rec4 was up to 10-fold higher in comparison to the AF199 isolate. It is concluded that isolate AF199, and those recombinants having the P1/HC-Pro coding region derived from this isolate, are better adapted than isolates having the P1-HC/Pro region derived from isolate E. This better adaptability could be related to the suppression of RNA silencing induced by P1/HC-Pro.

ASSUNTO(S)

lettuce mosaic virus lettuce lettuce mosaic virus potyvirus alface potyvirus fitopatologia resistência resistance

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