Complementations and exclusions between mutated versions of a potato virus Y genotype during mixed infections of Nicotiana hosts.

Understanding the processes that have led to the recent prevalence of necrotic genotypes in PVY populations is an important challenge for research programs studying this virus. Non-necrotic PVY(O)-139, necrotic PVY(N)-605 and point mutated versions of PVY(N)-605 (PVY(KRED), PVY(KR) and PVY(ED)), were used in mixtures to inoculate two Nicotiana hosts which express (N. tabacum cv. Xanthi) or not (N. clevelandii) necrosis symptoms in response to infection by PVY(N) group members. The comparison during serial passage experiments of proportions of PVY genotypes produced in mixed infected plants with those of the inocula was used to describe: (i) complementation between PVY(KR) and PVY(N) and between PVY(KRED) and PVY(O) genotypes; (ii) exclusion of the PVY(KRED) genotype, previously described as fitter, during mixed infections in the presence of one of the less fit PVY(N), PVY(ED) and PVY(KR) genotypes and (iii) the prevalence of the non-necrotic PVY(KR) genotype in the presence of PVY(N) parental sequence. These results indicate that the role of both A/G(2213) and A/C(2271) nucleotides in the fitness of PVY genotypes depends on other genetic information in the viral genome that has not yet been identified. Moreover, the collected data indicate that mutation of the nucleotide 2213 in the PVY(N)-605 sequence could lead to the prevalence, both in N. tabacum cv. Xanthi and in N. clevelandii, of the non-necrotic PVY(KR) genotype.