DIVERSIFICATION OF RESISTANCE RESPONSE OF SELECTED TOBACCO CULTIVARS (NICOTIANA TABACUM)

DIVERSIFICATION OF RESISTANCE RESPONSE OF SELECTED TOBACCO CULTIVARS (NICOTIANA TABACUM) DEPENDING ON THE USED POTATO VIRUS YISOLATESAnna Depta, Teresa Doroszewska, Anna Czubacka

Abstract

Potato virus Y (PVY) causes tobacco veinal necrosis. It be-longs to the group of ten most dangerous plant viruses respon-sible for large economic losses. Within the species Nicotiana tabacum, the resistance to this virus is conditioned by the single recessive va gene resulting from a deletion in the susceptibility Va gene. Many tobacco cultivars have this resistance, including VAM, Wiślica and Virginia SCR (V. SCR). However, their resist-ance is overcome by the virulent PVY isolates, so it is necessary to search for new sources of resistance or combine ones already known. The aim of the study was to identify cultivars with va resist-ance, and to assess its effectiveness depending on the used PVY isolate. Research also included the search for new resistance fac-tors within Nicotiana tabacum cultivars. Twenty five tobacco cultivars were tested for resistance to PVY in biological tests by artificial inoculation under greenhouse conditions. Four virus iso-lates with different levels of virulence were used for the studies. After four weeks, disease symptoms were observed, and DAS-ELISA tests were performed using specific antibodies to confirm the presence of the virus in plants. The tested cultivars showed a different degree of PVY susceptibility depending on the used isolate. The identification of the va gene was carried out by using PCR for amplification of two markers of the length 146 and 402 bp. The presence of amplicons indicated the presence of Va sus-ceptibility gene, while cultivars with the va resistance gene did not amplify the products. The highest resistance was character-istic of cv. VAM which was not infected with isolates IUNG 23 and IUNG 17, defined as weak and medium, although the remain-ing isolates, described as strong (IUNG 22 and IUNG20), caused vein necrosis and the presence of the virus was confirmed in plant tissues by a positive DAS-ELISA test result. Six cultivars that did not show disease symptoms only after applying the weak isolate, had a slightly lower resistance. Other cultivars with va resistance were infected by all used PVY isolates. Another five cultivars, after infection with four isolates, showed symptoms of tolerance, i.e. vein clearing and chlorotic spots of a leaf blade, but they did not have vein necrosis, in spite of that molecular tests confirmed the presence of Va susceptibility gene. Moreover, interesting re-sults were noted for cv. Węgierski Ogrodowy, that, despite the presence of the susceptibility gene, was not infected by weak isolate IUNG23. The last group included susceptible cultivars that reacted with vein necrosis to all used PVY isolates. Since virulent PVY isolates are able to break va resistance, the knowledge of the nature and stability of the resistance of cul-tivars is particularly important, especially within Polish cultivars. In addition, the rising number of necrotic isolates in Poland and in the world, capable of breaking existing sources of resistance, can cause an increased use of tolerant cultivars in tobacco breeding.

Keywords: PVY isolates, va gene, tolerance