Análise da resistência e da tolerância da cultivar de trigo BRS Timbaúva ao Barley yellow dwarf vírus-PAV

Abstract

The virosis, known as yellow dwarf, caused by Barley yellow dwarf virus - BYDV e Cereal yellow dwarf virus - CYDV species is one of the most important cereal deseases of the winter cereals, reducing the production in cultures around the world. BYDV and CYDV species are able to infect more than 150 species of plants in the Poaceae family, being transmited by various species of aphids (Hemiptera, Aphididae). Among the BYDV and CYDV species, BYDV-PAV predominates in the most of producing regions of the world, including brazilian wheat regions. So, it s important that the improvement programs consider the incorporation of resistance to this specie as to his aphids vectors.This study was conducted to determinate if the BRS Timbaúva capacity of keep high productivity when exposed to the virus-vector complex is caused only by the resistance to the aphid vector, or also presents BYDV-PAV resistance or tolerance. All the tests were done comparing BRS Timbaúva with Embrapa 16, one highly virus susceptible breed. The capacity or resistance to virus infection of the plant was evaluated through construction of curves of viral title (ELISA test) in different organs in a 28 days period. The tolerance was estimated evaluating morphological components and yield components in a comparative way between the breeds and consideratin the relative loss on plants infected by uncomtamined aphids. The possible resistance effect to the vector on the virus inoculation efficiency was evaluated ranging the number of aphids used (1, 2, 3, 4 e 5) to the inoculation and determining the number of infected plants and the effects on the reduction of production. The effect of the development stage of the host on the resistance or tolerance was evaluated by inoculation of plants in different development stages and evaluation of symptoms expression and the total weight of grains. The obtained results suggest that the BRS Timbaúva productivity, above the others genotypes averages in test with BYDV exposure, is caused mainly to the vector resistance. The aphid number that remained on the plant and the reproduction rate on the BRS Timbaúva were lower to the observed in the Embrapa 16 plants. Though the viral titles by season and by organ are similar, the curve of viral title is delayed on susceptible stuff, fact that can have relation with the vector behavior. The possibility of BRS Timbaúva presents a tolerance degree can t be entirely discarded, cause the losses related to the control plant (uncontamined aphids) always were higher to the Embrapa 16 plant