Evolution of the witch's broom disease and evaluation of resistance in cupuassu progenies

Abstract

This paper aimed to study the evolution and individual segregation of the witch's broom disease and estimate the genetic parameters in trials with 21 full sib families of Cupuaçú established in Belém, Pará. The progenies were obtained through control pollination involving resistant and susceptible parents in all three combinations. Three half-sib families were also evaluated as checks. The experiments were evaluated at individual level and all the analyses were based on the mixed model methodology (REML/ BLUP procedure) with unbalanced incomplete blocks design and common checks across trials. The evaluated traits comprised the percentage of resistant plants concerning the disease on the branches, on the flowers and on the mature and immature fruits from 2002 to 2007. The results showed that the disease is especially important between July and September. The disease evolution showed that pruning against the disease must be conducted at the end of the productive season in May/June and also in September/October. The breeding population can be successfully improved due to the high levels of genetic variability and heritability associated to the resistance traits. There were genetic segregations for all the traits. The integrated control of the disease, associating resistant genotypes and pruning is recommended.