Marcadores microssatélites relacionados com a resistência à vassoura-de-bruxa do cacaueiro

Abstract

Resumo -Os objetivos deste trabalho foram caracterizar a resistência à vassoura-de-bruxa de plantas de cacau originadas do cruzamento entre TSH 1188 e CCN 51 (população segregante), por meio de dois métodos de inoculação em condições de campo, e identificar marcadores microssatélites específicos para grupos de plantas resistentes e suscetíveis. As plantas-controle avaliadas pelos métodos de inoculação natural e inoculação artificial em campo produziram os mesmos padrões de sintomas. As plantas da população segregante também coincidiram os padrões de sintomas em 90%, por esses dois métodos. O método de inoculação artificial em campo permite detectar falso-resistentes. Dos 18 pares de primers microssatélites amplificados, 15 foram polimórficos entre os genitores, e seis entre os grupos de plantas segregantes contrastantes quanto à resistência à vassoura-de-bruxa. Foram confirmadas três marcas previamente associadas a QTL (locos para características quantitativas) relacionados com a resistência à vassoura-de-bruxa, comuns a outras populações. Também foram identificados três novos QTL para esta característica, típicos desta população, o que comprova sua utilidade para o melhoramento genético do cacaueiro.Termos para indexação: Theobroma cacao, Moniliophthora perniciosa, inoculação, marcador molecular, QTL, melhoramento genético. Microsatellite markers related to resistance of cocoa tree against witches'-broomAbstract -The objectives of this work were to evaluate cocoa tree resistance against witches'-broom, in plants originated from the crossing between TSH 1188 and CCN 51 (segregating population), by means of two methods of inoculation in field conditions, and to identify microsatellite markers specific for resistant and susceptible plants. The control plants bore identical symptoms as the plants of the segregating population in 90% of the cases under the two methods. The method of artificial inoculation in the field allows the detection of false resistance to the disease. Of the 18 pairs of microsatellite primers amplified, 15 were polymorphic between genitors and six were polymorphic between the two groups of plants evaluated for resistance to witches'-broom. Three previously characterized markers were confirmed as associated to QTL (quantitative trait loci) related to resistance to the witches'-broom, which is common in other populations. Three new QTL for this characteristic, typical of this population, were also identified, which proves the utility of this population for cocoa breeding.

Genetic molecular diversity, production and resistance to witches' broom in cacao clones

“…Sereno et al (2006), while studying the genetic diversity of the Amazonian cacao based on microsatellite markers, also observed a higher heterozygosity in high Amazonian materials (H o = 44,5%). However, it must be considered that TSH1188 is a hybrid involving six different clones in its genealogy (Santos et al 2007), which helps to explain its elevated H o , and a few FO clones in relation to clones collected in natural populations.…”

“…The primers were pre-developed (Lanaud et al 1999, Risterucci et al 2000 and used to amplify the samples individually and according to a previously described protocol (Santos et al 2007). The amplification products were separated by gel electrophoresis in denaturing polyacrylamide at 5% in an ABI 377 automatic sequencer (Bertolde et al 2009).…”

Inheritance of the Number of Ovules per Ovary and Selection of Cacao Genotypes

“…As this progeny is segregating for the NoOV trait, the adaptation of this population for genetic mapping and selection of superior genotypes is proved. The productive potential of the population is high, qualifying it for the development of improvement works directed to the obtaining of varieties with higher number of seeds per fruit and resistant to cacao's black pod and witch's broom disease [10,12].…”

“…The procedures of crossing and cultivation, the date and local of experiment were previously described [10]. Although there are around 600 plants in the experimental field, only those that had enough number of flower buds at the 2006/2007 year were sampled.…”

“…This population also shows segregation for resistance to cacao's black pod and witch's broom disease [10,12]. Additionally, the clones involved in the genealogy of these two genitor clones show variation in NoOV ( Table 1).…”