Submitted to: Tree Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/20/2009
Publication Date: 12/3/2009
Citation: Bertolde, F.Z., Almeida, A.A., Correa, R.X., Loguercio, L.L., Gomes, F.P., Gaiotto, F.A., Baligar, V.C. 2009. Molecular, physiological and morphological analysis of waterlogging tolerance in clonal genotypes of Theobroma cacao. Tree Physiology. 30:56-67. Interpretive Summary: Witches’ broom disease (WBD) is responsible for considerable loss of cacao production in Brazil. Outbreaks of this disease have adversely affected the social, economic and ecological environment of cacao producing regions. Grafting of WBD resistant cacao clones to susceptible cacao trees has been the main approach taken by Brazilian scientists to rehabilitate the infected farms. Resistant cuttings are propagated in conditions under high humidity to induce rooting. Waterlog conditions frequently occur, which can cause the death of up to 70% of the plants. Experiments were conducted in controlled conditions to evaluate the tolerance of witches’ broom resistant cacao plants to waterlog conditions. Leaf yellowing is a trait that appears to be useful for selecting plantlets that are tolerant to waterlogging. Such information will help cacao nursery managers and plant breeders in selection and mass propagation of disease resistant plantlets. Such efforts will help stabilize cacao production in Brazil and in the Americas.
Technical Abstract: In soil, hypoxia and anoxia conditions generated by waterlogging induce changes in genetic morphological, physiological processes, and as well as altering the growth and development of plant The mass propagation of cacao (Theobroma cacao) cuttings-to produce plantlets (clones) is affected by waterlogging caused by heavy rains and irrigation methods used to induce development of roots. An experiment was undertaken to assess the effects 45 days flooding (hypoxia and anoxia conditions) and non flooding of growth medium on physiological and morphological traits of 35 elite cacao genotypes. Emphasis of this research was to identify potential cacao genotypes having greater tolerance to growth medium flooding. Eighteen fluorochrome-labelled microssatelite (SSR) primer pair’s amplified 248 alleles were used to calculate similarity coefficients. Dendogram showed genetic variability among clones; further this indicted the presence of four major groups, of which two represent 60 % and 31% of the genotypes tested. A general trend toward high levels of heterozygosity was also found for physiological and morphological traits. The survival index (IS) for flood tolerance observed for the clones varied from 30 to 96%. The genotypes TSA-654, TSA- 656, TSA-792, CA-1.4, CEPEC-2009 and PH-17 showed IS value above 94%, whereas CEPEC- 2010, CEPEC-2002, CA-7.1 and VB-903 clones were affected most by waterlogging, with IS value below 56%. All genotypes displayed lenticel and adventitious root formation in responses to waterlogging, although with different intensities. A similarity-grouping analysis was performed using the ratio between waterlogged and control values to determine whether patterns of physiological response could be associated with tolerance to hypoxia and anoxia. No specific pattern of physiological and morphological responses to waterlogging was strictly associated with survival of plantlets, however, two out of six major groups revealed by similarity of dendogram which suggests that absence of leaf chlorosis may be a proper phenotypic trait that links to higher survival rates for flooding