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Title: Diallel analysis and growth parameters as selection tools for drought tolerance in young Theobroma cacao plants

item SANTOS, E - Universidade Estadual De Santa Cruz
item ALMEIDA, A - Universidade Estadual De Santa Cruz
item AHNERT, D - Universidade Estadual De Santa Cruz
item WHITE, M - Universidade Estadual De Santa Cruz
item VALLE, R - Comissao Executiva Do Plano Da Lavoura Cacueira (CEPLAC)
item Baligar, Virupax

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2016
Publication Date: 8/9/2016
Citation: Santos, E.A., Almeida, A.A., Ahnert, D., White, M.C., Valle, R.R., Baligar, V.C. 2016. Diallel analysis and growth parameters as selection tools for drought tolerance in young Theobroma cacao plants. PLoS One. doi:10.1371/journal.pone.0160647.

Interpretive Summary: Worldwide, drought is one of the most yield limiting factors for cacao (Theobroma. cacao ) production. Future cacao sustainability is greatly dependent on breeding drought tolerant cultivars. Few studies have been conducted to identify cacao adaptation strategies to water deficit. Morphological changes are a good indicators for early selection of cacao genotypes for tolerance to drought due to the direct impact of drought on the plant growth and development patterns. In this study we report the estimation of combining abilities, through diallel crosses, of T. cacao genotypes preselected for drought tolerance by using morphological and physical traits. Findings from this study will be useful to plant breeders, geneticists, physiologists and agronomists to setup drought tolerant breeding programs and select drought tolerant accessions based on morphological and physical traits as drought selection criteria. Drought tolerant accessions identified by such method will be useful cacao cultivars for improving yield potentials for drought prone regions.

Technical Abstract: Technical Abstract: This study was aimed to estimate the combining ability, through diallel crosses, of T. cacao genotypes preselected for drought tolerance. The experiment was conducted under greenhouse conditions at the Cacao Research Center (CEPEC), Ilhéus, Bahia, Brazil, in a completely randomized block, experimental arrangement 21 x 2 [21 complete diallel crosses and two water regimes (control and stressed)]. In the control, soil moisture was kept close to field capacity, with predawn leaf water potential ('WL) ranging from -0.1 to -0.5 MPa. In the drought regime, the soil moisture was reduced gradually by decreasing the amount of water application until 'WL reached -2.0 to -2.5 MPa. Significant differences (p < 0.05) were observed for most morphological attributes analyzed regarding progenies, water regime and its interaction. The results of the joint diallel analysis revealed significant effects between general combining ability (GCA) x water regimes and between specific combining ability (SCA) x water regimes. In general, the water deficit influenced the production of biomass in most of the evaluated T. cacao crosses, except for SCA-6 x IMC-67, Catongo x SCA, MOC-01 x Catongo, Catongo x IMC-67 and RB-40 x Catongo. The cross RB-40 x IMC-67 showed better results for the root/soot ratio when subjected to water deficit. In contrast, PUCALA x Catongo, PUCALA x MOC-01, IMC-67 x TSH-1188 and MOC-01 x IMC-67 proved to be intolerant to drought, with more significant reductions in total leaf area (TLA), leaf number(LN), leaf dry biomass (LDB), leaf area ratio (LAR), specific leaf area (SLA) , root diameter (RD), root volume (RV) and root area (RA). Multivariate analysis showed that stem diameter (CD), TLA, LDB, stem dry biomass (SDB), root dry biomass (RDB), total dry biomass (TDB), root length (RL), RV, RD <1 mm and 1