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Title: Path analysis of phenotypic traits in young cacao plants under drought conditions

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

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2018
Publication Date: 2/6/2018
Citation: Santos, E.A., Almeida, A.F., Branco, M.C., Santos, I.C., Ahnert, D., Baligar, V.C., Valle, R.R. 2018. Path analysis of phenotypic traits in young cacao plants under drought conditions. PLoS One. 13(2):1-16.

Interpretive Summary: Cacao is very sensitive to prolonged drought. Quantity and distribution of rainfall, have been a major cause of variation in cacao productivity and its sustainability in many parts of cacao growing regions. An increased understanding of plant traits that respond to drought conditions will help during the selection of cacao genotypes that are tolerant to drought. In this paper we report that drought affects the growth and development of roots, stem and leaves of cacao genotypes. The root volume was identified as the growth variable most influenced by the change in water availability. Such information will be of use to physiologists and plant breeders to identify and select drought tolerant cacao genotypes which could be useful in cacao improvement program to address drought prone areas.

Technical Abstract: This study aimed to evaluate phenotypic relationships and their direct and indirect effects through path analysis, and evaluate the use of the phenotypic plasticity index as criteria for the estimation of the basic and explanatory variables used to analysis several cacao progenies subjected to soil water stress. The greenhouse experiments were conducted in a randomized block 21 x 2 factorial arrangement [21 complete diallel crosses and two water regimes (control and stress)] and six replications. In the control treatment, soil moisture was kept close to field capacity, with predawn leaf water potential ('WL) ranging from –0.1 to –0.5 MPa. In the stress treatment, soil moisture was decreased by gradually reducing the water applied until 'WL reached between –2.0 to –2.5 MPa. In general, the water deficiency influenced the production of dry biomass in most progenies, except for SCA-6 x IMC-67, Catongo x SCA, MOC-01 x Catongo, Catongo x IMC-67 and RB-40 x Catongo crosses. The progeny of RB-40 x IMC-67 showed better results for root/shoot ratio when subjected to water stressed conditions. In contrast, progenies of PUCALA x Catongo, PUCALA x MOC-01, IMC-67 x TSH-1188 and MOC-01 x IMC-67 crosses proved to be more intolerant to drought, with significant reductions in total leaf area, leaf number, leaf dry biomass, leaf area ratio, specific leaf area, root diameter < 1 mm, root volume (RV) and root area. Comparing progeny growth under water stress and control conditions, showed the RV variable had the highest phenotypic plasticity index (0.86). Therefore, RV was identified as the growth variable influenced the most by water regimes among the evaluated cacao progenies. Stem and root diameters, as well as stem dry biomass were the growth variables that were important for explaining variation of RV under water limitation.