Photosynthetic response to low and high light of cacao growing without shade in an area of low evaporative demand

Abstract

Cacao (Theobroma cacao L.) breeding programmes in Ecuador have focused on obtaining high-yield clones with improved disease resistance. Cacao clones should also have photosynthetic characteristics which support increased productivity. Regarding the weather conditions at the coast of Ecuador, where most of the year there are overcasts and low air evaporative demand, there is the possibility to grow cacao without overhead shade. This study focused on the photosynthetic response at two different photosynthetic photon flux densities (PPFD) of Ecuadorian cacao clones. Seven-year old cacao clones were evaluated: eight clones of Nacional type and two commercial clones (CCN 51 and EET 103), used as controls. All clones showed an increase of 35 % on average in net photosynthetic rate (A) with increasing PPFD from the light saturation point for cacao (i.e. 400 µmol m -2 s ). Such light responsiveness in A has not been reported before. Higher A was associated with higher apparent electron transport rate, while high stomatal conductance was maintained under both PPFD conditions. Under high PPFD, low non-photochemical quenching values were found, suggesting low energy dissipation. All clones showed high maximum quantum yields of PSII (F v /F m ), suggesting the absence of damage of the photochemical system. Keywords: cacao yield, chlorophyll fluorescence, CO 2 assimilation rate, gas exchange. RESUMENLos programas de mejoramiento de cacao (Theobroma cacao L.) en Ecuador se han centrado en la obtención de clones de alto rendimiento con mayor resistencia a las enfermedades. Estos clones también deben tener características fotosintéticas que apoyen una mayor productividad. En las condiciones climáticas en la costa de Ecuador, donde la mayor parte del año hay alta densidad de nubes y baja demanda evaporativa, existe la posibilidad de cultivar cacao sin sombra. Este estudio se centró en la respuesta fotosintética de clones de cacao del Ecuador en dos diferentes densidades de flujo de fotones fotosintéticos (PPFD). Se evaluaron diez clones de cacao de siete años de edad: ocho clones de tipo Nacional recientemente desarrollados por el Instituto Nacional de investigaciones Agropecuarias, y dos clones comerciales utilizados como controles (CCN 51 y EET 103). Todos los clones de cacao mostraron un aumento del 35 % en promedio en la tasa fotosintética neta (A) con el incremento del PPFD desde el punto de saturación de luz para el cacao (400 μmol m -2 s -1 ) hasta valores altos (1000 μmol m -2 s -1 ). Dicha respuesta de A a estas condiciones de luz alta no se ha

Phenotypic plasticity to photon flux density of physiological, anatomical and growth traits in a modern Criollo cocoa clone

“…The P N and g s values in adult trees of Chuao cocoa in the field were similar to those of seedlings in the greenhouse experiment, which is not surprising, since daily PPFD growth was similar between ML and F; similar values of P N and g s have been reported in trees of other cocoa Criollos and Trinitarios cultivars (De Almeida et al , Tezara et al ). The low values of P N and g s measured in plants subjected to different PPFD in the greenhouse and in the field are similar to those reported in other cocoa clones under different growth conditions (Joly and Hahn , Miyaji et al , Daymond et al , Araque et al , Almeida et al , Ávila‐Lovera et al ) and lower than those reported for coffee (Rodríguez‐López et al ) and Ecuadorian sun cocoa (Jaimez et al ). The absence of differences in P N and g s between the greenhouse and field plants contrasts with observations done in coffee, in which the source/sink imbalance imposed by root restriction due to pot size severely reduced P N (Ronchi et al ).…”

“…This was more marked in adult trees, in which P Nsat was on average half the value in seedlings. Higher P Nsat and LSP in HL plants after 3 months, ML and HL plants after 6 months and F plants indicate that Chuao cocoa adapts to sun conditions, as in the case of Ecuadorian cocoa (Jaimez et al ). Values of LSP, 250 μmol m −2 s −1 on average, were relatively low in the greenhouse and similar to the value for other cocoa cultivars (Joly and Hahn , Balasimha et al , Baligar et al , Almeida et al , Tezara et al ), even lower values (110 μmol m −2 s −1 ) have been found in adult trees under natural conditions in this study.…”

“…Shade crops, such as coffee, are adapted to the understory of forests in their native habitat and hence often grow under shade (Martins et al ). It is generally accepted that cocoa is unable to adapt to high PPFD, since it has a considerable number of physiological traits that are typical of shade species; however, cocoa grows successfully under full exposure in Ecuador (Jaimez et al ), Brazil, Ghana and Ivory Coast (Herzog ). Likely these locations are characterized by high cloud density during most of the year, and therefore high humidity and low evaporative demand, allowing cacao plantations to establish without shade as reported recently (Jaimez et al ).…”

A disease and production index (DPI) for selection of cacao (Theobroma cacao) clones highly productive and tolerant to pod rot diseases

“…The development of the DPI was based on data collected over four years (February 2011 to December 2015) from an experiment carried out by the Cacao and Coffee Programme of the National Institute of Agricultural Research (INIAP) at the Pichilingue Tropical Experimental Station in Mocache, Los Ríos province, Ecuador. In this experiment, 30 clones were planted in March 2008 using a randomized complete block design with two blocks (Jaimez et al , ). Each block consisted of 15 rows with 10 plants per row.…”

“…Annual fertilization was based on a nutritional requirement analysis obtained when the plantation field plots were initiated (Jaimez et al , ). Shape pruning and sanitary pruning started the second year to maintain tree structure and to remove brooms caused by M. perniciosa , respectively.…”