Influence of low light intensity and soil flooding on cacao physiology

Authors: SILVA BRANCO, M - Universidade Estadual De Santa Cruz; ALMEIDA, A - Universidade Estadual De Santa Cruz; DALMOLIN, A - Universidade Estadual De Santa Cruz; AHNERT, DARIO - Universidade Estadual De Santa Cruz; Baligar, Virupax

Submitted to: Scientia Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2017
Publication Date: 2/10/2017
Citation: Silva Branco, M.C., Almeida, A.A., Dalmolin, A.C., Ahnert, D., Baligar, V.C. 2017. Influence of low light intensity and soil flooding on cacao physiology. Scientia Horticulturae. 217:243-257.

Interpretive Summary: In Brazil cacao is mainly grown under cabruca an agroforestry systems where low levels of irradiance (high shade) and frequent floods are the stresses that affects sustainable production of cacao. Better understanding of these two stresses on physiological responses and mechanisms of stress tolerance in cacao genotypes can help to improve production potentials of cacao grown under agroforestry systems. In this paper we report that flooding was the main stress or factor causing most physiological responses observed during the interaction between irradiance level and soil flooding the physiological changes were different among the clonal cocoa genotypes assessed. Information obtained will be beneficial to farmers to reduce excess soil water regime (flooding) and shade tree canopy management to reduce excess shading to improve yields and increase sustainability of cacao grown under agroforestry systems.

Technical Abstract: Growth and development of plants frequently are limited by multiple abiotic stresses that occur simultaneously in the environment. Cabruca’ an agroforestry system is a main cropping system invariably adapted for cultivation of cacao in southern Bahia, Brazil. In this system of management cacao is grown under the shade of native tree species of the Atlantic Forest. However, growing cacao under the shade of trees is still questionable due to higher incidence of pests and diseases and difficulty of evaporation of excess soil water in high rainfall periods that often causes flooding. The objective of the current study is to evaluate the performance of two clonal genotypes of cacao, contrasting for tolerance to soil flooding (TSA-792 - tolerant and TSH-774 – intolerant), subjected to four levels of irradiance and two water regimes, flooded and non flooded, in order to elucidate the mechanisms of tolerance to these stresses under ‘Cabruca’ environment. All the plants survived the period of flooding, however, with flooding stress visual symptoms like leaf chlorosis, lenticels hypertrophied on the stem base, and decomposition of roots were observed [ may be avoid this statement as there are no data presented for the last two observation?]. Obtained results demonstrated morpho-physiological and molecular changes in response to irradiance levels and irradiance level x soil flooding interaction. Significant effects (p<0.05) of isolated factors, double interaction and inter- and intra-genotypic differences (p<0.05) were observed for leaf gas exchange, chlorophyll fluorescence, and growth parameters.. Differences among irradiance level, water regime, organ (p<0.001), and for the interactions irradiance level x water regime and water regime x organ (p<0.01) were observed with respect to total soluble sugar content. Isolated factors and double and triple interactions (p<0.01) had significant effects on the starch accumulation. Triple interaction was also observed in the expression of genes coding for ADH, LDH and PDC enzymes and for aquaporin PIP1;2. Flooding was the main stressor factor for the most physiological responses observed during the interaction between irradiance level and soil flooding whose physiological adjustments were different among the clonal cocoa genotypes assessed.