Physiological and morphological adaptations as associated with drought tolerance in robusta coffee (Coffea canephora Pierre var. kouillou)

• Ano de defesa: 2004
• Autor(a) principal: Pinheiro, Hugo Alves
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Café - Fisiologia; Café - Resistência à seca; Fotossíntese; Plantas e água; Enzimas - Efeito do estresse oxidativo; Ciências Biológicas
• Link de acesso: http://www.locus.ufv.br/handle/123456789/10031

Clones of Coffea canephora Pierre var. kouillou with contrasting tolerance to drought stress have been chosen on the basis of their productivities under rainfed conditions. As little is known about physiological mechanisms associated with differences in drought tolerance in those clones, this work aimed to examine morphological traits, stomatal responses to both soil and atmosphere drought, water relations, water-use efficiency (WUE) and, in addition, whether drought tolerance in C. canephora may be linked to protection against oxidative damage. For these purposes, four clones of C. canephora representing drought-tolerant (14 and 120) and drought-sensitive (46 and 109A) genotypes were grown under screen house conditions, in 120 L pots, during eight months. Drought stress was imposed by withholding irrigation until leaf water potential at predawn ( Ψ pd ) reached about –3.0 MPa. Under full irrigation, soil-to-leaf hydraulic conductance (K L ), midday leaf water potential and total biomass were all greater in clones 109A and 120 than in the other clones. After 14 days without irrigation, Ψ pd decreased significantly in clone 109A in comparison with the other clones; seven days latter, Ψ pd dropped to about –2.3 MPa in clones 46 and 109A, against –0.8 MPa in clone 14 and –1.7 MPa in clone 120. Clone 109A attained –3.0 MPa at predawn earlier, followed by clone 46, clone 120, and then clone 14, in this order. Under drought stress, there was no elastic adjustment, while a slight osmotic adjustment was only noted in the clone 109A. Stomatal conductance (g s ) was strongly decreased with decreasing Ψ pd ; it declined modestly with increasing leaf-to-air vapour pressure deficit. Stomatal sensitivity to both soil and atmospheric drought was lower in clone 109A and similar among the other clones. Drought stress led to a significant increase in carbon isotope composition (δ 13 C) for all clones, suggesting an increased WUE; however, absolute values of δ 13 C were lower in clone 109A than in the other clones irrespective of the irrigation treatments. Clones 14 and 120 exhibited deeper root systems than drought-sensitive clones. This at least partially explain their better avoidance to drought as compared with the sensitive clones. On average, the larger K L in clone 120 than in clone 14 might largely explain why the latter was better able to postpone dehydration. For all clones, water potential, g s and K L recovered rapidly following re-watering; these facts, associated with the remarkable stomatal sensitivity to drought, should explain greatly why C. canephora responds strongly to irrigation. Independently of the clone examined, little or no effect of drought on the quantum yield of electron transport, photosystem II photochemical efficiency and photochemical and non-photochemical quenching coefficients was observed. Comparatively, the clone 120 showed a more tolerant photosynthetic apparatus to both drought and paraquat-induced oxidative stress, with no clear distinction among the other clones in this regard. Drought triggered increases in superoxide dismutase (clones 109A and 120), ascorbate peroxidase (clones 14, 46 and 109A), catalase and guaiacol peroxidase (clones 46 and 109A), and glutathione reductase (clone 46). Monodehydroascorbate reductase and dehydroascorbate reductase were not induced in drought-stressed plants; their maximal activities were much lower than that of ascorbate peroxidase, irrespective of the clone investigated. Oxidative damage, however, appeared to be evident only in clone 109A. In general, the clones herein investigated were able to preserve, or even to increase, their antioxidant defences at water potentials as low as –3.5 MPa. The combination of mechanisms that effectively postpone dehydration, associated with deep root systems, should contribute to survival and/or stability of crop yield of drought-tolerant clones in regions with unpredictable precipitation. Attributes such as osmotic and elastic adjustments and protection against oxidative damage induced by drought should be of minor importance to drought tolerance in this specie.