Influence of temperature on photosynthesis of sweet orange 'Pêra' with citrus variegated chlorosis.

Author(s)

Rafael Vasconcelos Ribeiro

• Document type: Master's Dissertation
• Press: Piracicaba. , gráficos, ilustrações, tabelas.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2002-07-03

Examining board members

Eduardo Caruso Machado; Ricardo Ferraz de Oliveira; Rogéria Pereira de Souza

• Advisor: Eduardo Caruso Machado
• Field of knowledge: Agronomical Sciences - Agronomy
• Indexed in: Banco de Dados Bibliográficos da USP-DEDALUS; Biblioteca Digital de Teses e Dissertações - USP
• Location: Universidade de São Paulo. Biblioteca Central da Escola Superior de Agricultura Luiz de Queiroz ; ESALQ-BC/t634.3; R484i; 79757

Abstract

The citrus variegated chlorosis (CVC) has became a great problem for the Brazilian citriculture during the last ten years. CVC, caused by the bacterium Xylella fastidiosa, causes a strong decrease in production of infected plants. Higher severities of the disease have been reported in areas with water deficit, high atmospheric demand and high temperatures. Photosynthesis, which has direct relationship with plant productivity, is a physiological process affected by CVC. The objectives of this study were to determine the effects of temperature upon photosynthesis of infected plants and to evaluate how the photosynthetic apparatus is affected by the presence of the bacterium. In order to achieve these objectives, two experiments (I and II) were carried out, using 9 months-old seedlings of sweet orange 'Pêra' (Citrus sinensis (L.) Osbeck), grown in 3L plastic pots under greenhouse conditions. In experiment I, prior to measurements, healthy and infected plants were moved to a plant growth chamber and exposed to temperature regimes of 25/20 and 35/20ºC (day/night) during 7 days each, CO2 and O2 atmospheric concentrations, 14h photoperiod, photosynthetically active radiation (PAR) of 600mmol m-2 s-1 and air vapor pressure difference of about 1 kPa. Simultaneous measurements of leaf gas exchange [CO2 assimilation (A); transpiration (E) and stomatal conductance (gs)] and chlorophyll fluorescence [potential (Fv/Fm) and effective (DF/Fm') quantum yield of photosystem II, apparent electron transport rate (ETR) and photochemical (qP) and non-photochemical (NPQ) fluorescence quenching] were taken in intact leaves, at 25, 30, 35 and 40ºC. In experiment II, light curves of photosynthetic oxygen evolution (Ao), and curves of photosynthesis induction were carried out, with simultaneous measurements of Ao, DF/Fm', ETR, qP and NPQ in leaf discs, at 35 and 45ºC. In experiment I, infected plants shown decrease in A, E and gs, and the differences between healthy and infected plants were greater at 35/20ºC, where the largest values of A, E and gs were observed. These variables decreased with increasing temperature, reaching minimum values at 40ºC for both temperature regimes. In experiment I, no differences between healthy and infected plants regarding chlorophyll fluorescence variables were observed. However, Fv/Fm of infected plants was higher in all conditions. The three most influenced variables by temperature were DF/Fm', ETR and qP, whereas the two first decreased while the last increased with increasing temperature. Largest values of Fv/Fm, DF/Fm', ETR, qP and NPQ were registered at 35/20ºC, confirming that this temperature regime was more adequate to plant photosynthetic activity. In experiment II, healthy plants showed the largest values of Ao, DF/Fm', ETR, qP and NPQ at 35ºC. The presence of the bacterium affected Ao induction in both temperatures, however, differences in DF/Fm', ETR, qP and NPQ for healthy and infected plants were only found at 35ºC. Results from this study indicated that increase in temperature affected the plant-pathogen system, amplifying the malfunction of the photosynthetic metabolism of infected plants. The smallest photosynthetic rates of sweet orange 'Pêra' infected by X. fastidiosa were caused by low stomatal conductance, biochemical injuries and photorespiratory activity. (AU)