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RESUMO -Avaliou-se o curso diurno e sazonal do potencial hídrico e das trocas gasosas foliares do coqueiro-anão (Cocos nucifera L.) sob condições de campo, no município de Ilha das Flores-SE. As quatro variedades estudadas (Anão Vermelho de Camarões -AVC, Anão Vermelho de Gramame -AVG, Anão Amarelo de Gramame -AAG e Anão Verde de Jiqui -AveJ) reduziram drasticamente a condutância estomática (gs) no período seco. Sob estiagem, os valores de transpiração (E) e fotossíntese líquida (A) foram reduzidos principalmente nas variedades AVG e AVeJ, as quais apresentaram aumento significativo nos valores de eficiência intrínseca do uso da água (A/gs), principalmente o AVeJ. Na estação chuvosa, as trocas gasosas foram condicionadas pela densidade de fluxo de fótons fotossinteticamente ativos (DFFFA) e pela gs. No entanto, durante a estação seca, as trocas gasosas foram condicionadas somente pelos valores de gs, sendo os valores de DFFFA não-limitantes desde as primeiras horas do dia. A variedade AVC apresentou pouca eficiência no controle da perda de água pela transpiração sob condições de estresse hídrico, atingindo os valores mais negativos do potencial hídrico foliar, mantendo, todavia, a fotossíntese líquida mais elevada durante o curso diurno. Por outro lado, o AVeJ controlou eficientemente a transpiração e, mesmo com menores valores de A, apresentou a maior razão A/gs que as demais variedades. Em cultivo tecnificado, como ocorre nos perímetros irrigados, a variedade AVC deverá manter um balanço de carbono mais favorável durante todo o ano, apresentando-se como uma variedade muito promissora. Termos para indexação: Cocos nucifera L., condutância estomática, transpiração, fotossíntese líquida.ABSTRACT -Leaf gas exchange and water potential (Ψ l ) were assessed daily and seasonaly in four varieties of dwarf coconut (Cocos nuficera L.) under field conditions: Cameroon Red Dwarf (CRD), Gramame Red Dwarf (GRD), Gramame yellow Dwarf (GYD) and Jiqui Green Dwarf (JGD). All varieties showed strong reduction of stomatal conductance (gs) values in the dry season. At this period, transpiration (E) and net photosynthesis (A) rates decreased largely in JGD and in GRD, when both genotypes presented greater values of intrinsic water use efficiency (A/gs) than in wet season, specially JGD. Taking in account all genotypes studied in wet season, the leaf gas exchange was conditioned by photosynthetic photon flux density (PFFD) and by gs values. On the other hand, during the dry season, leaf gas exchange was correlated only with gs values. The variety CRD did not restrict E in dry season, showing the lowest Ψ l but holding the highest A values per day among genotypes under drought. Contrastingly, the genotype JGD could control efficiently E intensity, maintaining the highest A/gs ratio despite of reduced A values in dry season. In dwarf coconut plantations with high technical management such as in irrigated areas, the CRD could be the most suitable variety to achieve favorable carbon balance during the year.

In February of 2004, at "Platô de Neópolis", Sergipe, Brazil, about 50 coconut plants were found bearing symptoms of a disease not yet recorded in Brazil. The trunk of diseased plants exhibited a reddish-brown or rust��colored liquid bleeding from scars. Inside the stem, the tissues under the lesions were rotting and turned brownish-yellow to black. Diseased palms had reduced growth and three to four months after the first symptoms were noticed the affected plants died. A fungus was isolated from diseased tissues and identified as Thielaviopsis paradoxa. Healthy plants were inoculated with the fungus and lesions developed demonstrating the pathogenicity of the isolate. Keywords: Ceratocystis paradoxa, Chalara, Cocos nucifera. The coconut tree (Cocos nucifera L.) is widely grown along the Northeastern coast of Brazil as well as in other areas of Brazil. There is a large and increasing demand for immature coconuts that are harvested and marketed for consumption of their liquid endosperm (coconut water). This is mostly supplied by dwarf variety plantations and average productivity has been limited in Brazil to around 3,400 fruits/hectare because of limited rainfall levels, pests and diseases (Cuenca, 1994). Warwick et al. (2004) noted the occurrence of what appeared to be a novel coconut disease for Brazil at Platô de Neópolis (State of Sergipe). About 50 coconut plants were observed to have symptoms of stem bleeding, a disease that was previously unrecorded in Brazil. RESUMOThe affected trunk areas exhibited dark discoloration and a reddish-brown or rust��colored liquid bleeding from different points (Figure 1). Diseased palms had reduced growth and a gradual but progressive necrosis of the lower pinnate leaf toward the midribs. Inside the stem, the tissues under the lesions were rotting and became brownish-yellow to black. Eventually the affected plants died. In every case, the plant showing symptoms was also being attacked by the weevil Rhynchophorus palmarum L. No attempt was made to treat the diseased plants, which died within 3-4 months of the observation of the early stem symptoms. Other biotic diseases that may be lethal to coconut palms in Brazil are: red ring, caused by the nematode Bursaphlelenchus cocophilus (Warwick & Bezerra, 1992); hartrot, caused by Phytomonas sp., a flagellate protozoa (Renard, 1989), and eye-rot caused by two species of Phytophthora (Quillec & Renard, 1984).In India, plants showing a similar disease were proven to be attacked by Thielaviopsis paradoxa (De Seynes) Höhn. (anamorphic Ceratocystidaceae). The studies in India showed that inoculation of healthy coconut plants with isolates obtained from diseased plants resulted in rusty brown discoloration of the bark within 2-8 weeks, followed by the oozing of a brownish liquid from stems. Re-isolation of T. paradoxa was made from such diseased tissues (Nambiar et al., 1986). Stem bleeding of coconut is known to occur in nearly all the countries which grow coconut (Ohler, 1964). The disease was first reported from Sri Lanka (Pe...

SUMMARYDaily courses of leaf gas exchange and leaf water potential (Ψleaf) of green dwarf coconut palm (Cocos nucifera) were measured in irrigated plantations on the wet coastal plateau and in a dry semi-arid area of northeast Brazil. At both sites, significant correlations were obtained between stomatal conductance (gs) and vapour pressure deficit (VPDair), Ψleaf and VPDair, leaf transpiration (E) and gs, and E-Ψleaf. Despite these similar relationships between sites, stronger correlations involving gs-VPDair and E-Ψleaf were found at the semi-arid site, where whole-plant hydraulic conductance (gp) was correlated significantly with VPDair. In addition, at the semi-arid site, only, the net photosynthesis (PN) was not correlated with E and Ψleaf, and the intrinsic water use efficiency (WUEi) was disconnected from VPDair and Ψleaf. The different behaviour of leaf gas exchange and Ψleaf between sites was probably caused by low gs in response to high VPDair at the semi-arid site. Our results indicate potential for significant alterations in the pattern of leaf gas exchange during future climatic changes with increasing temperature and concomitant increases in VPDair. The atmospheric water stress will probably reinforce the strength of connection among water relation variables (E, Ψleaf, gs, gp, and VPDair), but it will disrupt the linear relationship between net CO2 assimilation and leaf water relations such as PN-E, PN-Ψleaf, WUEi-VPDair and WUEi-Ψleaf.

The behavior of coconut (Cocos nucifera L.) stomata was studied under field conditions in adult plants. Hourly determination of relative stomatal opening and of stomatal conductance values revealed that coconut stomata were opened maximally between 0800 and 1600; by the end of this period, the stomata closed rapidly as solar radiation decreased. Changes in temperature and relative humidity of the air did not affect stomatal behavior. The maximum relative stomatal opening occurred at midday, when the water potential of the leaf is at its lowest point, showing that stomatal behavior depends mostly on solar radiation and does not control water loss efficiently under conditions of water stress.