Edson Eduardo Melo Passos

The influence of vapour pressure deficit on leaf water relations of Cocos nucifera in northeast Brazil.

Daily courses of leaf gas exchange and leaf water potential (psi(leaf)) 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 (VPD(air)), psi(leaf) and VPD(air), leaf transpiration (E) and gs, and E-Ψ(leaf). Despite these similar relationships between sites, stronger correlations involving gs-VPD(air) and E-Ψ(leaf) were found at the semi-arid site, where whole-plant hydraulic conductance (gp) was correlated significantly with VPD(air). In addition, at the semi-arid site, only, the net photosynthesis (P(N)) was not correlated with E and Ψ(leaf), and the intrinsic water use efficiency (WUEi) was disconnected from VPD(air) and Ψ(leaf). The different behaviour of leaf gas exchange and Ψ(leaf) between sites was probably caused by low gs in response to high VPD(air) 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 VPD(air). The atmospheric water stress will probably reinforce the strength of connection among water relation variables (E, Ψ(leaf), gs, gp, and VPD(air)), but it will disrupt the linear relationship between net CO2 assimilation and leaf water relations such as P(N)-E, P(N)-Ψ(leaf), WUEi-VPD(air) and WUEi-Ψ(leaf).

Comportamento sazonal do potencial hídrico e das trocas gasosas de quatro variedades de coqueiro-anão

Leaf gas exchange and water potential (Yl) 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 Yl 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.

Outbreak of stem bleeding in coconuts caused by Thielaviopsis paradoxa in Sergipe, Brazil

In February of 2004, at “Plato de Neopolis”, 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.