Although exhibiting limited genetic polymorphism, the very large genome of H. vastatrix (c. 797 Mbp) conceals great pathological diversity, with more than 50 physiological races. Gene expression studies have revealed a very precocious activation of signalling pathways and production of putative effectors, suggesting that the plant-fungus dialogue starts as early as at the germ tube stage, and have provided clues for the identification of avr genes.

Considerable success has been obtained in the use of classical breeding to control economically important plant diseases, such as the coffee leaf rust and the coffee berry disease (CBD). There is a strong consensus that growing genetically resistant varieties is the most appropriate cost effective means of managing plant diseases and is one of the key components of crop improvement. It has also been recognized that a better knowledge of both, the pathogens and the plant defence mechanisms will allow the development of novel approaches to enhance the durability of resistance. After a brief description of concepts in the field of plant disease resistance, we attempt to give a view of the research progress on coffee leaf rust and CBD concerned with the pathogens infection and variability, coffee breeding for resistance and coffee resistance mechanisms. Key words: Coffea, Colletotrichum kahawae, Hemileia vastatrix, coffee breeding, resistance.Resistência do cafeeiro para suas principais doenças: ferrugem alaranjada das folhas e antracnose dos frutos: Sucesso considerável tem sido obtido no uso do melhoramento clássico para o controle de doenças de plantas economicamente importantes, tais como a ferrugem alaranjada das folhas e a antracnose dos frutos do cafeeiro (CBD). Há um grande consenso de que o uso de plantas geneticamente resistentes é o meio mais apropriado e eficaz em termos de custos do controle das doenças das plantas, sendo também um dos elementos chave do melhoramento da produção agrícola. Tem sido também reconhecido que um melhor conhecimento do agente patogênico e dos mecanismos de defesa das plantas permitirá o desenvolvimento de novas abordagens no sentido de aumentar a durabilidade da resistência. Após uma breve descrição de conceitos na área da resistência das plantas às doenças, nesta revisão tentou-se dar uma idéia do progresso na investigação da ferrugem alaranjada do cafeeiro e do CBD relativamente ao processo de infecção e variabilidade dos agentes patogênicos, melhoramento do cafeeiro para a resistência e mecanismos de resistência do cafeeiro. Palavras-chave: Coffea, Colletotrichum kahawae, Hemileia vastatrix, melhoramento do cafeeiro, resistência.

No abstract

Anthracnose is an important disease affecting mature olive fruits, causing significant yield losses, and poor fruit and oil quality. In Portugal, high anthracnose incidence was recorded during 2003-2007 with 41% of 908 orchards surveyed displaying disease symptoms. In another 14% of the orchards, the pathogen was recorded in symptomless plants. Disease severity was on average 36%, frequently reaching 100%. In Portugal, anthracnose is endemic to neglected orchards of susceptible cultivars, but under favourable conditions it can also severely affect less susceptible cultivars. Pathogens were genetically heterogeneous, with Colletotrichum acutatum genetic group A2 as the most frequent (80%), followed by group A4 (12%) and group A5 along with C. gloeosporioides (3-4%), while groups A3 and A6 of C. acutatum were sporadic. Important geographic variations were observed in the frequencies of these populations, accompanied by year-to-year populational shifts. Epidemiology and histopathology studies showed the presence of the pathogens on vegetative organs year-round, particularly on olive leaves and branches, and on weeds. These represent inoculum reservoirs where secondary conidiation occurs, and conidia are then dispersed by spring rains reaching flowers and young fruits or by autumn rains reaching pre-mature fruits. Unripe fruits were colonized without showing symptoms up to penetration of the cuticle, but further colonization and symptom production was completed only as fruits matured. These findings challenge current control practices, particularly the timing of fungicide treatment, and contribute to improved disease management.

SUMMARY The beverage cash crop coffee (Coffea arabica L.) is subject to severe losses caused by the rust fungus Hemileia vastatrix. In naturally resistant coffee plants, a specific hypersensitive reaction (HR) may be elicited early to stop fungal infection. To isolate host genes involved in HR, we undertook an expressed sequence tags (ESTs) analysis. Two cDNA libraries were constructed using suppression subtractive hybridization (SSH) and 527 non-redundant ESTs were generated from 784 randomly picked clones. Classification of the ESTs into several functional categories showed that more than one-quarter of the predicted proteins might encode disease resistance (R) proteins, stress- and defence-proteins, and components of signal transduction pathways. Twenty-eight differentially screened sequences (DSSs) were selected after differential hybridization of 1000 cDNA clones from each library. Investigation of the expression patterns of a subset of 13 DSSs showed higher levels of gene expression in inoculated plants compared with control plants. HR-up-regulation of transcript accumulation occurred for 9 out of the 13 genes 24 and 48 h after H. vastatrix challenge. Two genes encoded homologues of the Arabidopsis DND1 and NDR1 proteins, suggesting conservation of resistance signalling pathways in perennial plants. Other HR-regulated sequences matched receptor kinases, AP2 domain- and WRKY transcription factors, cytochromes P450, heat shock 70 proteins, glucosyltransferases and proteins of unknown function. The ESTs reported here provide a useful resource for studying coffee resistance responses and for improving C. arabica for durable disease resistance.

A proteomic analysis of the apoplastic fluid (APF) of coffee leaves was conducted to investigate the cellular processes associated with incompatible (resistant) and compatible (susceptible) Coffea arabica-Hemileia vastatrix interactions, during the 24–96 hai period. The APF proteins were extracted by leaf vacuum infiltration and protein profiles were obtained by 2-DE. The comparative analysis of the gels revealed 210 polypeptide spots whose volume changed in abundance between samples (control, resistant and susceptible) during the 24–96 hai period. The proteins identified were involved mainly in protein degradation, cell wall metabolism and stress/defense responses, most of them being hydrolases (around 70%), particularly sugar hydrolases and peptidases/proteases. The changes in the APF proteome along the infection process revealed two distinct phases of defense responses, an initial/basal one (24–48 hai) and a late/specific one (72–96 hai). Compared to susceptibility, resistance was associated with a higher number of proteins, which was more evident in the late/specific phase. Proteins involved in the resistance response were mainly, glycohydrolases of the cell wall, serine proteases and pathogen related-like proteins (PR-proteins), suggesting that some of these proteins could be putative candidates for resistant markers of coffee to H. vastatrix. Antibodies were produced against chitinase, pectin methylesterase, serine carboxypeptidase, reticuline oxidase and subtilase and by an immunodetection assay it was observed an increase of these proteins in the resistant sample. With this methodology we have identified proteins that are candidate markers of resistance and that will be useful in coffee breeding programs to assist in the selection of cultivars with resistance to H. vastatrix.

No abstract

The extracellular space (ECS or apoplast) is the plant cell compartment external to the plasma membrane, which includes the cell walls, the intercellular space and the apoplastic fluid (APF). The present review is focused on APF proteomics papers and intends to draw information on the metabolic processes occurring in the ECS under abiotic and biotic stresses, as well as under non-challenged conditions. The large majority of the proteins detected are involved in “cell wall organization and biogenesis”, “response to stimulus” and “protein metabolism”. It becomes apparent that some proteins are always detected, irrespective of the experimental conditions, although with different relative contribution. This fact suggests that non-challenged plants have intrinsic constitutive metabolic processes of stress/defense in the ECS. In addition to the multiple functions ascribed to the ECS proteins, should be considered the interactions established between themselves and with the plasma membrane and its components. These interactions are crucial in connecting exterior and interior of the cell, and even simple protein actions in the ECS can have profound effects on plant performance. The proteins of the ECS are permanently contributing to the high dynamic nature of this plant compartment, which seems fundamental to plant development and adaptation to the environmental conditions.