Sensitive response and resistance to bery disease (Colletotrichum kahawae) of two coffee varieties (Coffea arabica and C. canephora) : histological comparisons of interactions.

Seedling hypocotyls and attached green coffee berries of 11 Coffea arabica varieties and a Robusta coffee cultivar, with different levels of resistance to coffee berry disease (Colletotrichum kahawae), were examined under a microscope for differences in the development of infections caused by single-conidium isolates of the fungus and the response by the host tissu. As compared to susceptibility, resistance was characterised by fewer infection sites, slower and distorted fungal growth, as well as cytoplasmic changes in host cells. This resulted in plant cell death, hypersensitive reaction, pathogen death and the formation of scabs and cork barriers of various appearances. It was concluded that, under favourable environmental conditions, mechanisms that slow or hinder the activity of the pathogen in order to allowing full development of cork barriers, were the most important in determining resistance. The possibility of using types of scabs and barriers to discriminate between categories of host resistance and pathogen aggressiveness was suggested.Le développement des infections causées par l'isolat issu d'un seul conidie de champignon et la réponse (ou les réactions) des tissus hôtes d'hypocotyles de « semence » et de « fruits verts » de 11 variétés de Coffea arabica, caractérisé par différents niveaux de résistance à la maladie des fruits (Colletotrichum kahawae) et d'un cultivar de Robusta, ont été étudiés au microscope photonique. Les résultats montrent que la résistance à la maladie caractérisée par : la réduction des sites d'infection, une croissance faible et anormale du champignon, des changements cytoplasmiques dans les cellules hôtes dus à la mort des cellules de la plante, suite à une réaction d'hypersensibilité, la mort des germes pathogènes et la formation de dépôts et d'appositions d'apparence variées. Dans les conditions environnementales favorables à la maladie, il apparaît que ces mécanismes qui freinent ou empêchent le développement du germe pathogène sont les plus importants dans la détermination de la résistance. La possibilité d'utiliser différents types de dépôts et d'appositions pour catégoriser la résistance des hôtes et l'agressivité du germe pathogène a été suggérée Keywords: Colletotrichum kahawae, Coffee, resistant, susceptible, Kenya.rd Agronomie Africaine Vol. 19 (3) 2007: pp. 233-24

In vitro propagation of the new disease resistant Coffea arabica variety, Batia

Batian is a true breeding commercial coffee variety that was released in Kenya in 2010. It is resistant to coffee berry disease and coffee leaf rust which are the main coffee diseases in Kenya. Coupled with early ripening, good beverage quality and high yields, demand for planting material has surpassed supply. Conventional propagation methods do not provide enough planting materials, hence the need to develop alternative methods. The objective of this study was to develop an effective in vitro protocol for propagating the coffee variety, Batian. Leaf explants were harvested and cultured on Murashige and Skoog (MS) media supplemented with different concentrations of cytokinins benzyl amino purine (BAP) and thidiazuron (TDZ) separately, 100 mg/l myo-inositol 3% sucrose and gelled with 0.3% gelrite. The results show differences among cytokinins levels in induction of somatic embryos. BAP at 13.3 µM gave the highest mean of embryos per explants, 6.06 ± 1.18 and highest percentage of embryogenic cultures of 58.33%. Development of somatic embryos was achieved on hormone free MS media with highest mean length of 0.32 ± 0.03 mm. Indole butyric acid at 9.8 µM was best for induction of a well-developed root system with a mean length of 1.22 ± 0.09 mm. This protocol opens new prospects for massive propagation of Batian in nine months.Keywords: Batian, somatic embryo, Coffea arabicaAfrican Journal of Biotechnology, Vol 13(24) 2414-241

Gene expression in coffee

Coffee is cultivated in more than 70 countries of the intertropical belt where it has important economic, social and environmental impacts. As for many other crops, the development of molecular biology technics allowed to launch research projects for coffee analyzing gene expression. In the 90s decade, the first expression studies were performed by Northern-blot or PCR, and focused on genes coding enzymes of the main compounds (e.g., storage proteins, sugars, complex polysaccharides, caffeine and chlorogenic acids) found in green beans. Few years after, the development of 454 pyrosequencing technics generated expressed sequence tags (ESTs) obviously from beans but also from other organs (e.g., leaves and roots) of the two main cultivated coffee species, Coffea arabica and C. canephora. Together with the use of real-time quantitative PCR, these ESTs significantly raised the number of coffee gene expression studies leading to the identification of (1) key genes of biochemical pathways, (2) candidate genes involved in biotic and abiotic stresses as well as (3) molecular markers essential to assess the genetic diversity of the Coffea genus, for example. The development of more recent Illumina sequencing technology now allows large-scale transcriptome analysis in coffee plants and opens the way to analyze the effects on gene expression of complex biological processes like genotype and environment interactions, heterosis and gene regulation in polypoid context like in C. arabica. The aim of the present review is to make an extensive list of coffee genes studied and also to perform an inventory of large-scale sequencing (RNAseq) projects already done or on-going