A. El Hadrami

Effect of Juglone on Active Oxygen Species and Antioxidant Enzymes in Susceptible and Partially Resistant Banana Cultivars to Black Leaf Streak Disease

The black leaf streak disease (BLSD), caused by Mycosphaerella fijiensis, is the most destructive disease of bananas and plantains around the world. Breeding for resistance is the most promising strategy to fight this disease especially in small farmer plantations. Mycosphaerella fijiensis produces many phytotoxins such as juglone, which can be used, jointly with field and inoculations under controlled conditions, for screening banana cultivars for BLSD-resistance. This non-host specific phytotoxin has been shown to act on chloroplasts and disturbs the proton electrochemical gradient across the plasmalemma membrane. Moreover, an involvement of the oxidative burst during the interaction has been suggested. The present study was carried out using two cultivars that differed for either their juglone-responses or their resistance to BLSD (cv. Grande Naine susceptible to BLSD and juglone and cv. Fougamou partially resistant to BLSD and highly tolerant to juglone). The production of active oxygen species (AOS) and the enhancement of the enzymatic and/or non-enzymatic AOS-scavenging systems were investigated after treatment of the two cultivars with juglone. The time-course of AOS-production and AOS-scavenging was shown to be the key difference between these two tested cultivars after treatment with juglone. Thus, an early release of AOS (O2− radical and H2O2) and a quick stimulation of a preferment anti-oxidant system (superoxide dismutases, catalases, and peroxidases) was observed for cv. Fougamou as compared to cv. Grande Naine for which a late and weak generation of AOS accompanied by a late stimulation of the anti-oxidant systems were detected.

Date Palm Genetics and Breeding

Date palm, Phoenix dactylifera L., is one of the oldest domesticated plants, but research to understand its diversity, evolution and adaptability is still lagging behind. One of the major limitations has been the lengthy life-cycle of this plant. Meanwhile, breeding challenges and opportunities are enormous, which in turn highlights the importance of how unraveling the evolutionary driving forces of this desert crop could help preserve its socio-economical, botanical and nutritional values. This review represents an up-to-date account of date palm progress in terms of genetics and breeding and underlines the challenges facing these two fields of research in this special crop. It also highlights some of the opportunities on the rise for breeding in this crop.

Pathogenic variation of Verticillium dahliae after serial passages through potato and sunflower

Verticillium wilt is a limiting factor in many field crops, including potato and sunflower. The causal agent, Verticillium dahliae Kleb., is known for its high level of diversity and pathogenic variability. In an earlier study, we showed such a high variability among isolates recovered from either potato or sunflower when inoculated on their original or alternative hosts. Verticillium dahliae isolates from potato were more aggressive on both potato and sunflower while the ones from sunflower were to a certain extent more adapted to sunflower than to potato. In the present study, we show the ability of weakly aggressive potato isolates to gain pathogenicity on either potato or sunflower when inoculated to a susceptible potato cultivar ‘Kennebec’ for four successive generations. However, some isolates showed a loss in pathogenicity after four successive passages on susceptible potato cultivar ‘Kennebec’, especially on the moderately resistant potato cultivar ‘Ranger Russet’. Results in terms of gain or loss of pathogenicity by potato and sunflower isolates are discussed in relation to the effect of successive passages through their original or alternative hosts. Key words: Verticillium dahliae Kleb., potato, sunflower, host of origin, alternative host, successive passages, pathogenicity gain/loss, pathogenicity index. La verticilliose constitue un facteur limitant pour de nombreuses cultures incluant la pomme de terre et le tournesol. L’agent causal, Verticillium dahliae Kleb., est connu pour son degré élevé de diversité génétique et de variabilité de pouvoir pathogène. Dans une étude précédente, nous avions montré la présence d’une telle variabilité entre des souches isolées soit de pomme de terre soit de tournesol, et inoculées sur leur hôte d’origine ou alternatif. Les isolats de V. dahliae provenant de pomme de terre étaient plus agressifs aussi bien sur pomme de terre que sur tournesol, tandis que ceux provenant de tournesol étaient relativement mieux adaptés sur tournesol que sur pomme de terre. Dans la présente étude, nous montrons la capacité de certains isolats peu agressifs, provenant de pomme de terre, d’acquérir un plus grand pouvoir pathogène, aussi bien sur pomme de terre que sur tournesol, après avoir été propagés pendant quatre générations sur le cultivar sensible de pomme de terre ‘Kennebec’. Par contre, après quatre passages successifs sur le cultivar ‘Kennebec’, certains isolats ont vu leur pouvoir pathogène diminuer, plus particulièrement sur le cultivar partiellement résistant ‘Ranger Russet’. Ces résultats sont discutés en termes de gain ou de perte de pouvoir pathogène, par des isolats provenant de pomme de terre ou de tournesol, dans le but d’élucider l’effet de leur passages successifs sur leurs hôtes d’origine ou alternatif. Mots-clés : Verticillium dahliae Kleb., pomme de terre, tournesol, hôte d’origine, hôte alternatif, passages successifs, gain/perte de pouvoir pathogène, index de pathogenicité.

Secondary Metabolites of Date Palm

Higher plants such as date palm accumulate a wide range of different chemicals in their tissue. These can conveniently be divided into two types of compounds: products of primary plant metabolism such as proteins, fats and carbohydrates, which guarantee the primary functions of growth and development; and products of secondary metabolism such as phenolics. Phenolic compounds are widely distributed in the plant kingdom. These organic compounds are not directly involved in primary metabolic processes of growth and development but are important constituents of resistance/tolerance to stress. These include lignins and other phenolics, which strengthen mechanically the cell walls while tannins, flavonoids, and some simple phenolics serve as defenses against herbivores, pathogens, ultraviolet radiation and other abiotic stress. In addition, some phenolics have allelopathic activity and may adversely influence the growth of neighboring plants. Other compounds such phytosterols, and alpha-tocopherols are also important in many growth and development processes. All these metabolites have been attributed to have nutritional and health-benefit value in the human diet. This chapter provides an overview on the work carried out on secondary metabolites in date palm, with special emphasis on the metabolic pathways involved, the regulation, potential functions, and health and nutritional benefits.

Somaclonal Variation in Date Palm

The exploration of somaclonal variation is an approach that could provide date palm breeding programs with new genotypes. Naturally occurring or induced variants may have superior agronomic quality and/or enhanced performance but could also harbor new traits such as tolerance to drought and salinity or resistance to major diseases i.e. bayoud. This chapter summarizes recent progress in terms of studying and exploring date palm somaclonal variation, and provides an outlook about future applications of this biotechnology in this socioeconomically important crop.

In Vitro Selection for Abiotic Stress in Date Palm

In vitro-selection of date palm cultivars with an enhanced tolerance to abiotic stress represents a great support to the breeding program. This could lead to variants with superior agronomic quality and/or enhanced performance but also to genotypes harboring new traits such as tolerance to drought and salinity. In an era where a race has started towards functional food and nutraceuticals, this source of variation could also be explored to improve the nutritional value of dates. This chapter summarizes the recent progresses in date palm in vitro-selection and provides an outlook about future applications of the technique in this socio-economically important crop. It also highlights some of the challenges faced by this crop with regard to climate change and global warming.