The modifications of cell wall composition and water status of cucumber leaves induced by powdery mildew and manganese nutrition.

Powdery mildew caused by Podosphaera fuliginea, is one of the most important diseases, damaging cucumber's yield worldwide. Among the different controlling ways, management of plant nutrition is an effective method. The present experiment was aimed to study the effects of foliar application of manganese (Mn) on disease suppression and to elucidate the possible mechanisms by which Mn-treated plants resist to fungal disease. Cucumber plants were hydroponically grown and sprayed by MnSO4 alone and in combination with lysine (Lys) and methionine (Met) four days before pathogen inoculation. The results showed that the foliar application of Mn reduced the fungal disease severity by increasing of lignin, cellulose and pectin contents of cell wall (CW) and improving of leaf water status. The reduction of disease severity by application of MnSO4, Mn + Lys and Mn + Met, were 40, 33, and 40% compared to control, respectively. The increases of lignin contents at the same treatments were 33, 27, and 36%, respectively. The leaf water potential (LWP) enhanced by foliar spray of above-mentioned fertilizers up to 15, 18, and 17%, respectively. The results of present study revealed that the Mn nutrition could control the cucumber powdery mildew by reinforcing of CW structure and reducing of water loss from infected leaves. The current findings are the first reports elucidating the CW-related defense mechanisms in which Mn has important role. The obtained results have a practical importance either in studies of plant physiology and biochemistry or in agricultural sciences for cost-effective control of powdery mildew in cucumber plants.

Permanent genetic resources added to Molecular Ecology Resources Database 1 August 2012 - 30 September 2012.

This article documents the addition of 83 microsatellite marker loci and 96 pairs of single-nucleotide polymorphism (SNP) sequencing primers to the Molecular Ecology Resources Database. Loci were developed for the following species: Bembidion lampros, Inimicus japonicus, Lymnaea stagnalis, Panopea abbreviata, Pentadesma butyracea, Sycoscapter hirticola and Thanatephorus cucumeris (anamorph: Rhizoctonia solani). These loci were cross-tested on the following species: Pentadesma grandifolia and Pentadesma reyndersii. This article also documents the addition of 96 sequencing primer pairs and 88 allele-specific primers or probes for Plutella xylostella.

Effect of Silicon Nutrition on Oxidative Stress Induced by Phytophthora melonis Infection in Cucumber.

The effect of silicon nutrition on root rot of cucumber caused by Phytophthora melonis was studied in a greenhouse experiment. Two cucumber cultivars (Cucumis sativus 'Dominus' and 'Super Dominus') fertilized with three concentrations of Si (0.0, 1.0, and 1.7 mM Si in the form of sodium silicate) were not inoculated or were inoculated with P. melonis. The P. melonis isolate significantly decreased root dry weights, although the magnitude of growth reduction varied with cultivar and Si concentration. Silicon nutrition at either concentration significantly reduced disease severity relative to the treatment that received no silicon. There was a significant negative correlation between the extent of root rot caused by P. melonis and the extent of electrolyte leakage of roots. Roots infected with P. melonis had greater root catalase (CAT) and ascorbate peroxidase (APX) activities. There was a positive correlation between silicon concentrations and CAT and APX activities in plants inoculated with P. melonis. Silicon improved activity of antioxidant enzymes, resulting in enhanced crop resistance to oxidative stress induced by P. melonis infection and improved cucumber growth.