Showing papers on "Biotic stress published in 1993"

Cold-Induced Disease Resistance

Abstract: In Poaceae species, cold hardening (1°C for 2 wks), increases the freezing resistance of the plants, and also increases the resistance to fungal diseases such as snow moulds, leaf spots, rusts and powdery mildews (Tronsmo 1984, and unpublished). In barley, resistance to powdery mildew may be induced by virulent and avirulent isolates of powdery mildew as well as by saprophytes (Bryngelsson and Collinge 1992 ). Are defence mechanisms induced by cold stress the same as those induced by biotic stress ?

Breeding methods and selection indices for improved tolerance to biotic and abiotic stresses in cool season food legumes

Abstract: The objective of breeding for stress tolerance is to improve productivity for a target level of stress. If tolerance is viewed as resistance to change in productivity with increasing stress, productivity under stress depends not only on stress tolerance, but also on maximum productivity. Index selection theory indicates that selection in non-stress environments will be more effective than direct selection for productivity under stress whenever the correlation between the two types of environments exceeds the heritability of productivity under stress. With high genetic correlation, selection should be conducted within a level of stress that maximizes heritability. In cases where heritability under non-stress is much higher than under stress, an index combining data from stress and non-stress environments is expected to be more efficient than selection based on evaluation only within stress environments.

Transcriptional Regulation of Phytoalexin Biosynthetic Genes

Abstract: In legumes, isoflavonoid derivatives function as antimicrobial phytoalexins, whereas phytoalexins of solanaceous species are of terpenoid origin. The phenylpropanoid and isoprenoid pathways leading to these phytoalexins are involved in the synthesis of a wide range of secondary metabolites with important functions in plant growth, development and responses to the environment. Elicitation of phytoalexin biosynthesis involves transcriptional activation of the genes encoding enzymes of general phenylpropanoid/terpenoid biosynthesis, and of the genes for the specific branch pathways leading to antimicrobial compounds. In order to understand the molecular controls determining the developmental and environmental regulation of the general and specific enzymes of phytoalexin synthesis, we are studying the promoter regions of three elicitor inducible genes, chalcone synthase (chs, isoflavonoid pathway, general), isoflavone reductase (ifr,isoflavonoid pathway, specific) and 3-hydroxy-3-methylglutaryl CoA reductase (hmgr,terpenoid pathway, general). We describe cis-elements and trans-factors involved in the expression of these genes in relation to their tissue specific expression and response to biotic stress. Two elements, the G-box and H-box, located within 50 bp of the TATA box, are important for regulation of expression of chs and probably hmgr, but are not present in the alfalfa ifr promoter.

Comparison of Eucalyptus Root Chitinase Patterns Following Inoculation, by Ectomycorrhizal or Pathogenic Fungi in Vitro

Abstract: Ectomycorrhizal symbiosis is characterized by a striking lack of taxonomic specificity However major differences in the colonization process appeared within hours of inoculation Some characteristics of ectomycorrhizal infection such as biotrophic dependance of fungi on their host, host-fungus specific aggressiveness, modification of symbionts protein patterns including appearance of ectomycorrhizines of low molecular weight, thickening of host cell wall, strongly suggest that early events leading to recognition between symbionts are similar to those implicated in plant-pathogen interactions Chitinases are known to be induced in numerous plants in response to abiotic or biotic stress such as infection by pathogens Does colonization by a mutualistic symbiont also induces root chitinase activity and does this determine specificity ?