The jasmonate pathway is involved differentially in the regulation of different defence responses in tobacco cells

International audienc

Lipoxygenases in Plant Signalling

International audienc

Genetic variability of tolerance to Verticillium albo-atrum and Verticillium dahliae in Medicago truncatula

Verticillium wilt caused by Verticillium albo-atrum and Verticillium dahliae is responsible for yield losses in many economically important crops. The capacity of pathogenic fungi to adapt to new hosts is a well-known threat to the durability of resistant crop varieties. In the present work, 25 Medicago truncatula genotypes from a core collection and six V. albo-atrum and V. dahliae strains were used to study the potential of non-host Verticillium strains isolated from different plant species to infect this legume plant and the plant's susceptibility to the pathogens. The experiment was designed as factorial with randomised complete blocks and with three repetitions. The wilt symptoms caused by V. albo-atrum and V. dahliae were scored on a disease index scale from 0 to 4, during 30 days after inoculation of 10-day-old plantlets. Disease severity was quantified by maximum symptom scores (MSS) and areas under the disease progress curves (AUDPC), which integrate the time course of symptom development. Highly significant differences were observed among plant genotypes and fungal strains, and their interaction was also significant. The correlation between MSS and AUDPC was 0.86. The most severe symptoms were caused by the alfalfa strain V. albo-atrum V31-2 and the least severe by V. dahliae JR2, as shown by mean values obtained on the 25 genotypes. M. truncatula genotype TN8.3 was the most susceptible genotype by mean values obtained with the six fungal strains, whereas F11013-3, F83005.9 and DZA45.6 were highly resistant to all strains studied. The results can be used to choose parents for studying the genetics of resistance in Medicago truncatula to Verticillium strains with different levels of aggressiveness

Quantitative trait loci associated with resistance to a potato isolate of Verticillium albo-atrum in Medicago truncatula

International audienceVerticillium albo-atrum is responsible for considerable yield losses in many economically important crops, among them alfalfa (Medicago sativa). Using Medicago truncatula as a model for studying resistance and susceptibility to V. alboatrum, previous work has identified genetic variability and major resistance quantitative trait loci (QTLs) to Verticillium. In order to study the genetic control of resistance to a non-legume isolate of this pathogen, a population of recombinant inbred lines (RILs) from a cross between resistant line F83005.5 and susceptible line A17 was inoculated with a potato isolate of V. albo-atrum, LPP0323. High genetic variability and transgressive segregation for resistance to LPP0323 were observed among RILs. Heritabilites were found to be 0 63 for area under the disease progress curve (AUDPC) and 0 93 for maximum symptom score (MSS). A set of four QTLs associated with resistance towards LPP0323 was detected for the parameters MSS and AUDPC. The phenotypic variance explained by each QTL (R2) was moderate, ranging from 4 to 21%. Additive gene effects showed that favourable alleles for resistance all came from the resistant parent. The four QTLs are distinct from those described for an alfalfa V. albo-atrum isolate, confirming the existence of several resistance mechanisms in this species. None of the QTLs co-localized with regions involved in resistance against other pathogens in M. truncatula

Use of transgenic plants to study the role of ethylene and polygalacturonase during infection of tomato fruit by Colletotrichum gloeosporioides.

The infection of tomato fruit by the postharvest pathogen Colletotrichum gloeosporioides did not proceed until the onset of ripening in response to ethylene. Compared with fruit from wild-type plants, infection progressed more slowly in transgenic fruit in which ethylene biosynthesis and ripening had been inhibited by an ACC oxidase (ACO) antisense transgene. In contrast, transgenic fruit deficient in polygalacturonase developed lesions at the same rate as the wild-type fruit. Ethylene biosynthesis increased rapidly in response to infection of ripe wild-type and ACO antisense fruit but was 25 times greater in the former. Fruit from the ripening mutant ripening inhibitor (rin), which are normally very resistant to infection, became infected quickly when incubated in the presence of ethylene, whereas fruit incubated in the absence of ethylene remained healthy. The ACO 1 mRNA accumulated to detectable levels within 24 h of inoculation of unripe wild-type fruit, prior to the development of visible symptoms, whereas there was no detectable expression in the inoculated ACO antisense fruit. ACO transcripts accumulated to maximum levels during the early stages of infection of ripe fruit, correlating with maximum ethylene biosynthesis. Northern analysis using gene-specific probes for each of the three ACO genes indicated that ACO 1 was the main gene expressed in response to infection and that there was no detectable expression of ACO 2 and 3