Comportement de quelques enzymes du metabolisme oxydatif au cours des interactions du piment (Capsicum annuum) avec le Phytophthora capsici ou avec le virus de la mosaique du tabac (VMT)

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : TD 81097 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Impact of UV-C radiations of strawberry plants on its sensitivity to Botrytis cinerea

International audienc

Impact of UV-C radiation on the sensitivity of three strawberry plant cultivars (Fragaria x ananassa) against Botrytis cinerea

International audienceSeveral studies suggest that UV-C radiation, known for its disinfecting effect, may also stimulate plant defenses. The objective of this study is to reduce the sensitivity of strawberry plants (Fragaria x ananassa) to Botrytis cinerea by application of non-deleterious doses of highly energetic UV-C light (254 nm) on leaves. Preliminary tests were carried out on strawberry plants: Cirafine, Charlotte and Candiss, to optimize the doses of UV-C to apply on plants and to test the sensitivity of these three cultivars to B. cinerea. The three cultivars showed different levels of susceptibility to B. cinerea: Cirafine was the most resistant followed by Charlotte and Candiss being the most sensitive. These observations were supported by histological examination and phenol levels in the leaves that indicated deeper penetration of B. cinerea into Candiss. Nine variations of treatments were applied to the plants, which were composed of varying UV-C doses and differing application frequencies. The treatment of UV-C applied at 0.85 and 1.70 kJ/m², four times every second day (p-value = 0.05), were shown to have a significant increase, around 25%, in the protection of Candiss against Bc1 strain of B. cinerea. Our observations show that exposing strawberry plants (Candiss) to low repeated doses of UV-C could improve their resistance against gray mold, while avoiding any apparent negative effects to the plants

Pre-harvest hormetic doses of UV-C radiation can decrease susceptibility of lettuce leaves (Lactuca sativa L.) to Botrytis cinerea L.

Post-harvest applications of UV-C radiation have proven very efficient in reducing the development of post-harvest diseases in many species including lettuce (Lactuca sativa L.). Several studies suggest that UV-C radiation is effective not only because of its disinfecting effect but also because it may stimulate plant defenses. Pre-harvest treatment with UV-C radiation may thus offer an interesting potential for lettuce protection, provided that application doses are effective while excluding any harmful effects on the plants. Here we provide evidence that 0.85 kJ m−2 and 1.70 kJ m−2 represent doses of UV-C radiation that are not deleterious for lettuce plants. We used several criteria to evaluated the effect of UV-C radiation on the plant, including histological observations; the concentration of malondialdehyde, an indicator of membrane integrity, as well as parameters derived from measurements of chlorophyll fluorescence, such as maximal efficiency of photosystem II (Fv/Fm) and the Performance Index of Strasser. We observed that a single dose of 0.85 kJ m−2 slightly increased plant resistance to grey mould (Botrytis cinerea L.) while a single dose of 1.70 kJ m−2 had the opposite effect. When a 0.85 kJ m−2 dose was applied 4 times, at two-day intervals, there was an increase in the total phenol content of leaves, and in PAL, CAT, and MDAHR activities. Leaves inoculated 2 days after the latter UV-C treatment showed significantly decreased sensitivity (−30%) when compared to the control

Preharvest hormetic doses of UV-C radiation can decrease susceptibility of lettuce to <em>Botrytis</em>

National audienc

Juvenile coffee leaves acclimated to low light are unable to cope with a moderate light increase

UMR AGAP, équipe Diversité, adaptation et amélioration de la vigne (DAAV)International audienceThe understorey origin of coffee trees and the strong plasticity of Coffea arabica leaves in relation to contrasting light environments have been largely shown. The adaptability of coffee leaves to changes in light was tested under controlled conditions by increasing the illumination rate on C. arabica var. Naryelis seedlings acclimated to low light conditions and observing leaf responses at three different developmental stages (juvenile, growing and mature). Only mature leaves proved capable of adapting to new light conditions. In these leaves, different major mechanisms were found to contribute to maintaining a good photosynthetic level. With increased illumination, a high photosynthetic response was conserved thanks to fast nitrogen remobilization, as indicated by SPAD values and the photorespiration rate. Efficient photoprotection was accompanied by a great ability to export sucrose, which prevented excessive inhibition of the Calvin cycle by hexose accumulation. In contrast, in younger leaves, increased illumination caused photodamage, observable even after 9 days of treatment. One major finding was that young coffee leaves rely on the accumulation of chlorogenic acids, powerful antioxidant phenolic compounds, to deal with the accumulation of reactive oxygen species rather than on antioxidant enzymes. Due to a lack of efficient photoprotection, a poor ability to export sucrose and inadequate antioxidant protection, younger leaves seemed to be unable to cope with increased illumination. In these leaves, an absence of induced antioxidant enzyme activity was accompanied, in growing leaves, by an absence of antioxidant synthesis or, in juvenile leaves, inefficient synthesis of flavonoids because located in some epidermis cells. These observations showed that coffee leaves, at the beginning of their development, are not equipped to withstand quick switches to higher light levels. Our results confirm that coffee trees, even selected for full sunlight conditions, remain shade plants possessing leaves able to adapt to higher light levels only when mature