Crops
Silvering
This non-parasitic disease, also called " silvering ", "chimera", "head silvering" ( head silvering) when it affects the leaves of the apex of the tomato, is relatively well known greenhouses (Figures 1 and 2) .
The few symptoms that can be observed in the photos are a good illustration of this condition, which mainly affects crops under cover in production areas rather located in northern latitudes. Note that these symptoms appear at any stage of tomato development and are characterized by:
- spots, more or less regular areas, of variable size, gray-green to silvery in color (figures 3 and 4);
- more or less important leaf deformations (smaller leaflets and / or cut, blistered (figure 4);
- the presence on the stem of streaks, or even stripes, in variable number and width;
- partial or total sterility of the flowers located in the areas of the vegetation affected by the silver plating (although these have a normal appearance);
- sometimes deformed fruits with silvery green streaks turning pale yellow at maturity in the event of partial manifestation (figure 5).
This disease is only really very damaging when the apex meristem is reached, causing symptoms to appear on an entire shoot and causing head silvering.
The silvering is due to an anomaly in the development of the palisade tissues of the limbus in particular, occurring at a very early stage of its development. This subsequently results in the constitution of large intercellular spaces in the tissues of the limbus, giving the latter a special silvery color.
Although all the factors conditioning the expression of this disease are not clearly defined, some of them already allow us to better understand and control it:
- early sowing of winter crops is more sensitive than those made later;
- temperature seems to be the most important environmental factor for inducing and influencing this phenomenon favorably or unfavorably. In fact, silvering manifests itself above all following more or less significant drops in temperature in shelters, in particular at the level of the apex meristem. This can be the case, for example, when a heat shield is removed too quickly, causing the cold air retained by the shield to drop onto the crop. It is the same after too much aeration of a confined tunnel inducing overevaporation of the plants and cooling of their apex. Note that low greenhouses are particularly vulnerable, especially if they are not very bright. Under these conditions, the apices can undergo temperatures of the order of 10 ° C. A contrario , high temperatures induce less silvering;
- many varieties currently cultivated are resistant to silvering thanks to the introduction of the gene "Wi" in tomatoes. This situation is unfortunately not generalized to all cultivars, and it is not uncommon to observe this problem on old varieties, on which the damage has sometimes been quite substantial (up to more than 10% plants expressing symptoms). Note that this resistance is also lacking in some new varieties in the pink, cherry and orange types. In addition, the acquisition of resistance to powdery mildew would sometimes be to the detriment of that of silvering.
For example, silver plating is particularly evident in France in plastic tunnels located in particular in the South-East. During the summer, temperatures quickly reach 30 ° C in the morning. The sudden opening of these shelters on both sides intensifies the transpiration of the plants and causes a lowering of the temperature, favorably influencing the expression of this physiological disease.
To avoid this genetic disease, it is especially advisable to use resistant varieties. In the case of sensitive varieties, it will be desirable to manage the climate of the shelters in such a way as to ban too sudden drops in temperature. If the plants show a silvering of the head, it may be advisable to top them and start again on an unaffected axilla.
The few symptoms that can be observed in the photos are a good illustration of this condition, which mainly affects crops under cover in production areas rather located in northern latitudes. Note that these symptoms appear at any stage of tomato development and are characterized by:
- spots, more or less regular areas, of variable size, gray-green to silvery in color (figures 3 and 4);
- more or less important leaf deformations (smaller leaflets and / or cut, blistered (figure 4);
- the presence on the stem of streaks, or even stripes, in variable number and width;
- partial or total sterility of the flowers located in the areas of the vegetation affected by the silver plating (although these have a normal appearance);
- sometimes deformed fruits with silvery green streaks turning pale yellow at maturity in the event of partial manifestation (figure 5).
This disease is only really very damaging when the apex meristem is reached, causing symptoms to appear on an entire shoot and causing head silvering.
The silvering is due to an anomaly in the development of the palisade tissues of the limbus in particular, occurring at a very early stage of its development. This subsequently results in the constitution of large intercellular spaces in the tissues of the limbus, giving the latter a special silvery color.
Although all the factors conditioning the expression of this disease are not clearly defined, some of them already allow us to better understand and control it:
- early sowing of winter crops is more sensitive than those made later;
- temperature seems to be the most important environmental factor for inducing and influencing this phenomenon favorably or unfavorably. In fact, silvering manifests itself above all following more or less significant drops in temperature in shelters, in particular at the level of the apex meristem. This can be the case, for example, when a heat shield is removed too quickly, causing the cold air retained by the shield to drop onto the crop. It is the same after too much aeration of a confined tunnel inducing overevaporation of the plants and cooling of their apex. Note that low greenhouses are particularly vulnerable, especially if they are not very bright. Under these conditions, the apices can undergo temperatures of the order of 10 ° C. A contrario , high temperatures induce less silvering;
- many varieties currently cultivated are resistant to silvering thanks to the introduction of the gene "Wi" in tomatoes. This situation is unfortunately not generalized to all cultivars, and it is not uncommon to observe this problem on old varieties, on which the damage has sometimes been quite substantial (up to more than 10% plants expressing symptoms). Note that this resistance is also lacking in some new varieties in the pink, cherry and orange types. In addition, the acquisition of resistance to powdery mildew would sometimes be to the detriment of that of silvering.
For example, silver plating is particularly evident in France in plastic tunnels located in particular in the South-East. During the summer, temperatures quickly reach 30 ° C in the morning. The sudden opening of these shelters on both sides intensifies the transpiration of the plants and causes a lowering of the temperature, favorably influencing the expression of this physiological disease.
To avoid this genetic disease, it is especially advisable to use resistant varieties. In the case of sensitive varieties, it will be desirable to manage the climate of the shelters in such a way as to ban too sudden drops in temperature. If the plants show a silvering of the head, it may be advisable to top them and start again on an unaffected axilla.
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5