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Plant protection in leafy vegetables

WORLDS BEST INNOVATION

IN PHYSIOLOGICAL CALCIUM DEFICIENCY

ON LEAFY VEGETABLE CROPS!



The problem?


Physiological Calcium deficiency (tipburn) is usually related to the inability of the plant to translocate adequate Ca to the affected plant part. It is a major limitation of the production. The unpredictability make the problem very serious. Losses could reach up to 50% of production. For example: Tipburn is a big problem for Norwegian greenhouse lettuce growers and can account for up to 20 % losses in production, equal to almost 20 million NOK/year.


Why?


Physiological Ca-deficiency has been an economic problem for commercial vegetable growers for many years. While this disorder has probably always been present, it has become more severe in recent years, possibly because more intensive production practices have been used. Ca-deficiency is usually related to the inability of a plant to translocate adequate Ca to the affected part, rather than being due to insufficient levels of soil Ca. Physiological Ca-deficiency is not generally prevented by Ca fertilisation, therefore it is quite difficult to protect plants against this disorder. Description. Tipburn is a Ca-deficiency disorder of cabbage, Chinese cabbage, brussels sprouts, lettuce, chervil, chicory, escarole, onion, fennel and potatoes and is usually characterised by necrosis at the edges of young, rapidly-expanding leaves. Injury may develop on more than half of the area of these leaves. This necrosis is often visible in leaf lettuce and chervil; but, in heading crops, the affected leaves are in the head and not observed until the head is used.


The role of Ca?


Ca is essential for the synthesis of cell walls. Ca is bound as Ca-pectate in the middle lamella and it is essential for strengthening cell walls and plant tissues. The degradation of pectates is mediated by polygalacturonase, which is inhibited by high Ca concentrations. Polygalacturonase activity is increased in Ca-deficient cells and tissues. Typical symptoms of Ca-deficiency are the disintegration of cell walls and the collapse of affected tissues such as petioles and the upper parts of the stem. Therefore when Ca content is increasing in plant tissues then tipburn symptoms are decreasing on plants. Plants are stronger against pests and diseases.


Trials done with chervil in order to reduce tipburn symptoms by negative DIF (DIF is the difference between day temperature (DT) and night temperature (NT)).

The plants were grown in growth chambers with different temperature regimes: 1. negative DIF (- 5 degrees of C) – temperature was set to 18 degrees of C during day and 23 degrees of C during night; 2. positive DIF (+ 5 degrees of C) – temperature was set to 23 degrees of C during day and 18 degrees of C during night. Each temperature treatment consisted of 42 plants. The numbers of tipburned leaves were counted every second or third day until harvesting.


Results

Development of injury. Chervil develops quite quickly. About 29 days after sowing the total number of leaves increased at the rate of about 0.3 leaf per 24 hours. The leaves developed quickest (ca. 0.6 leaf per 24 hours) 45 – 48 days after sowing. The number of total leaves developed similarly in both conditions. The tipburn injury appears quickly on chervil plants. The first leaves with injury symptoms were seen 34 days after sowing. The injury symptoms developed similarly in both conditions until 43 days after sowing. After this time the development of injury symptoms increased until harvesting under positive DIF conditions. The number of tipburned leaves developed quickest (0.58 leaf per 24 hours) 45 – 48 days after sowing under positive DIF conditions. At the same time under negative DIF conditions the number of injured leaves increased at the rate of about 0.03 leaf per 24 hours.

Height, the incidence of tipburn and Ca content in young leaves. The height of plants reduced in the negative DIF conditions. Plants grown in negative DIF conditions were more equal in height than plants grown in positive DIF conditions. The plants were elongated in the positive DIF conditions. At harvest the incidence of tipburn injury was lower in the negative DIF conditions.

The content of calcium in young leaves was significantly lower under positive DIF conditions.


Take home message


In negative DIF conditions – tipburn is decreasing and the need to use chemicals to prevent diseases and pests is reduced or totally absent. This method is replicable around the globe and can be used in organic agriculture and in vertical farming. It help to conserve the energy, because temperature is higher at night time, which period is shorter.


Would like to discover more:

“Olle, M. (2015). Methods to avoid Calcium deficiency on greenhouse grown leafy crops. LAP LAMBERT Academic Publishing. 88 p.”


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