Inbotany,chlorosis is a condition in which leaves produce insufficientchlorophyll. As chlorophyll is responsible for the green color of leaves, chlorotic leaves are pale, yellow, or yellow-white. The affected plant has little or no ability to manufacturecarbohydrates throughphotosynthesis and may die unless the cause of its chlorophyll insufficiency is treated and this may lead to a plant disease calledrusts, although some chlorotic plants, such as the albinoArabidopsis thaliana mutantppi2, are viable if supplied withexogenoussucrose.[1]
The wordchlorosis is derived from the Greekkhloros meaning "greenish-yellow", "pale green", "pale", "pallid", or "fresh".
Inviticulture, the most common symptom of poor nutrition in grapevines is the yellowing of grape leaves caused by chlorosis and the subsequent loss of chlorophyll. This is often seen invineyard soils that are high in limestone such as theItalian wine region ofBarolo in thePiedmont, theSpanish wine region ofRioja and theFrench wine regions ofChampagne andBurgundy. In these soils the grapevine often struggles to pull sufficient levels ofiron which is a needed component in the production of chlorophyll.[2]
Chlorosis is typically caused when leaves do not have enough nutrients to synthesise all the chlorophyll they need. It can be brought about by a combination of factors including:
However, the exact conditions vary from plant type to plant type. For example,Azaleas grow best in acidic soil andrice is unharmed by waterlogged soil.
Like many other plants,grape vines are susceptible to chlorosis, and symptoms of iron deficiency tend to be common on soils rich inlimestone. In the wake ofThe Great French Wine Blight, when EuropeanVitis vinifera were affected byPhylloxera, chlorosis became a greater problem inviticulture. To deal with the Phylloxera blight,V. vinifera was grafted ontorootstock based on American species of the genusVitis, such asVitis riparia,Vitis rupestris, andVitis berlandieri. However, many of these were less adapted to the lime-rich soils that were common in France's vineyards, in particular many of those that produced wines of top quality. Many grafted vines in lime-rich vineyards therefore showed signs of iron deficiency, and in France this specific form of chlorosis was termedchlorose calcaire. The problem was largely overcome by the selection of lime-resistant American vines as basis for hybrid vines used for rootstock material. However, since such rootstocks may be less than optimal in other respects, it is necessary for the viticulturalist to balance the need for chlorosis resistance against other viticultural needs. This is illustrated by one of the most common lime-resistant rootstocks, 41 B, which is a hybrid betweenV. vinifera cultivarChasselas andV. berlandieri, which generally has a sufficient, but not extremely high, Phylloxera resistance.[9][10]
Specificnutrient deficiencies (often aggravated by highsoil pH) may be corrected by supplemental feedings ofiron, in the form of achelate orsulphate,magnesium ornitrogen compounds in various combinations. If the soil is too acidic, applying lime can raise the pH to the proper range, making more nutrients available to the plant. Likewise, sulfur can be used to lower soil pH if it is too alkaline.[11]
