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  Section: Plant Nutrition » Micronutrients » Boron
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Deficiency Symptoms

Historical Information
  Determination of Essentiality
  Functions in Plants
    - Root Elongation and Nucleic Acid Metabolism
    - Protein, Amino Acid, and Nitrate Metabolism
    - Sugar and Starch Metabolism
    - Auxin and Phenol Metabolism
    - Flower Formation and Seed Production
    - Membrane Function
Forms and Sources of Boron in Soils
  Total Boron
  Available Boron
  Fractionation of Soil Boron
  Soil Solution Boron
  Hydrated Boron Minerals
Diagnosis of Boron Status in Plants
  Deficiency Symptoms
    - Field and Horticultural Crops
    - Other Crops
  Toxicity Symptoms
    - Field and Horticultural Crops
    - Other Crops
Boron Concentration in Crops
  Plant Part and Growth Stage
  Boron Requirement of Some Crops
Boron Levels in Plants
Soil Testing for Boron
  Sampling of Soils for Analysis
  Extraction of Available Boron
    - Hot-Water-Extractable Boron
    - Boron from Saturated Soil Extracts
    - Other Soil Chemical Extractants
  Determination of Extracted Boron
    - Colorimetric Methods
    - Spectrometric Methods
Factors Affecting Plant Accumulation of Boron
  Soil Factors
    - Soil Acidity, Calcium, and Magnesium
    - Macronutrients, Sulfur, and Zinc
    - Soil Texture
    - Soil Organic Matter
    - Soil Adsorption
    - Soil Salinity
  Other Factors
    - Plant Genotypes
    - Environmental Factors
    - Method of Cultivation and Cropping
    - Irrigation Water
Fertilizers for Boron
  Types of Fertilizers
  Methods and Rates of Application

Field and Horticultural Crops
Alfalfa (Medicago sativa L.). Symptoms are more severe at the leaf tips, although the lower leaves remain a healthy green color. Flowers fail to form, and buds appear as white or light-brown tissue (65). Internodes are short; blossoms drop or do not form, and stems are short (66). Younger leaves turn red or yellow (67,68), and topyellowing of alfalfa occurs (69) (Figure 8.1).

Barley (Hordeum vulgare L.). No ears are formed (70). Flowers were opened by the swelling of ovaries caused by partial sterility due to B deficiency (36). Boron deficiency was also associated with the appearance of ergot.

Beet (Beta vulgaris L.). Boron deficiency results in a characteristic corky upper surface of the leaf petiole (69). Beet roots are rough, scabby (similar to potato scab) and off-color (71).

Broccoli (Brassica oleracea var. botrytis L.). Water-soaked areas occur inside the heads, and callus formation is slower on the cut end of the stems after the heads have been harvested (72). Symptoms of boron deficiency included leaf midrib cracking, stem corkiness, necrotic lesions, and hollowing in the stem pith (73).

Brussels sprouts (Brassica oleracea var. gemmifera Zenker). The first signs of boron deficiency are swellings on the stem and petioles, which later become suberised. The leaves are curled and rolled, and premature leaf fall of the older leaves may take place (58). The sprouts themselves are very loose instead of being hard and compact, and there is vertical cracking of the stem (74).

Carrot (Daucus carota L.). Boron deficiency results in longitudinal splitting of roots (75). Boron-deficient carrot roots are rough, small with a distinct white core in the center and plants show a browning of the tops (71).

Cauliflower (Brassica oleracea var. botrytis L.). The chief symptoms are the tardy production of small heads, which display brown, waterlogged patches, the vertical cracking of the stems, and rotting of the core (74) (Figure 8.2). When browning is severe, the outer and the inner portions of the head have a bitter flavor (76). Stems are stiff, with hollow cores, and curd formation is delayed (77). The roots are rough and dwarfed; lesions appear in the pith, and a loose curd is produced (69).

Clover (Trifolium spp.). Plants are weak, with thick stems that are swollen close to the growing point, and leaf margins often look burnt (78). Symptoms of boron deficiency in red and alsike clover may occur as a red coloration on the margins and tips of younger leaves; the coloration gradually spreads over the leaves, and the leaf tips may die (65).

Symptoms of boron deficiency in alfalfa (Medicago sativa L.) showing red and yellow color development on young leaves
FIGURE 8.1 Symptoms of boron deficiency in alfalfa (Medicago sativa L.) showing red and yellow color development on young leaves.

Symptoms of boron deficiency in cauliflower (Brassica oleracea var. botrytis L.) showing brown, waterlogged patches, and rotting of the core of the head.
FIGURE 8.2 Symptoms of boron deficiency in cauliflower (Brassica oleracea var. botrytis L.) showing brown, waterlogged patches, and rotting of the core of the head.

Corn (Zea mays L.). Boron deficiency is seen on the youngest leaves as white, irregularly shaped spots scattered between the veins. With severe deficiency these spots may coalesce, forming white stripes 2.5 to 5.0 cm long. These stripes appear to be waxy and raised from the leaf surface (79). Interruption in the boron supply, from 1 week prior to tasselling until maturity, curtailed the normal development of the corn ear (80).

Oat (Avena sativa L.). Pollen grains are empty (70).

Peanuts or groundnut (Arachis hypogaea L.). Boron deficiency resulted in hollow-heart in peanut kernels at a few locations in Thailand (81).

Pea (Pisum sativum L.). Leaves develop yellow or white veins followed by some changes in interveinal areas; growing points die and blossoms shed (82). Unpublished data of Gupta and MacLeod (83) showed that boron deficiency in peas resulted in short internodes and small, shrivelled new leaves.

Potato (Solanum tuberosum L.). Deficiency results in the death of growing points, with short internodes giving the plant a bushy appearance. Leaves thicken and margins roll upward, a symptom similar to that of potato leaf roll virus (84). Boron deficiency resulted in rosetting of terminal buds and shoots, and the new leaves were malformed and chlorotic (85).

Radish (Raphanus sativus L.). Deficiency of boron in radish is also known as brown-heart, manifested first by dark spots on the roots, usually on the thickest parts (76). Roots upon cutting show brown coloration and have thick periderm (71).

Rutabaga (Brassica napobrassica Mill.). The boron deficiency disorder in rutabaga is generally referred to as brown-heart. Upon cutting, the roots show a soft, watery area (Figure 8.3). Under severe boron deficiency the surface of the roots is rough and netted, and often the roots are elongated (86). The roots are tough, fibrous, and bitter, and have a corky and somewhat leathery skin (58).

Snapbean (Phaseolus vulgaris L.). There is a yellowing of tops, slow flowering and pod formation (71).

Soybean (Glycine max Merr.). Boron deficiency results in necrosis of the apical growing point and young growth; the lamina is thick and brittle; and floral buds wither before opening (87). Boron deficiency induced a localized depression on the internal surface of one or both cotyledons of some seeds and resembled the symptoms of hollow-heart in groundnut seeds (88).

Symptoms of boron deficiency in rutabaga (Brassica napobrassica Mill.) showing a soft, watery area of a cut root
FIGURE 8.3 Symptoms of boron deficiency in rutabaga (Brassica napobrassica Mill.) showing a soft, watery area of a cut root.

Sunflower (Helianthus annuus L.). There is basal fading and distortion of young leaves with soaked areas and tissue necrosis (25).

Tomato (Lycopersicon esculentum L.). The growing point is injured; flower injury occurs during the early stages of blossoming, and fruits are imperfectly filled (72). Failure to set fruit is common, and the fruit may be ridged, show corky patches, and ripen unevenly. Wheat (Triticum aestivum L.). A normal ear forms but fails to flower (70). In the case of severe boron deficiency, the development of the inflorescence and setting of grains are restricted (87).

Other Crops
Cotton (Gossypium hirsutum L.). Boron deficiency causes retarded internodal growth (89). The terminal bud often dies, checking linear growth, and short internodes and enlarged nodes give a bushy appearance that is referred to as a rosette condition (90). Bolls are deformed and reduced in size. Root growth is severely inhibited, and secondary roots have a stunted appearance (91).

Sugar Beet (Beta vulgaris L.). Deficiency results in retarded growth, and young leaves curl and turn black (92). The old leaves show surface cracking, along with cupping and curling. When the growing point fails completely, it forms a heart rot (92).

Tobacco (Nicotiana tabacum L.). Boron deficiency results in interveinal chlorosis, dark and brittle newly emerging leaves, water-soaked areas in leaves, and delayed flowering, and formation of seedless pods (93). Tissues at the base of the leaf show signs of breakdown, and the stalk toward the top of the plant may show a distorted or twisted type of growth. The death of the terminal bud follows these stages (94).

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