Plant indices of major mineral deficiencies

Nitrogen

Nitrogen is required by pineapple in greater amounts than any other nutrient except potassium. Providing adequate supplies of N to rapidly growing plants is essential to maintain high rates of growth and produce good yields. Both leaf size and number may decrease when nitrogen is deficient and fruit and crown mass are consequently reduced. Slips may be absent on plants that normally produce them. Plant indices for nitrogen include leaf colour and nitrate-nitrogen in leaf basal white tissue, total nitrogen in green tissue and leaf chlorophyll content. Soil indices for N, if used, only provide an indication of the N required for early growth of plants. Many tropical soils contain small amounts of nitrogen, so meeting crop N requirements is an important and challenging task.

Leaf colour is an important diagnostic index for nitrogen and is the most important index defined in the pineapple crop log of Nightingale (1942a). When N is deficient, leaves are yellowish green to yellow. However, symptoms in the field are different from those normally found in solution culture. Normally a well-exposed nitrogen-deficient plant will have yellow older leaves because the nitrogen in those plants is translocated to the younger leaves. In the case of nitrogen-deficient plants grown in the field, the older leaves remain green despite the removal of nitrogen from them because of mutual shading of lower and older leaves by adjacent plants. In the field, it is the younger leaves that are yellow. Thus, leaf colour is an integrated index that estimates the nitrogen requirement of pineapple on the basis of its relative carbohydrate status (Nightingale, 1942a; Table 7.2).

The colour indices defined for assessing plant nitrogen status are given below.

• No. 0 colour: yellow. Leaves having no. 0 colour (similar to Plate 15, right-hand leaf) are senescing or senescent and so are relatively inactive physiologically. A high percentage of leaves having no. 0 colour may be observed on newly planted slips and crowns during drought.

Table 7.2. Characteristics of the four ranges of pineapple leaf colour (after Nightingale, 1942a; Sanford, 1962).

Cell starch Carbohydrate

Designation Colour capacity (%) relative to N Leaf texture

No. 0 Yellow Variable Variable Variable

No. 1 Yellow-green 75-100 High Stiff

No. 2 Olive-green 50-75 Intermediate Soft-stiff

No. 3 Black-green 25-50 Low Soft

• No. 1 colour: yellow-green (similar to Plate 15, second leaf from the right). These leaves are characteristic of those that are exposed to full sunlight. The cells of such leaves are filled with starch granules to within 75-100% of their total capacity. Consequently, the amount of carbohydrate in relation to protein nitrogen is high. The leaf texture of such plants is stiff and the leaves will break with a crackling sound when flattened. While additional nitrogen fertilizer could decrease the percentage of leaves with no. 1 colour, there is little evidence that vegetative growth over the first several months is restricted by lack of nitrogen.

• No. 2 colour: olive-green (similar to Plate 15, middle two leaves). Leaves that are olive-green in colour are associated with many different kinds of healthy pineapple crops grown in full sunlight. Cell starch capacity in these leaves is 50-75% of capacity.

• No. 3 colour: blackish-green (similar to Plate 15, left most two leaves). The leaves in this range are very dark green in colour with definite black overtones. Such leaves are characteristic of healthy plants grown in shade. Leaf texture is soft. In contrast to leaves having no. 1 colour, flattening of these leaves does not normally cause them to rupture. The cell starch capacity of these leaves is low relative to the amount of protein nitrogen.

The evolution of leaf colour on a growing 'Smooth Cayenne' plant during the crop development cycle in Hawaii (autumn planting with natural induction occurring 14 months later in the following winter) was described (W.G. Sanford, 1991, personal communication) as follows.

The leaves of crowns, slips or suckers prior to and immediately after planting in the autumn of the year become dehydrated and begin to senesce as the root system becomes established. For approximately the first 3 months after planting, no new leaves emerge so the visible leaves are primarily no. 0 colour or yellow. Such leaves are not physiologically active and will not become so after growth commences. As roots develop and new leaves appear, the fraction of leaves that are of no. 1 colour or yellow-green increases and these leaves are physiologically active. As plant leaf area expands and plants begin to shade each other, the older leaves will become no. 2 colour or olive-green due to this shading by younger leaves. At 6 months after planting, 40% of the leaves will exhibit no. 0 colour (all at the base of the plant) and 60% will have no. 1 colour (all at the top of the plant). By 10 months after planting, 25% of the leaves will be no. 1 colour (youngest leaves), 50% will be no. 2 colour (intermediate-aged leaves) and 25% of the leaves will be no. 3 colour (oldest leaves). By 14 months after planting, the upper and youngest leaves will be no. 1 colour (yellow-green), the intermediate leaves will be no. 2 colour (olive-green) and the lower and oldest leaves will be no. 3 colour (blackish-green) because of shading by the upper leaves and adjacent plants.

In Hawaii, experimental results have shown that the greatest responses to N fertilizer occur when plants are in the no. 1 and no. 2 colour ranges. For that reason, leaf colour estimates report the percentage of leaves exhibiting no. 1 colour, although during the early period of growth both no. 0 and no. 1 colours are combined in the visual estimate. In experiments where no. 1 colour readings ranged between 90 (mostly yellow-green) and 15% (mostly olive green) near the time of floral induction, in almost every case average fruit mass increased with added fertilizer N as the percentage of leaves having no. 1 colour decreased. In practice, a hypothetical trend line of decreasing leaf no. 1 colour readings with increasing plant age and increasing plant mass is followed (Sanford, 1962; Swete Kelly, 1993) and N is applied to maintain leaf colour on this hypothetical line. Thus, where foliar application of nitrogen is the practice, nitrogen fertilizer is applied in amounts and at frequencies approximately related to the increase in plant mass over time. Leaf no. 1 colour decreases and then increases after each nitrogen application, but the long-term objective is to decrease plant no. 1 colour readings to about 15% at the time of forced induction of flowering.

Since the use of no. 1 colour readings is based on greenness, which is in fact a measure of leaf chlorophyll content, any nutrient or other factor that influences leaf chlorophyll levels can interfere with the use of this index. Deficiencies of iron, magnesium and phosphorus are most likely to interfere with the use of this index because these deficiencies decrease leaf chlorophyll concentrations. Application of excessive amounts of herbicides can also reduce leaf chlorophyll levels. Therefore the successful use of no. 1 colour readings is dependent on eliminating, minimizing, or recognizing all factors other than nitrogen that can also influence leaf colour.

Young et al. (H.Y. Young, B.H. Krauss and W.A. Gortner, 1961, unpublished results, Pineapple Research Institute of Hawaii) proposed that measures of both chlorophyll and total leaf nitrogen would provide a more quantitative substitute for the leaf colour index. Chlorophyll and total nitrogen were measured on the middle one-third of the green tissue of 'D' leaves while whole-plant per cent no. 1 colour was estimated visually. Leaf chlorophyll decreased approximately linearly as 'D' leaf total nitrogen decreased, while the reverse was true for per cent no. 1

colour (Table 7.3). Other than via the use of the leaf colour index, no information was found to indicate that a chlorophyll-based index has been used to assess N nutrition in pineapple. Although a direct-reading chlorophyll meter exists, it is likely that plant-to-plant variations in chlorophyll would make it an unsuitable index of nitrogen sufficiency.

In terms of leaf N levels, a plant having 0.1% (1000 p.p.m.) or less nitrogen on a fresh-mass basis (1.2% or 12,000 p.p.m. on a dry-mass basis) in the middle third of 'D' leaves would be considered quite deficient. A similar N index based on whole 'D'-leaf analysis (Martin Prevel, 1959, 1970; Marchal et al., 1970; Lacoeuilhe and Gicquiaux, 1971a,b,c) assumes that, where N is less than 1%, growth will be limited by N and all N greater than 1% of leaf dry matter is assumed to be available for the growth of new tissues. Variations in nitrogen concentrations in successive 'D' leaves can be correlated with the growth of each 'D' leaf. The quantity of nitrogen available for growth can thus be determined in relation to the nitrogen content in the leaf. Leaf analyses made in a large number of fertilization trials showed that the critical mass of nitrogen

Table 7.3. Relationship between chlorophyll (mg kg-1 fresh mass) in the middle third of 'D'-leaf green tissue, total nitrogen (%, fresh-mass basis) in the same tissue and per cent no. 1 colour at two plant age ranges (H.Y Young, 1961, Pineapple Research Institute of Hawaii, Honolulu, unpublished data).

Table 7.3. Relationship between chlorophyll (mg kg-1 fresh mass) in the middle third of 'D'-leaf green tissue, total nitrogen (%, fresh-mass basis) in the same tissue and per cent no. 1 colour at two plant age ranges (H.Y Young, 1961, Pineapple Research Institute of Hawaii, Honolulu, unpublished data).

Chlorophyll

6-11 months

12-15 months

Nitrogen

No. 1 Colour

Nitrogen

No. 1 Colour

400

0.35-0.40

15

0.32-0.36

0

380

0.31-0.34

25

0.28-0.31

10

360

0.29-0.30

30

0.26-0.27

15

340

0.27-0.28

35

0.24-0.25

20

320

0.25-0.26

45

0.22-0.23

30

300

0.23-0.24

55

0.21

35

280

0.22

65

0.20

45

260

0.21

70

0.19

55

240

0.20

75

0.18

60

220

0.19

85

0.17

70

200

0.17-0.18

95

0.15-0.16

75

180

0.15-0.16

100

0.13-0.14

Chlorophyll (C) and N, 6-11-month plants: N = -0.01252 + 0.000879C; r2 = 0.947. Chlorophyll (c) and N, 12-15-month plants: N = -0.1673 + 0.000808C; r2 = 0.943. Chlorophyll (c) and no. 1 colour (%), 6-11-month plants: % = 171.23 - 0.3907C; r2 = 0.995. Chlorophyll (c) and no. 1 colour (%), 12-15-month plants: % = 149.49 - 0.3732C; r2 = 0.995.

required in the 'D' leaf at flower induction to obtain a fruit of 1.8 kg (without crown) was 100 mg (Marchal, 1975, as cited by Py et al., 1987).

Nitrogen in soil is generally not measured, but, in Australia where farmers send their fruit to a cooperative cannery, soil nitrogen is measured as a means of helping to keep fruit nitrate levels below the 8.0 p.p.m. level considered to be critical for processed fruit. The optimum level of nitrogen in soil, based on water extraction after a 14-day incubation, is 120+ p.p.m. nitrate (NO3), which is equivalent to 27 p.p.m. of N (Swete Kelly, 1993). The preplant nitrogen recommended is based on preplant levels of nitrate found in soil (Table 7.4). Total plant-crop requirements for nitrogen for pineapple range from 250 to 700 kg ha-1 (i.e. 4 to 10 g plant-1), depending on the soil and ecology of the site, plant population density, expected fruit mass and other environmental or management factors. Calibration experiments, leaf colour indices and tissue indices can all be used to guide growers to the correct amount of nitrogen required for optimum growth. Details of fertilizer types and methods of application are discussed in Hepton (Chapter 6, this volume).

Phosphorus

The growth of all plant parts is depressed as a result of phosphorus deficiency. However, the phosphorus requirement of pineapple is low and plants can extract P from soils having very low levels of that nutrient. The plants P requirements can almost always be met by applying P prior to planting. Soil P (modified Truog method) is the primary index used to assess the P requirement of pineapple, and levels of 20 p.p.m. or greater are adequate to sustain pineapple growth. The symptoms of P deficiency are observed at soil levels below 5.0 p.p.m. (Swete Kelly, 1993).

The visual symptoms of phosphorus deficiency are not commonly seen and are not particularly specific. They can be confused with plants suffering from root injury due to such causes as drought, nematode damage or mealybug wilt. Phosphorus-deficient plants have erect, long, narrow leaves. Older leaves show leaf-tip dieback preceded by a chlorotic or red-yellow area, which extends downward along the margins of the leaves. Young leaves, primarily because of the contrast, appear to be dark green but with considerable red pigment.

Plants with a phosphorus content of 0.009% (90 p.p.m.) or less, fresh-mass basis (0.108% or 1080 p.p.m. on a dry-mass basis), in the basal white tissue of the 'D' leaves will have the described symptoms. Phosphorus analysis of the basal white tissue of 'D' leaves was developed by Nightingale (G.T. Nightingale, 1946, unpublished results, Pineapple Research Institute of Hawaii) as the index for determining P fertilizer requirements. However, critical values are difficult to define because leaf P tends to decrease when growth is rapid. Mycorrhizal associations exist in pineapple roots (Mourichon, 1981). However, mycorrhizal fungi appar

Table 7.4. Preplant nitrogen and potassium recommendations for 'Smooth Cayenne' pineapple in Australia with varying amounts of residual soil nitrate-nitrogen and potassium (Swete Kelly, 1993).

Preplanting level

Preplant application (kg ha-1)

Nitrogen

125

0

100

20

75

45

50

70

25

95

0

100

Potassium

150

0

120

75

100

125

80

175

60

225

40

275

20

325

0

375

ently do not contribute significantly to the P nutrition of pineapple, except where soil P is extremely low, much less than 0.02 mg l-1 of soil solution (Aziz et al., 1990), or in in vitro conditions (Guillemin et al., 1997). In a recent study, which did not include data on P in soil or leaves, average fruit mass and yield per 12 m2 plot were significantly greater where plants were inoculated with Glomus mosseae and Glomus manihotis (Thamsurakul et al., 2000) relative to the control or to either mycorrhiza species alone. If mycorrhyzae did facilitate P uptake, they would only postpone the time when P fertilization would be required.

The leaf may not be as important as the soil as an index for P, but leaf analysis provides a check on the adequacy of soil supplies. Leaf P in the 'D'-leaf basal white tissue naturally increases with age - for instance, from 0.01% (100 p.p.m. in 'D'-leaf basal white tissue on a fresh-mass basis) at 5 months to about 0.02% (200 p.p.m.) at flower induction (Swete Kelly, 1993). According to Py et al. (1987), leaf P in the whole 'D' leaf should be 0.8% of dry matter at the time of flower induction.

Potassium

Potassium, like nitrogen, is required in large amounts to sustain pineapple plant growth. Potassium deficiency would decrease photosynthesis and thus plant growth, fruit mass and slip production (Swete Kelly, 1993). With potassium deficiency (Plate 16), fruits have reduced sugar and acid levels and have a pale colour (Py et al., 1987; Swete Kelly, 1993), presumably because of reduced carotenoid development. Where K is deficient, the fruit peduncle diameter is reduced (Py et al., 1987), the peduncle is weak (Swete Kelly, 1993) and fruits are more prone to lodging and sunburn and have lower acidity and aroma development.

As with phosphorus, the primary index for K is the level in the soil, because K is well retained by most soils. The optimum soil level at planting is 150 p.p.m. and potassium deficiency symptoms are observed when the soil level is below 60 p.p.m. (Swete Kelly, 1993). The soil level in p.p.m. and the recom mended amount of preplant K is shown in Table 7.4.

The high requirement of pineapple for potassium has made it relatively easy to reproduce deficiency symptoms. Low levels of potassium are associated with shorter leaves that are narrower in relation to their length, growth is reduced, necrotic spots can be seen in the green photosynthetic tissue (chlorenchyma) of the leaves and leaf tips die back (Py et al., 1987; Swete Kelly, 1993). During the early stages of potassium deficiency, leaves are dark-green and narrow (Plate 16), but, if the deficiency is prolonged, leaves eventually become yellow.

Potassium analysis is done on the basal white tissue of 'D' leaves (Swete Kelly, 1993) or whole 'D'-leaf samples (Py et al., 1987). Visual potassium deficiency symptoms are evident when there is less than 0.20% K (2000 p.p.m.), fresh-mass basis (2.4% on a dry-mass basis), in the basal white tissue of 'D' leaves. The critical leaf K level at flower induction is reported to be 0.30% (3000 p.p.m.) on a fresh-mass basis (3.6% on a dry-mass basis) for basal white tissues (Swete Kelly, 1993; W.G. Sanford, personal communication) or 2.2-3% for the whole 'D' leaf on a dry mass basis (Dalldorf and Langenegger, 1976; Py et al., 1987). Swete Kelly (1993) recommends that leaf K of plants 3-5 months old should range between 3500 and 4000 p.p.m. (basal white, fresh-mass basis).

Calcium

Pineapple has a very low requirement for calcium, but deficiencies can occur on highly weathered soils low in basic cations and on soils where pH has been lowered by long-term use of acidifying fertilizers, such as ammonium sulphate. For optimum growth, soils should contain greater than 100 p.p.m. of Ca, a level approximately one-tenth that normally recommended for most crops, and deficiency symptoms are observed when the level is less than 25 p.p.m. Calcium is commonly applied to amend soil pH as well as to supply Ca, but, in many areas, the soil pH is kept at or below 5.5 to limit the incidence of heart and root rots caused by Phytophthora spp. Since the amount of cal cium required to adjust pH varies with soil cation exchange capacity, the lime requirement should be based on a lime titration curve developed specifically for each soil type in which pineapple is grown. Gypsum can be used where it is desirable to supply calcium without changing soil pH. However, only one reference (Hartung et al., 1931) was found indicating that gypsum might have been evaluated as a source of calcium for pineapple.

Visual symptoms of calcium deficiency on vegetative (Plate 17) and reproductive plants (Fig. 7.2) were documented at the Pineapple Research Institute of Hawaii (Sanford, 1961), both in sand culture and in the field. Sanford (W.G. Sanford, personal communication) observed that leaf colour of calcium-deficient plants was abnormal, a grimy grey-green rather than the more normal clean yellow-green or green. The initial growth of calcium-deficient pineapple plants may not be stunted, but as the deficiency becomes more severe, growth depression is very evident.

Calcium deficiency symptoms, as with those of boron, are most likely to be seen initially on the fruit because the demand for both calcium and boron in the growing point is highest at the time of floral differentiation. When Ca deficiency is severe, cells at the growing point fail to divide and other cells tear apart because of weak cell walls, so new leaves may appear to be cut off or tipless, with serrations or scalloping along the margins, and leaves may develop callus, be abnormally thick and have streaks of corky tissue running parallel to their length. With extreme deficiency, the growing point may die, resulting in the growth of side-shoots, which may be initially symptom-free. In some cases, plants fail to produce an inflorescence and continue to grow vegetatively. In this case, the leaves become progressively shorter as they develop. Roots are thicker than normal and, as a result, such plants are more difficult to pull out of the ground than a normal plant. Fruits may be abnormal in size and shape. Symptoms have been

Figure 7.2. Multiple fruit of 'Smooth Cayenne' pineapple resulting from severe calcium deficiency (photo courtesy of W.G. Sanford).

observed only for plants having a concentration of 0.002% or less, fresh-mass basis (0.024%, dry-mass basis), in the basal white tissue of the 'D' leaf. The critical concentration at flower induction is 0.015% fresh mass (0.18%, dry-mass basis) in the basal white tissue, and deficiency symptoms develop when the level is less than 0.004% (Swete Kelly, 1993). In the whole 'D' leaf, leaf Ca should be 0.10% of dry matter at the time of induction (Py et al., 1987).

Magnesium

Magnesium is a component of the chlorophyll molecule, and a deficiency will reduce chlorophyll concentration, photosynthesis and growth. This nutrient is mobile in the plant and the predominant visual symptom of magnesium deficiency is bright yellow older leaves (Plate 18), particularly those leaves or parts of leaves exposed to sunlight. Such leaves will frequently have bands of green that run diagonally across the leaf as a result of being shaded by leaves above them (Py et al, 1987; Swete Kelly, 1993). Sanford (W.G. Sanford, personal communication) notes that the symptoms of Mg deficiency are most pronounced just prior to floral differentiation and all leaves may be yellow during fruit development. The stems of Mg-deficient plants are short and have a small diameter. The root systems tend to be weak, so magnesium-deficient plants are easily pulled from the soil. Fruits are reported to be low in acidity, sugar content and aroma (Py et al., 1987). This symptom probably reflects the plant's reduced capacity to assimilate CO2 via photosynthesis.

At planting time, the optimum level of Mg in soil is 50 p.p.m. and Mg deficiency occurs at levels below 10 p.p.m. (Swete Kelly, 1993). Swete Kelly (1993) states that deficiency symptoms begin to develop when Mg in the basal white tissue of 'D' leaves reaches 0.015% fresh mass (0.18%, dry-mass basis) and symptoms are present when the Mg content in the basal white tissue of 'D'-leaves is 0.009% or less, fresh-mass basis (0.108%, dry-mass basis). The critical concentration in fresh 'D'-leaf basal tissue at floral induction is reported to vary from 0.025% (in low-potassium soils) to 0.027% (in high-potassium soils) (0.30% and 0.32%, respectively, dry basis) (Swete Kelly, 1993). Magnesium in the whole 'D' leaf should be 0.18% of dry matter at the time of induction (Py et al, 1987).

Sulphur

Sulphur deficiency is rare, probably due to the fact that many fertilizers contain sulphates. Deficient plants have bright lemon-yellow leaves that are broader than normal. As contrasted with magnesium deficiency, where chlorosis occurs mainly on older leaves, both young and old leaves of sulphur-deficient vegetative plants are yellow. As the deficiency progresses, later-formed leaves become narrow, plants are stunted and fruit size is reduced (Py et al., 1987). The symptoms described above were associated with a sulphur level of 0.005%, fresh-mass basis (0.06% on a dry-mass basis) in the middle third of 'D' leaves.

Iron

Iron is an immobile nutrient so iron-deficiency symptoms always appear first on young leaves. In Hawaii, a visual index was developed based on the percentage of the leaf area ('B' through 'F' leaves only), if any, that exhibited chlorotic mottled areas characteristic of this deficiency (W.G. Sanford, personal communication), and this index has also been adopted in Australia (Swete Kelly, 1993). Total iron in the middle third of 'D'-leaf green tissue expressed on a fresh-mass basis was also used in Hawaii as an index for determining iron requirements. Where the 'D'-leaf level is 8 p.p.m. or higher in the absence of high levels of soluble manganese, visual iron deficiency is 40% or lower, a level considered adequate for maximum growth. In the presence of soluble soil Mn, the iron content of leaves is not well related to the existence of deficiency symptoms. Also, unlike the situation with other nutrients, pineapple plants can show visual symptoms of iron deficiency with no decrease in yield.

Where soluble manganese is high - a common situation in soils having high man ganese and low pH - the ratio of soluble iron to soluble manganese in the soil and in the whole 'D' leaf is more important than the absolute amounts of either element (Hopkins et al, 1944). Py et al. (1987) report that iron deficiency occurs and visual symptoms are observed where iron in the 'D' leaf is between 60 and 475 p.p.m., dry-mass basis, and the Fe:Mn ratio is less than 0.4. Manganese deficiency occurs and visual symptoms are observed if Mn in the 'D' leaf is between 29 and 78 p.p.m., dry-mass basis, and the Fe:Mn ratio is greater than 10.5. Iron deficiency has been observed in Queensland, Australia, when cold, wet soils prevent the uptake of iron or where roots have been damaged by pests (Swete Kelly, 1993).

Visual symptoms of iron deficiency on pineapple grown in Hawaii were first described by Johnson (1916). The initial symptoms appear as interveinal chlorosis of the younger leaves; leaf veins, which run parallel to the length of the leaf, remain green whereas the areas between the veins are yellow-green or yellow. When the deficiency is mild, the leaves become yellow, with green mottling (Swete Kelly, 1993). As the deficiency becomes more severe, the entire surface of the leaves may be pale yellow (Plates 19 and 20) or creamy white, with considerable red pigmentation at the terminal ends. Such leaves are also soft and leathery, rather than rigid, and have considerable tip dieback. Plants with severe iron deficiency will have fruit that are small, hard and reddish in colour and with cracking between the fruitlets. The crowns will be light yellow or creamy white in colour. In the absence of high soluble manganese levels, severe deficiency symptoms have been associated with 3.0 p.p.m. or less of iron, on a fresh-mass basis (36 p.p.m. on a dry-mass basis), in the middle third of 'D' leaves. As noted above, with high levels of soluble manganese, the ratio of iron to manganese is more critical than the absolute amounts of either element. Iron sulphate sprays, often applied biweekly, are used to correct the deficiency. To be effective, the iron in iron sulphate sprays must be applied in reduced form, and good storage conditions are required to prevent oxidation.

Zinc

Zinc deficiency can occur in soil with a pH of 6.0 or higher, with low organic-matter content (observed in Hawaii in such conditions) or where lime or phosphorus were not well incorporated or were applied in excessive amounts (calcium- or phosphorus-induced zinc deficiency). Zinc deficiency is widespread in Queensland, Australia (Swete Kelly, 1993), especially on previously uncultivated land. The deficiency has also been observed in Hawaiian soils that have low native fertility. When the deficiency is severe, the plant's central cluster of leaves is curved (crook-neck) (Plate 21), especially with younger plants (Swete Kelly, 1993). When the deficiency develops in older plants, the surfaces of the leaves develop yellowish-brown, blister-like (elevated) spots. The centre leaves may on occasion have rips or serrations on their edges. In less severe cases, the blisters occur only on the older leaves and the centre leaves are only slightly curved. Occasionally, the curved leaves will be seen without blisters. At times, zinc-deficient plants, like calcium-deficient plants, have been observed to remain continuously vegetative. Zinc deficiency is distinguished from calcium deficiency by the curved central leaves and the presence of blisters on the leaf surfaces. Zinc concentration in the 'D' leaf is not diagnostic of zinc deficiency. A level of 4 p.p.m., fresh-mass basis, in the stem apex is considered adequate and 3.0 p.p.m. or less, fresh-mass basis (36 p.p.m. on a dry mass basis), in the stem apex will be associated with typical zinc-deficiency symptoms. The deficiency is easily correctable with sprays of zinc sulphate.

Boron

Boron deficiency has not been observed in Hawaiian pineapple fields, but has been observed in Australia, Côte d'Ivoire, Costa Rica, Honduras, Martinique and the Philippines. Boron deficiency in leaves and fruit was induced in sand culture (D.H. Smith, B.H. Krauss and K. Pfenninger (1962) PRI News 10, 95-97; D.H. Smith, B.H. Krauss and K. Pfenninger (1965) PRI News 13,

263-274; unpublished results, Pineapple Research Institute of Hawaii), with the symptoms being first observed on the fruit. Fruitlets of immature fruit showing boron deficiency appear glossy and green in contrast to the scurfy, dull and whitish appearance of a normal fruit at this stage. The glossy appearance is due to the absence of trichomes (multicellular plant hairs). As the fruit develops, small, shallow cracks appear between the fruitlets and within 2 weeks these cracks become corky (see Fig. 9.29). Fruit borne on plants having severe boron deficiency are much smaller than normal fruit, and multiple crowns are also reported (Py et al., 1987). The symptoms of boron deficiency seen on fruit may be similar in some conditions to the symptoms of interfruitlet corking caused by Penicillium funiculosum (see Rohrbach and Johnson, Chapter 9, this volume).

The symptom of boron deficiency on vegetative leaves, if it occurs, is death of the tips of the youngest leaves, sometimes with serrations on the margins. In extreme cases, death of the growing point will occur. In such a plant the central leaves will be stiffer and shorter than normal and lateral buds will eventually develop. The symptoms of boron and calcium deficiency on vegetative plants are similar. As in the case of calcium, the initial symptoms of boron deficiency in the field are most likely to be observed on the fruit rather than on vegetative plants, because the greatest demand for both boron and calcium is at the growing point as it shifts from the production of vegetative structures to reproductive ones. Symptoms of boron deficiency can be expected to occur when boron is 0.2 p.p.m. or less, on a fresh-mass basis (2.4 p.p.m. on a dry-mass basis), in the middle third of 'D' leaves approximately 10 months after planting. Fruit symptoms were associated with a level of 0.4 p.p.m. or less boron in the middle third of the longest crown leaves 4.5 months after floral differentiation. In Australia, boron deficiency is prevented by forcing of flower induction with sprays that contain 0.5% borax. Borax provides a source of B as well as raising the pH of the ethephon solution to about 9.0 to enhance its effectiveness, especially when warm temperatures make induction difficult (Sinclair, 1994).

Manganese

Manganese deficiency is rare and occurs in soils high in calcium with a high pH. Py et al. (1987) report that manganese deficiency symptoms are not specific. Affected leaves are marbled with pale green areas, mainly where vessels are located. Despite the presence of high levels of soluble manganese in many tropical soils, including those in Hawaii, symptoms of manganese toxicity have not been observed. Pineapple growing in acid soils tolerates high levels of both soluble manganese and aluminium where other plants show symptoms of toxicity. In acid, high-manganese soils, high levels of soluble manganese appear to interfere with iron absorption and translocation (Sideris, 1950) or utilization. As noted above, the iron: manganese ratio is more important than the absolute amount of either element.

Copper

The leaves of plants deficient in copper are lighter green than those of normal plants and are distinctly U-shaped in cross-section relative to normal leaves. Tips of leaves curve downward instead of being erect. The deficiency is common in the heavily leached sandy soils of southern Queensland, Australia (Swete Kelly, 1993), and has also been observed in Malaysia on peat soils. The optimum range in the 'D'-leaf basal white tissue is 10-50 p.p.m. on a fresh-mass basis. Copper deficiency is easily corrected with a copper sulphate spray.

Molybdenum

There are no known reports of visual symptoms of molybdenum deficiency on pineapple and also little indication of a pineapple growth response to Mo. Molybdenum is essential for proper functioning of the nitrate reductase enzyme, and it was reported that application of Mo can reduce the nitrate level in fruit juice (Chairidchai, 2000). Much additional work in Queensland, Australia, has failed to demonstrate any change in juice nitrate levels as a result of spraying plants with Mo (Scott, 2000).

Deficiency problems

Deficiencies of the macronutrients N, P, K, Ca and Mg are likely to occur anywhere that pineapple is grown if quantities removed by the crop and lost by leaching are not replaced through fertilization. Deficiencies of S and of the micronutrients Fe, Zn, B, Mn, Cu, Mo and Cl are likely to be localized in specific areas where pineapple is grown. The sulphur requirement of pineapple, which probably is as high as that for P, will be met by S-containing fertilizers if iron, potassium and zinc sulphate are applied to pineapple fields, though this situation could change if the application of these fertilizers is reduced or eliminated. Since the main function of Mo in higher plants is related to nitrate reduction, there is little chance that a Mo deficiency will occur in pineapple in most regions because most N taken up by pineapple is in the form of ammonium or urea, both of which can be absorbed through the leaves. However, Mo deficiency, at least in terms of insufficiency to reduce plant-absorbed nitrate, has been reported in Thailand (Chongpraditnun et al., 2000). Boron and copper deficiency are already found in a few countries and these two nutrients may eventually become limiting in other pineapple-growing regions. Iron deficiency is common in many pineapple growing regions while zinc deficiency seems to be somewhat less widespread.

As long as fertilizers are readily available and inexpensive relative to the value of the crop and the technology is available to apply these fertilizers after the deficiencies appear, deficiencies of most nutrients should not limit the productivity of pineapple where the crop is grown for commercial purposes. This is because most deficiencies are readily correctable by foliar application of soluble sources of nutrients. The pineapple plant is ideally suited for foliar fertilizations and most nutrients are readily absorbed through the leaves or are taken up when solutions containing essential nutrients flow to the leaf axils, where roots commonly exist to absorb them.

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Responses

  • christopher
    Why do pineaples show yellow colouring matter on their leafs?
    2 years ago

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