Effects of boron deficiency and toxicity on faba bean (Vicia faba L.)

Eur. J. Agron., 1995, 4(1), 127-134

Effects of boron deficiency and toxicity on faba bean (Vicia faba L.) D. Poulain

1*

and H. Al Mohammad 2

Chaire de Science du Vegetal, Ecole Nationale Superieure Agronomique, 65 rue de Saint Brieuc, 35042 Rennes Cedex, France Laboratoire d'Agronomie, Institut National de la Recherche Agronomique, 65 rue de Saint Brieuc, 35042 Rennes Cedex, France.

1

2

Accepted 14 october 1994

* Abstract

To whom correspondence should be addressed.

Two cultivars and six pure lines of faba bean were grown in a nutrient solution containing six different boron concentrations: 0, 0.05, I, 2, 8 and 32 mg 1~1 B. In deficient plants, stem growth was reduced and the terminal bud occasionally died; the young leaves were wrinkled, thicker and of a dark blue-green colour; irregular chlorosis appeared between the veins before leaf abscission. Flower buds were shed without opening and black spots appeared on the rare developing pods. Faba bean appeared resistant to boron toxicity, symptoms of which began with a yellowing of the mature foliage, followed by a marginal necrosis and finally by the death of the whole plant. Stem elongation was also reduced. Boron accumulation in plant tissues can be held to be a passive mechanism, but the existence of genotypic differences suggested a genetic control. The optimum production was obtained with a whole plant content of 25-100 /lg B g ~ 1 dry matter. Seed set was very susceptible to boron deficiency. The numbers of internodes, of flowers per internode or of seeds per pod were less affected, or not at all. Some genotypes showed narrow optimum boron requirements, while others were rather indifferent to the amount of available boron. Key-words: boron, deficiency symptoms, faba bean, toxicity symptoms, genotypic sensitivity, yield, yield components.

INTRODUCTION Although boron (B) has long been recognized as an essential micronutrient for vascular plants (Agulhon, 1910), its primary role and mode of action remain unknown. It is presumed to be involved in diverse cellular processes such as protein synthesis (Hundt et at., 1970, Krueger et at., 1987) and meristematic activity (Gupta, 1979) and has been found essential not only for general growth, but also for the reproductive cycle. In the latter case, aspects that may be affected by B deficiency are inter alia pollination (Dickinson, 1978), seed and fruit sed and production (Blarney et at., 1979). Given the favourable consequences of B application to many crops, it has become usual practice to provide it by fertilization in addition to the soil supply. For more than fifty years, boron deficiency has been known to be involved in the appearance of the 'heart ISSN 1161·03011951011$ 4.001© Gauthier-Villars - ESAg

rot' disease of beets. More recently, many workers have shown possibilities of yield improvement with boron. Sunflower crop yield, for example, may be reduced by more than 50 per cent as a result of B deficiency (Rerkasem et at., 1988); a 48 per cent increase after B application was reported by Blarney

et at., (1979).

Some plant species have high B requirements (e.g.

Ficus spp., Papaver spp., and many of the Chenopodiaceae). Among these, the Faboideae, and soybean

especially, have not only a high requirement of boron, but also a high tolerance to boron. Reports of yield response of soybeans to B fertilization have been various (Sherrell, 1983). Schon and Blevins (1987), using a stem infusion technique to inject 0.1 mM boric acid (H 3 B0 3 ) solution directly into soybean stems from flowering through physiological maturity, obtained a significant 84.8 per cent increase in the number of pods on branches and a 17.6 per cent

D. Poulain and H. AI Mohammad

128

increase in total seed weight per plant. Foliar applications of boron also produce a significant increase in the number of pods per plant, seeds per plant and seed yield per plant (Schon and Blevins, 1990). With faba bean (Vicia faba L.), grown under field conditions in the presumed absence of B deficiency, a high percentage of flowers (80-90 per cent, according to many authors) fails to develop into mature pods; Poulain and Al Mohammad (1992) demonstrated that boron can improve yield by increasing the number of mature pods per internode, and consequently the number of grains per plant. It also increased the thousand seed weight.

Table 1.

Macronutrients mg 1-1

KH 2P04

Micronutrients mg or m!

HC!, I N, aqueous 176.9 Iron masquolate (30 per cent solution) ZnS04, 7 H 2 0

K2S04 MgS04, 7 H 2 0

CUS04' 5 H2 0 166.4 (NH4)6Mo7024' 4 H2 0 105.9 MnS04 , H2 0

CaC!2' 2 H20

182.3

H 3 B0 3 H 3 B0 3 H 3 B0 3 H 3 B0 3

This study was initiated to determine the effects of B deficiency and excess on growth parameters and yield components of faba bean.

MATERIAL AND METHODS Plant material

Two cultivars (ev. Blandine, ev. Alfred) and six pure lines (lines AEC, VB, 1268, 3891, 3892 and 469) of spring faba bean were sown mid February in pots in a glasshouse. They were differentiated by their tannin and protein contents for another experiment whose results are not reported here. Culture conditions

very deficient: 0 B very deficient: 0.05 B normal: I B normal: 2 B

rl 0.76 0.03 1.00 0.25 0.05 2.00

0.0 0.286 5.72 11.43 45.74 182.97

plots. Each elementary plot comprised one pot, each pot containing 3 plants. There were five randomized blocks of the treatments. Plant measurements

During the flowering period, each internode was identified by its flowering date and the number of flowers it bore; thus, after flowering, the total number of flowers had been assessed.

Plants were grown in plastic containers, filled with 'Perlite': in the conditions of the experiment, this artificial support can be considered to be inert. Supplementary artificial lighting prevented etiolation during the growth period. Adequate mineral nutrition for faba bean was ensured by using a nutrient solution without nitrogen (Table 1). Rhizobium leguminosarum, produced on Petri dishes, was introduced to each pot 21 days after emergence, to permit nodulation and nitrogen fixation.

During their growth, 8 plants from each treatment were sampled at random to determine total B content (ef irifra: boron analysis). At the end of the experiment, the 7 last plants of each treatment were harvested: total height, number of internodes, total dry weight, number of pods and seeds, seed number per pod and thousand seed weight were measured for each plant. The pod set was calculated for each plant as a percentage of total pod number on total flower number.

Treatments comprising six concentrations of boron (0 and 0.05 mg 1-1 corresponding to deficiency, 1 and -) 2 mg 1 corresponding to a normally adequate concentration and 8 and 32 mg 1-1 corresponding to excess) were included with the nutrient solution. Each pot was watered daily with an equal quantity of this solution (depending on water consumption and plant stages), from 30 days after sowing until harvesting, except between days 75 and 96 when B supply was interrupted in order to prevent the consequences of excessive accumulation.

To compare the genotypic performances with regard to boron, the value of a characteristic of a genotype at a given concentration was assessed as a percentage of the highest value obtained for this characteristic and the genotype.

The experiment was of a split-plot design, with B concentrations as main plots and genotypes as sub-

Boron analysis

Sampling was carried out at six stages during plant life: seed, seedling, vegetative period, beginning of flowering, full flowering or beginning of grain filling, and maturity, i.e. 0, 30, 48, 75, 96, 148 days after sowing respectively. Eur. 1. Agron.

Effects of boron deficiency and toxicity on faba bean (Vicia faba L.)

The B content was measured on each sample according to the method described by Maurice and Trocme (1965): i.e. dry ashing at 500°C for 4 hours and quantitation by spectrophotometry at 620 nm after colour development with dianthrimide-l, 1 'dianthraquinoyl-l,l 'amine. Each sample was measured twice.

RESULTS AND DISCUSSION Boron deficiency symptoms Probably because of slight B contamination and also seed reserves, the first symptoms of deficiency were observed only 45 days after sowing in the treatment without boron: they were reduction in the growth and later death of meristematic regions of plants for all genotypes. The youngest leaves were misshapen, wrinkled and subsequently thicker, leathery and of a darkish blue-green colour; irregular chlorosis appeared between the intercostal veins, and finally premature abscission of all leaves was observed. Flower buds were shed without opening and normally no fruit was formed. On the small developing pods, black spots appeared on the sides when the suture line of the carpel darkened. The apex of the shoot became blackened and died. General blackening started at the top and progressed slowly down the stem. The whole plant became stunted. Such symptoms have been described for broad bean: terminal bud blackening, dark green colour of leathery leaves (Dennis, 1937), growth stunted, leaves near growing point restricted and chlorotic, growing point killed and lateral shoots breaking near the base of plant (Wallace, 1961); however, the influence on flowering and pod formation does not appear to have been reported.

129

growth. General symptoms shown by the mature foliage (older leaves) were yellowing and subsequent death of the marginal tissue, first at the tips of the leaves, and, as more of the margin was affected, towards the mid-vein or leaf base: boron being translocated mainly through the xylem (Raven, 1980), toxicity combined with effects of temperature and increased transpiration results in rapid accumulation in the mature leaves. Pod and grain formation were only affected at the highest concentration (32 mg 1-1), which appeared to be a severely toxic level, as evidenced by spots and deformation on them. Boron accumulation There was a significant difference in B concentration measured in the whole plant between each level in nutrient solution. Regression of the rate of B accumulation in plant tissues on B concentration in the nutrient solution was highly significant: during the first period of B supply, between days 30 and 48, B accumulation, expressed in ~g per g of dry matter per day, was 0.59 times the B level of the nutrient solution, expressed in mg 1-1 (Figure 1). So the higher the B content of the nutrient medium, the higher that of the plant tissues.

20

y = 0.016 + O.594x R2

= 0.993

Boron toxicity symptoms o*-~~~-.----~~~~~~-.--~~~

Apart from similar symptoms reported on soybean by Oertli and Roth (1969), no detailed observation has been made on morphological aspects of B toxicity in faba bean. In our experiment, these symptoms of toxicity were evident before reduction in plant growth at the highest concentration (32 mg I-I B) was observed. All the plants of all genotypes grown at this concentration developed leaf chlorosis and/or necrosis within 40 days after sowing. The severity of the leaf injury was directly related both to B concentration and genotype sensitivity. The main effect of B toxicity on faba beans with every genotype seemed to be a reduction of vegetative Vol. 4. n" J - 1995

o

10

20

30

40

B content in nutrient solution (mg.l- 1)

Figure 1. Influence of B concentration in the nutrient solution on daily B accumulation in plant tissues (calculated over the period between days 30-48).

However there was evidence of genetic variation as all the genotypes did not show the same accumulation dynamics, particularly at high B levels (Figure 2) : for example, at 8 mg 1-1, B concentration in cv. Alfred, cv. Blandine, line UB, line 469, and in line 3891 was approximately half that in line 1268 or in line 3892.

D. Poulain and H. Al Mohammad

130

60 per cent of the maximum flower number (Table 2). Pod set was the most sensitive characteristic, either in the case of B deficiency (14 per cent of the maximum value with 0 mg 1-1) or in the case of excess (34 per cent with 32 mg 1-1).

0>

co

0

0,05

M

Genotypes

B contcnt in nutrient solution (mg.l- 1)

Figure 2_ Influence of B concentration in the nutrient solution on the B accumulation by the different genotypes.

At 32 mg 1-1, only cv. Alfred, line UB and especially line 3891 had a lower concentration in comparison with the others. Similar genotypic differences have been described for tomato by Brown et al. (1972). Bradford (1966) reported tissue analyses useful for indicating B status in a large number of species. For faba bean, it seems that the boron content of whole plants showing deficiency symptoms is under -1 25 Ilg Bg of dry matter and that of whole plants showing toxicity symptoms is over 100 Ilg Bg -1 of dry matter. Our results do not allow us to assess whether these critical levels are different at various developmental stages. Growth, development and yield components

At harvest, plant height, number of internodes and total dry weight were greatest at B concentrations of -1 1, 2 or 8 mg 1 (Table 2). Plant form reduction was always slightly more severe in deficient plants (0 or 0.05 mg 1-1) than in those receiving the highest B concentration (32 mg 1-1). The number of internodes was the least sensitive to B concentration in the nutrient solution. In contrast, total dry weight was most sensitive, with a reduction of at least 50 per cent in the case of deficiency as well as in the case of excess. For almost all the variables related to flowering and the pod setting period, maxima were obtained with a B supply between 1 and 8 mg 1-1. The mean flower number per internode did not depend on the B level: even in case of deficiency, it was still 70 per cent of the maximum. Thus flower number per plant was not much affected: a plant grown with 0 mg 1-1 had

Yield and yield components values (grain number per plant and thousand grain weight), were statistically identical at 1, 2 and 8 mg 1-1, except for grain number which was least at 8 mg 1-1. For each characteristic studied, toxicity (32 mg 1-1) reduced the yield less than deficiency. In a situation of deficiency or excess, the thousand grain weight was always modified less than was grain number. The grain number per pod was appreciably reduced only at 0 mg 1-1 (53 per cent of the maximum) ; the number of grains per plant depended chiefly on the number of pods per plant (Table 2). These results agree in part with those reported by Weaner et al. (1985) who observed yield increases in Phaseolus vulgaris after foliar application of boron. These authors attributed this to increased pod retention due to the role of boron in pollen tube growth. Mo1gaard and Hardman (1980) also reported increases in pod number of fenugreek (Trigonella foenumgraecum), a legume with a high B requirement, with increases of B concentration in culture solution, and subsequent decreases of the pod number as B levels became toxic. Schon and Blevins (1990) reported that boron increased the number of branches and pods per branch in soybeans. In conclusion, during the yield formation period, pod set was the first to be affected by the B level, and, as a consequence, grain number; and secondly, grain filling, and therefore thousand grain weight, were also affected. Other components were less severely affected (number of grains per pod) and some remained almost unchanged (number of internodes and mean number of flowers per internode). These results confirm the importance of boron for pollination, fruit setting and fruit development (Dickinson, 1978). Variation among genotypes in boron sensitivity

The characteristics of growth and development being very different between the genotypes, the measured absolute values have been assessed as a percentage of the maximum recorded for each genotype, in order to permit the comparison of B effects. However, such comparisons of relative differences may be misleading for genetic characters at low rates of boron application; these are likely to be less affected by deficiency on a percentage basis. The most extreme values, recorded at deficiency ( 0 mg C I) as well as at excess (32 mg 1-1) levels, differed among genotypes (Table 3). Severe responses occured in some cases: with line 3891, for example, Eur. J. Agron.

131

Effects of boron deficiency and toxicity on faba bean (View faba L.)

Table 2. Influence of boron concentration in the nutrient solution on plant form, fruit-setting characters, yield and yield components (mean of all genotypes), Within columns, means followed by the same letter are not significantly different (Newman-Keuls test, p = 0.05). Standard errors are in italics.

B. Cone. (mg I-I)

Height (em)

0

117.7 e 18.5 119.0 c 11.9 183.3 a 22.3 185.6 a 24.6 178.1 a 22.2 141.7 b 37.0

0.05

2

8

32

Number of internodes

30.8 c 3.9 30.9 e 3.0 38.4 a 3.9 37.4 a 4.5 37.8 a 4.4 34.0 b 7.9

Dry weight (g) 7.90 b 2.04 8.29 b 1.31 18.56 a 4.55 18.17 a 4.87 17.84 a 5.95 9.05 b 4.06

Flowers per plant

Pods per plant

Abortion rate

Seeds per pod

Grain number per plant

73.0 d 41.7 90.1 e 31.8 124.4 a 39.0 113.9 ab 44.8 124.0 a 45.9 105.9 b 54.7

1.1 e 0.9 3. 1 b 1.7 9.8 a 2.3 10.1 a 2.4 9.2 a 2.5 3.9 b 2. 1

98.6 e 1.0 95.5 b 5.3 91.4 a 3.7 90.1 a 4.3 91.7 a 3.3 96.5 b 1.8

1.08 b 0.61 1.67 ab 0.98 1.89 ab 0.35 2.02 a 0.52 1.91 ab 0.38 1.59 ab 0.80

1.3 e 1.0 4.2 d 2.3 18.1 ab 3.8 19.8 a 4.5 17.4 b 5.0 6.8 e 3.6

where B absence led to a zero pod set, or with line 469, where B excess prevented flower formation. In the other cases, the influence of boron varied according to genotype: when boron was lacking, genotypic variability was important for number of flowers per internode, pod set (Figure 3) and therefore pod and grain number per plant (Figure 4), grain weight and yield. The other characters for the most sensitive genotypes were about half the value recorded - 1 on the less affected ones; for example, at 0 mg I the total dry weight of line 3892 was only 26 per cent of the maximum, while it reached 57 per cent in cv. Alfred. When boron was in excess, the greatest differences were obtained for plant height (Figure 5), total dry weight, grain number per plant and yield (Figure 6). As above, the expression of the other characters for the most susceptible genotypes was only about half the value recorded on the less affected - J ones; for example, at 32 mg I , the number of internodes of line 469 was only 48 per cent of the maximum while it reached 96 per cent for line UB. It is interesting to note that the pod set of some genotypes revealed a differing or even opposite behaviour, with regard to the other studied characteristics: although line 1268 appeared as one of the less sensitive genotypes to deficiency as well as to excess, its pod set was one of the most affected in both cases. On the other hand, line AEC, very sensitive to B deficiency, showed in this case one of the best pod sets of all genotypes compared (Figure 3). Taking into account all characteristics studied, some genotypes appeared slightly susceptible to deficiency Vol. 4 . nO 1 - 1995

1000 grain weight (g)

Yield per plant (g)

82.1 e

0.29 e 0.30 1.30 be 0.54 8.19 a 1.78 8.20 a 1.89 7.32 a 2.38 2.32 b 1.26

239.9 461.6 419.5 449.4 290.9

85.5 b 92.7 a 89.8 a 67.0 a 101.7 b 134.4

o

Genotypes

B content in nutrient solution (mg.!-l)

Figure 3. Influence of B concentratioll in the lIutrient solution the pod set of the different genotypes.

011

(for instance cv. Alfred, cv. Blandine, and to some extent, line UB and line 1268), while other genotypes were markedly affected (line 3891, line 3892 and line 469). In the case of excess, line AEC and line UB were considerably less sensitive than line 3891, line 3892 and especially line 469. It was thus possible to identify genotypes (line 469 or line 3891) which had a narrow range of B requirements for their best performance (they were as much affected by deficiency as by excess), and comparatively insensitive ones whose characteristics reacted

D. Poulain and H. Al Mohammad

132

Table 3. Sensitivity of the given characters to boron supply for the genotypes studied (values are expressed as percentages of the maximum obtained with an optimal boron supply).

Boron Excess

Boron Deficiency Characters

56

Number of internodes

69

Height

54

46

26 Total dry weight

Flowerslinternode

29

26 43

Line 3892 Line 3891

Line 3892 Line 3891

Line 3892 Line VB

Line 3891 Line AEC

91 90

74 72 71 57 49

Flowers per plant

35

Line AEC Line 3891 and Line 3892

cv. Blandine Line 1268

Line 1268 Alfred CV. Blandine CV.

43

Alfred Line 1268 cv. Blandine

86

CV.

79

74 34

Very susceptible genotypes

Least susceptible genotypes

Very susceptible genotypes

76 71

CV.

Alfred cv. Blandine Line 1268

cv. Alfred and Line 1268 cv. Blandine

48

36

Line 469

Least susceptible genotypes

96 95 94

Line VB cv. Blandine Line AEC

65

Line 469 Line 3891

94 85

Line VB cv. Alfred

8 22

Line 469 Line 3891

64 62

cv. Blandine Line 1268 Line AEC

58

o 63

79 80

Line 469 Line 3891

100

Line 3892 and Line 1268

cv. Alfred Line VB and Line AEC

96

Line 1268 Line 3892 and Line 3891

92

*

o Pod sct

Pods per plant

6

8

2 6

Line 3891 Line 3892 Line 1268 and Line 469

32 29

17 15

Line VB cv. Alfred and cv. Blandine

Line AEC Line VB

96

#

67

Line 3892 cv. Alfred Line 1268

Line 3892 Line 469

12

Line 3892 Line 469

41

Seeds per plant

43

2 3

75

8

#

o Thousand seed weight

9

2

Yield

3

Line 469 and Line 3892 Line AEC # Line AEC Line 1268

30

34

cv. Blandine Line 1268

*

#

Seeds per pod

Line VB Line AEC

cv. Alfred cv. Blandine and Line VB

57 48 44

28 29

cv. Blandine Line 3891

55

41

Line 3891 Line 3892

100

55

21

22

Line 3891 Line 3892

44

Line AEC cv. Alfred Line VB

Line AEC Line 1268

96

Line 1268 and cv. Blandine Line VB

53 52

Line AEC Line 1268

80

* 44

55 30 28

cv. Alfred Line VB cv. Blandine

55

8 6

cv. Alfred cv. Blandine

15 16

Line 3891 Line 1268

*

72 71

Line VB cv. Blandine Line 3892 cv. Alfred

Line 3892 Line 3891

43 37

Line AEC Line VB

78

#, ., ¢ #: in line 3891 this character had a zero value or was impossible to measure because of the lack of fertilization; in line 469 this character had a zero value or was impossible to measure because of the too small size of the seeds;
Bur. J. Agron.

Effects of boron deficiency and toxicity on faba bean (Vida faba L.)

133

0 5

:§ C eo

ceo "5. ......

.'"

"5.

... .D '"

Co

0

Co

'C

'a::

E

;;;

'"

c c .;

.

" ~O

0,05

(J)

1

co

B contcnt in nutrient solution (mg.I· 1)

Genotypes

(J)


'" ....

Figure 4. Influence of B concentration in the nutrient solution on the number of grains per plant of the different genotypes.

30

Genotypes

0,05

1

B contcnt in nutrient solution (mg.I- 1)

Figure 6. Influence of B concentration in the nutrient solution on the yield per plant of the different genotypes.

deficiency is also controlled by a single recessive gene (Wall and Andrus, 1962) in tomato cultivars. This large genotypic variability in sensitivity to boron in faba bean, as in other species, may explain the relative imprecision of Bradford's (1966) classification of cultivated species sensitivity to boron.

o 0,05

Genotypes

1

B content in nutrient solution (mg.I- 1)

Figure S_ Influence of B concentration in the nutrient solution on the height of the different genotypes.

little to the vanatlOn in B supply: cv. Blandine, cv. Alfred, line 1268 and line UB. Eaton (1935) reported that, for different crop species, some genotypes are probably found growing on particular soils or areas because of the narrow range of B concentration to which they are adapted. Scott (1941) assessed 44 cultivars of grapes on the same soil and found 14 cultivars severely B deficient, 19 cultivars moderately deficient, and 11 cultivars nondeficient. A range of 0 to 76 per cent roots with black rot was obtained by Kelly and Gabelman (1960) among a collection of 67 cu ltivars of red beet. Pope and Munger (1953) established that a single gene controls B utilization in celery; susceptibility to B Vol. 4. nO 1 - 1995

CONCLUSION B accumulation in plant tissue increased with the B concentration in the substrate, but differences in the mode of accumulation or in the maximum content suggested the existence of genetic variation. A concentration between 25 and 100 I-lg B g- 1 of dry matter in the whole plant was adequate for obtaining the maximum yield. This range, probably too wide to be of practical relevance, needs to be made more precise and to take account of plant age or field conditions. Furthermore, there may be critical stages with different requirements. Nevertheless, in the conditions of the present investigation, boron increased the yield components and especially pod set, but the various characteristics of all genotypes were more severely reduced by deficiency than by excess. Marked differences existed between susceptible and tolerant genotypes: some of them, s uch as line 469 or line 3891, were very susceptible to both effects of excess and deficiency, when others were affected either by excess or by deficiency. On the contrary, Blandine, Alfred, line 1268 and line UB were comparatively indifferent to B supply. It appears likely that the yield of faba bean could be increased or stabilized either by complementary

134

supplies when boron soil supply is lacking, or by the use of genotypes tolerant of deficiency, if the costs of boron application preclude chemical treatment.

ACKNOWLEDGEMENTS The authors are grateful to Dr J. Le Guen, Plant Breeding Station, Rennes, France, for providing seeds of lines 469, 3891 and 3892 and to Dr. G. Duc, Plant Breeding Station, Dijon, France, for lines 1268, VB and AEC.

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D. Poulain and H. Al Mohammad

Kelly J. F. and Gabelman W H. (1960). Variability in the tolerance of varieties and strains of red beets (Beta vulgaris L.) to boron deficiency. Proc. am. Soc. hortic. Sci., 76, 409-415. Krueger U. R., Lovatt J. C. and Albert L. S. (1987). Metabolic requirements of Cucurbita pepo for boron. Plant. Physiol., 83, 254-258. Maurice J. and Trocme S. (1965). Observations sur Ie bore dans Ie sol et dans les plantes. Ann. agron., 16, 3, 287-299. Molgaard P. and Hardman R. (1980). Boron requirement and deficiency symptoms of fenugreek (Trigonella foenumgraecum) as shown in a water culture experiment with inoculation of Rhizobium. J. agric. Sci., 94, 455-460 Oertli J. J. and Roth J. A. (1969). Boron nutrition of sugar beets, cotton and soybean. Agron. J., 61, 191-195. Pope D. T. and Munger H. H. (1953). The inheritance of susceptibility to boron deficiency in celery. Proc. am. Soc. hortic. Sci., 61,481-486. Poulain D. and Al Mohammad H. (1992). Studies of some effects of boron supply on field bean. Second International Food Legume Research Conference. Abstracts. 12-16 April 1992. Cairo, Egypt. 47. Raven J. A. (1980). Short and long distance transport of boric acid in plants. New Phytol., 84, 231-249. Rerkasem B., Netsangtip R, Bell R. W., Loneragan J. F. and Hiranburana N. (1988). Comparative species responses to boron on a typic tropaqualf in Northern Thailand. Plant Soil, 106, 15-21. Schon M. K. and Blevins D. G. (1987). Boron stem infusions stimulate soybean yield by increasing pods on lateral branchs. Plant Physiol., 84, 969-971. Schon M. K. and Blevins D. G. (1990). Foliar boron applications increase the final number of branchs and pods on branchs of field grown soybeans. Plant Physiol., 92,602-607. Scott L. E. (1941). An instance of boron deficiency in the grape under field conditions. Proc. am. Soc. hortic. Sci., 38, 375378. Sherrell C. G. (1983). Effect of boron application on seed production of New Zealand herbage legumes. N. Z. J. expo Agric., 11, 113-117. Wall J. and Andrus C. R (1962). The inheritance and physiology of boron in the tomato. Am. J. Bot., 49, 481-486. Wallace T. (1961). The diagnosis of mineral deficiencies in plants. London: H.M.S.O. 3rd Ed. Weaner M. L., Timm H., Ng H., Burke D. W, Silbernagel M. J. and Foster K. (1985). Pod retention and seed yield of beans in response to chemical foliar applications. Hortscience, 20, 3, 429-431.

Eur. 1. Agron.