EFFECT OF NUT STORAGE, NUT SIZE AND LENGTH OF NUT SOAKING IN WATER ON NUT SPROUT IN CASHEW: ANACARDIUM OCCIDENTALE L.

INTRODUCTION

The cashew plant, Anacardium occidentale is a native of Central and South America with its main centre of variation in eastern Brazil. However, cashew is now grown in many parts of the world including Nigeria (Ohler, 1979; FAO, 2001; Udoh, 2005; FAO, 2007).The annual world production of cashew nut - the main commercial product of the cashew plant – is over 1.2 million tonnes, with India topping production, followed by Mozambique and Tanzania (FAO, 2001; Udoh, 2005). Nigeria was a foremost producer, before being overtaken by Tanzania, Cofe D’Ivorie and Guinea Bissau in 2006 (FAO, 2007). Kogi State, Nigeria, is one of the highest producers of cashew in the category of Kwara, Anambra, Oyo, Imo, Edo and Lagos States. It is grown to a lesser extent in Niger, Ondo, Delta, Ogun and Osun States. It is found all the way from the coast to the north but mostly as windbreaks and soil erosion prevention in the northern parts of Nigeria.

In addition to the nuts, cashew nut shell oil is obtained from the nut pericarp; the cashew apple is a valuable source of raw material for the manufacture of both soft and alcoholic drinks and as livestock feed ingredient after the extraction of the juice; the roots and young leaves are used as herbal remedies in the treatment of malaria, while the sap from the bark provides indelible ink and the exudates is useful as adhesive (Udoh, 2005).

Cashew, as a crop plant that is very tolerant of poor soils, low soil moisture content and low rainfall, has proven to be a good cash crop in area where other tree crops produced little or nothing. It is less selective and demanding in terms of soils type and fertility requirements compared with other plantation crops, thereby having wide adaptability (Udoh, 2005). It has great potentials as a foreign exchange earner and source of industrial raw material.

Seed nuts are vital to the propagation of the cashew plant (Udoh, 2005; FAO, 2007). In Nigeria, these are usually obtained from current season harvests, sun dried and stored under ambient temperature before sowing. The germination of viable seed nuts is a product of many variables, but of significant importance is water imbibition, which depends among other factors on seed size (Auckland, 1961; Ibikunle and Komolafe, 1973; Turner, 1956), the level of water available in the seed; this determines the ‘thirst’ for water and lastly the permeability of the seed nut coat.

Cashew nuts possess thick seed coat thus requiring considerable time for water imbibition to prompt nut germination. Slow imbibition of dry intact seed nuts is reported to be the main cause of delayed germination in cashew (Subbaiah, 1982/1983), a problem which is greatest in the larger seeds (Auckland, 1961; Ibikunle and Komolafe, 1973; Turner, 1956). However, early germination can be induced by the following means: cracking the seed nut coat: a delicate operation which must be carried out with care to avoid damage to the embryo; treatment with dilute sulphuric acid (H2SO4); soaking in water for 24 to 36 hours (Auckland, 1961; Ibikunle and Komolafe, 1973; Turner, 1956). Pre-soaking for 1 or 2 days (Ibikunle and Komolafe, 1973; Rao et al., 1957a; Rao et al., 1957b) or the removal of the waxy layer of the pericarp by treating with chloroform or acetone (Subbaiah, 1982/1983), which was observed to promote imbibition and reduce the time taken to germinate and increase the proportions of seed nuts germinating. Light (Rocchetti and Panerai, 1968; Rocchetti and Panerai, 1970; Adams, 1975) and gibberellins (Ayfer and Serr, 1961; Shanmugavelu, 1970; Dahab, et. al., 1975) are also reported to promote germination in cashew seed nuts.

This experiment therefore, addressed the following objectives: (1) Evaluation of length of nut storage on nut viability, (2) Evaluation of nut size on sprouting and seedling vigour, (3) Evaluation of length of nut soaking on nut sprouting.

MATERIALS AND METHODS

Experimental Area:

The study was carried out between February and June, 2009 at the Faculty of Agriculture, Kogi State University (Longitude 7006N: 6043E), Anyigba in the Southern Guinea Savanna ecological zone of Nigeria.

Collection of nuts:

Nuts of current season with no sign of damage, insect pest attack or disease symptoms collected from a single mother tree in the Faculty of Agriculture, Kogi State University, Anyigba, Kogi State, Nigeria were used in the trial.

Soil Collection and Poly Bags Filling

Top soil 5 – 9 cm depth was collected from fallow farm land around Faculty of Agriculture, Kogi State University, Anyigba, Kogi State, Nigeria for the trial. Soils were freed of extraneous materials: plant roots, weed seeds, and pebbles. The soil was then filled into poly bags of size 25 x 15 cm to 2.5 cm from the brim to allow for watering and placed under pavilion shade.

Nut Sowing

A nut was sown at 4 – 5 cm depth with concave end upward into poly bag of size 25 x 15cm placed under pavilion shade and observed daily for emergence of sprout.

Treatment:

Treatments investigated were storage length, nut size and soaking period and their interactions.  

Storage length: Three storage lengths were investigated (0, 2, and 4 weeks after nut gathering). The nuts, packed into jute bags, were stored at ambient temperature, after adequate sun drying, for the stipulated time periods.

Nut Size: Cashew nuts were visually graded according to size into large, medium and small, with nuts size ranging between 8 – 11.9 g/nut for large nuts, while medium nuts ranged between 4 – 7.9g and small nuts between 2 - 3.9 grams per nut.

Nut Soaking: Four soaking periods were investigated: soaking in one litre of borehole water for 12, 24 and 36 hours, in addition to the control.

Experimental Design

The trial a split-split plot design with three replications had storage as main plot factor, while seed size was a sub plot factor and soaking the sub-subplot factor. All treatments were replicated three times.

Data Collection / Days to Germination)

Data were collected on days to sprout emergence, sprouting percentage; as a ratio of number of nuts sown relative to nuts that sprouted, data was also be collected on seedling vigour as a measure of height gained over a given time, plant gilt, number of leaves at the time of the termination of the trial, leave area and number of formed branches.

Data Analysis

Data generated were subjected to analysis of variance using SAS Statistical Package (SAS Institute, 1996) as described for Split-split Plot Design. Treatments means found to be statistically significant (p<0.05) were compared using appropriate comparative tools (Least Significance Difference for main treatment means, or Standard Error of Means for the means of interaction effects).

RESULTS AND DISCUSSION

Effect of Nut Storage on Days to Sprout Emergence:

The least mean-day to sprout emergence was observed when nuts were stored for 2 weeks (26 ± 9.7), the control treatment (no storage), gave a mean-day to nut sprouting of 27 ± 8.2, while storing nuts for 4 weeks recorded 27 ± 3.8 days to sprout emergence. However, the least standard deviation (± 3.8) was recorded when nuts were stored for 4 weeks, thus implying that the treatment gave better convergence of sprout emergence. No significant statistical differences were, however, observed between the storage lengths investigated as they affect mean-day to sprout emergence in cashew plant (Table 1). This observation reported is within the limit of the length of storage (0 - 4 weeks) investigated. It is not unlikely to observe a different out come with longer nut storage.

Effect of Nut Size on Days to Sprout Emergence:

Contrary to the non significant effect of nut storage, on mean-day to sprout emergence, within the limit of the storage length investigated (0 – 4 weeks), nut size significantly (p<0.05) influenced days to sprout emergence, with the least days to sprout emergence being observed in small nuts (26 ± 6.7), while the large nuts were the last to sprout (28 ± 8.1 days). There were however, no significant differences between small and medium sized nut in respect of days to sprout emergence, or between medium nuts and large nuts in respect of the same parameter (Table 1).

Previous observations revealed that slow imbibition of dry intact seeds is the main cause of delayed germination in cashew (Lemaistre, 1959; Nimadzhanova, et. al., 1977; Subbaiah, 1982/1983), with the nut covering structures and epicarp presenting a formidable barrier to embryo growth and germination (Joley, 1960), and the endocarp reducing the rate of imbibition (Crane and Forde, 1974), a problem, which was reported to be greatest in the larger seeds (Turner, 1956; Auckland, 1961; Ibikunle and Komolafe, 1973; Maggs, 1973; Crane and Forde, 1974; Casini and Conticini, 1979). These factors may have been responsible for the observed delayed in sprout emergence with increase in nut size.

Large seed nuts are usually more vigorous than small seed nuts, thus are more desirable to farmers, however, these are likely to sprout last due to the presence of thicker seed nut coat (Casini and Conticini, 1979; Crane and Forde, 1974; Maggs, 1973). To enhance early sprouting in large seed nuts, there may be need to thin down or crack the seed coat (Auckland, 1961; Ibikunle and Komolafe, 1973; Turner, 1956) or to remove the waxy layer of the pericarp by treatment with chloroform or acetone (Subbaiah, 1982/1983), which will further promote imbibition and reduce the time taken to germinate and increase the proportions of seeds germinating. In this way the farmer ensures early sprouting while enjoying the benefits of sowing large seed nuts.

Effect of Nut Soaking on Days to Sprout Emergence:

Soaking nuts in water significantly (p<0.05) reduced days to nut sprout emergence as compared with the control (Table 1). The least days (25 days) to sprout emergence was recorded when nuts were pre-soaked in water for 24 or 36 hours before sowing, while pre-soaking nuts for 12 hours was not significantly different from the control treatment, which recorded 28 days to sprout emergence. In previous research, Amoah (2005), while researching into the germination and early growth of cashew, observed that Cashew seeds soaked in water for 24 hour and sown at 4cm depth gave better germination and growth than cracked seeds or those sown at 8 or 12 cm. Pre-soaking nuts for 24 - 48 hours (Turner, 1956; Auckland, 1961; Kravchenko, 1961; Hartmann, 1967; Joley and Opitz, 1971; Ibikunle and Komolafe, 1973; Crane and Forde, 1974) was reported to promote imbibition and reduce the time taken for seeds to germinate and increase the proportions of seeds germinating. The out come of this research is therefore in line with previous findings as reported above.

Interaction Effects on Days to Nut Sprout in cashew:

Analyzed data revealed significant interactions (p<0.05) between nut storage and nut size (Table 2); nut storage and nut soaking (Table 3); nut size and nut soaking (Table 4) on sprout emergence in cashew plant. The three way interaction was however, not significant (Table 5).

The problem of slow imbibition of dry intact seeds is (Lemaistre, 1959; Nimadzhanova, et. al., 1977) is said to be more pronounced in larger seeds (Casini and Conticini, 1979; Crane and Forde, 1974; Maggs, 1973) thus stressing the correlation between nut size and water inbibition. The thick shells in larger nuts pose greater obstacle to water uptake than in medium or small nuts. This factor must have been responsible for the significant nut size - nut soaking interactions. Inability of large nuts to readily take up water, as a result of thicker seed coat, must have accounted for the observed interactions between nut size and nut soaking on sprout emergence.

CONCLUSION

Trial conducted at the Faculty of Agriculture, Kogi State University, Anyigba, Kogi State, Nigeria in the Southern Guinea Savanna ecological zone investigated sprouting in cashew as affected by storage length, nut size and nut soaking in water. No significant differences were observed between the storage lengths and the control (within the limit of the length of nut storage) as it affects days to sprout emergence. It is however, not unlikely to observe a different out come with longer period of nut storage. Contrary to the non significant effect of nut storage, on days to sprout emergence, nut size significantly (p<0.05) influenced days to sprout emergence with small nuts being the first to emerge, while the large nuts where usually the last to sprout. In addition, soaking nuts in water significantly influenced (p<0.05) days to nut sprouting. Pre-soaking nuts in water for 24 or 36 hours gave the best result. Interaction effects revealed significant interactions between nut storage and nut size; nut storage and nut soaking; nut size and nut soaking as it affect sprouting in cashew.

In conclusion, pre-soaking nuts in water for 24 - 36 hours which was observed to reduce days to sprout emergence is recommended for farmers raising cashew seedlings from seed nuts. To achieve early nut sprout, sowing small nuts is recommended as this gave the least mean days to sprout emergence - there is however the problem of seedling vigour.  

REFERENCES

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FAO (2007). Food and Agriculture Organization, Online Production Statistics Division.

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Table 1: Effect of Length of Nut Storage, Nut Size and Length of Soaking on Mean-Days to Sprout Emergence

Treatment

Parameter Measured

Days to Sprout Emergence

Std. Deviation

Nut Storage

 0 Week

27

8.2

 2 Weeks

26

9.7

 4 Weeks

27

3.8

LSD

3.2

Nut Size

 Small Nut

26b

6.7

 Medium Nut

27ab

11.7

 Large Nut

28a

8.1

LSD

3.2

Nut Soaking

 0

28

8.6

 12hrs

28

8.0

 24hrs

25

5.8

 36hrs

25

12.6

LSD

3.7

CV %

25.6

Treatment means followed by unlike letters are statistically significant at 5% probability level.

Table 2: Length of Nut Storage and Nut Size Interaction Effects on Mean-Days to Sprout Emergence

Treatment

Days to Sprout Emergence

Storage  x Nut_size

Large Nut

Medium Nut

Small Nut

0 Week

28ab

26ab

26ab

2 Weeks

29a

26ab

24b

4 Weeks

26ab

28ab

26ab

SE±

2.8

Treatment means followed by unlike letters are statistically significant at 5% probability level.

Table 3: Storage and Nut Soaking Interaction Effects on Mean-Days to Sprout Emergence

Treatment

Days to Sprout Emergence

Storage  x Nut_soaking

0 hrs

12hrs

24 hrs

36 hrs

0 Week

29ab

30a

25ab

23b

2 Weeks

26ab

26ab

25ab

27ab

4 Weeks

28ab

27ab

27ab

25ab

SE±

3.2

Treatment means followed by unlike letters are statistically significant at 5% probability level.

Table 4: Nut Size and Nut Soaking Interaction Effects on Mean-Days to Sprout Emergence

Treatment

Days to Sprout Emergence

Nut _size x Nut _soaking

0 hrs

12hrs

24 hrs

36 hrs

Large Nut

32a

27abc

24abc

28abc

Medium Nut

26abc

30ab

28abc

22c

Small Nut

26abc

26abc

25bc

25bc

SE±

3.2

Treatment means followed by unlike letters are statistically significant at 5% probability level.

Table 5: Storage, Nut Size and Nut Soaking Interaction Effects on Mean-Days to Sprout Emergence

Treatment

Days to Sprout Emergence

Storage x Nut _size x Nut _soaking

Nut _size

0 hrs

12hrs

24 hrs

36 hrs

0 Week

Large Nut

35

31

23

23

2 Weeks

Medium Nut

25

31

26

21

4 Weeks

Small Nut

27

29

26

24

0 Week

Large Nut

31

25

24

36

2 Weeks

Medium Nut

24

29

27

22

4 Weeks

Small Nut

24

24

24

24

0 Week

Large Nut

29

26

25

24

2 Weeks

Medium Nut

29

31

30

24

4 Weeks

Small Nut

27

26

24

28

SE±

5.6ns

Treatment means followed by unlike letters are statistically significant at 5% probability level.