African Crop Science Journal African Crop Science Society ISSN: 1021-9730 EISSN: 2072-6589 Vol. 4, Num. 2, 1996, pp. 159-166

K. P. BAIYERI

Department of Crop Science, University of Nigeria, Nsukka, Nigeria

(Received 15 July, 1994; accepted 28 October, 1995)

Code Number: CS96053
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Plantain suckers (Musa sp.) raised under four nitrogen rates (0, 100, 200 and 300 kg ha^-1) and three watering intervals (6, 9, 12 days) were subjected to water stress in a glasshouse experiment. Nitrogen rates did not significantly affect growth before water stress. After water stress induction, suckers grown with 300 kg ha^-1 produced more photosynthetically active leaves, larger leaf area and thicker pseudostems. Nitrogen at 200 kg ha^-1 resulted in highest total dry matter accumulation while 100 kg ha^-1 favoured more root development. Frequently watered plants (6-day interval) initially produced more leaves which were not sustained during the water stress, but the 9-day watering intervald higher total number of leaves and taller suckers after water stress. Suckers watered at 12-day intervalid higher leaf nitrogen content and leaf dry matter than other watering regimes. A positive relationship between dry matter production and nitrogen rates after water stress was observed. Suckers raised with 200 kg ha^-1 and watered at 9-day interval were more vigorous and tolerant to water stress. This combination is recommended as a practice for raising plantain suckers in areas where dry seasons are unavoidable after field establishement.

Key Words: Assimilate partitioning, fertilizer effect, growth responses, stress tolerance

Resume

Les rejets de plantain (Musa sp.) eleves sous 4 nivaux d'azote (0, 100, 200 et 300 kgN/ha) et 3 intervalles d'eau (6,9,12 jours) etaient soumis au stress d'eau sous serre experimentale vitree. Les taux d'azote n'ont pas significativement affecte la croissance avant le stress en eau. Apres l'induction du stress d'eau, les rejets plantes avec 300 kg de N/ha produisaient de feuilles plus larges et plus actives photosynthetiquement et des pseudotroncs plus epais. 200 kg de N/ha permettaient l'accumulation de la plus grande quantite de matiere seche alors que 100 kg de N/ha favorisait le developpement des racines. Les intervalles d'eau de 6 jours produisaient au debut plus de feuilles qui n'etaient plus soutenues durant le stress d'eau, mais 9 jours d'intervalles d'eau produisaient le nombre total des feuilles le plus eleve et des rejetons plus grands apres les stress d'eau. Les rejetons arroses tous les 12 jours d'intervalle avaient des feuilles avec le niveau d'et de matiere seche le plus eleve que les autres regimes d'arrosage. Un rapport positif entre la production de matiere seche et le taux d'apres le stress d'eau etait observe. Les rejets eleves avec 200 kg de N/ha et arroses tous les 9 jours d'intervalle etaient plus vigoureux et tolerant au stress d'eau. Cette combinaison etait recommandee comme une pratique de dressage de rejetons de plantain lˆ o les saisons seches sont inevitables apres leur etablissement au champ.

Mots Cles: Repartition d'assimilates, effet d'engrais, reponses ˆ la croissance, tolerance au stress

INTRODUCTION

Water stress inhibits crop growth and restricts crop productivity (Crafts, 1968; Day, 1981; Khanna- Chopra, 1988). Plantain (Musa sp.) is a staple in most humid tropical countries. In West and Central Africa, it is estimated that about 70 million people derive 25% of their food energy requirement from plantain (IITA, 1992). Besides the recent sigatoka disease problem, one of the major hindrances to commercial production of the crop is limited availabiltiy of certified planting material (suckers). An earlier study by Ndubizu and Obiefuna (1982) showed that peeper (a young sucker just merging from the ground), which is an inferior propagating material, was improved to good quality sucker for field planting using polybag nursery technique. Baiyeri and Ndubizu (1994), however, showed that cultural practices (such as false decapitation, total decapitation, earthing-up and mulching) previously used to raise plantain suckers affected their field restablishment and general growth performances.

Several studies ( Butler, 1960; Murray, 1960; Simmonds, 1966; Arunachalam et al., 1976; du Montchel,1987)had shown the importance of nitrogen fertilisation to the growth and yield of banana. Metcalfe and ElkinsÕ (1984) review of effects of fertility on crop water requirements, however, showed that for most grain crops (maize, sorghum, wheat, oats and barley), water requirement was decreased by 20% when optimum fertilisation was applied. Such studies have not been done on plantain suckers. Also, since inferior plantain propagules can be upgraded through polybag nursery, the need to study water requirement in combination with nitrogen fertilizer at this growth stage is important. Obiefuna (1986) established the months of August till December as the best (in terms of yield cycle) for field planting of plantain suckers in southern Nigeria. But by November, evaporative demand normally exceeds rainfall in most agro-ecological zones of southern Nigeria. The resulting water deficit which coincides with the early vegetative period of plantain suckers affects the rate of development which in turn influences the time of fruiting and the overall yield of plantain. This study was, therefore, initated to (1) understand the growth responses of plaintain suckers under different watering regimes to nitrogen levels and water stress; and (2) study the possibility of conferring water stress tolerance on plantain suckers through the cultural practices under which it was raised.

MATERIALS AND METHODS

This study was conducted in a sun-lit glasshouse of the Department of Crop Science, University of Nigeria, Nsukka, between March and August, 1993. Nsukka lies in a derived Savanna belt of Nigeria (lat. 6 degrees 52/N; long. 7 degrees 24/E and 419 m above sea level). During the study period, the average daily maximum glasshouse temperature was in most cases above 30 C.

Twelve kilograms of topsoil of a sandy loam Ultisol (Nsukka series) were weighed into each of 120 polyethylene bags. Details of soil characteristics have been described elsewhere (Mbagwu and Adesipe, 1987). Each bag was adequately perforated to provide for free drainage. The diameter of the polybag was 40 cm. The experimental soil received basal application of P at the rate of 0.17 g bag-1 (26.7 kg ha^-1) as single super phosphate and K at the rate of 2.9 g bag-1 (480 kg ha^-1) as muriate of potash. A systemic insecticide, Furadan 5G, was applied and throughly mixed with the soil at the rate of 1 g bag^-1 (172 kg ha^-1).

The planting material was false-horn (Agbagba) plantain peeper (Musa cv. AAB) (an inferior plantain propagule just emerging from the ground). The peepers were cured under shade before planting. Treatments included nitrogen at 4 levels, namely, 0, 100, 200 and 300 kg Nha^-1 using ammonium sulphate (20% N); three watering intervals, at 6, 9 and 12 days intervals starting from planting. The fertilizer materials were thoroughly mixed with the soil before planting. To avoid leaching of nutrient elements watering was done at 90% field capacity (FC) of the soil type.

The experimental design was a completely randomised design with each polybag placed 0.5 by 0.5 m apart in the glasshouse. Treatments were imposed after two weeks of planting by which time all the peepers had produced at least a leaf. Treatments were replicated ten times.

Twelve weeks after planting, two plants were sampled for growth and dry matter production. Watering was thereafter discontinued for four weeks and re-introduced for another four weeks before two other plants were sampled from each treatment and assessed for growth and dry matter production. Growth parameters measured were plant height, plant girth (at soil level), total number of leaves produced, number of senesced leaves, number of functional leaves and leaf area following Obiefuna and Ndubizu's (1979) method. For dry matter (DM) determination, each sampled plant was separated into roots, corm, pseudostem and leaves which were dried at 79 C to constant weights. Leaves were analysed for nitrogen content using the Kjeldahl method.

Two-way ANOVA was used to test the significance of the treatments (Steel and Torrie, 1980). Significant treatment means were separated using Duncan's New Multiple Range Test (DNMRT).

Table 1

Growth. The effects of nitrogen application rates on growth components of plantain suckers before and after water stress induction are shown in Table 1. Total number of leaves produced, number of functional leaves, senesced leaves, leaf area, plant girth and height were all similar (P <0.05) at all the nitrogen levels. After the water stress, however, higher (200 and 300 kg Nha^-1) nitrogen rates resulted in a significant (P<0.05) increase in the number of functional leaves, leaf area and plant girth, and decreased the leaf senescence.

Table 2 shows the influence of watering interval on growth of the plantain plants. Total number of leaves produced before water stress was highest (8.5) in the frequently (6-day intervals) watered plants. The 9-day watering interval resulted in highest leaf area, plant girth and height. After water stress, however, 9-day watering intervals gave significantly (P<0.05) higher (9.5) total number of leaves. Plants watered at 6 and 9 days had more live leaves (8.2 leaves plant-1) than those watered at 12-day interval. This trend also occurred for leaf area, plant girth and height (Table 2). Nine-day watering interval enhanced sucker growth both before and after the water stress.

Table 2

Nitrogen in the leaf was highest (2.5%) with the highest nitrogen rates before water stress. After the stress, however, N content was inconsistent; the control treatmentha^-1d the highest leaf nitrogen content of 2.1%.

Suckers watered frequently (6-day interval) produced more total DM before and after water stress (Table 4). However, the distribution of DM was such that suckers that were watered at longer intervals (9 and 12 days) partitioned more DM to the leaf, while those watered more frequently partitioned greater DM to the roots both before and after the water stress. The 12-day watering interval enhanced the leaf nitrogen content.

Mean DM distribution and leaf nitrogen content as influenced by time of stress. Table 5 shows a two-sample statistic comparing mean dry matter production and distribution, and nitrogen content of sucker leaves before and after water stress. Leaf nitrogen content was significantly (P< 0.05) depressed by water stress. Also, water stress significantly (P<0.05) depressed DM of the leaves (5.6 g against 9.5 g before stress) and the above ground components of plantain sucker. Total DM, root DM, corm DM, pseudostem DM and below ground component DM were similar before and after water stress imposition.

Table 3

Table 4

Table 5

Table 6

DM distribution was significantly dependent on nitrogen rates only after the suckers were stressed, with leaf (r = 0.53), pseudostem (r = 0.40) and total DM (r = 0.39) increasing as the nitrogen rates increased.

DISCUSSION

A direct opposite effect of nitrogen fertilizer on plantain sucker growth before and after water stress is of interest. The non-significant nitrogen effect before water stress supports the earlier report of Obiefuna (1984) that plantain suckers did not suffer growth retardation when fertilizer application was delayed for three to four months. Also Butler (1960) showed that sucker corm is a nutrient reserves which could support growth for sometime prior to foliage development. However, the significant nitrogen effect after water stress arose probably because the applied nitrogen had earlier enhanced water uptake by the suckers which was utilised later during the stress. Moreover, Metcalfe and Elkins (1984) showed that nitrogen fertilisation enhanced water use efficiency of a crop. Thus, suckers that grew under high nitorgen rates utilised limited moisture during stress more efficiently.

Ndubizu and Okafor (1976) ealier reiterated the importance of moisture availability on leaf production in plantain. This greenhouse experiment confirms the importance of water availability on leaf production in plantain, with the frequently watered suckers producing more leaves before the water stress. The longer watering intervals, however, created a mild water stress tolerance in the suckers before severe stress was induced and thus were able to grow better after the stress. This is because the earlier mild stress induced osmoregulation in the leaves such that the latter did not suffer photosynthetic inhibition even after the stress imposition (Downton, 1983).

Assimilate production and distribution of DM in plaintain suckers seems to be influenced by complex factors unexplainable from this experiment, especially under non-water stress growth conditon. Under water stress conditions, nitrogen fertilizer aided the photosynthetic mechanisms of the suckers (Table 3). Although total dry matter was depressed as a result of water stress irrespective of nitrogen rates and watering intervals, root DM was generally favoured especially at 100 kg Nha^-1. In treatments with a larger fraction of dry matter in the roots, one would expect a better supply of water and nutrients to the shoots because of larger absorbing surface (Turner and Lahav, 1983), this was, however, not clearly evident in this present study.

Suckers watered more frequently (6-day interval) accumulated more total DM both before and after water stress. This frequent watering favoured root DM but depressed DM partitioned to the leaves and pseudostems after water stress. Longer watering interval (12 days) induced water stress torelance into the suckers by enhancing greater leaf nitrogen content and DM partitioned to the leaf after water stress. The implication is that such suckers will be able to re-establish better under field conditions. Also, root and corm DM which were not seriously depressed by water stress will enhance recovery of the suckers from the effect of the stress.

The supply of nutrient to a plant is directly related to water movement into roots, and when such movement ceases because of lowered soil moisture roots are limited to those nutrients within the range of diffusion (Crafts, 1968). Thus, when water stress was imposed on the suckers, nutrient absorbed was poorly translocated to the leaves, the consequence was a significant reduction in leaf nitrogen content after water stress.

In most seedlings, dry matter is partitioned to the leaves, stem and roots. But in plantain suckers, corm is invariably a more important photosynthetic sink than other parts. Corm DM correlated with the total DM with r = 0.93 and 0.96, before and after water stress, respectively. The corm DM accounted for more than 80% of the total sucker DM. The positive relationship between DM production after water stress and nitrogen fertilisation is an indication that nitrogen fertilisation enhances survival of plantain suckers during water stress by extending the leaf longevity.

It is deduced from this study, therefore, that nitrogen fertilizer aided water use efficiency of the suckers especially during water stress. More so, longer watering intervals induced water stress tolerance in the suckers. A combination of 9-day watering interval at 90% FC and 200 kg Nha^-1 is recommended as a cultural practice for raising plantain suckers. Suckers produced using this combination should, however, be tested under local field conditions before final adoption as a standard practice.

REFERENCES

Arunachalan, T.S.B., Ramaswany, N. and Mathukrishnan, C.R. 1976. Studies on the nutrient concentration in leaf tissue and fruit yield with N-level for Cavendish clones. Progressive Horticulture 8:21-26.

Baiyeri, K.P. and Ndubizu, T.O.C. 1994. Variability in growth and field establishment of Falsehorn plantain suckers raised by six cultural methods. MusAfrica 4:1-3

Butler, A.F. 1960. Fertilizer experiment with ÒGross MichelÓ banana. Tropical Agriculture (Trinidad) 37:31-50.

Crafts, A.S. 1968. Water deficit and physiological process. In: Water Deficit and Plant Growth. Vol. 11. Kozlowski, T.T. (Ed.), pp. 85-124. Academic Press, N.Y.

Day, W. 1981. Water stress and crop growth. In: Physiological Processes Limiting Plant Productivity. Johnson, C. B. (Ed.), pp. 119-215. Butterworths, London.

Downton, W.J.S. 1983. Osmotic adjustment during water stress protects the photosynthetic apparatus against photoinhibition.Plant Science Letter 30:137-143.

Du Montcel, H.T. 1987. Plantain Banana. Tropical Agriculturists. CTA Macmillan Publishers, London. 106pp.

International Institute of Tropical Agriculture (IITA). 1992. Plantain and Banana Improvement Program - 1991 Annual Report. IITA, Ibadan. 30pp.

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Mbagwu, J.S.C. and Adesipe, F. A. 1987. Response of three okra (Abelmoschus esculentus L. Moench) cultivars to irrigation at specific growth stages. Scientia Horticulturae 31:35-43.

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Murray, D.B. 1960. The effect of deficiencies of the major nutrients on growth and leaf analysis of the banana. Tropical Agriculture (Trinidad) 37:97-106.

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Ndubizu, T.O.C. and Obiefuna, J.C. 1982. Upgrading inferior plantain propagation material through dry-season nursery.Scientia Horticulturae 18:31-37.

Obiefuna, J.C. 1984. Effect of delayed fertilizer application on the growth and yield of plantains in South Western Nigeria. Fertilizer Research 5:309-313.

Obiefuna, J.C. 1986. The effect of monthly planting on yield, yield patterns and yield decline of plantains (Musa ABB).Scientia Horticulturae 29:47-54.

Obiefuna, J.C. and Ndubizu, T.O.C. 1979. Estimating leaf area of plantain. Scientia Horticulturae 11:31-36.

Simmonds, N.W. 1966. Banana. 2nd Edition. Longmans, London. 512 pp.

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Turner, D.W. and Lahav, E. 1983. The growth of banana plants in relation to temperature. Australian Journal of Plant Physiology 10:43-53.

Copyright 1996 The African Crop Science Society

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