Phosphorus mobilisation to uneconomic tissues and
effects of bunch trimming regimes in banana
S. Kurien
*, B.K. Anil, P.K. Rajeevan, V. Bharathan, S. Krishnan
College of Horticulture, Kerala Agricultural University, Vellanikkara, Trichur, Kerala 680 654, India
Accepted 30 March 1999
Abstract
The movement and mobilisation of phosphorus in various tissues of banana was studied using
32P. The isotope was given by pseudostem injection and activity measured in various tissues. It was
inferred that the male inflorescence, rhizome, fruit and fruit peduncle are the major nutrient sinks. The activity pattern in different hands showed that the highest activity was in the fourth followed by the third, second and fifth (terminal) and least in the first hand (first to emerge) in a five hand system. Another experiment conducted on various intensities of bunch trimming in a eight hand system revealed that trimming of three terminal hands improved yield and finger characters like length, girth and weight. The trimmed hands could be used as a vegetable and the retained hands for yielding quality fruits. Thus the same bunch serves the dual purpose of vegetable and fruit. The study underlines the imperative need for removing the male bud, fruit peduncle and undeveloped hands.#2000 Elsevier Science B.V. All rights reserved.
Keywords: Bunch; Finger; Radiotracer technique; Musa; Maturity; Counts per minute; Liquid scintillation counter
1. Introduction
The wide gap between production potential and realised productivity is reduced by efficient crop management techniques. Normally, these focus on productivity linked plant characters and very rarely, directly on the management of economic parts such as bunch characters in banana. In banana, this may be more important
* Corresponding author. Fax: +91-487370019.
E-mail address:[email protected] (S. Kurien)
as simple practices such as bagging or bunch covering with trash have been found to affect yield both qualitatively and quantitatively (Trupin, 1959; Perumal and Adam, 1968; Walker, 1975; Israeli et al., 1980; Daniells et al., 1987).
Consumer preferences vary from place to place. However, finger characters such as grade, colour and freedom from post harvest diseases form the priority characters that govern the preference. Hence, any treatment that can improve finger characteristics may have a say not only on improving yield but also on consumer preference and thereby a pronounced effect on net returns.
Finger characters progressively decline from the upper hand to the lower hand rendering the last hands unattractive and less acceptable. Walker (1975) and Stevenson (1976) have reported that dehanding can improve yield and stressed the necessity of pruning. Hence, a study was undertaken to analyse the extent to which the different tissues act as competing nutrient sinks to the fruit, the extent to which the lower hands compete with upper hands for nutrients and the influence of bunch trimming regimes on yield and quality of finger in the cultivar Mysore which is the most important and widely cultivated clone of Southern India.
2. Materials and methods
The study was undertaken in the Department of Pomology attached to the College of Horticulture in the main campus of Kerala Agricultural University during 1995±1996. This study used the banana cv. Mysore synonym Palayankodan which belongs to the `AAB genomic group' the most important and widely cultivated clone of Southern India and which finds a place of prominence in the homestead gardens of the State of Kerala.
The orchard is situated at 12.328N latitude and 74.28E longitude at an altitude of 22.52 m above MSL. The area enjoys a warm humid tropical climate. The soil belongs to the great group Eutroorthox, order ± Oxisol, Vellanikkara series with a pH of 5.3, organic carbon content of 0.47%, CEC of 10.4 C mol kgÿ1 and pore space of 42.83%. Two different experiments were undertaken.
2.1. Experiment I
The plants were spaced at 22 m and planted in blocks of nine plants each with the central plant forming the experimental unit. Though a large number of identical blocks were maintained, the study was finally restricted to four blocks to have uniformity for flowering dates, number of hands and other biometric characters.
32P procured from Bhaba Atomic Research Station (BARC), Bombay was
pre-standardised (Kurien et al., 1996). One millicurie of 32P was injected in each plant in the afternoon (1.00±1.30 pm) using a micropipette into pre-bored holes and the holes were covered with tape after application. The isotope was given at the early fruit development stage of plant (three weeks after complete emergence of the bunch). Samples from different tissues namely corm, pseudostem, leaves, peduncle, fruit and male inflorescence were collected on 25 and 35 days after application. The samples were dried, digested and activity measured in a liquid scintillation counter (model Pharmacia Wallac 1409). The counts were corrected for background radiation, checked for counter efficiency and reduced to a common zero hour (coinciding with the time at which the total dose was standardised upon supply of isotope by BARC, Bombay) and finally expressed as counts per minute of dry matter of each part (cpm/g).
The percentage activity in a hand/row was calculated using the formula
Activity in hand=row cpm=g
Total activity in all hands=rows100:
2.2. Experiment II
Another separate experiment was laid out to study the effect of bunch trimming. Uniform plants having eight hands were selected for the purpose. The treatments comprised of different regimes of bunch trimming, viz. pruning last terminal hand (T1), pruning last two terminals (T2), pruning last three terminal hands (T3), pruning peduncle beyond region of fruits and male bud (T4), pruning male bud alone (T5) and control (no pruning). The experiment was replicated eight times and the design was a completely randomised design.
The finger characters, namely length, girth and finger weight, were measured taking the characters of the `D' finger, i.e. middle finger in top row of the second hand (Gottreich et al., 1964).
The data on activity were appropriately transformed and analysed in a completely randomised design using the analysis of variance technique. In the case of yield, the analyses of co-variance was applied taking the number of fingers as a co-variate (Panse and Sukhatme, 1978).
3. Results
3.1. Experiment I
The results of the mobilisation of 32P in various tissues presented in Table 1
than the second best tissue namely the corm and was more than 13 times more than that mobilised by the fruit. The gradation observed between tissues was as follows: Male inflorescence>corm>fruit>fruit peduncle>leaf>pseudostem. The bunch stalk position i.e. the fruit peduncle beyond which the fruits are attached also contained an appreciable quantity of activity.
The activity pattern in different hands based on the recovery of activity is presented in Table 2. Maximum activity was observed in the fourth hand followed by the third, second, last hand (terminal hand) and the least in the first emerged hand. Though not statistically significant, the data revealed an important trend. The distinct dominance of mobilisation of more32P in the outer row over
Table 1
Recovery of radioactivity (cpm/g of dry matter) in various tissues of banana (cv. Mysore) by pseudostem injection technique 32P
Tissue Sampling
First Second
Corm 16254.34a(3.647) 14509.63ab(3.34) Fruit peduncle 1886.22ab(2.624) 1400.02ab(1.844) Pseudostem 336.32b(1.658) 284.26b(1.153)
Leaf 1000.48ab(2.788) 344.84b(1.410) Fruit 9386.17ab(2.825) 7649.49ab(2.646)
O inflorescence 123936.90a(2.624) 104634.2a(1.844)
Ftest * *
SEM (23 d.f.) 4.988 (0.279) 5.866 (0.381)
* P0.05.
Table 2
Recovery of radioactivity (cpm/g of dry matter) and percentage activity in different hands in a bunch
Hands Rows Percent activity
Outer Inner Outer Inner
First hand 256516.83 (5.2) 100062.95 (4.94) 9.74 3.80 Second 308970.52 (5.35) 247181.07 (5.27) 11.73 9.38 Third 301483.00 (4.93) 261055.52 (5.36) 11.44 9.91 Fourth 282077.09 (5.39) 357634.81 (5.37) 10.71 13.58 Fifth 251781.91 (5.35) 267326.45 (5.37) 9.56 10.15 Mean 280166.03 246652.16
Ftest NS NS
the inner row was seen and was very explicit in the first hand. This dominance gradually decreased in the second and third hand and in the fourth and fifth hand, the inner row accounted for more activity (Fig. 1).
3.2. Experiment II
The data on the effect of various trimming treatments is presented in Table 3. The different regimes of bunch trimming except in the case of male bud removal reduced the time taken to harvest. On the contrary, the days taken to ripening were more in all trimming treatments except in the above treatment and control. In both cases the results were not significant.
In the case of bunch weight, all the trimming treatments increased the yield compared to the control. Trimming three hands followed by trimming of male bud and peduncle were at par and significantly superior over all other treatments. The same trend was observed in the case of `D' hand weight and `D' finger weight.
The finger characters viz. the length and grade were also superior in case of three hand removal and male bud and peduncle removal. The bunch weight and `D' hand weight superiority in the above treatments are actually a reflection of the finger characters.
4. Discussion
The results of the study revealed that a large proportion of the nutrients are diverted to the male inflorescence and the bunch stalk (rachis) beyond the region of the last emerged hand. The fruits only rank third in the mobilisation of nutrients and this shows that other tissues act as competing sinks thus denying the fruits the chance for development to their full potential. Cannel (1985) suggests an order of priority between sinks where developing seeds followed by fruit tissues appear to have priority for assimilates with roots and storage tissues among the last. Banana being parthenocarpic lacks seeds but contrary to Cannel's findings the present study reveals the competing efficiency of the male bud. The favourable effect on bunch weight of trimming the male bud after bunch emergence could be interpreted from three different angles. Firstly as the utilisation of energy, otherwise lost for opening of flowers for finger development (Simmonds, 1959; Sanpaio and Simao, 1970; Walker, 1973; Meyer, 1975; Jaramillo, 1982; Amma et al., 1986). Secondly, it supports the findings of Daniells et al. (1994) who opined that the dry weight analysis indicated that the male bud represents a competing photosynthetic sink and thirdly, the sink activity of the male bud is high though its size is small (Walker and Ho, 1977). Organs such as the corm, the pseudostem and leaf are required for structural support and to perform complementary functions related to bunch development, whereas the male bud and the unproductive long bunch stalk after the full emergence lack any specific role and instead only compete with the developing fingers.
Similarly, the distribution pattern in the hands revealed that the younger hands mobilise more activity. Identical studies in this line are not available but other
Table 3
Effect of bunch trimming on yield, days to harvest and finger characters Hand system Finger characters SEm (35 d.f.) 0.1456 0.663 0.0412 0.224 0.4763
***
work done on banana, but in clone `Nendran' belonging to the same genomic group, showed that in the first and second week, growth was more focussed on peel development and from third to fifth week the pulp region is seen as an active cell division area (Kurien et al., unpublished). The mobilisation of more nutrients by the younger hands may be caused by similar changes.
Removal of the terminal hands improved the yield and also the grade of fruits. Similar results have been obtained by removal of the false hand and one or two of the smallest apical hands by Trupin (1959), Perumal and Adam (1968) and Walker (1973). However, in the works of Hasselbach and Idoe (1973) and Stevenson (1976) in Congo bananas and Amma et al. (1986) in cv. Palayankodan, dehanding did not increase the average bunch weight but gave better sized finger. In the present study both yield and quality of fingers were better because the small developing fruits of the three terminal hands were observed to act as more efficient sinks drawing more nutrients. These nutrients should have been diverted to the remaining hands avoiding unnecessary inter-finger competition and thereby improving the grade of the retained hands.
The immature hands of cv. Palayankodan are extensively used as a cooked vegetable in South India. The hands that are removed by trimming can also be used as a cooked vegetable. Thus the same bunch serves the dual purpose of vegetable and fruit.
Finally, it may be concluded that the male inflorescence and the bunch stalk beyond the region of the hand after complete emergence of the hands act as competing sink and should necessarily be removed. The terminal hands particularly those containing undeveloped and under-developed fingers should also be removed or else they will compete with normal hands and impair their full development.
Acknowledgements
The authors express their thanks to the Director of Research, Kerala Agricultural University.
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