Flowering performance of Polianthes tuberosa Linn. cv. ëcalcutta Doubleí as influenced by thermal regime

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1 , Vol. 6(4), 2007, pp Flowering performance of Polianthes tuberosa Linn. cv. ëcalcutta Doubleí as influenced by thermal regime Introduction Tuberose (Polianthes tuberosa Linn.) cv. Calcutta Double, commonly grown for the last two decades, is an excellent and popular cut flower with huge potential for commercial cultivation in the growing floriculture industry of West Bengal. This cultivar shows marked variation in flowering, opening of florets and spike yield in response to temperature 1. So an understanding Arpita Khan 1, Abhijit Saha 2 and P Pal 1 * 1 Department of Floriculture and Landscaping, Faculty of Horticulture 2 Department of Agricultural Meteorology, Faculty of Agriculture Bidhan Chandra Krishi Viswavidyalaya (BCKV), Mohanpur , Nadia, West Bengal, India *Correspondent author, pal_pranabananda@yahoo.co.in Received 16 August 2005; Accepted 14 May 2007 Abstract In order to study the role of climatic parameters on different performance indicators of tuberose, Polianthes tuberosa Linn. (Double type), an experiment was carried out at Horticulture Research Farm, Bidhan Chandra Krishi Viswavidyalaya (BCKV), Mohanpur, District Nadia (West Bengal) during The crop was planted on 28 th March 2002 with standard cultural practices. Dates corresponding to emergence (E), appearance of first (FFO) as well as last floret (LFO) corresponding to each tagged spike (27 th October to 29 th December 2002) were noted. Maximum and minimum temperature regime enjoyed by each spike during E-FFO and FFO-LFO stage were utilized to derive different thermal indices to study the rate of phenological development as well as status of different performance indicators. Correlation studies showed that all the thermal indices pertaining to E-FFO stage and CHU (Cumulative heat units) during FFO-LFO stage were highly associated with different performance indicators. Regression studies showed that value of these indices during E-FFO stage could explain 55-82% variability of different indicators. Rate of reproductive development during E-FFO has been found to be a quadratic function of mean temperature (R 2 =0.74) where o C mean air temperature showed maximum rate. Relationship developed in this study can be useful for predicting the performance of tuberose ahead of the harvest and assessing its worthiness in the market. A mean air temperature around 22 o C during E-FFO is useful in early harvesting as well as obtaining higher rachis length and thereby the market value of this crop. Keywords : Tuberose, Polianthes tuberosa, Tuberose cv. Calcutta Double, Air temperature, Flowering performance, Performance indicators. IPC code; Int. cl. 8 A01G 9/00 regarding the influence of thermal regime is urgently needed by the producers to develop a production schedule to get a targeted quantity and quality of spikes to match the demand in the market. Exposure of shoots to different thermal regime prior to visible bud formation had little influence on final flower size; however, that at the time of visible bud formation has a prominent effect on such performance indicator of tuberose 2. Nothing in particular is known about the control of thermal regime on tuberose cv. Calcutta Double, although it has been noted that in winter (8-15 o C) these plants produce better quality spikes (in first crop) than during period of higher temperature. The aim of this study was to understand the role of thermal regime, as assessed from different indices of temperature, enjoyed by the crop from the onset of reproductive stage and onwards, upon the rate of reproductive development as well as different floral characters of commercial importance at harvest. 322

2 Materials and Methods The experiment was carried out at Horticulture Research Station of Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia (West Bengal) from March 2002 to December The bulbs having cm diameter were planted at 20 cm 20 cm spacing in the field on 28 th March Three replications were used each of size 11m 2m and containing 550 bulbs of tuberose and standard cultural practices were adopted. Plants received similar thermal regime during their vegetative stage. Emergence of flower spike (spike just visible with naked eye) ranged between 27 th October to 30 th December 2002 and almost each spike was exposed to different combination of thermal regime during their developmental stages. Entire reproductive stage was divided into two sub-phases of apparently uniform rate of phenological development as follows for better understanding of plant-temperature relationship. 1) Emergence of spike to first floret opening; 2) First floret opening to last floret opening. Table 1 : Temperature indices used Each flower spike was tagged at the time of its emergence and subsequently the dates of opening of first and last floret were recorded. Daily temperature data corresponding to these periods were obtained from Principal Agrometeorological Observatory situated in nearby area of the experimental field. The rate of reproductive development which was the reciprocal of the duration of this stage was plotted as a function of mean air temperature to measure the extent of such relationship. Thermal indices given in Table 1 were used to understand the functional relationship between temperature and performance indicators of tuberose like spike length and diameter, rachis length, number of florets/ spike, weight of flower spikes and number of unopened florets. Correlation coefficients were also studied to obtain the degree of association between these temperature variables and the performance indicators at harvest. Finally, regression equations were developed to obtain a quantitative estimate of these parameters as a function of different temperature variables. Weather Index Equation Reference Cumulative Heat Unit Σ {(Tmax.+Tmin.)/2 T b }, Mavi 3 where T b = 10 o C Average daytime temperature Tmax. 0.4 (Tmax. Tmin.) Venkataraman and Krishnan 4 Average night time temperature Tmin (Tmax. Tmin.) Venkataraman and Krishnan 4 Diurnal variation of temperature Average daytime temperature Average night time temperature Results and Discussion Phenological development of tuberose as influenced by thermal regime While studying the rate of reproductive development of tuberose as influenced by mean air temperature (Fig. 1a-b) it was found that out of two phenological stages studied, the rate of development between first floret opening to last floret opening had no systematic relationship with mean air temperature to which the individual spikes were exposed. However, mean air temperature had a very strong relationship with the rate of reproductive development between ing. For this, a quadratic equation was fitted to the experimental data which was found to explain around 74% (R 2 =0.735) variability of the rate of reproductive development between emergence of spike to first floret opening. This type of relationship can also be helpful for monitoring the progress of reproductive development of tuberose with respect to air temperature. The relationship also reveals that increase in mean air temperature makes the reproductive development faster and thereby reduces the phase duration between emergence of spike to first floret opening up to o C beyond which the trend is not persistent. In order to assess the amount of cumulative heat units received by the reproductive stages corresponding to spikes emerged at different times, value of this index from emergence of spike to first floret opening as well as from first floret opening to last floret opening were computed and these values were studied Vol 6(4) July-August

3 with advancement of the date of spike emergence from 27 th October to 22 nd December 2002 as recorded in the experiment. It was observed (Fig.2) that with delay in the emergence of spike from October through December, the amount of cumulative heat unit received by both the phenological stages (emergence of spike to first floret opening and first floret to last floret opening) gradually decreased and eventually showed a linear trend. Floral characters of tuberose as influenced by thermal regime In general, thermal environment between emergence to first floret opening was found to be more associated with difference performance indicators as evidenced from their higher and significant values of correlation coefficient. The exposure of thermal environment during day and during night time has no separate influence as compared to mean daily temperature (Table 2). Among the indices studied mean daily temperature has maximum degree of association with all the performance indicators except that of number of unopened florets. Cumulative heat units corresponding to both and from first floret open to last floret open were strongly and positively correlated to each of the performance indicators studied. Accumulated values of diurnal variation of temperature during the showed strong negative and significant correlation with different performance indicators studied which indicated that these characters of tuberose crop favours similar day-night temperature regime. While exploring the type of statistical relationship exists between 324 Cumulative Heat Unit ( C-days) Mean Temp ( C) Mean Temp ( C) Fig. 1 a-b : Rate of phenological development of tuberose as influenced by mean air temperature Fig. 2 : Cumulative heat units during reproductive stage of tuberose as a function of time of spike emergence a b

4 Table 2 : Correlation coefficient among different performance indicators of tuberose and climatic parameters studied Variables Emergence to first floret First floret opening to last Emergence to last opening floret opening floret opening Mean CHU Day Night Acc. Mean CHU Day Night Acc. Mean CHU Day Night Acc. temp temp temp DV # temp temp temp DV temp temp temp DV Spike 0.76* 0.69* 0.76* 0.76* -0.66* * * 0.70* 0.75* 0.70* 0.70* -0.39* length Spike 0.79* 0.61* 0.79* 0.78* -0.75* * * 0.69* 0.69* 0.69* 0.69* -0.46* diameter Spike 0.72* 0.61* 0.73* 0.72* -0.66* * * 0.66* 0.66* 0.69* 0.65* -0.44* weight No. of 0.81* 0.65* 0.81* 0.81* -0.73* 0.34* 0.67* 0.36* 0.33* * 0.77* 0.79* 0.79* -0.60* florets Rachis 0.90* 0.68* 0.91* 0.89* -0.85* 0.32* 0.73* 0.33* 0.31* 0.30* 0.84* 0.82* 0.84* 0.84* -0.63* length No. of * * unopen florets *Significant at P=0.05 # Accumulated diurnal variation of temperature different performance indicators of tuberose and mean air temperature enjoyed by the crop during emergence of spike to opening of first floret, it was noted that a curvilinear relationship existed between most of these variables except spike length which showed a linear relationship (Fig. 3a-e). It was interesting to note that mean air temperature alone could explain 82% variability of rachis length of tuberose. However, for other performance indicators, variability to the extent of 55-71% could be accounted for by this weather variable during emergence of spike to first floret opening stage. Using mean air temperature (MT), cumulative heat unit (CHU) and Table 3 : Multiple regression equations showing quantitative relationships of mean temperature, cumulative heat unit and accumulated diurnal variation of temperature during emergence of spike to first floret opening stage with different performance indicators of tuberose Multiple Regression Equation R 2 Spike Length (Y) = 1.15 MT 0.03 CHU ADV * Spike Diameter (Y) = 1.1 MT 0.2 CHU ADV * Spike Weight (Y) = MT CHU ADV * Number of Florets (Y) = 2.58 MT 0.77 CHU ADV * Rachis Length (Y) = 2.14 MT 0.64 CHU ADV * * Significant at P=0.05 MT = Mean Temperature ( o C) CHU = Cumulative heat unit ( o C-days) ADV = Accumulated diurnal variation of temperature ( o C-days) Vol 6(4) July-August

5 a c b d Conclusion With increase in mean air temperature from 16 to 22 o C during stage, a reduction in the duration of around 14 days was noted. Mean air temperature around 22 o C during this stage also has a potential to develop a long rachis of around 40 cm. So, a combination of earliness and higher rachis length at this temperature increases the marketability of this flower crop. Since all these variables were taken from emergence of spike to first floret open stage, these multiple regression equations has got a definite predictive value of all the performance indicators prior to harvest. So, this information derived much ahead of the harvesting may be useful in planning harvesting, processing, transport, storage and marketing of this crop. e References 1. Bose TK, Maity RG, Dhua RS and Das P, Floriculture and Landscaping, Naya Prokash, Calcutta, Pearson S, Parker SRA, Adams SR, Hadley P and May DR, The effects of temperature on the flower size of Pansy (Viola wittrockiana Gams.), J Hortic Sci, 1995, 70, accumulated diurnal variation of temperature (ADV) corresponding to stage as independent variables, five different multiple regression equations were developed to study the quantitative relationship of these weather indices with different performance indicators of 326 Fig. 3 a-e : Effect of mean air temperature during emergence to first flower opening on different performance indicators of tuberose tuberose (Table 3). All the regression equations have been found to be statistically significant at 5% level. While comparing the individual regression it was observed that these three independent variables could explain maximum variability of rachis length (83%) followed by number of florets (69.6%). 3. Mavi HS, Introduction to Agrometeorology, Oxford & IBH Publishing House, 1994, 281p. 4. Venkataraman S and Krishnan A, Crops and Weather, ICAR, New Delhi, 1992, 586p.