Yield and quality performances of four tea test clones

An experiment was carried out during 1994–2007 to investigate the yield and quality performances of four vegetatively propagated test clones of tea viz. SH/D/11/13, SH/D/11/333, B/HB/2/3 and B/HB/6/4. Two clones, BT1 and TV23, were used as check for quality and yield, respectively. Cuttings of the test clones were collected from the selected bushes of Shumshernugger Tea Estate and hybrid lines of Bangladesh Tea Research Institute (BTRI) and were raised at BTRI nursery. Then the saplings were managed for long term yield and quality trial following randomized complete block design with 5 replications. The green leaf was harvested at weekly interval during the plucking season starting from mid March to mid December throughout the experimental period. The overall cup quality of the test clones was assessed by conventional organoleptic test. At the immature stage (2–5 year after plantation), all test clones showed similar yield trend as that of check BT1. At the mature stage (6–13 year), the test clones SH/D/11/333 and B/HB/6/4 gave the significantly higher average yield (3095 and 3342 kg ha made tea, respectively) compared to the check BT1 (3042 kg ha made tea). The cup quality of all the test clones and BT1 was found to be “Above Average” while the cup quality of TV23 was “Average”. Considering the overall performances, the test clones SH/D/11/333 and B/HB/6/4 have been released as BT13 and BT14, respectively for commercial plantation in the tea estates.


Introduction
Tea, one of the most important cash crops in Bangladesh, is an important beverage commodity of international trade.Tea export income is accounting for ca.0.35% of the total export income of Bangladesh (BBS, 2011).In 2010, Bangladesh produced only 60.6 million kg made tea when the world production was 4,162 million kg (ITC, 2011).The annual tea production of Bangladesh remains static for last 10 years, but the domestic tea consumption has been increasing very fast.Taking the current rate of domestic consumption into consideration, the country will need to import ca.20 million kg of tea to meet internal demand after five to six years (Islam, 2009).The yield of Bangladesh tea is quite low compared to other tea growing countries of the world.Some of the major causes for lower yield are very old seedling population, inferior planting materials with lower yield potential, low plant population density, bad soil management practices, etc.The increasing cost of production as well as the adverse climatic conditions has also led to marginal economic return to the tea industry.In these circumstances, the industry needs to replant and extend new tea areas with improved planting materials of higher yield potential and good quality.
Due to the heterogenous nature of tea seedlings, the seed available except biclonal stocks, could not guarantee the production of improved planting material (Njuguna, 1990).Emphasis should be given on selection and plantation of vegetatively propagated material i.e., high yielding quality clones for better yield and quality of tea (Dutta and Alam, 2001).Clonal selection is the most popular practice in tea for evolving better cultivars.As tea plant is an allogamous species, a large variation of characters occurs from bush to bush in existing seedling tea population and cross pollinated progenies.Such variation is exploited through selection programs to develop new tea cultivars with enhanced traits (Ranatunga et al., 2009).Procedure of clonal selection is more or less same in all the tea growing countries (Tubbs, 1946;Visser and Kehl, 1958;Wight, 1961;Barua, 1964;Waheed et al., 2001).
With an objective of evolving planting materials with high yield and quality potential Bangladesh Tea Research Institute (BTRI) has put its priorities on clonal selection and hybridization programme since its inception.As an outcome of these works, the institute so far released eighteen vegetative clones in the BT (Bangladesh Tea)-series to the industry (Hossain and Dutta, 2010).In this pathway, the present experiment was carried out to study the long term yield and quality performances of four vegetatively propagated test clones; SH/D/11/13, SH/D/11/333, B/HB/2/3 and B/HB/6/4, compared with two check clones; BT1 and TV23.

Materials and Methods
The experiment was carried out in the main farm of BTRI with four test clones viz.SH/D/11/13 and SH/D/11/333 selected from Shumshernugger Tea Estate (T.E.) and B/HB/2/3 and B/HB/6/4 from BTRI hybrid lines, and two check (control) clones viz.BT1 and TV23 during the period from April 1994 to December 2007.The local standard clone BT1 and a popular Indian yield clone TV23 were used as check for quality and yield comparison, respectively (Table 1).General characteristics of four test clones and two check clones are given in Table 2. Cuttings were collected from the selected bushes of Shumshernugger T.E. and BTRI hybrid lines during 1994, which were raised at BTRI nursery.After rooting trial in the nursery, the selected test clones viz.SH/D/11/13, SH/D/11/333, B/HB/2/3 and B/HB/6/4 were put to long term yield and quality trial during 1996 at BTRI Farm.The experiment was laid out in a randomized complete block design with 5 replications at the standard (105cm x 60cm) spacing (Dutta and Alam, 2001).The experiment is conducted in rainfed condition.Fertilizer was applied at young and mature tea as per BTRI recommendations (Kibria and Rashid, 1994;Kibria and Uddin, 1998).Young and mature tea pruning were followed as per BTRI recommendations (Rashid, 1986;Shahiduzzaman et al., 2002).Yield data was collected during the cropping seasons throughout the experimental period.The green leaf was harvested at weekly interval during the plucking season starting from mid March to mid December throughout the experimental period.Yield data were recorded and analyzed statistically in MSTAT programme.The mean values were adjudged by Duncan's new multiple range test (DMRT).The yield was expressed as mean yield of green leaf (g plant -1 ) and has presented separately for immature (2 nd -5 th year) and mature (6 th -13 th year) stages.The made tea (kg ha -1 ) was also calculated on the basis of 23% recovery from green leaf with the population density 15,875 plants ha -1 (at 105cm x 60cm spacing).The quality performances of all the test and check clones, manufactured by crush, tear and curl (CTC) method in the BTRI mini tea factory, were assessed weekly by conventional organoleptic test and scored numerically.

Yield performance
The mean yield of green leaf (g plant -1 ) over the experimental years for immature stage (2 nd -5 th year) and mature stage (6 th -13 th year) are presented in Table 3 and Table 4, respectively.Green leaf yield was converted as made tea (kg ha -1 ) over the experimental period.The converted made tea yield (kg ha -1 ) for immature and mature stages is presented in Table 5 and Table 6, respectively.At the initial stage of growth all the test clones showed similar yield trend as the check BT1 (Table 3).When the data were analyzed year-wise, their yield differences were significant.Also the test clones varied significantly when data were analyzed over the years.At immature stage (2 nd -5 th year), the test clone B/HB/6/4 exhibited significantly higher yield in average (1683 kg ha -1 ) over check BT1 (1527 kg ha -1 ), the yield of the test clone SH/D/11/333 (1502 kg ha -1 ) was also comparable with the check BT1 (Fig. 1).The other test clones SH/D/11/13 and B/HB/2/3 gave lower (average) yield than the check.The standard clone TV23 yielded highest (1857 kg ha -1 ) among the clones at immature stage.The production of larger number of medium sized, thick leaf was one of the causes of higher yield in B/HB/6/4 (Table 2).The higher yield of B/HB/6/4 might be controlled by the genetic make-up of the clone (Alam et al., 1997).However, it was noteworthy that the yield of TV23 drastically reduced in 1999 (Table 3), when Bangladesh faced prolonged and severe drought condition in tea growing regions (Dutta and Alam, 2000).On the other hand, all the Bangladeshi clones (both the test and the check) performed better in the same year (Table 3).This may indicate that the Bangladeshi clones are more tolerant to drought condition compared to TV23.At the standard productivity level (from 6 th to 13 th year), yield variations were significant among the clones (Table 6).The average yield of those 8 years also showed significant differences between the clones.Average yield data showed that the test clones B/HB/6/4 and SH/D/11/333 gave significantly higher yield (3342 and 3095 kg ha -1 , respectively) over the check BT1 (3042 kg ha -1 ), but the yield of other test clones SH/D/11/13 (2784 kg ha -1 ) and B/HB/2/3 (2634 kg ha -1 ) were lower than the check BT1 (Fig. 2).Indian clone TV23 that was used as a standard clone for yield in this study, maintained its superiority in yield over other clones throughout the experimental period, although, it has susceptibility to drought condition (Table 5).The recommended pruning cycle, in mature tea, was as follows: Light prune-Deep skiff-Medium skiff-Light skiff (Rashid, 1986).Therefore, the 10 th year yield becomes less compared to that of 9 th year due to the plant undergoes lower cut (light prune) in the 10 th year.Similar trend was also observed in this experiment (Table 4 and 6).

Quality performance
Cup quality is an inherent character and one of the most important considerations in selecting potential commercial cultivars.The overall quality performances of the test and the check clones assessed by conventional organoleptic test are shown in Table 7.It was observed that the cup characteristics of all the test clones and the BT1 were categorized as "Above Average" while only the TV23 as "Average".They have bright infusion, coloury liquour with useful strength and briskness (Table 7).The test clones SH/D/11/333 and B/HB/6/4 also appeared quite potential in respect of nursery rooting, drought tolerance and other field performances during its selection and field trial periods (Dutta andAlam, 2000, 2002).Considering the overall performances throughout the study period compared to the check BT1, the test clones SH/D/11/333 and B/HB/6/4 appeared superior and confirmed their earlier provisional released as standard clones.After the severe drought condition of 1999, there was a growing demand of drought tolerant clones from the tea industry.Moreover, these test clones, SH/D/11/333 and B/HB/6/4, appeared so promising that they have immediately provisionally released as standard clones in BT series for commercial use in the tea industry before completion of the long term field trial.The test clones SH/D/11/333 and B/HB/6/4 were renamed and provisionally released as BT13 (Dutta and Alam, 2000) and BT14 (Dutta and Alam, 2002), respectively.