Variability studies and identification of high yielding plus trees of cocoa ( Theobroma cacao L . ) in Tamil Nadu

One hundred and fifty one (151) cocoa trees in the farmers’ field of Tamil Nadu were assessed for their variability and yield performance. Ten year old trees in five different plantations of Tamil Nadu were observed for their morphological, pod, bean and yield characters. Variability among the tree, pod, bean and yield trait characters were also studied for all the trees selected. Plus trees or promising mother trees were identified from the trees having the following traits: Dry bean yield per tree (> 2.4 kg), number of pods per tree (60), number of beans per pod (> 35) and single dry bean weight (> 1 g). In this analysis, the trees which had necessary economic traits were screened. A total of 27 trees viz., KUL-2, 18, 25, SMJ3, 4, 10, 15, 18, 21, 25, 33, 34, 37, 50, SME 2, 5, 6, 9, 16, 21, 24, 26, 28, 29, VPS12, 13 and 15 were found to be superior for important economic traits and identified as plus trees.


INTRODUCTION
Cocoa dried beans are the raw materials for cocoa powder and butter, chocolate, confectionaries, beverage and cosmetic industries (Prasannakumari et al., 2009).Cocoa is gaining tremendous importance for its growing demand across the world.In India, the production of cocoa confined majorly into Southern states viz., Kerala, Karnataka, Andhra Pradesh and Tamil Nadu (Elain Apshara et al., 2009).It occupies an area of 46,318 ha with the production of 12,954 MT and the national productivity is 550 kg dry beans per ha.Kerala leads in production of cocoa from an area of 11,044 ha with production of 6344 MT.The productivity of cocoa beans in the state is 592 kg per hectare.Tamil Nadu occupies third position in cocoa cultivation with an area of 9347 ha.It produces 900 MT cocoa beans with the productivity of 443 kg dry beans per hectare (DCCD, 2011).To meet the growing demand of cocoa beans, there is need for Identification of new high yielding trees.Selection of superior plants or parents, their subsequent development into clones and exploitation the hybrid vigour are considered as the easy approaches in perennial crops, especially in cocoa improvement (Christian, 2003).Hence, this study is undertaken to identify the promising tress of cocoa for high yield and quality for further crop improvement work.plus trees of cocoa.About 151 trees were selected based on yield, pod and bean characters.The trees were marked and observations were made for morphological and yield parameters.

Locations and trees under study
The location as well as the number of trees selected is given in Table 1.The age of cocoa trees identified was 10 years and above in all plantations and cocoa was intercropped in coconut plantation with age ranging from 15 to 20 years.All the area surveyed and trees identified were F1 seedling progenies, raised through seedlings (of F1's) supplied by Kerala Agricultural University and Central Plantation Crops Research Institute, Vittal.One row of cocoa was planted in between two rows of coconut at 10 feet distance and one cocoa plant in between two coconut trees in a row.The cocoa plants were given cultural practices as per the package of practices standardized by Kerala Agricultural University.
Pruning was regularly done in the identified trees where in excess chupons arising from main stem and fan shoots were removed before and after each monsoon.All the plantations were flood irrigated during the study period.The preliminary observations were recorded in 2008 and later during subsequent year (May, 2009to April, 2010) the data for yield and quality traits were recorded in the marked trees.
The tree morphology, pod, bean and yield traits were recorded.First branching height of the tree was measured in meters as the vertical distance from ground level upto the first jorquetting point, using a measuring tape.The girth of the tree was measured at 15 cm above the ground and expressed in centimeter.The fan branches arising from first jorquette was counted and expressed in numbers.Canopy spread of the tree was measured as North-South and East-West and expressed in metre.The pod length was measured from each selected tree and the length measured from stalk to apex and expressed in centimeter using scale and the average was calculated.Girth of the pod was measured at the centre of the pod by using thread and expressed in centimetre.The weight of each pod was measured in grams using a common balance and the data recorded.The thickness of pod wall at ridges and furrows were measured for each pod harvested after cutting open the pod and measured by using vernier callipers and expressed in millimeters.For all the above pod characters ten pods per each tree was taken and the average was calculated.Bean characters like number of beans per pod, wet bean weight per pod, single dry bean weight were calculated.Yield traits like number of pods per tree, dry bean yield per tree were worked out.The pod value can be defined as number of pods required to produce one kilogram of dry beans.The pod value was obtained using the yield data.The statistical mean was calculated using the method suggested by Goulden (1952).
Phenotypic coefficient of variation was computed according to Burton and Devane (1953).
The trees having the following traits like dry bean yield per tree (> 2.4 kg), number of pods per tree (60), number of beans per pod (> 35) and single dry bean weight (> 1 g) were screened as plus trees for further breeding works.

Morphological characters of cocoa trees
Morphological observations taken from the cocoa trees are presented in Table 2.The first branching height showed variation ranging from a minimum of 0.36 m to a maximum of 2.25 m with the mean of 1.22 m.The first branching height was minimum (0.36 m) in SEB 18, followed by 0.45 m in SEB 17 and was maximum in KUL 2 (2.25 m) and in SMJ 46 (2.10 m).The coefficient of variation for the jorquetting height was 26.90%.Observations on tree girth of all trees studied varied from a minimum of 22.30 cm (SEB 10) followed by 22.80 cm (SEB 7) to the maximum of 51.00 cm (SME 24) followed by 50.20 cm (VPS 17).The mean value for tree girth was 35.22 cm and the coefficient of variation was 16.13%.Number of fan branches arose from the jorquette of all trees was recorded.The number of fan branches per tree varied from 2 to 5 with the mean value of 3.90.The coefficient of variation for the trait fan branches was 22.69%.The tree spread in east to west ranged from 2.40 m to 7.53 m with the mean value of 4.46 m.The maximum spread of 7.53 m was recorded in the tree KUL 2 and the minimum spread (2.40 m) in the tree SEB 13.The tree spread across north-south ranged from 1.69 m to 8.28 m with the mean value of 4.50 m.The maximum spread of 8.28 m was recorded in the tree VPS 4 and the minimum spread of 1.69 m was recorded in the tree SMJ 47.Jorquetting height in cocoa is an important criterion for selection of plus trees as higher the jorquetting height, more could be the yield as the lengthier jorquette could allow more number of flower cushions in the trunk, thus leading to higher yield.The positive correlation between these two traits in this study also supports this.Further a tree with good tree girth, more number of fan branches and tree spread reflect the vigour of the trees indirectly  The quantitative characters of the pod like pod weight, pod length, pod girth and pod wall thickness at ridges and furrows also registered greater diversity among the trees.In cocoa, ideal genotypes should possess medium to large sized pods with thin to medium pod wall thickness.The wider variability for the pod weight, length, girth and volume existed in the population might be due to both genetic factors and environmental factors including soil moisture and nutrient status.Being a highly heterozygous crop, the pod characters range was strikingly high.Elain Apshara et al. (2008) studied the pod characters for 21 superior progenies of different cross combinations in cocoa and reported the variability for pod weight, pod length, pod girth and pod wall thickness.The results are in agreement with those obtained by Subramanian and Balasimha (1981), Mallika et al. (1996), Maharaj et al. (2006) and Elain Apshara et al. (2009) in cocoa.

Bean characters of cocoa trees
Bean characters studied are given in Table 3. Observations on number of beans per pod in all trees studied varied from a minimum of 25.50 in KUL 15 to a maximum of 50.50 in SMJ 7. The mean value of the number of beans per pod of all trees was 39.45.The coefficient of variation for the number of beans per pod was 11.01%.The wet bean weight per pod in all trees studied varied from a minimum of 73.79 g in SME 21 to a maximum of 210.50 g in VPS 7 with a mean value of 121.42 g.The coefficient of variation for the wet bean weight per pod was 20.00%.Single bean dry weight of all trees studied varied from a minimum of 0.59 g in tree SMJ 43 to a maximum of 1.71 g in tree SMJ 36 with an overall mean of 1.00 g.The coefficient of variation for the single bean dry weight was 17.93%.
In cocoa, pods possessing higher number of beans per pod, wet bean weight per pod before and after fermentation and dry bean weight per pod are preferred.The wider variation for the number of beans per pod, wet bean weight per pod before and after fermentation, dry bean weight per pod, single bean wet and dry weight, bean length and girth are mainly due to the genetic factors with possibility of external influence like environment and nutrient status.These results are in consonance with the findings of Enriquez and Soria (1968), Adomako and Adu-Ampomah (2003), Lachenaud and Oliver (2005), Assemat et al. (2005) and Elain Apshara et al. (2008Apshara et al. ( , 2009) ) in cocoa.

Yield traits of cocoa trees
The yield traits recorded in the present study is given in Table 3. Observations on number of pods per tree in 151 trees studied varied from a minimum of 32 in SEB 15 to a maximum of 108 in SMJ 11, with an overall mean of 60.49.The coefficient of variation for the number of pods per tree was 22.39%.
The yield per tree of all trees studied varied from a minimum of 0.85 kg in SMJ 40 to a maximum of 3.96 kg in SME 24.The mean value of the dry bean yield per tree of all trees was 2.39 kg.The coefficient of variation for the yield per tree was 28.76%.Pod value of all trees    varied from a minimum of 15.29 in tree SMJ 36 to a maximum of 52.88 in tree KUL 26, with an overall mean value of 26.54.The coefficient of variation for the pod value was 23.68%.
In cocoa, yield is determined by yield contributing characters such as number of pods per tree, dry bean yield per tree and pod value.In cocoa, lower pod value is preferred to have higher bean yield.These characters are influenced both by genetic as well as environmental factors including soil moisture and nutrient status.The results are in consonance with the findings of Latchman et al. (2000), Bekele and Bidaisee (2006), Adomako and Adu-Ampomah (2003), Lachenaud and Oliver (2005), Assemat et al. (2005), Lambert et al. (2006) and Elain Apshara et al. (2008Apshara et al. ( , 2009)).

Identification of plus trees or promising trees
Plus trees or promising mother trees were identified based on the economic traits like dry bean yield per tree (> 2.4 kg), number of pods per tree (60), number of beans per pod (> 35) and single dry bean weight (> 1 g).The trees which had necessary economic traits were screened.A total of 27 trees viz., 18,25,4,10,15,18,21,25,33,34,37,50,5,6,9,16,21,24,26,28,29,13 and 15 were found to be superior for important economic traits and identified as plus trees.These promising trees are potential genetic material for plant breeding programmes in cocoa.The results go in accordance with the findings of Desai, (2008) in cashew and Raveendra et al. (1987) in coconut.From the present study, it could be inferred that the diversity exists in cocoa plantations in Tamil Nadu and can be exploited in crop improvement research.Plus trees identified have to be observed for both yield and quality parameters for few more years.Promising trees have to be clonally raised and tested before using in breeding programmes.

Table 1 .
Locations and trees under study.

Table 2 .
Tree morphology and pod characters of cocoa trees.

Table 3 .
Bean and yield characters of cocoa trees.