Thumbnail Image

Theses

Browse

20131
Reset filters
Subject: Plant Breeding × Author: Asna, A C × Author: KAU × Start date: 1991 × Type: Thesis × Thesis Type: M.Sc ×
Reset filters

Search Results

Now showing 1 - 1 of 1
  • Thumbnail Image
    ThesisItemOpen Access
    Performance analysis of selected accessions of cocoa (Theobroma cacao L)
    (Department of Plant Breeding and Genetics, College of Horticulture, Vellanikkara, 2013) Asna, A C; KAU; Presannakumari, K T
    The spreading cultivation of cocoa as an intercrop in states like Kerala, Tamil Nadu, Andhra Pradesh and Karnataka necessitated the development of high yielding hybrids with pest and disease resistance and adaptability to various agro climatic zones. The success of any hybridization programme particularly in perennials depends on the proper selection of parental lines having genetic divergence. The present study entitled “Performance analysis of selected accessions of cocoa (Theobroma cacao L.)” was taken up in this background at COH, Vellanikkara during 2011-13 to evaluate and characterize the selected cocoa accessions and to assess the genetic divergence among them. Fifty accessions of cocoa comprising of both exotic and indigenous ones which are in the full bearing stage and maintained at Cocoa Research Centre, Vellanikkara formed the material for the study. These accessions were subjected to morphological and biochemical evaluation. The morphological evaluation based on 13 qualitative and 25 quantitative characters was done using the descriptor developed by Bekele and Butler (2000). Fat and total polyphenol contents were estimated following standard procedures for biochemical characterization. The clustering of the accessions based on these characters was done by unweighted pair group method (Sneath & Sokal, 1973) and the genetic divergence was estimated by D2 statistics developed by Mahalonobis (1936). Wide variability was observed among the accessions for all the qualitative traits except colour of staminodes and hardiness of husk. Variations expressed by the accessions in terms of both floral and pod quantitative traits were also high. Among the exotic accessions, COCA 3370-3 was having the highest pod weight, pod length, pod breadth, ridge thickness and furrow thickness. However, its wet bean weight accounted only for 14.79 percent of the pod weight. Among the indigenous types, Konni local 2 was the best performer for these traits. The characters of economic interest viz., pod weight, number of beans/pod, dry weight of peeled bean, percentage of flat beans/pod and pod index ranged from 318.67g to 1268.33g, 22.93 to 49.27, 0.58g to 1.72g, 0.00 to 12.60 percent and 12 to 49 respectively among the exotic accessions. The corresponding traits in the case of indigenous accessions ranged from 416.67g to 719.33g, 31.60 to 46.27, 0.93g to 1.52g, 0.75 to 7.86 percent and 17 to 34 respectively. Among the accessions evaluated R (10) (MEX) was found to be a desirable one with low pod index value (12) and flat bean content/pod (0.81%) coupled with high number of beans/pod (49.20) and dry weight of peeled bean (1.68g). This is followed by EET 400 having a pod index of 15. The exotic accessions Criollo, KER 9 and CLM 90 failed to satisfy the international standard for dry weight of peeled bean viz., 0.8g or more. The fat content ranged from 40 percent to 60 percent and total polyphenol content from 2.25 percent to 9.09 percent. The cluster analysis based on qualitative and quantitative characters resulted in nine and seven clusters respectively for exotic accessions and five and three clusters respectively for indigenous ones. The accessions belonging to same qualitative cluster were found to fall in different quantitative clusters indicating that even though they are similar at qualitative level they are different at quantitative level. With respect to biochemical characters majority of accessions were remaining as independent units even at one percent similarity level and hence could not be clustered. Among the exotic types, the maximum genetic divergence was observed among the accessions falling in quantitative cluster I and V as indicated by the highest inter cluster distance (33763.40). In the case of indigenous ones maximum divergence was found among the accessions falling in cluster I and II (148447.4). Mealy bug and tea mosquito bug were the major pests and black pod was the major disease affecting the pods resulting in yield loss. Besides, rodents like rats and squirrels also caused damage to the pods. Among the accessions evaluated, COCA 3370-3 having high husk thickness was found to be tolerant to the major pests and diseases affecting the pods and can serve as donor parent in resistance breeding programme. A statistical key was developed using key qualitative and quantitative characters which can serve as a preliminary tool for predicting the performance of the accessions.