CHARACTERIZATION OF GAMMA IRRADIATED TEA ACCESSIONS USING BIOCHEMICAL AND MORPHOLOGICAL MARKERS

Abstract

Mutation breeding as an alternative method of crop improvement has widely been used to broaden the genetic variability of most cultivated plants except tea. A study was carried out to determine the effect of different gamma ray treatment (0, 50 and100Gy) on tea. The trial comprised of six open-pollinated seed stocks along with untreated controls totaling to 72 accessions. Data was collected for three seasons (dry - January to March, warm wet -September to December, and cold wet - April to August). Biochemical characterization indicated that gamma irradiation had significant effects on gallic acid (GA), epicatechin (EC) and total polyphenols (TP). Most of the traits were significantly (p<0.001) influenced by cultivar type. Compared to parental clones, progeny from clone TRFK 303/1199 registered an increase in GA (0.42%) whereas progenies from clones TRFCA SFS150 and EPK C12 registered an increase in EC at 2.00% and 2.56% respectively at 100 Gy. Cultivar means showed that progenies of clone TRFK 301/4 had the highest EC levels of 2.66%, whereas those of GW Ejulu had the lowest levels of 1.63%. 100 Gy treatment resulted in increased TP in progenies of clones TRFK 303/1199, TRFCA SFS150, and TRFK 301/1 that registered 0.6, 2.8 and 8.6% increase, respectively. Seasons affected all traits studied in tea (p<0.05) except GA% and C%. Twenty-one growth parameters were recorded for each treatment based on UPOV Tea Test Guidelines. Pattern of variations in measured characters were determined by Principal Component Analysis (PCA) using mean values of morphological observations. Evaluated germplasm were grouped by cluster analysis using the unweighted pair group method analysis (UPGMA) based on the similarity matrix of Euclidean distances of the morphological data. Morphological characterization revealed that pubescence, an important character of young shoots impacting quality of specialty teas such as white and orthodox teas was present in all the studied germplasm. Principal Component Analysis (PCA) using 17 descriptors showed that the first 8 principal components accounted for 78% of the total variance. PCA showed that 15 of the descriptors were informative and highly contributed to the phenotypic diversity among the gamma-treated progenies. Cluster analysis further revealed that characters of young shoot anthocyanin colouration at base of the petiole and leaf blade intensity were the most discriminating descriptors resulting to 4 phenotypically well-defined groups. Most traits showed significant correlation, indicating that they could be used for selection for tea improvement. This study has demonstrated that mutation breeding could be used to create genetic variability in tea for selection of novel varieties leading to enhanced foreign earnings and livelihoods for the rural population in tea growing regions of Kenya