Mridul Hazarika

Diversity of Catechin in Northeast Indian Tea Cultivars

Tea (Camellia sinensis L.) leaf contains a large amount of catechins (a group of very active flavonoids) which contribute to major quality attributes of black tea. Based on morphological characters tea plants were classified as Assam, China, and Cambod varieties. The present study is an attempt for biochemical fingerprinting of the tea varieties based on catechin composition in green leaf of cultivars grown in Northeast India. Assam variety cultivars contained the highest level of catechins followed by Cambod and China. The average catechin contents were 231 ± 7 mg g−1, 202 ± 5 mg g−1, and 157 ± 4 mg g−1 of dry weight of green leaf for Assam, Cambod, and China cultivars, respectively. Among the individual catechins the variations in epigallocatechin gallate (EGCG) and epigallocatechin (EGC) were the most prominent among the varieties. High EGC content was found to be a characteristic of Assam variety which was further corroborated through multivariate analysis.

Catechin and catechin fractions as biochemical markers to study the diversity of Indian tea (Camellia sinensis (L.) O. Kuntze) germplasm.

The heterogeneous Indian tea germplasm includes ‘China’, ‘Assam’, ‘Cambod’, and their hybrids which were evaluated using biochemical markers viz., total catechin and their fractions, for varietal identification and characterization. Principal component analysis (PCA) of biochemical characters showed that the total catechin and trihydroxylated catechin has higher eigenvalues. The first two principal components (PCs) could differentiate more than 90% of the clones studied. This grouping based on first two principal component matrices differentiated ‘China’, and their hybrids with ‘Assam’ and ‘Cambod’ variety. Morphologically indistinct large‐leaved ‘Cambod’ variety and ‘Assam’ varieties could not be differentiated using biochemical markers, since both varietal types taxonomically belong to a single species. Clones of ‘China’ type showed low total catechin content and catechin ratio which are distinctly grouped. The ‘China–Assam’ and ‘China–Cambod’ hybrids formed intermediate groups between ‘China’ PC group and ‘Cambod’/‘Assam’ PC groups, providing evidence for genetic control of catechin ratio variation. Tea clones which are differentially positioned in the PC group could be explained based on the genetic contribution by other varietal type as parents. This biochemical characterization will be a useful tool in the development of quality‐tea clones with different proportion of total catechin and their fractions.

Breeding of the Tea Plant (Camellia sinensis) in India

The indigenous Assam tea plant was discovered by Robert Bruce in 1823. However, commercial tea cultivation was initiated in India during 1834, using a China tea plant. The better cup quality produced by the Assam tea plant popularized it as an important planting material in the tea industries of the country. Seeds were the only source of propagation until the discovery of the vegetative method. As a result, seed jat populations of unknown parents created a wide range of genetic variation and resulting inconsistency in their performance. Considering the need for improved planting materials for the tea industry, Tocklai Experimental Station (TES) Tea Research Association, initiated a tea breeding programme in 1930, under which germplasms were collected based on trait specific phenotypic characteristics. Promising plants selected from heterogeneous jat populations as well as from wild tea patches were characterized and preserved in the gene bank of TES, along with some of the non-tea Camellia species for utilization in the breeding programmes. The Tea Research Foundation, United Planters’ Association of Southern India (UPASI), initiated a similar program in 1963 and collected germplasms were preserved in their gene bank. The technique of vegetative propagation, standardized in 1955, provided scope for developing improved clonal cultivars as well as biclonal seed cultivars through hybridization. From the selected plants from old seed jats and progenies of biclonal hybrids, 153 locally adapted and 31 universal clones were developed for the tea industry. Under polyploid breeding triploids, tetraploids and aneuploids were produced through hybridization, out of which high yielding quality triploid plants were selected, cloned and made available for plantation. Water logging tolerant genotypes have been selected and used as parents in the breeding programme for the development of tolerant cultivars and progenies. EST’s have been developed from Camellia species and a cDNA library was constructed. Marker development for draught resistance and blister blight disease is under progress using cDNA-AFLP and EST-SSR techniques. Transgenic technology has been developed and vector construction is completed to confer resistance against blister blight. The micropropagation technique has also been standardized for quick multiplication of these biotechnologically modified plantlets. Details of tea breeding in India are discussed in this chapter.

Managing declining yields from ageing tea plantations.

Strong growth in the demand for tea requires further increases in the productivity of plantations. Declining or stagnant yields are commonly observed in older plantations. Possible controlling factors for yield decline are reviewed including ageing of plants, chronic disease and sub-optimal soil conditions such as excess soil acidity and low soil organic matter. Management options for addressing these factors are evaluated, including replanting. A systematic approach to decision-making about replanting is presented. Practice for replanting is reviewed and it is concluded that evidence to support a general case for replanting is limited, unless based on the introduction of more productive clones and/or better plant spacing.