Growth and quality of green tea (Camellia sinensis var sinensis)
Creators: name: Botwright, Tina
Publisher: name: University Of Tasmania
Year: 2023

description: Green tea (Camellia sinensis var sinensis) is a potential introduction to the range of crops produced in Tasmania. Information is required regarding growth and development of green tea in relation to harvested yield and quality, which is fundamental to the successful production of tea. In this study, shoot growth of green tea at four stages of development was used to examine changes in photosynthesis, assimilate partitioning and the concentration of endogenous plant hormones occurring during rhythmic growth. The effect of environment on rhythmic growth, harvested yield and quality of green tea was also examined under controlled conditions. Shoot growth in green tea occurs in repeating cycles of growth and dormancy. Morphological and anatomical characteristics of vegetative shoots defined four key stages of development of rhythmic growth. These stages include stage I, bud burst, expansion of cataphylls and start of shoot growth; stage II, expansion of flush leaves and shoot extension; stage III, cessation of shoot extension and expansion of the final flush leaf to expose the dormant bud; and stage IV, completion of leaf expansion. Leaf primordia initiate during dormancy, and expand during shoot extension. The newly expanded leaves of the flush are subsequently harvested as the green tea crop. Photosynthetic capacity, the pattern of assimilate partitioning and the concentration of endogenous plant hormones vary during shoot growth, as defined by the stages of development. Netphotosynthesis of mature, fully expanded leaves is lowest (13 umol CO2 m-2 s-1 ) during stage III, dormancy, and highest (18 umol CO2 m-2 s-1 ) during stage I, at the beginning of flush growth. Starch reserves in leaves and internodes reach a maximum of 22 % (dw) and 5 % respectively at dormancy, during stage III, and decline significantly to 9 % and 0 % respectively at the start of flush growth, during stage I. At the start of flush growth, the majority of 14C labelled assimilate is partitioned to the bud, with the developing leaf primordia and intemodes assumed to be the major sink organs as leaf initiation has ceased. During shoot extension, in stage II, labelled 14C assimilate is instead partitioned to expanding leaves and intemodes. During stage III, dormancy, import of 14C labelled assimilate declines as leaves became net exporters of assimilate. The concentration of endogenous abscisic acid increases during stage 111, and, as an inhibitor of growth, may be involved in the maintenance of bud dormancy during rhythmic growth in tea. Gibberellin reaches its highest concentration in buds during stage I, at the start of shoot growth. The concentration of zeatin riboside decreases during stage II, shoot extension, and may be involved in the cessation of leaf initiation at the apex. Changes in sink activity and ontogeny are linked to changes in photosynthesis, partitioning of assimilates and endogenous plant hormone concentration during shoot growth and culminate in rhythmic growth of tea. Environment affects the initiation of primordia, rate of growth and shoot production during rhythmic growth in tea. Environmental conditions of long days (16 hours) and a high night temperature of 15 ¬¨‚àûC increases the number of leaves initiated and subsequent rate of growth. Growth and yield in these conditions are then significantly greater than in other combinations of day length and night temperature. Achieving maximum yields by harvesting four, rather than two leaves and a bud, under conditions of long days and high night temperatures, was, however, at the expense of quality, which declined. Growth of tea following pruning, used to encourage growth of new shoots, is delayed by both long days and a night temperature of 7 ¬¨‚àûC, and short days of 9 hours and a night temperature of 7 ¬¨‚àûC, where production of shoots in the latter treatment was insufficient for harvesting. Pruning, under natural conditions, increases the time to harvest and reduces yield, but does not affect quality. A suitable compromise between yield and quality is to harvest three leaves and a bud, under conditions of long days and a low night temperature.