Some Factors Limiting Yields of Tea (Camellia sinensis)

Abstract

Measurements indicate that the tea crop-which consists of young shoots-is sink-limited and that the plucking of immature shoots, essential for quality tea, is a major factor limiting yields of the crop. The importance of this aspect in selecting for high-yielding plant material is discussed.The world tea crop comes from the perennial shrub Camellia sinensis L. The quantity of tea produced from clonal bushes is increasing, but the bulk of the crop comes from unselected or poorly selected planting material, which exhibits a high degree of polymorphism in the field. This variation in phenotypes can be attributed to the diverse genetic origin of tea (Wight, 1962) and the outcrossing nature of the species (Cobley, 1956; Ellis, 1964). Tea breeding programmes have been severely hampered by the minimum of 8 years required to complete one cycle of a breeding programme, the outcrossing nature of the bush and the time taken to assess new clones. Many distinct morphological characters can be recognized in the field, but nothing is known of their heritability or whether any of the characters are associated with high yield, and the diverse genetic material has yet to be exploited.The protracted nature of breeding programmes make it essential to use the correct selection criteria. In deciding which morphological and physiological characters of the tea bush limit yield it is essential to know whether yield is determined mainly by the strength of the sources or sinks (source-limited or sink-limited). It has generally been assumed that tea, like many of the vegetative crops of the world, is source-limited and investigators have consequently studied characters known to be associated with photosynthesis (Barua, 1964;Sanderson and Sivapalan, 1966;Hadfield, 1975; Magambo, 1975; Devanathan, 1975). However, this approach has not been satisfactory, and where significant correlations between characters associated with photosynthesis and yield have been found, they have often been incorrectly interpreted or over-emphasized. This paper assesses evidence which indicates that the crop is sink-limited and identifies the major factors which limit crop production. METHODAnnual dry matter production was determined for 7-year-old, irrigated tea, clone SFS 204, at Nsuwadzi Research Station in the 1976/77 growing season. The plants, at a population of 8612 ha" 1 , had been pruned and tipped prior to the start of sampling and fertilizer applied at the rate of 802 kg h a -1 of tea mixture

Ecophysiology of tea

“…2-3 leaves and a bud) is only a small fraction (0.05-0.15) of its total biomass production (Callander, 1978;Tanton, 1979). Therefore, both Tanton (1979) and Squire and Callander (1981) argued that assimilate supply cannot be a limiting factor in yield determination, when harvested yield is such a small fraction of total biomass production. Instead, tea leaf yield per unit land area is strongly correlated with N sh .…”

“…Instead, tea leaf yield per unit land area is strongly correlated with N sh . Hence, Tanton (1979) concluded that tea yield is sinklimited rather than source-limited. Based on the results of a simulation model, Matthews and Stephens (1998a) also suggest that assimilate supply is unlikely to limit shoot growth under most conditions.…”

“…Respiration rate also influences growth rates of a crop as respiration uses part of the photoassimilates as the substrate. Tanton (1979) estimated that mature tea which accumulates biomass at a rate of 17.5 t ha -1 yr -1 uses 67% of its photoassimilates for respiration. Hadfield (1974) estimated the respiratory losses to be 85%.…”

Effect of Total Solar Radiation and Rainfall on Yield of Different Tea (Camellia sinensis [L.] O. Kuntze) Clones at Two Sites in Kenya

“…For solar radiations above 350 Wm -1 require 700-800 Wm -1 , a value equivalent to full sunlight in the cooler seasons of many high altitude tea areas, and account for 75% of full sunlight in the warmer rainy seasons. The factors that have been documented to limit yield include: removal of young shoots (Tanton, 1979), air temperature (Ng'etich, Stephens, & Othieno, 2001); Tanton, 1982a;, soil temperature confounded with dry air (Tanton, 1982a;Odhiambo, Nyabundi, & Chweya, 1993;Chen & Fong, 1994;Nixon, Burgess, Sanga, & Carr, 2001), hail (Ng'etich et al, 2001;Othieno et al, 1992), day-length (Tanton, 1982b), soil temperature (Ng'etich et al, 2001) and solar radiation (Squire, 1977). Falling temperatures and soil physical and chemical conditions greatly limits tea yield (Ng'etich et al, 2001).…”

Yield decline in mechanically harvested clonal tea (Camellia sinensis (L) O. Kuntze) as influenced by changes in source/sink and radiation interception dynamics in the canopy

“…Tea bushes may therefore have an inadequate number of growing shoots to use photo-assimilates produced by photosynthesis (Mohotti & Lawlor, 2002;Squire, 1977;Tanton, 1979). This situation is likely to be exacerbated under continuous mechanical harvesting, where removal of shoots is indiscriminate of age and often the strongest sinks are removed, which are the single buds and single leaf and a bud (Manivel and Hussain 1986).…”