Abstract:
An experiment set up at four sites in Kericho, Kenya was used to investigate
Genotype x Environment interactions of four tea clones of commercial and scientific
interest.
Small differences in environment resulted in large variations in dry matter production
and yield between sites and clones. The largest dry matter was from clone TNI 4/3
(291 ha'1) but it had low yield (2.11 ha'1/ 1). By contrast, the largest yield was from
clone S15/10 (3.81 h a 'V 1), which gave the smallest dry matter ( I S th a 1). These
contrasting responses in dry matter and yield were analysed in terms of the interception
of solar radiation, radiation use efficiency, partition of dry matter and components of
yield. The differences in clonal dry matter production were attributed to site to site
variability in solar radiation and temperature which affected the rates of ground cover
development and the solar radiation interception. The differences in yield were attributed
mainly to differences in air temperature and saturation deficits of the air between the
sites which affected the shoot replacement cycles through rates of shoot extension and
development.
Differences in measured and derived environmental variables between the sites were
found. Incident solar radiation differed between the sites by up to 2.4M Jm 2 d 1.
Differences in mean air and soil temperatures between the extreme sites were 2.5 °C and
3 °C respectfully. A lapse rate of 6.1 “Ckm*1 for mean air temperature was found.
Annual rainfall amounts also differed between the sites by up to 700 mm. There were no
differences in wind speeds, but there were large differences were in saturation deficits
(0.5 kPa) and évapotranspiration (1 mm d*1).
During the course of the experiment light interception ranged from less than 5% at
planting to more than 80% in April 1994. Radiation use efficiencies for dry matter
ranged from 0.30 to 0.45 g MT1 in the clones studied and appeared conservative with
respect to temperature across the sites.
Clone TNI4/3 had the lowest base temperature for shoot extension (6.1 °C), while
clone BB35 had the highest (10.4 °C). The base temperatures for shoot extension were
1.3 to 2.9 °C higher than those for development, hence the differences in shoot lengths
between sites. Shoot replacement cycle ranged from 57 days to 110 days between the
sites and was the main determinant of yield.
Abstract
Silsoe College
WK Ng’etich
PhD. 1995
CranfisM,m
The dry matter content of shoots varied between sites and seasons and ranged from
18% to 33%. Mean shoot dry mass was inversely proportional to temperature, ranging
from 6 to 12% difference between extreme sites.
Loss in yield due to water stress during the dry seasons ranged from 14 to 20%
across the sites. Yield losses due to ‘hut sites’ ranged from 10 to 50%, while that from
hail damage accounted for up to 20% of annual yields.
These results are discussed in the light of other work in Kericho and southern
Tanzania. The thesis concludes by considering the implication of the results for the tea
industry.