PhD

Black pepper (Piper nigrum L.) is the most valued spice crop of India. "Bush
pepper" and "vine pepper" are two morpho-types of the crop, regenerated by planting
laterals (Plagiotropic) and runner vines (orthotropic) respectively. Most of the area under
black pepper in India is occupied by vine pepper trailed on live standards. Bush pepper,
because of its bushy growth, shade tolerance, early and year round bearing offer great
scope for growing in terrace gardens, kitchen gardens, homesteads and as an under-storey
crop in coconut plantations and agroforestry systems. The productivity of the crop is very
low in India. Seasonal water stress due to uneven distribution of rainfall is considered as
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the major constraint in increasing the productivity of black pepper. This problem can be
solved to a great extent by growing drought tolerant varieties and/or providing
supplementary irrigation. Knowledge about the optimum percentage of depletion of
available water and the root zone of the crop is necessary to schedule irrigation. Hence
experiments were conducted to screen and characterize water stress tolerant black pepper
varieties and to compare the response of bush pepper-and vine pepper to soil moisture
stress. The optimum percentage of depletion of available soil moisture and the root zone
of bush pepper for scheduling irrigation were estimated. The best drip irrigation schedule
for field planted bush pepper was also found out. For this three pot culture experiments
were conducted at Kerala Agricultural University Campus at Vellanikkara, Thrissur, from
December 1997-May 1999 and two field experiments at Peruvannamuzhi farm of IISR,
Kozhikode, during December 1998 to January 2000.





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Forty four varieties were screened for water stress tolerance. From these, six
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watcr stress tolerant varieties and one sensitive variety were selected based on relative
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water content, membrane stability and number of days taken for wilting, when
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progressively water stressed. These varieties were subjected to mild, moderate and severe
water stress and compared with an unstressed plant, in a pot culture experiment, laid out
in completely randomized design and replicated four times. In another pot culture
experiment the response of bush pepper to mild, moderate and severe water stresses were
compared with vine pepper. Root distribution of bush pepper was studied using 32P_plant
injection technique in a completely randomized design experiment, replicated five times.
Seven drip irrigation levels (2, 4, 6, 8, 12,,16 L October-May and 16 L October-March)
were compared with daily pot watering (10 L) in another field experiment, in mature
coconut garden, laid out in randomized block design and replicated thrice.
Out of 44 varieties, 15 wilted by second day of water stress and only six varieties
survived water stress for four days. The six survived varieties maintained high relative
water content and membrane stability, when water stressed. The height, number of leaves
and leaf area decreased in all the varieties due to water stress.
The increases in the activities of peroxidase, catalase and superoxide dismutase,
III response to water stress were more in Panniyur-5 and Padarpan. The maximum
percentage increase in peroxidase and catalase activities, in response to water stress were
in Padarpan and the least in Panniyur-L High level of lipid peroxidation was observed in
Panniyur-I. Chlorophyll content decreased in all the varieties due to severe water stress.
The epicuticular wax content was the highest in Panniyur-5 and the least in Panniyur-I.



Accumulation of proline, sugar ami amino acid were observed in response to water stress
in some of the varieties. Percentage increase in proline content of the leaves over control
was maximum in Poonjarmunda and the least in Padarpan. Among the water stressed
plants maximum sugar content •was observed in the variety Kalluvally-4 followed by
Poonjarmunda and Padarpan. The amino acid content increased due to water stress, in
varieties Poonjarmunda, Panniyur-I, Panniyur-5 and Padarpan. Electrophoretic pattern of
protein revealed additional bands in water stressed plants of Panniyur-5, Kumbakodi. In
Poonjarmunda, Padarpan and Panniyur-I the number of protein bands were less in water
stressed plants as compared to the unstressed plants. The N, P, K, Ca, Mg, Cu, Zn content
of leaves increased in general due to water ~tress whereas Fe and Mn decreased.
The variety Panniyur-I had low epicuticular wax, less thickness of cuticle and
sclerenchyma tissue on leaves and stem.
The bush and vine type of Panniyur-I did not survive one to three days of water
stress cycle for more than twenty days and it is deduced that both bush and vine types of
Panniyur-I are very sensitive to water stress. In Panniyur-5, which survived the water
stress, there was no significant variation between bush and vine pepper in most of their
biometric characters. Stomatal conductance, transpiration rate and leaf water potential of
Panniyur-5 showed variations between bush and vine type, when water stressed.
In bush type of Panniyur-S, 14C02 fixed .by the leaf was translocated to the spike
on the corresponding node as well as to other spikes, when exposed to mild and moderate
water stress, whereas, in unstressed plants the translocation was mainly from the leaves to
the corresponding spike on the node. In Panniyur-I, there was no translocation of 14C02 from the leaf to other spikes, in water stressed as well as in daily irrigated plants; 14C02
was translocated to the spike on the corresponding node only. In water stressed plants of
Panniyur-5, without berries, 14C02 translocation was observed towards the stem and ~ther
leaves, whereas in Panniyur-1, 14C02 accumulated in the stem and there was no
translocation to other leaves.
For scheduling irrigation the optimum percentage of allowable depletion of soil
moisture for bush pepper was fifty per cent. Biometric characters such as number of
leaves, total number of branches, shoot dry weight, root dry weight and total dry weight
were more in plants irrigated at fifty per cent depletion of available soil moisture and the
lowest in plants irrigated at seventy five per cent depletion. Similarly, dry berry weight
and oleoresin content of the berries were higher in plants irrigated at fifty per cent
depletion of soil moisture.
The root zone of field planted bush pepper was at a lateral distance of 30 cm and
depth of 60 cm. The effective foraging zone for the crop was between 20-30 cm lateral
distance and 40 cm depth.
The vegetative growth of bush pepper was superior with 16 L (October-May) and
pot watering 10 L per day. But the yield contributing characters like the number of
spikes, length of spikes, number of berries, hundred berry weight, berry volume, green
and dry berry yield and oleoresin content of berries were maximum in plants irrigated
with 8 L drip and the least in 2 L drip. It was deduced that 8 L drip irrigation is better
than daily irrigation (10 L pot per day) for three years old bush pepper variety Karimunda
grown in coconut garden.