Tamarind monograph.pdf - Crops for the Future

6.3 Anthesis and stigmatic receptivity
Observations carried out in Sri Lanka revealed that anthesis starts at 16.30-
21.00 hrs and flowers completely open by 04.00hrs. Anther dehiscence
occurs from 7.00-11.00 hrs. In India, anthesis starts at about 16.00-20.00 hrs
and flowers are completely open by 02.00 hrs. Anther dehiscence occurs
from 08.00-10.00 hrs in the morning (Thimmaraju et al., 1977; Nagarajan et
al., 1997). Tamarind stigmas are receptive for nearly 48hrs with peak
receptivity on the day of anthesis (Thimmaraju et al., 1977; Nagarajan et al.,
1997). Based on the timing of stigma receptivity and anther dehiscence,
tamarind is classified as a protogynous species.
6.4 Pollen morphology and pollination vectors
Pollen grains are dimorphic, radially symmetrical, tricolporate, oblatespheroidal
in shape and sticky (Perveen and Qaiser, 1998). Nagarajan et al.
(1997) showed pollen dimorphism in tamarind with two distinct sizes of
pollen grains : 40-42 μm and 22-25 μm. This size variation was attributed to
resource limitation towards the latter part of the flowering season. Smaller
pollen grain counts increased during the later part of the flowering. Pollen
sterility is very low in tamarind (less than 2%). Under ambient conditions
(37-40 0 C) pollen viability was observed to be 88% for three days, while
pollen stored at 4 0 C remained 97% viable up to 100 days. Variation of
pollen sterility, dimorphism and viability of different tamarind clones are
given in Table 6.2.
Studies carried out in Sri Lanka revealed that tamarind pollen grains are
sticky and the flowers produce nectar. Sticky pollens are not efficient for
wind pollination. Honey bees (Apis spp.) are common visitors to tamarind
flowers particularly between 08.00-11.00 hrs and 16.00-18.00 hrs.
Observations of honey bee activity on flowers and their visitation patterns
suggest that they are effective pollinators. Thus, pollination is mostly by
honey bees. Prasad (1963) also suggested that tamarind is insect pollinated
due to its floral characters and the presence of copious levels of nectar.
Similar observations were also made in India by Nagarajan et al. (1997) and
Thimmaraju et al. (1977). Arroyo (1978) also suggested that honey bees are
the most common pollination vector among leguminous species including
tamarind. Insect visitation in tamarind peaks between 08.00 hrs and 11.00
hrs which is compatible with stigmatic receptivity and anther dehiscence.
Studies in Coimbatore in India observed the foraging of flower visitors.
Tamarind flowers mid-May to mid-July but natural fruit set is low: 3-5%
compared to 70-90% in controlled experiments. A range of insects
belonging to Hymenoptera, Lepidoptera, Hemiptera, Diptera and
Thysanoptera visited. Bees are the major pollinators. Domesticated
honeybees ensure pollen transfer and fruit set (Sasidharon et al., 2003).
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