Báo cáo lâm nghiệp: "Pollen-limited seed set in ( Tamarindus indica L.)"

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Pollen-limited seed set in pods of tamarind ( Tamarindus indica L.) V. Bhaskar K.R. K. Usha Thimmaraju, Vignana Kendra, Bangalore 560 065, India University of Agricultural Sciences, Gandhi Krishi of Introduction Agricultural Sciences, Bangalore, India, using 50 flowers for each set of observations: 1) pol- len grains/stigma of intact and abscised flowers, 2) number of fertilized ovules, 3) percentage of A negatively skewed distribution of seeds flowers set into fruits, and 4) resource limitation: per pod, where the frequency of many- selected branches of approximately equal size seeded pods is higher than that of the few were defoliated to an extent of 25 (n= 10), 50 seeded ones, is a common feature of a (n= 10) and 75°/a (n= 10) and fruit set in these was compared with control branches; 5) effect majority of the multiovuled species (Lee of pollen quality: flowers (n = 50) were either and Bazaaz, 1982), However, disturban- self-pollinated, artificially crossed with pollen ces of this negatively skewed distribution from different trees or allowed to pollinate have been reported for certain other spe- naturally. The seed set percentage of these was cies. The adaptive reasons for and compared. mechanisms causing such deviations are less well known. In this paper, we have analyzed 3 factors causing positively Results skewed distribution (PSD) of seeds per pod in T. indica: 1) resource limitation, 2) Pod and seed set were low in tamarind; post-fertilization abortion of seeds, and 3) about 25% of the flowers set pods and pollen grain limitation. most contained few (1-4) seeds (Fig. 1). ). Resource limitation did not cause this reduction in pod setting and seed filling; Materials and Methods even 50% defoliation of leaves did not reduce the pod-setting percentage, al- though 75% defoliation did cause signifi- Tamarindus indica L. (Caesalpinae) is tropical a cant reduction (11.5%). tree cultivated for the pulp of the fruit, which is used in culinary preparations. It exhibits varied In tamarind, as in other species (Wilson patterns of seed distributions per pod of which and Schemske, 1980), there is selective PSD is the most common. Data were gathered abortion of pods. The percent pods with from 4 tamarind trees in and around Gandhi Kri- many seeds reaching maturity is higher shi Vignana Kendra Campus of the University
(Fig. 2). This indicates the existence of than those with few seeds. Thus selective pollen-stigma interactions. Such interac- abortion does not cause the observed tions can occur at 2 levels viz. 1) number- PSD. dependent inhibition of pollen grain germi- In tamarind, the ovary contains 8-10 ovules and 40% of the flowers received nation (Ganeshaiah et al., 1986) and 2) partial incompatibility of pollen grains. more than 10 pollen grains. Hence pollen Although cross-pollination did not affect grain number limitation cannot explain the the fruit set percentage, it significantly reduced seed set. However, until 15 pollen affected the number of seeds per pod. grains were deposited, the stigma did not seem to allow fertilization of ovules, after- While self-pollinated pods showed a PSD, wards, for the addition of every 3-4 pollen crossed pods showed a negatively skew- ed distribution of pods. This is suggestive grains, an additional ovule was fertilized
certain amount of of the existence of a partial self-incompatibility (Table I). Discussion and Conclusion In tamarind, PSD appears not to be under the regulation of the maternal parent, but to be a consequence of genetic dif- ferences among the pollen grains. the ovules to set seeds appears not to be due to the limitation of either pollen grains Tamarind produces an average of 8-10 0 or resources. Post-fertilization abortion ovules among which very few generally also does not explain PSD. However, the develop into seeds. Failure of the rest of
References partial self-incompatibility appears to re- pod in self- and duce the seed number per open-pollinated flowers, as indicated by Ganeshaiah K.N. & Umashankar R. (1988) the increased seed set in crossed over Regulation of seed number and female initiation self- or open-pollinated flowers. It is not of mate competition by a pH-dependent protein- aceous inhibitor of pollen grain germination in clear, whether the reduced seed number Leucaena leucocephala. Oecologia 75, 110-113 3 per pod in the self-pollinated flowers is Ganeshaiah K.N., Umashankar R. & Shiva- due to the failure of pollen grains to shankar G. (1986) Stigmatic inhibition of pollen germinate or due to the abortion of less grain germination - its implication for frequency competent zygotes. In either case, it can distribution of seed number in pods of Leu- be concluded that the PSD is driven by caena leucocephala (Zam) de wit. Oecologia 70,568-572 the pollen grain differences. Janzen D.H. (1982) Variation in average seed size and fruit seediness in a fruit crop of a gunacaste tree (Leguminoasae) Enterolobium cyclocarpum. Am. J. Bot. 69, 1169-1178 Acknowledgments Lee T.D. & Bazzaz F.A. (1982), Regulation of fruit and seed production in annual legume The authors are grateful to the authorities of the (Cassia fasciculata). Ecology 63, i 363-1373 University of Agricultural Sciences, Bangalore, Willson M.F. & Schemske D.W. (1980) Pollina- India, for providing facilities to conduct this tor limitation, fruit production and floral display investigation. They are highly indebted to Dr. in pawpaw (Asimina triloba). Bull. Torrey Bot K.N. Ganeshaiah for critically reviewing the Club 107, 401-408 manuscript.