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

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Báo cáo lâm nghiệp: "Pollen-limited seed set in ( Tamarindus indica L.)"Pollen-limited seed set in pods of tamarind( Tamarindus indica L.) V. BhaskarK.R. K. Usha Thimmaraju, Vignana Kendra, Bangalore 560 065, IndiaUniversity of Agricultural Sciences, Gandhi Krishi ofIntroduction 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 ofA 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 sizeseeded pods is higher than that of the few were defoliated to an extent of 25 (n= 10), 50seeded 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) effectmajority of the multiovuled species (Lee of pollen quality: flowers (n = 50) were eitherand Bazaaz, 1982), However, disturban- self-pollinated, artificially crossed with pollences of this negatively skewed distribution from different trees or allowed to pollinatehave been reported for certain other spe- naturally. The seed set percentage of these wascies. The adaptive reasons for and compared.mechanisms causing such deviations areless well known. In this paper, we haveanalyzed 3 factors causing positively Resultsskewed distribution (PSD) of seeds perpod 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 andpollen 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 isused in culinary preparations. It exhibits varied In tamarind, as in other species (Wilsonpatterns of seed distributions per pod of which and Schemske, 1980), there is selectivePSD is the most common. Data were gathered abortion of pods. The percent pods withfrom 4 tamarind trees in and around Gandhi Kri- many seeds reaching maturity is highershi Vignana Kendra Campus of the University (Fig. 2). This indicates the existence ofthan 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 8-10ovules 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 affectgrain number limitation cannot explain the the fruit set percentage, it significantlyreduced seed set. However, until 15 pollen affected the number of seeds per pod.grains were deposited, the stigma did notseem 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 suggestivegrains, an additional ovule was fertilized certain amount ofof the existence of apartial self-incompatibility (Table I).Discussion and ConclusionIn tamarind, PSD appears not to be underthe regulation of the maternal parent, butto 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 res ...