Pollination Biology Of Acacia Mangium And A. Auriculiformis

Pollination biology of Acacia mangium and A. auriculiformis were investigated at aspects of floral phenology, floral morphology, anthesis, pollen shedding, pistil receptivity, insect visitors to flower and so on through routine observation combined with light microscopy and scanning electron microscopy (SEM) in clone seed orchard at Shadui Town, Jiangmen City, Guangdong Provence. And breeding system of Acacia mangium was revealed by controlled pollination, in which the relationship between floral morphology, insect foraging behavior and breeding system was discussed and factors that may affect fruit set and seeds production were analyzed. The findings will provide a theoretical basis for the seed orchard management of both species. The main conclusions are as following:1. Acacia mangium flowers between September and October. Its flowering was not continuous, but 3~5 flowering days and 6~15 non-flowering days occurred in cycles. Individul flowered in synchrony, showing the"mass-flowering pattern". Spike-like inflorescence consists of 172.7±27.1 flowers, including hermaphrodite flowers and male flowers. Male flowers account to 10.35±7.78% per spike. The pistil contained 14.11±1.05 ovules with a long, solid style was surrounded by 83.2±10.3 stamens. Cup-liked stigma was suitable for one polyad, which comprising 16 pollen grains. It was supposed that one polyad had the potential to set a full pod following a single pollination event, since 59.4% stigmas that we calculated were just one polyad. A. auriculiformis flowered from October to December with the similar phenology as A. mangium. The spike consists of 114.8±11.9 flowers, bearing 124.1±16.4 anthers for each flower; pistil contains 14.4±1.9 ovlues. P/O'of A. mangium valued 1.13 while A. auriculiformis valued 1.11, which showed self-incompatible somehow.2. Anthesis were similar between the two acacias, spikes opened at night and would boom in the next morning. A. mangium Pistil was the first organ to extend and receptive making protogynous sensible, but differently, A. auriculiformis was homogamy. Stigmas gone through morphology changes showed as exudates were emerged apparently during the first half-day after anthesis. The process of flowering was divided into five stages. SEM revealed that the dehiscent lines existed at Stage2 both in the two species, however, Anthers began to dehisce at Stage 4 for A. mangium but at Stage 3 for A. auriculiformis.3. Anthers dehiscence occurred at 0700h~0900h following abundant pollen shedding at 0900h~1200h. Pistil receptivity last for two days with the peak receptive period began at 1000h in the first day. Stigmas vitality was extremely low in the third day for A. mangium. On the opposite, A. auriculiformis stigmas could keep high vitality in the third day and pistil could keep straight for 3~4 days even after pollen shedding, which showed a longer pistil receptivity.4. Acacia mangium provide both nectar and pollen as reward for flower visitors. Such reward could attract diverse insects, including Apis cerana, Allograpta javana. Calliphora Spp., Ceratina flavipes, butterflies, wasp and so on. Within which, Apis cerana was main pollen collector and also the most frequent and effective pollinator. Open pollination success was 78.3%, which was not low compared with other acacias. Therefore, lack of pollinators can not explain the low fruit set.5. Acacia mangium had high level of outcrossing and controlled pollination showed it was self-incompatible. ISI was to 0, or close to 0 in the six test trees. Knowing the flower was protogynous, artificial pollination could be carried out in female stage to avoid the tough emasculation process.6. Fruit set through open pollination was extremely low with an average of 0.09%. Frozen injury, typhoons might be the main environmental factors affecting fruit set. The automatic self-pollination success up to 33.6% showed a high lever of selves'polyads reaching stigmas, making few pods for the existence of self-incompatibility. Thus, we propose that high level of self-pollination rate was the major biological factor limiting the fruit set. Besides, fruit set could be improved to 27.5% though artificial pollination. Matured pod comprising 10.3 seeds and most frequently 11 seeds, lower than the average ovules number of 14. Maybe, this might be affected by the factor such as unvitality of pollen, posing manner of polyad on stigma, seeds abortion and so on.