Self-incompatibility evidenced through scanning electron microscopy and pollination behaviour in Stevia rebaudiana

Abstract

Floral development of stevia [Stevia rebaudiana (Bertoni)], as followed by light and scanning electron microscopy (SEM), was differentiated into 9 distinct stages, each having distinct landmark features. Tetrad formation takes place at stage-2 and microspore production starts. Highest pollen viability (72.8 per cent) was observed at stage 4, whereas, pollen grain production was recorded to be highest at stage-5. The stages-4 & 5 can be best utilized for pollen collection by dissecting out anthers for manual pollination as the pollen viability was recorded to be highest with maximum pollen production. These stages are important for pollen collection to achieve hybridization and get good seed set. Based on viable seed formation and per cent germination in different pollination treatments studied, pollinations using bumble bee thorax was most successful. No stevia pollen was observed to be dispersed at 2m away from the plant. The results indicate low pollen dispersal through air suggesting entomophilous pollination behavior of the crop. Whereas, no seed set was observed through selfing with bagging as well as selfing by hand-pollination. None of the self pollen adhering to the stigma was found germinated while emerging through anthers in a selfed flower. Although, a good seed set was observed in open pollination suggesting self-incompatibility in the crop.

Keywords

• Floral biology
• Pollination
• Pollen dispersal
• Scanning electron microscopy (SEM)
• Stevia rebaudiana