Evaluating the precision of staining methods in determining pollen viability and in vitro pollen germination in two endemic varieties of Humboldtia brunonis Wall. (Fabaceae-Detarioideae)

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The genus Humboldtia, restricted to the Western Ghats of India and Sri Lanka, is mainly propagated by the seeds. However, the seed set is very low in a few species, which includes Humboldtia brunonis and its varieties. One important factor that restricts seed formation may be the viability of the pollen grain employed in cross-pollination operations. Considering this, the present study aims to report the pollen viability and pollen germination of H. brunonis var. brunonis and H. brunonis var. raktapushpa. Pollen viability was determined by Fluorochromatic reaction test (FCR) and 3, 3’- Diamino benzidine test (DAB) based on the pollen and in vitro pollen germination was determined in different sucrose concentrations of Brewbaker and Kwack (BK) medium. The pollen viability test using DAB revealed that more than 73 % of pollen was viable. However, 68.6 % of pollen in H. brunonis var. brunonis and 67.8 % of pollen in H. brunonis var. raktapushpa showed viability under FCR test. More interestingly, at the same time, only 67.27 % of pollen germination was exhibited in the BK medium. Pollen viability by FCR and in vitro pollen germination significantly correlates with the results; on the contrary, in vitro germination is not correlated with the DAB test. Along with the in vitro staining and in vitro pollen germination, detailed macro-morphology and pollen morphology of the selected taxa are given herewith.