Pollen viability in the genus Silene (Caryophyllaceae) and its evaluation by means of different test procedures

Various direct and indirect tests are used to estimate pollen viability. Results obtained with these tests,however, are contradictory for different species and do not always match with naturally occurring pollen germination. To investigate naturally occurring pollen germination of four Silent species a new method of scoring germinated pollen grains in vivo directly on the stigmas of intact flowers was developed. Germination percentages found with the in vivo test ranged from 67 to 77%. The results of two indirect tests that are commonly used to assess pollen viability, aniline blue in lactophenol staining (ALS) and fluorochromatic reaction (FCR), were compared with the results of the newly developed in vivo test for the same four species. ALS revealed high pollen viability, ranging from 82 to 93%, whereas FCR revealed lower viability, ranging from 28 to 50%. Our suspicion that ALS overestimates natural pollen germination in Silent was confirmed by testing viability of dry-stored and n-Hexane-stored pollen grains with both indirect tests. Because of the known short viability of trinucleate pollen grains, dry-stored grains should be dead. Storage in n-Hexane, however, conserves pollen viability because of its positive effect on the integrity of the pollen membrane. ALS showed high viability for both dry-stored and n-Hexane-stored pollen grains. In contrast, FCR-treated pollen showed viability only after n-Hexane-storing but not after dry-storing. Of the two indirect tests, FCR should be given preference over ALS because it reflects at least trends of viability in pollen grains, however, it is not accurate enough to reflect natural germination percentages of trinucleate Silene pollen as found with the in vivo test.