Abstract
Grasses produce large amounts of pollen and are among the main causes of pollen allergy worldwide. Quantification of the roles of individual grass species in airborne pollen is an important task, because morphologically indistinguishable pollen grains of different species may differ in allergenicity. This requires knowledge of the pollen production of individual grass species; however, accumulated data are insufficient in this respect. Attempting to fill this gap, we studied pollen production per inflorescence in 29 grass species which are widespread in Middle Russia and India. Pollen production per inflorescence is determined by the number of grains per anther, the number of flowers in a spikelet and the number of spikelets per inflorescence, with the latter parameter being the most variable. We support the hypothesis that pollen production per inflorescence differs significantly between annual and perennial grasses. The greater pollen production of perennials can be interpreted as a tendency to guarantee cross-fertilization of species with self-incompatibility. The inferred pollen/ovule (P/O) ratios suggest the occurrence of facultative xenogamy in all annuals and obligate xenogamy in most perennials in the present dataset, though some self-incompatible annuals exist outside our sampling. Earlier data indicated that the P/O ratio of the annual cereal crop rye (Secale cereale) is higher than in any annual or perennial species sampled here. A ratio of pollen production to seed set (P/S ratio) is suggested to be another efficient parameter in reproductive biology of grasses. We highlight a need for detailed studies of reproductive biology in grasses that include both pollen and seed production. We found a correlation between pollen production per anther and anther length. A rough approximation of c. 1000 pollen grains per 1 mm of the length of an anther provides an instrument for estimates of pollen production in plant communities.
Highlights
Grasses (Poaceae) make up the second-largest monocot family, comprising more than 11,000 species worldwide [1]
The aim of our study was (1) to evaluate pollen production per inflorescence in common grass species in Maharashtra and Middle Russia [54,55]; (2) to compare the pollen production of species with different life forms; (3) to evaluate the variability of all traits that determine pollen production; and (4) to determine whether pollen production is correlated with the size of pollen grains and anther length in a large-scale analysis that includes various grass species that differ in ecology and reproductive biology
We found no difference in pollen production between male and bisexual flowers of Arrhenatherum elatius (t-test; p-value > 0.05); in subsequent analyses, we used our measurements of this species as a single dataset
Summary
Grasses (Poaceae) make up the second-largest monocot family, comprising more than 11,000 species worldwide [1]. The importance of this group lies in the number of species and their wide distribution; interactions between grasses and humans are multidimensional, and go far beyond their use as crop cereals [2,3] and pasture plants [4]. The very high pollen production characteristic of many grass species is related to their reproductive strategy. Besides reproductive strategies and local conditions, pollen production -of grass species depends on the life form (annual or perennial). Perennial grasses are known to produce more pollen than annuals [27,28,29]
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