Factors Affecting the Number of Pollen Grains per Male Strobilus in Japanese Cedar (Cryptomeria japonica).

Hiroyuki Kakui,Eriko Tsurisaki,Yoshinari Moriguchi,Rei Shibata

doi:10.3390/plants10050856

Abstract

Japanese cedar (Cryptomeria japonica) is the most important timber species in Japan; however, its pollen is the primary cause of pollinosis in Japan. The total number of pollen grains produced by a single tree is determined by the number of male strobili (male flowers) and the number of pollen grains per male strobilus. While the number of male strobili is a visible and well-investigated trait, little is known about the number of pollen grains per male strobilus. We hypothesized that genetic and environmental factors affect the pollen number per male strobilus and explored the factors that affect pollen production and genetic variation among clones. We counted pollen numbers of 523 male strobili from 26 clones using a cell counter method that we recently developed. Piecewise Structural Equation Modeling (pSEM) revealed that the pollen number is mostly affected by genetic variation, male strobilus weight, and pollen size. Although we collected samples from locations with different environmental conditions, statistical modeling succeeded in predicting pollen numbers for different clones sampled from branches facing different directions. Comparison of predicted pollen numbers revealed that they varied >3-fold among the 26 clones. The determination of the factors affecting pollen number and a precise evaluation of genetic variation will contribute to breeding strategies to counter pollinosis. Furthermore, the combination of our efficient counting method and statistical modeling will provide a powerful tool not only for Japanese cedar but also for other plant species.

Highlights

Pollen grain number is an important trait in plants
Hereafter we discuss only male strobilus weight, as it is a trait that can be determined and it is considered more precise than area
Cell counter results indicated that larger/heavier male strobili tended to have more pollen grains (Figure 2), and that pollen size varied among samples (Figure 2d–g)

Summary

Introduction

Pollen grain number is an important trait in plants. The number of pollen grains produced has a direct effect on the number of offspring, and is known to vary among mating systems. Outcrossing plants tend to produce more pollen grains compared to closely related selfing species [1,2,3,4]. Wind-pollinators tend to produce more pollen grains than animalpollinated species [5,6]. While domesticated crop species such as rice or wheat tend to produce fewer pollen grains, effective pollination with abundant pollen grains is sometimes needed for purposes such as breeding hybrid crops or artificial pollination [7,8,9,10,11,12]. Pollen is important from a medical standpoint, because it triggers an allergic reaction called pollinosis around the world [13,14]

Methods

Results

Conclusion