Vertical infection of Zucchini yellow mosaic virus via pollen transmission occurs at a lower frequency than ovule transmission

Seed transmission of Zucchini yellow mosaic virus (ZYMV) has been demonstrated in a variety of cucurbits, including wild Cucurbita species, and pollen transmission of viruses is common in the family Potyviridae. Consequently, vertical transmission of ZYMV may occur via the pollen of infected wild squash as opposed to ovule transmission. To determine if vertical infection of ZYMV occurs via pollen transmission, we pollinated flowers on virus-free Cucurbita pepo ssp. texana plants with pollen from ZYMV infected plants. We found that seed infection of ZYMV via pollen occurs at a rate of 0.13 %. This rate is much lower than expected based on previously reported rates of seed transmission, which suggests that while seed transmission via pollen does occur in C. pepo, it is not the main mechanism for vertical infection. Because seed transmission of ZYMV has been shown in virus-resistant transgenic plants, it is possible that ZYMV infection of transgenic plants via pollen may contribute to the seed transmission and geographic distribution of this virus.