A final observation from this research was that pistil-inoculation circumvented the PE layer and deposited A. citrulli in the embryos of watermelon seeds. This conclusion was based on the observation that significantly higher percentages of embryos were infested with A. citrulli in pistil-inoculated seeds compared to pericarp-inoculated seeds. Additionally, removal of PE layers and testae did not affect BFB transmission for pistil-inoculated seeds, whereas BFB transmission was significantly reduced for pericarp-inoculated seeds. At present, it is unclear how A. citrulli cells become deposited in different seed tissues based on the pathway of bacterial ingress. However, bacterial deposition might be influenced by the timing of development of the different seed layers. To date, PE layer development has not been described in detail for watermelon seed but in cucumber seeds the PE layer begins to form by 15 day post anthesis (DPA) and matures by 35-45 DPA (24, 40, 41). At 15 DPA, a lipid layer differentiates in the epidermis of the four- to five-layered nucellus. An immature callose layer appears on the surface of the PE layer by 25 DPA, and by 35 DPA the lipid layer matures and a callose layer is deposited on the endosperm surface (40). At 45 DPA, the nucellar cells degrade to form a mature PE layer. While similar details on watermelon PE layer development are not available, preliminary experiments showed that inoculation of female watermelon blossoms with A. citrulli resulted in ovule contamination by A. citrulli within 24h (data not shown). Since the PE layer is not full developed by this time, it is possible that bacteria can gain access to the seed embryos. In contrast, Frankle and Hopkins (6) showed that the window for A. citrulli to migrate through the pericarp of immature