<i>Aspergillus tubingensis</i> Is a Pre-Emergent Pathogen of Date Palm Seedlings

• Main Authors: Maryam Alomran, Jos Houbraken, George Newcombe
• Format: Article
• Language: English
• Published: MDPI AG 2020-12-01
• Series: Forests
• Subjects: desert ecology; cryptic pathogens; fungi; primary symbionts
• Online Access: https://www.mdpi.com/1999-4907/11/12/1327

Many diseases of date palm are known. However, pathogens that might affect seed germination and seedling emergence from soil are poorly studied, perhaps because date palm cultivars are propagated vegetatively. Here, we first determined the effects of date seed fungi on the germination and emergence of 600 seeds overall (i.e., 200 of each of three cultivars: ‘Thoory’, ‘Halawi’, and ‘Barhi’). In each cultivar, 100 seeds were from Saudi Arabia (part of the native range), and 100 were from the southwestern USA (where the date palm was introduced around 1765). Just four fungal genera (i.e., <i>Alternaria, Aspergillus, Chaetomium,</i> and <i>Penicillium</i>) were isolated from the surface-sterilized date seeds. <i>Aspergillus</i> isolates all belonged to <i>Aspergillus</i> sect. <i>Nigri</i>; collectively they were in the highest relative abundance at 39%, and significantly more common in Saudi Arabian seeds than in American seeds. <i>Aspergillus</i> reduced seed germination and also reduced emergence when germinated and non-germinated seeds were planted in potting mix in a greenhouse. In contrast, <i>Penicillium</i> species were more common in American than in Saudi seeds; <i>Penicillium</i> did not affect germination, although it did have a positive effect on seedling emergence. In a second experiment with 17 seeds of the ‘Halawi’ cultivar, fungus-free seeds were either inoculated with isolates of <i>Aspergillus</i> sect. <i>Nigri</i> or not, and then planted. Controls emerged whereas <i>Aspergillus</i>-inoculated seeds did not. Finally, a third experiment was conducted with <i>Aspergillus tubingensis</i> Mosseray, a sect. <i>Nigri</i> member, as sole inoculum of 100 ‘Halawi’ seeds versus 100 uninoculated controls. <i>Aspergillus tubingensis</i> exerted the same pathogenic effects on germinating and emerging seedlings as the isolates identified only to <i>Aspergillus</i> sect. <i>Nigri</i>. <i>Aspergillus tubingensis</i> is thus a previously unreported, seedborne pathogen affecting date palm seedlings. Our findings also suggest that <i>A. tubingensis</i> may be more common in seeds in the host’s native range than in its introduced range.