Onion endophyte colonization of Thrips

Endophytic fungi, which live within host plant tissues without causing any visible symptom of infection, are important mutualists that mediate plant-herbivore interactions. Thrips tabaci (Lindeman) is one of the key pests of onion, Allium cepa L., an economically important agricultural crop cultivated worldwide. However, information on endophyte colonization of onions and their impacts on the biology of thrips feeding on them are lacking. We tested the colonization of onion plants by selected fungal endophyte isolates with two inoculation methods. The effects of inoculated endophytes on T. tabaci infesting onion were also examined. Seven fungal endophytes used in our study were able to colonize onion plants either by seed or seedling inoculation methods. Seed inoculation yielded 1.47 times higher mean percentage post-inoculation recovery of all the endophytes tested at (48.48 ± 8.1) as compared to seedling inoculation (32.87 ± 5.5). The lowest thrips numbers were recorded in Hypocrea lixii F3ST1 (1.6 ± 0.6) colonized plants as compared to the control (9.5 ± 1.5). Onion plants colonized by Clonostachys rosea ICIPE 707, Trichoderma asperellum M2RT4, Trichoderma atroviride ICIPE 710, and H. lixii F3ST1 had significantly lower feeding punctures as compared to the other treatments. Lowest number of eggs were laid by T. tabaci on H. lixii F3ST1 (1.5 ± 0.6) treatments followed by C. rosea ICIPE 707 and T. harzianum ICIPE 709 as compared to the control (18.6 ± 2.2). The number of feeding punctures and eggs were positively correlated (r = 0.805, d.f. = 30, P < 0.001). These results extend the knowledge on colonization of onions by fungal endophytes and their effects on Thrips tabaci.

内生真菌（endophytic fungi）是一类定殖于宿主植物组织内且不会引发任何可见感染症状的重要共生体，可介导植物与植食性昆虫间的互作。烟蓟马（Thrips tabaci Lindeman）是洋葱（*Allium cepa* L.）的主要害虫之一，而洋葱是全球广泛栽培的重要经济农作物。然而，目前关于洋葱内生真菌定殖以及其对取食洋葱的烟蓟马生物学特性影响的相关研究仍较为匮乏。本研究采用两种接种方法，探究了筛选得到的7株内生真菌分离物对洋葱植株的定殖能力，并检测了接种的内生真菌对取食洋葱的烟蓟马的影响。本研究选用的7株内生真菌均可通过种子接种或幼苗接种两种方式定殖于洋葱植株体内。相较于幼苗接种的定殖回收率（32.87 ± 5.5），种子接种的供试内生真菌平均定殖回收率达（48.48 ± 8.1），为前者的1.47倍。接种长枝腐质霉（Hypocrea lixii）F3ST1的洋葱植株上的烟蓟马种群数量最低，为（1.6 ± 0.6），显著低于对照组的（9.5 ± 1.5）。接种粉红粘帚霉（Clonostachys rosea）ICIPE 707、棘孢木霉（Trichoderma asperellum）M2RT4、深绿木霉（Trichoderma atroviride）ICIPE 710以及长枝腐质霉（Hypocrea lixii）F3ST1的洋葱植株，其烟蓟马取食刺孔数均显著低于其他处理组。烟蓟马在长枝腐质霉（Hypocrea lixii）F3ST1处理组的洋葱植株上产卵量最低，为（1.5 ± 0.6），其次为粉红粘帚霉（Clonostachys rosea）ICIPE 707与哈茨木霉（Trichoderma harzianum）ICIPE 709处理组，均显著低于对照组的（18.6 ± 2.2）。烟蓟马的取食刺孔数与产卵量呈显著正相关（r=0.805，自由度df=30，P<0.001）。本研究结果拓展了关于内生真菌定殖洋葱及其对烟蓟马影响的相关认知。