Abstract
In agricultural ecosystems, insect pests, pathogens, weather patterns, and reduced soil fertility pose major challenges to crop productivity and are responsible for significant yield losses worldwide. Iris yellow spot virus (IYSV) vectored by Thrips tabaci Lindeman, is a major hindrance to onion production in eastern Africa. Control measures often rely on insecticides with deleterious effects. Endophytes are one key alternative as they can play important roles in mediating induced systemic resistance. Hence, we examined the potential effect of endophytic fungus Hypocrea lixii (F3ST1) on feeding and replication of IYSV on endophyte-colonized (E+) and endophyte-free (E-) onion plants. For more precise assessment, replication was also tested using leaf disk bioassays and individual thrips. The number of feeding punctures was significantly lower in E+ as compared to E- plants. Disease level was significantly lower in E+ as compared to E- plants for four weeks post-exposure to thrips. IYSV replication was reduced by 2.5-fold in endophytic treatment on both whole plant and leaf disk assays. Thrips tabaci showed 2 times higher feeding activities on endophyte-free onion leaf disks as compared to the endophyte-inoculated leaf disks. Our results suggest potential utility of the endophytes to reduce feeding damage and virus infection on onion plants. Further studies should be conducted to elucidate the secondary metabolites involved in such endophyte-thrips-virus mediated interaction and determine whether the interactions extend for this and other onion varieties and viruses under field conditions.
Highlights
Onion, Allium cepa L. (Asparagales: Amaryllidaceae), is an important vegetable crop grown for its benefits in subsistence or commercial farming systems worldwide
Initial cultures of T. tabaci were field-collected from onion plants at the International Centre of Insect Physiology and Ecology organic farm, Duduville, Nairobi, Kenya
Hypocrea lixii (F3ST1) was the best performing isolate (Muvea et al, 2014), which was selected for the current study
Summary
Allium cepa L. (Asparagales: Amaryllidaceae), is an important vegetable crop grown for its benefits in subsistence or commercial farming systems worldwide. Induced Resistance to Thrips-Transmitted Tospoviruses and worldwide (Trdan et al, 2005; Waiganjo et al, 2008). They cause direct damage by feeding on leaf tissues resulting in a reduction of photosynthetic ability and reducing onion bulb size and yield (Rueda et al, 2007; Birithia et al, 2014). Bulb onion yield losses of up to 60% have been reported in Kenya due to thrips damage alone (Waiganjo et al, 2008). To remain effective, control programs have to integrate several disease management tactics that explores next-generation agriculture including the use of beneficial micro-organisms such entomopathogenic fungi which have been reported to play multiple roles in nature (Vega et al, 2008)
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