Morphological and histological aspects of Solanum tuberosum plants infested by Macrosiphum euphorbiae aphids

Abstract

Despite the important yield loss caused by Macrosiphum euphorbiae on potato crops, little is known about its direct effect on Solanum tuberosum plant. These phloemophagous insects use their piercing mouthparts (stylets) to follow intercellular pathway till reaching phloem sap. Consequently, host cells are punctured and aphid saliva is injected periodically to seal off the pores. Thus, host tissues are challenged by both mechanical wounding as well as salivary compounds delivered by aphids which might elicit or prevent the early defence responses. Our results display the main symptoms of compatible interaction between M. euphorbiae and its host plant S. tuberosum characterized at macroscopic and microscopic levels. Polyphenol deposits such as lignin and suberin associated with salivary sheath appear within 72 h after infestation resulting in cell wall thickening. Callose deposition was induced earlier in the apoplasm of epidermal and mesophyll cells beneath the feeding site and in the sieves tubes of distal leaves. Continuous aphid feeding led to a remarkable repression of callose in the mesophyll that appears to be co-localized with polyphenols surrounding the aphid stylet track. At high aphid density, localized cell death was observed on the foliar limb resulting in a drastic reduction of aphid’s growth at 4 days. Our results indicate that plant symptoms are tightly dependant on modality and time of aphid infestation which highlights the importance of taking all aspects into consideration when studying plant resistance to herbivores. The use of cytological approach is very promising tool for screening plants for aphid resistance.