Abstract: To elucidate aphid resistance mechanisms in three wheat cultivars Ww2730, Xiaoyan22 and Batis, Rhopalosiphum padi L. (Homoptera: Aphididae) feeding behavior was examined using the electrical penetration graph (EPG) technique. The results showed that the initial probing of R. padi on Xiaoyan22 occurred the latest and probing duration was also the shortest among the three cultivars examined. Highest frequency and longest duration of intercellular piercing (F waveform) of R. padi feeding was recorded on Ww2730 R. padi spent significantly more time feeding on mesophyll tissue to ingest actively (G waveform) on the both Ww2730 and Xiaoyan22 when compared with Batis. R. padi ingested from phloem of Batis with much more watery salivation and less excretion (E1 waveform), and ingested passively (E2 waveform) for the longest duration among all three cultivars examined. In contrast, before initiating ingestion on Xiaoyan22, aphids probed, withdrew uninterruptedly and with extended watery salivation (E1 waveform), the duration of passive ingestion (E2 wave) was also the shortest, although their stylets reached to phloem the earliest. We concluded that Ww2730 and Xiaoyan 22 were resistant to R. padifeeding, while Batis was susceptible to R. padi feeding.  It was inferred that physical and biochemical factors in plant tissues (e.g., epidermis, mesophyll and phloem) prevented R.padi from feeding on Xiaoyan22, mechanical restriction between the cells restricted R. padi  to feed on Ww2730, while Batis is a susceptible variety to R. padi.

Key words: Rhopalosiphum padi, wheat, feeding behaviour, resistance, electrical penetration graph (EPG)