Testing Putative Factor and Categories of Resistance in Wheat to Schizaphis, Graminum (Rondani) Using, Direct Current Electrical Penetration Graph (Dc-Epg) Technique

The green bug (Schizaphis graminum) (Homoptera: Aphididae) is a major aphid species attacking wheat crop in Pakistan, and is also reported as a major wheat pest across the world. Host plant resistance is an integral part of Integrated Pest Management (IPM). Several green bug resistant genes have been identified and introduced in commercial high yielding cultivars of wheat to manage green bug. There are three known insect resistance categories, including antixenosis, antibiosis and tolerance. Furthermore, using direct current electrical penetration graphs (DC-EPG) indicated that Parameters related to sieve element phases the aphid reached quickly on susceptible cultivar compared to ‘resistant’ plants. The percentage of time left available after first sieve element phase, Schizaphis graminum stayed for a significant longer period on susceptible cultivar compared to the resistant cultivars. The aphid penetrated sieve elements phase and phloem ingestion behavior was initiated with unequal success on resistant and susceptible genotypes. EPG indicates that phloem ingestion behavior is significantly reduced on resistant wheat lines compared to the susceptible cultivar. The duration of probing the pathway phase by S. graminum, was significantly different between control plants and the tested genotypes. Similar response was observed during the last parameter ‘mean proportion time’ where the aphid has spent significantly longer time on susceptible cultivar compared to the resistant genotypes.