Categories of resistance in wheat to green bug Schizaphis,Graminum (Rondani) through a novel technique direct current electrical penetration graph (DC-EPG)

The green bug,schizaphis,graminum (rondani) is a cosmopolitan pest of bread wheat triticum,aestivum l; and sorghum sorghum,bicolor l. seven wheat lines were evaluated for the three known insect resistance categories,including antixenosis,antibiosis and tolerance. no antixenosis was found during the screening tests. wheat accessions,‘molly’ exhibited antibiotic effects toward green bug in the form of reduced rate of natural increase. the (rm) of green bug on wheat lines ‘molly,“magnum and caldwell” was significantly lower than that of s. graminum on plants of susceptible cultivar jagger. measuring leaf chlorophyll content,spad chlorophyll meter,was used for tolerance determination. the tolerance resistance in molly proved to be the result of a combination of antibiosis and tolerance categories. 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 ‘molly,magnum and caldwell plants. this pattern was followed by the potential drops. the percentage of time left available after first sieve element phase,schizaphis graminum stayed for a significant longer period on susceptible cultivar ‘jagger’ compared to the tested entries; “molly,caldwell and magnum” (7.10,3.21%,3.93 and 15.81% respectively. 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 tested wheat lines “molly,magnum and caldwell” genotypes compared to the susceptible cultivar ‘jagger’. the duration of probing the pathway phase by s. graminum,was significantly different between control plants and the tested genotypes (molly,magnum and cladwell). similar response was observed during the last parameter ‘mean proportion time’ where the aphid have spent significantly longer time on susceptible cultivar as compared to the resistant genotype. © 2015,pakistan botanical society. all rights reserved.