Greenbug, Schizaphis graminum (Rondani), an important vector of barley yellow dwarf mosaic virus, is a major pest of cereals in many countries. A preliminary survey conducted in the Punjab and North Western Frontier Province of Pakistan revealed medium to heavy infestations at Charsadda (density 12 apterous greenbugs/25 plants), Sher Shah (Multan) (density 33) and Malkot (Murree) (density 114). However, it was found in small numbers at many other locations.
A culture of greenbugs collected from Charsadda, was established on susceptible wheat cultivar Faisalabad-83 at 27 ± 3°C, 60% r.h. and 16:8 hr day:night regime. A seedling bulk test using local and exotic host differentials indicated that DS-28A and Largo wheat were susceptible, whereas Amigo wheat, Post and Will barley were resistant. This indicates that the population of greenbug from Charsadda culture was different from greenbug biotypes occurring in the USA. Therefore, it was designated as biotype PK-I for future reference.
Of the 44 recommended wheat cultivars in Pakistan, Punjab-85 was found to be resistant (visual damage rating (DR) 3 at 0 to 9 damage scale; 0, healthy; 9, dead). Faisalabad-85 had a DR of 4, PARI-73, Sandal and Yecora had a DR of 5, and PAK-81, WL-711, Sutluj-86 and Nuri-70 had a DR of 6. All the remaining cultivars were highly susceptible to greenbug (DR ≻ 6).
Three tests, namely, antixenosis (non-preference), antibiosis and tolerance, were conducted to determine the nature of resistance in selected entries. In the antixenosis test, PARI-73, WL-711 and Yecora were found to be the least preferred. The lowest fecundity (antibiosis) of the greenbug was on Punjab-85. In the tolerance test, the lowest damage was recorded on PARI-73 (DR= 4.1), followed by Sandal (DR= 4.8) and Punjab-85 (DR= 4.8). These three tests indicated that resistance in Punjab-85 is mainly due to antibiosis and a low level of tolerance.
During this study 439 native wheat germplasm lines were also tested. Of these, 16 germplasm lines (PAK 15081, PAK 15115, PAK 15139, PAK 15242, PAK 15433, PAK 15479, PAK 15481, PAK 15519, PAK 15992, PAK 15994, PAK 15995, PAK 15997, PAK 16007, PAK 16008, PAK 16010 and PAK 16190) were found to have a high level of resistance (DR ≺ 3). Of the test entries, 114 were moderately resistant (DR= 4–6) and the remainder were susceptible (DR ≻ 6) to greenbug. The germplasm lines found resistant may have different genes for resistance which can be exploited in breeding programmes.