Lack of plant resistance in Raya, Brassica juncea (L.) varieties against two aphid species in Southern Punjab.

Cabbage aphid (Brevicoryne brassicae L.) and mustard aphid (Lipaphis erysimi (Kalt.)) are important pests of brassicas in Pakistan. We evaluated available varieties of Raya, Brassica juncea (L.) for comparative resistance against cabbage and mustard aphid at Multan and Bahawalpur during crop years 2002-2003 and 2003-2004. Varieties BARD-1, BRS-3, PIIR-1, UCD-6/10, P63R5, UCD-44/4, UCD-636, P-37 and RC-280 were planted during 2002-2003. Two more varieties, i.e. 95101/163 and 95102/51 were also included in trials during 2003- 2004. To determine the degree of resistance, the densities of aphids of both the species were recorded from the top 10cm of the inflorescence by gently beating it 10 times on a white plastic sheet. For this purpose six plants were selected randomly from each treatment. Observations were recorded weekly from the initiation of aphid attack till maturity of the crop. The densities of B. brassicae were significantly different across the tested varieties during 2002- 2003 on four sampling dates out of seven at Multan and that of L. erysimi were non-significant during same year at this location on all sampling dates. Population of B. brassicae and L. erysimi was also non-significantly different during 2002-2003 at Bahawalpur and 2003-2004 at Multan and Bahawalpur. Based on the results no variety could be declared resistant to cabbage aphid or mustard aphid.