author(s)
Harjindra Singh, HL Deshwal, Renu and Amar Chand

abstract
The present research was carried out at College of Agriculture, Bikaner, India during 2013-2014 & 2014-2015 by sowing ten varieties of mustard crop in pots of 30 according to randomized block design. Observations on aphid population were recorded soon after appearance of the pest from 10 cm terminal portion of central shoot of the plants. Weekly observations were recorded from appearance of aphid to harvesting of the crop and depicted least mean aphid population on variety T-59 (11.98 aphids) followed by Bio-902 (16.22 aphids) and both were at par to each other. However, Bio-902 varieties had no significantly differed from RGN-73 (21.90 aphids), Pusa bold (23.26 aphids). The maximum infestation was recorded on RN-393 (43.37 aphids) followed by Parasmani-8 (42.40 aphids) and Dron (41.17 aphids). However, these varieties were statistically at par to each other. RGN-73 (21.90 aphid) was at par with Pusa bold (23.26 aphid), RGN-48 (25.12 aphid), Laxmi (27.12 aphid) and Asherwad (29.01 aphid). These varieties were at par to each other. Seed yield of different varieties were also recorded after harvesting of the crop and Based on pooled data of peak aphid population. Categorization of varieties were done on the basis of statistical formula X + s, where the average value was (X= 57.15) and standard deviation (s = 23.91). Thus, three distinct groups of aphid population were obtained i.e. below 33.25, between 33.26 to 81.06 and above 81.06. Taking into consideration the above parameter, the varieties T-59 and Bio-902 were categorized as least susceptible. The varieties Pusa Bold, Laxmi, RGN -48, RGN-73 and Asherwad were categorized as moderately susceptible while varieties Dron, Parasmani -8 and RN -393 were highly susceptible