Abstract
Ten varieties of mustard namely, 'Nap-3', 'Shambol', 'Safal', 'Agrani', 'YS- 52', 'Sampad', 'SS-75', 'Sangam', 'BS-5' and 'Tori-7' were tested against the mustard aphid, Lipaphis erysimi (Kalt.) under natural and artificial conditions. during two consecutive seasons (1993-94 and 1994-95). Field experiments were conducted at two locations - - Mymensingh and Ishurdi. Experimental results showed that the resistant or less susceptible varieties had lower aphid infestation. Generally, aphid infestation showed a rising trend from the flowering stage, reached the peak at pod formation stage, and then tended to decline in all the varieties.
Plants having darker and non-waxy leaves, hardy slender inflorescence and loosely packed buds were less susceptible or resistant. Taller plants, more number of branches and pods, number of seeds per pod and greater pod length were responsible for less aphid infestation. In spite of aphid infestation, 'Safal' and 'Agrani' produced the higher yield because of the fact that these varieties had the inherent characteristics of withstanding aphid infestation. Mymensingh region was found better for mustard crop production than Ishurdi: Lower fecundity, survival percentage, nymphal period and longevity of aphids were observed in less infested. varieties. Moderately resistant or less susceptible varieties viz., 'Nap-3' (Brassica napus), 'Shambol' (B. juncea), 'Safal' and 'Agrani' (B. campestris) exhibited tolerance mechanism of resistance against aphid. Other six varieties of B. campestris failed to confirm the mechanism of resistance.
Lower amount of nitrogen (N) and higher amount of phosphorus (P) and potassium (K) in plant tissues were found responsible for aphid resistance. On the contrary, the concentrations of calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), copper (Cu), zinc (Zn) and sulphur (S) failed to indicate either positive or negative effect on aphid infestation. Seeds of less susceptible varieties.