Based on dominance, degree of dominance and backcross values, resistance was inferred to be polygenic, autosomal and inherited as a recessive trait.

The glucosinolate content of the 3 host plants, viz. yellow sarson, Brassica campestris L. var. yellow sarson, Chinese cabbage, Brassica campestris L. var. pekinensis and taramira, Eruca sativa Lam. var. ITSA differed qualitatively as well as quantitatively mainly with respect to allyl-, methylthiobutyl-, pcnt-d-enyl-, methyl-and benzylglucosinolates. The mean number of total probes on feeding media incorporated with crude extracts containing glucosinolates from 0,25, 0·50 and 1·0 g green parts of taramira per ml of feeding media was 5,8, 6·7 and 8·4, respectively. Such probes in case of yellow sarson and Chinese cabbage were 2,6, 2·2 and 1'5; and 2'6, 2·0 and 3'0, respectively. The mean number of probes on feeding media containing sinigrin (K + -allylglucosinolate) at the rate of 0,125, 0'25, 0·50 and 1'0% was 1,9, 3-3, 3-9 and 5'2, respectively. Uptake of feeding media incorporated with extracts containing glucosinolates from taramira, yellow sarson and Chinese cabbage varied from 4'05-9'40, 31,5-52,0 and 30'5-51'3%, respectively. Similarly, the uptake in the case of feeding media containing sinigrin (0'125-1~~) varied from 1·6-44·95%.Two of the 3 crucifers selected for the present studies, yellow sarson, Brassica campestris L. var. yellow sarson; Chinese cabbage, B. campestris L. var. pekinensis are susceptible and third, taramira, Eruca sativa Lam. var. ITS A, is resistant to the attack of mustard aphid, Lipaphis erysimi (Kalt.). For the purpose of extraction and analysis 695

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Screen house experiments were conducted under no choice conditions, to determine the tolerance, a mechanism of resistance, in cotton under a population pressure of 150 and 300 pairs of whiteflies Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae). Twelve cotton genotypes, viz., four resistant (NHH 44, Supriya, LD694 and PA 183), four susceptible (F 846, IS-376/4/ 1/20/72, LK 861 and RS 2013) and four with moderate reaction (T x Maroon 2-78, MRC 6304Bt, RS 2098 and CNH 911) to B. tabaci were assessed in terms of decrease in plant height, number of nodes and chlorophyll content (a, b and total) from control. The study revealed that all three characters are important to identify tolerance. A strong tolerance mechanism is operating in NHH 44. The genotypes LD 694 and PA 183 were rated as moderately tolerant, however, IS 376/4/1/20/72, Tx Maroon 2-78, MRC 6304Bt, F 846 and CNH 911 exhibited no tolerance mechanism and were categorized as the most susceptible genotypes.

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