Biochemical mechanism of resistance in some Brassica genotypes against Lipaphis erysimi (Kaltenbach) (Homoptera: Aphididae)

*Corresponding author E-mail : [email protected] INTRODUCTION The genus Brassica comprises an important group of cultivated vegetable and oilseed crops and have great economic importance worldwide. The cultivated species of Brassica include cabbage, cauliflower, kale, broccoli, Brussels sprouts, turnip, swede, oilseed rape, various mustards and other leafy vegetables (Hong et al. 2008). As oilseed crop, rapeseed contributed 58.56 million metric tons out of total oilseed crop production of 446.97 million metric tons amounting 13.1% in the year 2010-11 (Source: Foreign Agricultural Service, Circular Series FOP 04–11, USDA). India is one the leading producers including Canada, USA, EU, Australia and China. In India, under the name rapeseed and mustard three cruciferous members of Brassica species are cultivated; B. juncea (Indian mustard or commonly called rai) being the chief oil-yielding crop, while three ecotypes of B. rapa ssp. oleifera, viz. brown sarson, yellow sarson, toria and B. napus are grown to a limited extent. Among the biotic stresses, the damage caused by aphids is a major constraint in the productivity of these crops. Among the three taxonomic variants that infest oilseed Brassicas in India, the turnip/mustard aphid, Lipaphis erysimi (Kaltenbach) (Homoptera: Aphididae), damages the crop ranging from 9 to 96 per cent in different agro-climatic conditions of the country (Singh and Sharma 2002) and is a major pest on oilseed brassicas in Indian sub-continent, while Brevicoryne brassicae (L.) has global presence with strong yield reducing impact, especially in vegetable brassicas (Kumar et al. 2011). Because of prolific Two years study was carried out during 2006-07 and 2007-08 crop seasons to study the response of different genotypes of oilseeds Brassica to Lipaphis erysimi (Kaltenbach) infestation both under field and screen house conditions and to find out the relationship of various biochemical constituents to aphid infestation. Among the various genotypes, the population of L. erysimi was significantly high on Brassica rapa variety brown sarson cv. BSH 1 and B. rapa var. yellow sarson cv. YST 151 in unprotected set i.e. 53.7 and 52.3 aphids/ plant, respectively. However, it was the lowest on Eruca sativa cv. T 27 (4.7 aphids/plant) followed by B. carinata cv. DLSC 2 (20.9 aphids/ plant) which suffered the least yield loss i.e. 5.79 and 10.59 per cent, respectively. Almost similar trend was observed in seedling mortality, which was the maximum in BSH 1 and YST 151, while no seedling mortality was observed in the case of T 27 during both the years of study. Analysis of various biochemical constituents revealed that glucosinolates, total phenols and ortho-dihydroxy phenols had inverse relationship with the aphid infestation. Higher amount of these biochemical constituents in T 27 and DLSC 2 was responsible for lower aphid infestation on these genotypes.