Impact of Cropping Patterns on seed bank and emergence of Orobanche in infested field.

Abstract

Orobanche is a genus of more than 200 species of parasitic herbaceous plants in the family Orobancheaceae that cause damages to the important vegetables and field crops in many parts of the globe including Nepal. Orobanche is a problematic parasitic weed in tomato and brinjal fields of Lalbandi, a major tomato growing areas in Nepal. Orobanche emergence in the early sown six tomato and one brinjal fields, and in late sown six tomato and one brinjal fields were recorded along with the past history of each fields. The soil samples from these seven early sown and seven late sown fields were collected for the Orobanche seed bank study. The Orobanche seed bank study was conducted using the flotation technique of Ashworth (1976) with some modification (Acharya et al., 2003).From this study on Orobanche emergence at early and late sown tomato and brinjal fields, it can be concluded that the severity of the parasitic weed in a field cannot be ascertain with the Orobanche shoot emergence alone. The Orobanche seed bank study gave the real picture of parasitic weed infestation in the field. In the early sown tomato fields F7,Orobanche seeds/100g soil was significantly lowest, and this filed had a history of only cultivation of cucumber for last 5 years with no winter crops and tomato was grown only after five years as winter crop. This clearly indicates that gapping of tomato cultivation reduces Orobanche seed bank in the fields. Similarly, reduction in Orobanche seed bank was also recorded in early sown fields like F1 and F4, where hand pulling of Orobanche shoot was in practice, as well as have the field history with the intervention of crop rotation with lentil and chickpea, respectively. Among the late sown fields of tomato and brinjal, Orobanche seeds/100gsoil was found to be less than in early sown fields. The Orobanche seeds/100g soil in late sown fields was significantly (P=0,05) low in F5 and F1 which had a history of growing only paddy for last 3 years and 2 years, respectively (with no winter crop), and then tomato was cultivated as winter crop after 3 and 2 years, respectively. This indicated that gapping the cultivation of host plants for some years also helps in reducing the seed bank of parasitic weeds. Beside this when Orobanche seed bank/100 g soil was compared between the paddy and maize fields of early and late sown tomato/brinjal fields, most of the paddy fields were recorded to have less Orobanche seed bank than at the maize fields. From the Orobanche seed bank study of early and late sown tomato and brinjal fields it can be concluded that late sowing helps in reducing the Orobanche seed bank in soil.