Abstract

Citrus indica Tanaka, commonly known as Wild Indian Orange, is the most primitive of all citrus fruits found around the world. This plant is found growing in the wild only in Nokrek Biosphere Reserve of Garo Hills, Meghalaya. The plant is of great significance among the local people for various traditional medicines and spiritual purposes. The objective of the study was to identify the disease causing pathogens and soil microbes inhabiting the rhizosphere of C. indica in the three zones of Nokrek Biosphere Reserve, as well as to assess the relationship between soil microbes and occurrence of plant pathogens. Nine diseases caused by fungal pathogens and one disease caused by algae were observed. Change in zone exerted a significant influence on occurrence of pathogens in C. indica. Occurrence of soil microbes in the rhizosphere of C. indica was significantly influenced by change in zone, soil depth and season. Soil microbes were found to be more in top soil than sub-soil. Among the identified soil microbes, Aspergillus flavus, Penicillium digitatum and Rhizopus nigricans were the dominant ones. At 0–15 cm soil depth, soil microbes Curvularia lunata, Drechslera oryzae and Aspergillus niger exerted positive influence on occurrence of plant pathogens Capnodium citri, Cephaleuros virescens, Alternaria citri and Mycoshaerella citri, while plant pathogens like Acrosporium tingitanium, Diaporthe citri, Penicillium digitatum and Phytophthora citrophthora were antagonistically affected. At 15–30 cm soil depth, soil microbe Drechslera oryzae positively influenced the occurrence of plant pathogens Alternaria citri and Cephaleuros virescens, while Colletotrichum falcatum at 15–30 cm soil depth positively influenced the occurrence of plant pathogens Acrosporium tingitanium and Diaporthe citri.