Indian Phytopath. 61 (2) : 212-225 (2008) DNA and some laboratory tests of nematode suppressing efficient soil isolates of Aspergillus niger MUJEEBUR RAHMAN KHAN* and M. ARSHAD ANWER Department of Plant Protection, Aligarh Muslim University, Aligarh 202 002 ABSTRACT: Sixteen isolates of Aspergillus niger collected from different crop fields were subjected to RAPD- PCR using 20 Operon primers and 8 synthetic primers. Twenty two primers led to amplification of 727 fragments ranging from 3500 bp (OPA-11) to 200 bp (Primer-06), and two bands were found to be monomorphic where as rest of them polymorphic. Three amplicons produced by OPA-16 were recorded as isolate specific as 2300 bp by AnC 2 and AnR 3, and 2800 bp by AnC 2 only. High degree of genetic similarity (0.79) was measured between AnC 2 and AnR 3 and least similarity (0.17) between AnC 2 and AnR 2 . Multivariate analysis of genetic similarity have revealed three major clusters categorized as Group I, Group II and Group III. The isolates AnC 2 and AnR 3 , which produced highest amount of siderophore, HCN, NH 3 and solubilized greatest amount of phosphorus belonged to a subgroup of Group I. When eggmasses of Meloidogyne incognita were incubated in the culture filtrate of the isolates of A. niger the egg hatching was greatly suppressed and 28 to 100% mortality in the hatched juveniles was recorded. Pot experiment conducted to examine the effect of A. niger isolates on the development of root-knot caused by M. incognita on eggplant showed significant (P£0.001) suppressing in the galling and egg mass production and a decrease in the soil population of the nematode. Key words: DNA test, Root-knot, RAPD-PCR, Aspergillus niger, Meloidogyne incognita Aspergillus niger is a versatile phosphate solubilizer and is abundantly present in different soil types (Gaur, 1990). The fungus possesses considerable potential to suppress plant parasitic nematodes (Goswami et.al.,1994; Sharma et.al., 2005) and have been found effective to enhance the yield of infected plants (Sharma et.al., 2005). Some researches have, however, shown the effectiveness of the fungus against pathogens may vary with the isolate (Mittal et.al., 1999; Patibanda and Sen, 2004). Accurate characterization of an isolate is an important aspect of exploration and search for efficient biocontrol agents. Quite often genetically similar isolates are treated as different isolates due to lack of proper characterization and vice-versa. Moreover, isolates can not be differentiated by morphological and other conventional methods. Study of genomic DNA through RAPD-PCR is one of the common tests for initial assessment of genomic variation within and between fungal populations, and closely related individuals of fungi (Dalgleish and Jacobson, 2005). The RAPD assay has been extensively used in the differentiation of isolates of A. niger (Pekarek et al., 2006), A. fumigatus (Lin et al., 1995; Brandt et al., 1998), A. parasiticus (Yuan et al., 1995) and A. flavus (Bayman and Cotty, 1991; Tran-Dinh et al., 1999). Root-knot nematode, Meloidogyne spp. is a major pest of most of vegetables, pulses and several other crops and causes considerable reduction in the yield (Khan and Ejaz, 1997) and may reduce the yield by 5-43% (Sasser, 1989). The present paper was aimed to collect soil isolates of A. niger from different crop fields to identify efficient isolates for the management of root knot of eggplant caused by Meloidogyne incognita. MATERIALS AND METHODS Isolation, identification and pure culture of Aspergillus niger Soil was collected from various crop fields of *Corresponding author: mrkhan777in@yahoo.co.in