Screening of Some Common Weeds for Nematicidal Activities against the Root-Knot Nematode Infestation on Tomato (Lycopersicum Esculentum L.) in Plateau State, Nigeria.

Abstract

The screening of some common weeds for nematicidal activities on Meloidogyne incognita infestation on tomato (Lycopersicum esculentum L.) was carried out at the Botanical nursery and Biology Laboratory, Plateau State Polytechnic, Barkin ladi, Nigeria, with a view to establishing their potential for organic amendment or as trap weeds for the control of Meloidogyne incognita. The common weeds were surveyed and identified by a taxonomist based on botanical nomenclature and voucher number to include Ageratum conyzoides, Crotalaria breviflora, Crotalaria juncea, Crotalaria retusa, Crotalaria spectabilis, Euphorbia hirta, Portulaca oleracea and Tridax procumbens. The common weeds were uprooted and taken to the laboratory for extraction and Phytochemical screening using standard procedure. Phytochemical screening of the test plants revealed the presence of Alkaloids, Carbohydrates, Flavonoids, Glycosides, Saponins, Sterols, Tannins, and Terpenes, which suggest that they are the active ingredients against Meloidogyne incognita, acting separately or in combinations. The root exudates of test plants were also prepared and collected by growing young actively growing seedlings of the test plants in test tubes wrapped with black carbon paper for five days under lighted florescent bulbs. Egg masses from root galls of tomato plants was teased out and identified. The eggs were placed in the exudates of susceptible tomato test plants for 24 hours to stimulate hatching of eggs. The resulting juveniles from hatched eggs were transferred in various concentrations of 1g in 5mls, 1g in 10 mls and 1g in 15 mls of extracts extracted with ethanol using soxhlet extractor and exudates of the test weeds. The set up were observed after an interval of 6 hours, 12 hours and 24 hours for live and dead juveniles in an in vitro study. The results of the in vitro studies reveal that at exposure time of twenty four (24) hours at concentration of 1g in 5 mls all the seventeen (17) juveniles were dead. The effects varied with concentration of the extracts and exudates (P< 0.05) using analysis of variance (ANOVA). The effects of the test plants in terms of reduction in nematode population of soil increase in growth and yield of susceptible tomato plants grown in soil amended with decomposed test plants at concentration of 5 kg, 10 kg and 15 kg to beds measuring 120 x 240 cm was determined. Decomposed test plants in soil amendments also significantly reduced nematode populations at the varying application rates. The effects of decomposed plant parts (DPP) had a minimum mean number of thirty six (36) galls per three (3) tomato plants and with highest mean number of fruit yield of two hundred and fifty six (256) per three tomato plants. The results thus confirmed that all the test plants are potentially viable trap weeds, and can be used in organic amendments of soils for the control of Meloidogyne incognita infecting tomato variety UC 82 B and should be employed as such. The test plants, most of which are legumes have the added advantage of enriching the soil through nitrogen fixation. These test weeds can be composted and incorporated in soil organic amendment as well as grown on fallow fields as trap or catch plants to reduce nematodes populations and increase growth and yield of crops susceptible to Meloidogyne incognita. Farmers can now substitute the use of synthetic chemical of high cost for these obnoxious weeds.