Effect of Root-knot Nematode ( Meloidogyne incognita ) on the Nodulation of Some Varieties of Cowpea ( Vigna unguiculata L. Walp)

Abstract Screenhouse and field trials were conducted at the University of Ilorin, Nigeria in 2013 and 2014 to investigate the effect of root knot nematode ( Meloidogyne incognita ) on the nodulation of five varieties of cowpea (IT89 KD -288, IT82 D -994, IT93 K -452-1, T89 K -391 and TT97 568-18). Half of the experimental plants were inoculated with Meloidogyne incognita eggs ( n = 1500) while the remaining half served as uninoculated control plants. Data on growth and yield of cowpea, root gall, nodulation, and nematodes population densities in nodules were collected. Other parameters assessed included colour of dissected infected and uninfected nodules, texture of the nodules and varietal performance of the cowpeas. The results of both screenhouse and field trials were consistent in yield and visual observations of texture and colour. The yield of nematode-free varieties was significantly higher than that of M. incognita- infected ones. Infected nodules were dark brown in colour while the healthy ones were pink. For the field trials, nodulation counts in nematode inoculated plants were inversely proportional to the number of galls in their uninoculated counterparts in some varieties. Of all varieties, IT89 KD -288 was most resistant to M. incognita. Due to high cost involved in the management of nematodes, especially with synthetic chemicals, variety IT89 KD -288 is recommended for use in nematode endemic areas in Nigeria. Further study needs to be done on the histopathology of the infected and uninfected roots and nodules of these cowpea varieties.