PATHOGENICITY OF TYLENCHORHYNCHUS-ZAMBIENSIS TO MAIZE

Two greenhouse experiments were conducted to determine the effect of T ylenchorhynchus zambiensis on growth of maize (Zea mays L.) hybrid MO1 7 x A634 and to determine the population levels required to adversely affect maize. Initial nematode population levels (Pi) evaluated were 0 .0, 0.4, 4.0, or 42 nematodes/cm(3) of soil (respectively, 0, 500, 5 0 00, or 50 000/pot). Al additional treatment evaluated the effect of ne matode associated microorganisms (AM) which accompanied the highest le vel of nematode inoculum. After 60 days, plant height, fresh and dry f oliar and root weights and numbers of nematodes were determined. In bo th experiments plant height, fresh and dry foliar weight, root weight, and total plant weight were reduced significantly (P less than or equ al to 0.05) by T. zambiensis at the highest inoculum level. In both ex periments when Pi = 500 or 5 000 nematodes, effects of T. zambiensis o n maize growth were inconsistent. Although roots appeared healthy, the AM treatment had a significant negative effect on root weight in expe riment 1 and was numerically less in the second experiment. The highes t final population (Pf) of T. zambiensis (Pi = 1825 000 nematodes/pot) was obtained when Pi = 5 000 (4.0 nematodes/cm(3) of soil). The repro ductive factor (R = Pf/Pi) was 1184.0, 365.8, and 25.2, respectively f or Pi = 500, 5 000, or 50 000. These data indicate that T. zambiensis is a weak pathogen and requires a large population to affect maize gro wth.