CORESTA Meeting, Agronomy/Phytopathology, Oxford, 1995

The effect of genetic resistance against meloidogyne spp. in tobacco on nematode populations

BOTHA-GREEFF M.S.; VAN BILJON E.R.; CLAASSEN A.
ARC, Tobacco & Cotton Research Insitute, Rustenburg, South Africa
An integrated nematode control research strategy, with the accent on genetic resistance, crop rotation and chemical control, is presently followed at TCRI. Promising tobacco breeding lines with resistance or tolerance against Meloidogyne javanica and M. incognita races 2 and 4 were evaluated against naturally occuring nematode populations in the field. Five trials were done in fields where single or combinations of Meloidogyne spp. occurred as the dominant nematode spp in the presence of ectoplant-parasitic nematodes such as Pratylenchus spp., Rotylenchulus spp. and Criconematinae . Tobacco breeding lines evaluated, included NOD 8, NOD 20, NOD 31, NOD 90, NG 38 and OD 469 which were compared with TL 33 and LK 3/46. A completely randomized block trial design was used including two main effects, viz., fumigated and unfumigated plots. Observations that were done included nematode counts in the soil at -2, 6 and 12 weeks after planting and in root samples at 6 and 12 weeks after planting. A root gall index was done at the end of the season. Yield and quality of tobacco leaf were determined and chemical analyses, with the accent on nicotine and sugar content, were done on green and cured leaf as well as the roots. Lower nematode numbers were found in the fumigated plots than in the unfumigated plots but although resistant breeding lines had a low visual root gall index, Meloidogyne spp. numbers increased in the roots. A certain amount of interaction occurred with ectoparasitic nematodes present in the soil which, after long-term use of genetic resistance in the host plant, may result in species drift within a nematode population.