A comparative study of the development and reproduction of Meloidogyne enterolobii and other thermophilic South African Meloidogyne species
Meloidogyne enterolobii, a highly pathogenic root-knot nematode species, infects fruit, grain, oilseed, ornamental and vegetable crops causing severe damage to agri-and horticultural crops worldwide. The species is infamous for its ability to render host plant resistance ineffective since it damages crops exhibiting resistance against other thermophilic species; M. incognita and M. javanica. This study commenced with an extensive desk-top study; a collective review (consulting 274 articles) about the global distribution, biology, pathogenicity and management of M. enterolobii, with special reference to sub-Saharan Africa. The research aim of the glasshouse study was to determine the life-stage development, life-cycle duration and reproduction potential of a South African M. enterolobii population compared to its counterpart species, M. incognita and M. javanica. Seedlings of three crops, maize (‘P-2432-R’), soybean (‘DM-5953-RSF’) and tomato (‘Moneymaker’), were inoculated with motile second-stage juveniles (J2) of each species. Ambient temperature regimes maintained in the glasshouse were 19-32 ºC, 15-32 ºC and 18-32 ºC for the maize, soybean and tomato experiments, respectively, over 25 days. Random isolation of 20 life stages of each species from root systems of crop seedlings followed at time intervals of 3, 5, 10, 15, 20, and 25 days after inoculation (DAI), including five replicates of each crop and species. Infected crop roots were removed, for each time interval, and the nematode life stages stained using the sodium-hypochlorite-acid-fuchsin method. Egg-masses were present on the crop’s root surfaces 20 DAI and were first stained with eosin-Y before the life stages inside the roots were stained with the sodium-hypochlorite-acid-fuchsin method. Ten egg-masses were randomly removed from each crop seedling’s root system, for each of the species, and the number of eggs per egg-mass counted. Data were subjected to Factorial Analyses of Variance and the degree days (DD) were calculated for each species. Morphological and molecular identification verified the identity of the three species used. Significant (P≤0.05) differences existed for the number of each of the life stages, of each species, among some of the time intervals. Meloioigyne enterolobii developed more rapidly from one life-stage to the other compared to the other two species. Although females were observed for all three species 15 DAI, single eggs were observed for M. enterolobii only. Egg masses were, however, produced by females of all three species 20 and 25 DAI. The presence of second J2 generations of M. enterolobii and M. javanica from 20 DAI compared to those of M. incognita (recorded from 25 DAI only) confirmed the quicker development of M. enterolobii as well as M. javanica. Ultimately, the shorter DD needed by M. enterolobii to complete its life cycle in roots of all three crop genotypes compared to those of M. javanica and M. incognita represents novel information, both fundamentally and for its applicability. An improved advisory approach to farmers can now, for example, focus on rather using crop genotypes with shorter growing periods. Other management strategies can also be streamlined to focus on combatting M. enterolobii by, for example, interfering with its rapid life-cycle duration.