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Root-knot Nematodes, Meloidogyne spp. Associated with Crop Plants in Thailand
Dissertation Abstract:
A survey of crop plants infected by root-knot nematodes, Meloidogyne spp. was undertaken in 22 provinces in Thailand. Four new hosts were reported for the first time, namely: garden balsam (Impatiens balsamina Linn.), alyce clover (Alysicarpus sp.), sting weed (Eryngium foetidum Linn.) and roselle (Hibiscus sabdariffa Linn.).
Three root-knot nematode species were identified from 57 pure nematode isolates maintained. They were Meloidogyne incognita (Kofoid and White, 1919; Chitwood, 1949); M. javanica (Treub, 1885; Chitwood, 1949); and M. graminicola (Golden and Birchfield, 1965). M. incognita was the most common and widespread, M. javanica second, and M. graminicola the least.
Comparative morphometry among and within species of perineal patterns, second-stage characters. Susceptibility and biological, physiological and chromosomal variability were studied.
Distance between plasmids and from anus to tail terminus of M. graminicola was table and smaller than those of M. incognita and M. javanica. There was much variation in the perineal pattern characters between population among and within species of M. incognita and M. javanica. Body and tail length of M. graminicola were longer than those of the other two species. Overlapping in such dimensions was observed in some populations of graminicola and javanica as well as of incognita and javanica. Style length of the three species showed insignificant differences although some graminicola populations had longer dimensions than the other two. The a- and c-ratios of graminicola were more stable and smaller than those of incognita and javanica species.
Rated as resistant to M. incognita were cotton ‘Reba BTK 12’, peanut ‘SK 38’, sesame ‘Nakornsawan’, tobacco ‘NC 95’, corn ‘Suwan 1’, roselle (native variety) and soybean ‘SI 2’. Susceptible crops were native varieties of cowpea, jute, mungbean, pepper, peanut ‘California Wonder’ and watermelon ‘Charleston Grey’. Corn, cotton, pepper, peanut, roselle, sesame, jute and soybean were resistant to M. javanica, while cowpea, mungbean, tobacco, and watermelon were susceptible. All the test plants, including tomato ‘Manapal’, were resistant to M. graminicola.
Eight physiological races were detected from 36 M. incognita populations and two races from 15 M. javanica populations. None were detecte from M. graminicola.
Chromosome number of selected M. incognita and M. javanica isolates varied from 21 to 33 and from 23 to 48, respectively. Chromosome number of graminicola showed species characteristics with haploid number and diploid number 36.
A suggested key for identifying root-knot nematode species found in Thailand was given.
