Development and pathogenesis of Meloidogyne javanica in cotton roots

Abstract

Root-knot nematodes (Meloidogyne spp.) have long been known to cause serious damage to cotton (Gossypium hirsutum L.). Brodie and Cooper (1964) in an experiment with five single egg-mass isolates of Meloidogyne spp., representing four species found that the roots of cotton seedlings were penetrated in equal numbers and growth was significantly reduced. One isolate of M. incognita reached the egglaying stage, while isolates of M. arenaria, M. javanica, M. hapla and a second isolate of M. incognita did not develop beyond the second larval stage. McClure et al. (1974) stated that larvae of M. incognita penetrated susceptible cotion roots and matured within 14 days following inoculation, whereas nematode development in resistant roots was greatly retarded and many galls contained no nematodes. Minton (1961) showed that a highly resistant wild selection of G. barbadense L. was more hypersensitive to M. incognita acrita than the G. hirsutum cultivars Auburn 56 and Rowden. He noted that hypersensitivity resulted in tissue necrosis and consequently the nematode was unable to complete its life cycle. Previous studies by Khalil (1977) showed that G. barbadense cv. Giza 69 was highly susceptible to M. javanica, while G. hirsutum cv. Acala 4-42 was resistant. The present work describes the development of M. javanica (Treub) Chitw. in cvs Giza 69 and Acala 4-42 and the related histopathology of the infected roots. The nematode inoculum used in this study was originally obtained from cotton roots infested with M. javanica collected from Abees, Alexandria. A single egg mass of an identified female was isolated and the hatched larvae were then reared on cotton plants cv. Giza 69. Cotton seeds of cvs Giza 69 and Acala 4-42 were planted in steamed sandy clay soil in 20 em clay pots. Seven days after emergence, the seedlings were thinned to two per pot and each pot was inoculated with 3,000 second stage larvae. Root samples of both cultivars were collected at 12, 24, 48 hrs and then at intervals of 2 days until 40 days after nematode inoculation; root samples of Acala 4-42 were then collected at 4 day intervals up to 76 days after inoculation. Galled parts of infected root samples were fixed in FAA solution and processed as described previously by Ibrahim and Masso1Jd (1974) for studying nematode development and the related histopathology.