Rearing and Conservation of Nematode Populations Under Greenhouse or Axenic Conditions

Once a nematode has been identified, to conduct studies for screening programs or pathogenicity tests, it is necessary a supply of large numbers of nematodes from field crops or reproduced and stored to be used in periods of the year when they are not available from fields. Therefore, nematodes must be reared in greenhouse or under in vitro conditions and stored for future needs. In this chapter, suggestions are given on how to obtain nematodes from fields and reproduce most of them on host plants in greenhouse (mainly Meloidogyne spp. and Globodera spp.) or in vitro. Reproductions in vitro include: On suitable callus of host plants (Pratylenchus spp., Ditylenchus spp.) On fungal cultures mainly of Botrytis cinerea or Alternaria spp. for Aphelenchoides spp. and other aphelenchids, including Bursaphelenchus xylophilus. On carrot disks for Pratylenchus spp. and Ditylenchus spp. Other specific media, such as garlic, potato, and sweet potato for D. destructor, and cocoyam disks for Radopholus similis. Guidelines are also given to store different nematodes for rather long times, including in vitro methods and in infected seeds, hay, and other plant parts. No information is given on how to prepare and store fixed materials.

Detection of Resistance, Susceptibility, Tolerance, and Virulence in Plant-Nematode Interactions: Part I-Sedentary Endoparasitic Nematodes

The use of nonhost, tolerant, or resistant plants, to manage plant parasitic nematodes (PPNs), is an appealing, economic, and environmentally friendly agronomic practice, which is effective when precise information on the identification of PPN species and their virulence to target host crops is available. This chapter describes suggested protocols to evaluate the reaction of the most important crops and fruit trees to infestation by the most damaging PPN with sedentary endoparasitic habits, with the aim of assessing resistance and tolerance traits, sources of resistance in progenies from breeding programs, the reaction to nematodes of newly released cultivars, and the virulence of the most noxious PPNs. These protocols consist of classical screening techniques not involving biochemical and molecular analyses. PPN species and genera considered in this chapter include (i) the most important species of root-knot nematodes Meloidogyne spp., including also M. chitwoodi, M. enterolobii, and M. graminicola, and (ii) the cyst-forming nematodes of the genera Globodera and Heterodera, such as the potato cyst nematodes (PCNs) Globodera rostochiensis and G. pallida, and also Heterodera avenae group, H. ciceri, H. glycines, and H. schachtii. Schemes are given to identify virulence groups for most of these nematodes.

Biology, pathotype, and virulence of Globodera rostochiensis populations from Kenya

The potato cyst nematodes (PCN), Globodera rostochiensis (Woll.) and G. pallida (Stone), are important pests of potato globally. Due to their extensive damage potential and the challenge of managing them, these nematodes are under strict regulations in many countries; however, despite these regulations, PCN continue to spread into new areas and countries. In Kenya, G. rostochiensis was first reported in 2015 and G. pallida was reported three years later, both in Nyandarua County. Research was conducted to characterize the biology, pathotype, and virulence of G. rostochiensis populations from Kenya in glasshouse and laboratory studies. The development of G. rostochiensis was assessed in roots of susceptible potato ‘Désirée’ and resistant ‘Laura’ carrying the H1 resistance gene. The ‘HAR1’ population from Kenya and ‘Ecosse’ from Germany were not able to produce females in the roots of the resistant potato ‘Laura’. The rate of root penetration by G. rostochiensis juveniles did not differ (p > 0.05) between populations and cultivars. However, in the resistant cultivar, juveniles developed into males only. A total of 736 cumulative degree-days at 6°C base temperature (DD₆) were required by ‘HAR1’ to complete the life cycle on ‘Désirée’, whereas ‘Ecosse’ completed the life cycle within 645 DD₆. The Kenyan populations lacked obligatory diapause and high numbers of juveniles hatched immediately after maturity. Consequently, the Kenyan populations had the potential to complete up to three reproduction cycles in less than a year. On selected potato cultivars, the populations from Kenya failed to reproduce on 10 out of 13 commercial cultivars tested. The 10 cultivars carried the H1 resistance gene, which suggests that the G. rostochiensis populations tested belong to the Ro1/4 pathotype group. The virulence of the G. rostochiensis populations from Kenya did not differ from that of the standard reference population ‘Ecosse’ and therefore can be effectively managed with the commercially available potato cultivars carrying the H1 resistance gene.