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.