Rootrot of Bulbs Caused By Pratylenchus and Hoplolaimus Spp

Abstract

Rootrot caused by nematodes is widespread in Holland on bulbs and corms. It occurs most commonly in narcissi and affects sandy or peaty soils in the bulb-growing area. The primary cause of rot is Pratylenchus penetrans (COBB) SHER & ALLEN but Cylindrocar pon radicicola WR. plays a secondary role. Tulips, hyacinths, gladioli, crocusses and scillas are also affected. Bulbs and corms suffer more than other crops because of their restricted root production which enables relatively small nematode populations to cause severe rootrot. In the narcissus-growing district, lilies of the valley are attacked by Pratylenchus pratensis DE MAN. This nematode does not harm narcissus roots. Lilies of the valley are occasionally attacked by P. penetrans. In Kennemerland, lilies of the valley suffer severely from rootrot with heavy losses. As with narcissi, the primary parasite is a nematode, Pratylenchus sp. or Hoplolaimus uniformis THORNE with Cylindrocarpon radicicola WR. as a secondary agent. Many fields are heavily infected with both nematodes. Experiments suggest that P. penetrans consists of a series of subspecies or races. Rootrot in bulbs is limited to the roots. The nematodes do not invade the bulbs and, therefore, it is impossible to transmit the disease with bulbs with well dried roots. Infested soils are fumigated on a large scale with Shell DD which, besides controlling the nematodes, appears to 'stimulate' the growth of narcissi. African marigolds grown on infected soil reduce the Pratylenchus population considerably.