Response of Resistant and Susceptible Alfalfa Cultivars to Regional Isolates of Stem Nematode¹

Abstract

Nine stem nematode [Ditylenchus dipsaci (Kühn) Filipjev] isolates were collected from different nematodeinfested regions of the United States and Canada. They were tested for variations in pathogenicity at 15, 20, and 25 C on ‘Ranger’ and ‘Moapa’ (susceptible and ‘Lahontan’ and ‘Caliverde 65’ (resistant) alfalfa (Medicago sativa L.) to determine if variations in plant responses to different nematode isolates should be considered when breeding for resistance to stem nematode. All isolates were generally capable of parasitizing alfalfa; however, a difference in virulence was detected among isolates. Isolates did not demonstrate an interaction with temperature or with alfalfa cultivars. We concluded that a resistant alfalfa developed in a breeding program using one pathogenic isolate would probably be resistant to stem nematode isolates from other regions.

Virulence and pathogenicity of four Ditylenchus dipsaci populations on sugar beet

“…While penetration was similar for the four nematode populations, the Seeland population showed a significantly greater reproduction. This finding correlates with the observation of Elgin et al (1977), where D. dipsaci populations did not differ in their ability to invade the host plant but differed in reproducing in their host. All four D. dipsaci populations did not show a significant variation of nematode incidence, defined by the percentage of plants affected by D. dipsaci.…”

“…Variations in the pathogenicity of D. dipsaci populations challenge breeders in their search for resistant cultivars. Ditylenchus dipsaci populations have been shown virulent to cultivars of alfalfa, white clover, and faba bean (Vicia faba L.), previously described as resistant towards D. dipsaci populations from other geographic origins (Elgin et al, 1977;Plowright et al, 2002;Whitehead, 1992). Therefore, breeders should consider the pathogenicity and virulence of nematode populations from target regions for commercial cultivars right when choosing the reference population at the start of the breeding process.…”

Nematode Inoculum Propagated in Monoxenic Plant Tissue Cultures ‐Nematode Bank1

“…We propagated 1 1 RC-populations and three LU-populations in this way, though of course it would be easier to handle a lower number. However, there is so far no conclusive evidence of practically important differences between geographically different RC-populations (Bingefors & Eriksson, 1968) or LU-populations (Elgin et al, 1977). Bearing this in mind, it might prove (( safe o, not to bother too much about the origin of the populations when extracting the inoculum, but use those cultures where multiplication is most successful.…”