Kenneth R. Barker

Greenhouse and field resistance in cucumber to root-knot nematodes

Ten cultigens were evaluated for resistance to Meloidogyne arenaria races 1 and 2, and M. javanica under greenhouse and field conditions. Resistance to M. arenaria races 1 and 2, and M. javanica was verified in Cucumis sativus var. hardwickii line LJ 90430 and to M. arenaria race 2 in C. sativus var. sativus Southern Pickler and Mincu in a greenhouse test. Another cultigen of C. sativus var. hardwickii (PI 215589) was found to be resistant to M. arenaria race 2 but not to other root-knot nematode species tested. LJ 90430 is the cultigen of choice to develop root-knot nematode resistant cucumbers, since it has multiple root-knot nematode resistance and is cross-compatible with cucumber. Greenhouse and field data were positively correlated (r = 0.74) over both years. Experiment repeatabilities were calculated from the cultigens infected with root-knot nematodes under both greenhouse and field conditions. Four environments (greenhouse and field over 2 years) were used in the analysis. Repeatabilities were high in all instances (ranging from 0.83-0.99) and indicated that the environment (field or greenhouse) was not an important factor in assessing root-knot nematode resistance for the cultigens evaluated. Resistenz von Gurkengegen Wurzelgallennematoden im Gewachshaus undim Freiland - Unter Gewachshausund Freilandbedingungen wurden zehn Cultigene auf ihre Resistenz gegen Meloidogyne arenaria Rassen 1 und 2 und gegen M. javanica gepruft. Bei Cucumis sativus var. hardwickii Linie LJ 90430 wurde im Gewachshausversuch Resistenz gegen M. arenaria Rassen 1 und 2 sowie gegen M. javanica nachgewiesen, und in C. sativus var. sativus Southern Pickler und Mincu Resistenz gegen M. arenaria Rasse 2. Cultigen C. sativus var. hardwickii (PI 215589) war resistent gegen M. arenaria Rasse 2 aber nicht gegen die anderen gepruften Arten von Wurzelgallennematoden. LJ 90430 ist das Cultigen der Wahl bei der Entwicklung von Gurken, die gegen Wurzelgallennematoden resistent sind, da es multiple Resistenzen gegen Wurzelgallennematoden besitzt und kreuzungsvertraglich mit Gurke ist. Die Ergebnisse der Gewachshaus- und Feldversuche waren uber beide Versuchsjahre hin positiv korreliert (r = 0,74). Ausgehend von den Cultigenen, die im Gewachshaus und im Freiland mit Wurzelgallennematoden infiziert waren, wurden die Wiederholbarkeiten der Versuche berechnet. Dabei wurden vier verschiedene Umweltbedingungen (Gewachshaus und Freiland uber zwei Jahre) verwendet. Die Wiederholbarkeiten waren in allen Fallen hoch (0,83-0,99) und zeigten an, dass die Umwelt (Freiland oder Gewachshaus) kein wichtiger Faktor bei der Bestimmung der Resistenz gegen Wurzelgallennematoden bei den gepruften Cultigenen war.

Genetic Analysis of Meloidogyne arenaria Race 1 Resistance in Tobacco

Inheritance of resistance to the peanut root-knot nematode (Meloidogyne arenaria (Neal) Chitwood race 1) was investigated in the flue-cured tobacco cv. Speight G 28 and the breeding lines 81-RL-2K and SA 1214. The genetic relationship of this resistance in Speight G 28 to the resistance of the same cultivar to races 1 and 3 of M. incognita was also studied. Crosses were made between the root-knot nematode-susceptible flue-cured tobacco cv. NC 2326 and the three resistant genotypes. Parental, F1, F2 and backcross generations (BC1P1, BC1P2) were grown for each cross in randomized complete block designs with five replications in the greenhouse. Data indicated that resistance to M. arenaria race 1 in the three resistance sources is conditioned by a single dominant gene, but this resistance is partial compared to that for M. incognita races 1 and 3. Further, resistance to races 1 and 3 of M. incognita and resistance to M. arenaria race 1 in cv. Speight G 28 appear to be controlled by the same gene. These results, combined with the absence of segregation in the F2 populations of the crosses between resistant parents 81-RL-2K × SA 1214, 81-RL-2K × Speight G 28, and SA 1214 × Speight G 28, suggest allelism of resistance among these genotypes.

Response of root-knot resistant tobacco to concomitant populations of Meloidogyne species

Ngambi, T. B. S., Rufty, R. C., and Barker, K. R. 1995. Response of root-knot resistant tobacco to concomitant populations of Meloidogyne species. Plant Dis. 79:1008-1013. Mixed populations of Meloidogyne species commonly occur in most flue-cured tobacco (Nicotiana tabacum L.) fields in the southeastern United States. The interaction of Meloidogyne arenaria race 2 (Ma) and M. incognita race 3 (Mi) on the Mi-resistant flue-cured tobacco cv. Speight G-28 and on a root-knot susceptible flue-cured tobacco cv. NC 2326 (control) was evaluated under greenhouse conditions. Plants of both cultivars were inoculated with 1,500 or 3,000 eggs of Ma or Mi alone, or with a combination of 1,500 eggs of each species. Root penetration (number of juveniles per g of root) with the mixed population assessed 10 days after inoculation (DAI) was comparable to that of Ma alone on the Mi-resistant tobacco cultivar, and of either nematode species alone on the susceptible cultivar. Also, nematode population density (number of nematodes per g of root, all stages except eggs), numbers of mature females per g of root, root damage (percent root area galled), and nematode reproduction (number of eggs per g of root) on Speight G-28 30 and/or 48 DAI with mixed population were not greater than those attributable to Ma alone. Indeed, inoculation with the mixed population resulted in slightly lower nematode population density (except at 48 DAI), root damage, and nematode reproduction on Mi-resistant cultivar than with Ma alone at the 1,500 egg inoculum level. The concomitant inoculation of Ma and Mi on NC 2326 did not differ from single inoculation with Ma for all variables measured, except reproduction at 48 DAI. These data indicate that Speight G-28 resistance to Mi was not reduced with concomitant infections of Ma and Mi. Fewer Mi than Ma mature females were recovered from the susceptible cultivar in the mixed population, indicating that Ma was more competitive than Mi.