John W. Potter

Overexpression of glutamate decarboxylase in transgenic tobacco plants confers resistance to the northern root-knot nematode

Previous research suggests that the endogenous synthesis of gamma-aminobutyrate (GABA), a naturally occurring inhibitory neurotransmitter, serves as a plant defense mechanism against invertebrate pests. Here, we tested the hypothesis that elevated GABA levels in engineered tobacco confer resistance to the northern root nematode (Meloidogyne hapla). This nematode species was chosen because of its sedentary nature and economic importance in Canada. We derived nine phenotypically normal, homozygous lines of transgenic tobacco (Nicotiana tabacum L.), which contain one or two copies of a full-length, chimeric tobacco glutamate decarboxylase (GAD) cDNA or a mutant version that lacks the autoinhibitory calmodulin-binding domain, under the control of a chimeric octopine synthase/mannopine synthase promoter. Regardless of experimental protocol, uninfected transgenic lines consistently contained higher GABA concentrations than wild-type controls. Growth chamber trials revealed that 9–12 weeks after inoculation of tobacco transplants with the northern root-knot nematode, mature plants of five lines possessed significantly fewer egg masses on the root surface when the data were expressed on both root and root fresh weight bases. Therefore, it can be concluded that constitutive transgenic expression of GAD conferred resistance against the root-knot nematode in phenotypically normal tobacco plants, probably via a GABA-based mechanism.

Long-term evaluation of cover crop and strip-tillage on tomato yield, foliar diseases and nematode populations

A 6-yr (1987–1992) experiment, continuous on the same site, evaluated potential problems for yield, nematodes and diseases with tomatoes (Lycopersicon esculentum Mill.) grown in a strip-till system. Treatments consisted of conventional tillage (CT) and strip tillage (ST), rye (Secale cereale L.), wheat (Triticum aestivum L.) and perennial ryegrass (Lolium perenne L.) cover crops and a 2-yr rye-tomato rotation. Results of the first 5 yr indicated a decrease in tomato yield over time for both tillage treatments and cover crops. However, yield rebounded overall for treatments in 1992 with the highest yield in the rye-tomato rotation. We suspect this was a result of high populations of root-knot nematodes which collapsed over the winter of 1991/1992. Tomato yields were lower following wheat and perennial ryegrass than rye. In only 1 yr out of 6, strip-tillage reduced yield compared with conventional tillage. Bacterial speck/spot symptoms on foliage, although minor, were significantly greater in ST than in CT ...

Partial isolation of a water soluble pheromone from the sugar beet cyst nematode, Heterodera schachtii, using a novel bioassay

The sex pheromone of female Heterodera schachtii, the sugar beet cyst nematode, was partially isolated using high performance liquid chromatography (HPLC). Female-conditioned medium (FCM), produced by incubating 20 H. schachtii females in 1 ml of ultrapure water, attracted males in a concentration dependent manner. The attractive material was not contained within the female gelatinous matrix and did not attract second stage juveniles (J2). Characterisation of FCM revealed that the attractive material was water soluble and heat stable. Male H. schachtii exhibited stylet thrusting behaviour upon exposure to FCM, and this behaviour was used as a novel indicator of biological activity.

Crop Rotation with Forage Pearl Millet for Control of Root-Lesion Nematodes in On-Farm Trials with Potato

ABSTRACT In Canada, root-lesion nematode (Pratylenchus penetrans Cobb) (RLN) is a major soil pest in many crops. Crop damage is reduced by controlling the RLN populations below economic threshold level by soil fumigation, rotation with non-susceptible crops and growing RLN-re-sistant varieties. Agriculture Environmental Renewal Canada has developed a forage pearl millet (Pennisetum glaucum L.) variety “CFPM 101” (Canadian Forage Pearl Millet 101) adapted to Eastern Canadian growing conditions. On-farm crop rotation trials with CFPM 101 and corn (Zea mays) were conducted in commercial potato (Solanum tuberosum L.) fields in Ontario. In the following year, potato was grown. RLN populations were monitored three times (Spring, Summer, and Fall 2000) during the rotation crop and two times (Spring and Summer 2001) during RLN susceptible potato crop. Rotation crop, season, and crop Xyear interaction significantly affected the RLN levels. Soil RLN population did not change in rotation year 2000 and susceptible (potato) year 2001 with CFPM 101, whereas corn increased it over 200 to 700% after one year of rotation, suggesting the traditional potato.corn.potato rotation increases RLN populations. Results confirm that crop rotation with CFPM 101 is an effective way to control RLN populations, thus offering an environmentally friendly alternative to soil fumigation. In the pearl millet rotation, it is critical to maintain weed-free conditions to optimize the nematode-suppression.

ROTATION WITH TAGETES SP. FOR CONTROL OF ROOT-LESION NEMATODES AFFECTS FLUE-CURED TOBACCO GROWTH, YIELD, QUALITY, AND COST OF PRODUCTION

Abstract The root-lesion nematode (Pratylenchus penetrans) can cause significant reduction in tobacco yield and quality. This nematode also is a parasite of cereal rye (Secale cereale), which is a common rotation crop in tobacco areas. Row fumigation prior to transplanting tobacco in the spring is practiced by >95% of Ontario growers to control nematode populations. Planting of Tagetes sp. (marigold) also reduces nematode populations, and when used instead of rye as a rotation crop with tobacco, can provide an alternative to chemical fumigation. Field trials were conducted from 1996 to 1998 to compare the impacts of marigold rotation vs. a traditional fall rye rotation crop, with and without chemical fumigation, on flue-cured tobacco yield, quality, and cost of production. Both the marigold rotation and the non-fumigated rye rotation resulted in slightly less early season N available in the following tobacco crop year compared to the rye + fumigation check. Plant height in July and days to flowering, both...