Sylvie Jenni

Plastic mulches and row covers for early and midseason crisphead lettuce produced on organic soils

Plastic mulches and row covers for early and midseason crisphead lettuce (Lactuca sativa L. ‘Ithaca’) grown on organic soils were investigated over 2 yr. For early production, four mulch treatments (infrared transmitting, silver-on-black co-extruded polyethylene, white-on-black co-extruded polyethylene and a bare soil control) with and without an agrotextile low tunnel were tested. For midseason production, the same mulch treatments were evaluated in combination with normal and high planting densities (54 400 plants ha-1 and 65 200 plants ha-1). Low tunnels combined with mulches accelerated early growth and maturity by 10 d for infrared-transmitting mulch, 7–8 d for silver mulch and 3–5 d for white mulch, relative to production on bare soil control without a low tunnel. Infrared-transmitting mulch alone increased plant biomass early in the season and produced a lettuce head of heavier or similar weight relative to that from bare soil, even if harvested 3–4 d earlier. Lettuce heads grown on silver and whit...

Row Covers Reduce Insect Populations and Damage and Improve Early Season Crisphead Lettuce Production

Insect damage on cripshead lettuce (Lactuca sativa L.) can reduce its marketability and cause significant crop losses. There is increasing interest in using alternative control strategies to replace or reduce pesticide use for this purpose. Crisphead lettuce cv. Ithaca grown under two densities 10 (ARC10) and 17 (ARC17) g/m2 of polypropylene applied as floating covers or low tunnels were compared with an uncovered control. Effects on tarnished plant bugs and aphids, air and soil temperature, and lettuce growth and development were recorded. Aphids and tarnished plant bug were almost completely excluded by covers. Once removed, insect population in the covered treatments increased but was 5.5 times less than in uncovered control. Covered plots had higher air and soil temperatures than uncovered plots. Air temperatures were higher under the floating covers than tunnels. ARC17 had higher soil temperatures than ARC10. Row covers promoted earlier growth and maturity. Head weights of lettuce covered with ARC17 were 1.4 times heavier than those of ARC10, which in turn were heavier than the control. Head weights were similar for floating covers and low tunnel treatments.

Reduction of Insect Damage in Radish with Floating Row Covers

ABSTRACT Radish (Raphanus sativus L.) is a short season direct seeded crop with multiple seedlings starting as soon as the ground has thawed to ensure continuous supply. Floating row covers can be used to protect crops from low temperature to stimulate germination and to exclude insect pests. There is a need to optimize the use of floating row covers for early and mid-season radish production with floating row covers of different weave and weight. Two types of floating row covers (Agryl P10 and Agryl P17) and an uncovered treatment were compared in a randomized block design experiment with four replicates in the muck soil region of southwestern Quebec. The floating row covers completely excluded cabbage maggots (Delia radicum L.) and significantly reduced beetle (Phyllotreta spp.) damage by 60% compared to control plots. Both floating row covers increased daytime temperatures relative to the control, with Agryl P17 producing the warmest microclimate. Covering the seeded plots increased total emergence by 19% and decreased mean emergence time by 1.3 days but did not affect the uniformity of seed germination as expressed by the spread of emergence. For the three sowing dates, the floating row covers accelerated growth relative to the control, resulting in heavier leaf weight and larger root diameter at harvest. Radish plants covered with Agryl P17 in the late season showed a decrease in foliage health, which likely resulted from excessive heat. Plants covered with Agryl P17 and Agryl P10 were harvested respectively 10 days ± 4 days and 7 days ± 5 days earlier than the control.

Plastic Mulches and Low Tunnels to Reduce Bolting and Increase Marketable Yield of Early Celery

Abstract Canadian celery (Apium graveolens L. var. duke) growers are transplanting crops earlier to lengthen the growing season. This increases the risks of vernalization (exposure to temperatures <14°C), which induces bolting and makes the plants unmarketable. Combinations of mulches and low tunnels were tested in 1999 and 2000 to determine whether they could increase air and/or soil temperatures to inhibit bolting. Mulches increased maximum soil temperatures by up to 10°C compared with the control. Low tunnels, particularly polyethylene tunnels combined with clear mulch, increased both air and soil temperatures. In 1999, few if any plants bolted. In 2000, covering celery with tunnels significantly reduced bolting. Covering celery with a single layer of spunbonded polyester produced the most consistent benefits in terms of reducing bolting and increasing marketable yield.

FRET hybridization probes for the rapid detection of disease resistance alleles in plants: detection of corky root resistance in lettuce

We describe the development of a non-electrophoresis PCR-based assay for allele discrimination at a disease resistance locus. The assay is based on the emission of light by fluorescence resonance energy transfer (FRET) upon annealing of two hybridization probes. The analysis of melting curve profiles of the probes and templates allowed the detection of single nucleotide polymorphisms. The assay was applied to the detection of alleles at the cor locus in lettuce (Lactuca sativa) that confers recessive resistance to corky root disease. Probes and primers for the assay were designed after the characterization of a single nucleotide polymorphism between alleles of PCR products amplified using a linked marker. That polymorphism was validated in a collection of lettuce varieties representing different genetic backgrounds. The FRET hybridization probes approach provided fast and accurate genotyping of breeding material directly in a one-tube reaction. The absence of electrophoresis makes this approach suitable for applications that require automation and high-throughput genotyping analyses such as marker-assisted selection programs.

Yield and Quality of Crisphead Lettuce Cultivated on Organic or Mineral Soils

ABSTRACT A 2-year experiment was conducted to determine the potential for crisphead lettuce production on mineral soils compared to the production on organic soils of Quebec, during the warmest period of the season when quality often decreases. For each soil type, there were three experimental sites and two planting dates. For each soil type by site by planting date combination, three varieties, ‘Ithaca’, ‘Emperor’ and ‘Salinas 88’ were tested within four blocks. Transplanting occurred from 11 to 28 June 1999, and from 11 June to 5 July 2000, and harvest was from 21 July to 5 August 1999, and from 27 July to 10 August 2000. Lettuce on organic soils matured 4 to 7 days earlier and generally produced larger and heavier, firmer and more uniform heads. Soil type did not affect percentage of heads with the physiological disorders rib blight and tipburn. ‘Ithaca’ produced large, heavy and very firm heads, particularly on organic soil. Although this variety showed tolerance to bolting, it was susceptible to rib blight (50%), but less to tipburn (19%). ‘Emperor’ had heads that were lighter than those of the other two varieties on organic soil and matured later, and it had significantly less rib blight (22%) but more tipburn (34%) than the other two varieties. Although it produced a head with good weight, ‘Salinas 88’ tended to be fluffy and bolted early on both soil types. The potential for mid-season production of crisphead lettuce seems limited under current production methods.

Partial Aphid Resistance in Lettuce Negatively Affects Parasitoids

ABSTRACT This study investigated the effects of partial plant resistance on the lettuce aphid Nasonovia ribisnigri (Mosley) (Hemiptera: Aphididae), a major pest of cultivated lettuce (Lactuca sativa L.), and one of its parasitoids, Aphidius ervi Haliday (Hymenoptera: Braconidae). Aphids were reared on susceptible (L. sativa variety Estival; S) or partially resistant (Lactuca serriola L. PI 491093; PR) lettuce, and next parasitized by A. ervi females. Fitness proxies were measured for both aphids and parasitoids. Developmental time to adult stage took longer for alate and apterous aphids (an average of 3.5 and 1.5 additional days, respectively) on PR than on S lettuce, and fecundity of alate aphids reared on PR lettuce was reduced by 37.8% relative to those reared on S lettuce. Size (tibia length) and weight of aphids reared on PR lettuce were lower than for aphids reared on S lettuce from the third and second instar onward, respectively. Parasitism of aphids reared on PR plants resulted in lower parasitoid offspring emergence (-49.9%), lower adult female (-30.3%) and male (-27.5%) weight, smaller adult female (-17.5%) and male (-11.9%) size, and lower female fecundity (37.8% fewer eggs) than when parasitoids developed from aphids reared on S plants. Our results demonstrate that partial aphid resistance in lettuce negatively affects both the second and third trophic levels. Host plant resistance in cultivated lettuce may therefore create an ecological sink for aphid parasitoids.

Patch Experience Changes Host Acceptance of the Aphid Parasitoid Aphidius ervi

We investigated patch quality assessment by the parasitoid Aphidius ervi Haliday (Hymenoptera: Braconidae) when exploiting colonies of the lettuce aphid Nasonovia ribisnigri Mosley (Hemiptera: Aphididae). Three host patches of different qualities were sequentially offered to a naïve female parasitoid. High quality patches (HQ) consisted of 20 N. ribisnigri reared on susceptible lettuce; low quality patches (LQ) consisted of 20 N. ribisnigri reared on partially resistant lettuce and mixed quality patches (MQ) consisted of equal numbers (10) of aphids reared on both lettuce types. Parasitized aphids were reared until parasitoid emergence; number of mummies and sex ratio were noted. On the first host patch encountered, the mean number of A. ervi mummies produced was significantly higher for HQ host patches (X ± SD; 7.1 ± 5.0) than for LQ host patches (3.8 ± 4.5). This suggests that female A. ervi do not need prior experience to assess patch quality; females probably using an innate estimate of patch quality when encountering a first host patch. This initial patch quality assessment can be modified with experience. When females encountered a MQ patch, they kept their exploitation level constant on the following patch, whatever its quality. Females increased their level of host acceptance on the third patch when three LQ patches were offered successively; accepting low-quality hosts could be preferable when better hosts are not currently available in the habitat. These results suggest that A. ervi females behave in a manner consistent with a Bayesian updating process when foraging for hosts.

Testing irrigation, day/night foliar spraying, foliar calcium and growth inhibitor as possible cultural practices to reduce tipburn in lettuce

Corriveau, J., Gaudreau, L., Caron, J., Jenni, S. and Gosselin, A. 2012. Testing irrigation, day/night foliar spraying, foliar calcium and growth inhibitor possible as cultural practices to reduce tipburn in lettuce. Can. J. Plant Sci. 92: 889-899. Most of the lettuce produced in Quebec, Canada, is grown in organic soils in the area south of Montreal. Regularly, producers experience tipburn damage to their crop, a physiological disorder associated with Ca deficiency along the margins of young actively growing leaves. Therefore, active research is ongoing to reduce damage associated with this disorder. Two greenhouse trials on Romaine lettuce (Lactuca sativa L. ‘Sunbelt’) were conducted to measure the effect of day and night foliar water spraying, irrigation, foliar application of prohexadione calcium (a growth inhibitor) and foliar application of Ca on lettuce growth and incidence of tipburn. None of the treatments had a significant effect on biomass, dry weight, leaf number or leaf area in lettuce. However, the results show that frequent foliar applications of Ca as low as 90 mg L-1 Ca2+ resulted in a significant decreases in the number of leaves and percent leaf area with tipburn, and significant increases in Ca content in young leaves. Foliar water spraying, irrigation and foliar application of prohexadione calcium resulted in no significant differences in tipburn in greenhouse experiments. As greenhouse and field conditions may differ importantly, Ca application should be tested further at the field scale.

Yield, quality and revenue of pickling cucumbers with irrigation and supplemental N fertilizer under a humid climate

A 5-yr field experiment was conducted in southern Quebec to investigate yield, gross revenue and quality of pickling cucumbers (Cucumis sativus L. ‘Fancipak’) in response to sprinkler irrigation. In addition, supplemental nitrogen treatments (40 kg ha-1 foliar and granular) following application of 80 kg ha-1 N preplant, as well as non-fertilized and over-fertilized controls (80 kg ha-1 N preplant, 40 kg ha-1 N granular and 60 kg ha-1 N slow-release) were compared in a 2-yr trial under irrigated and non-irrigated conditions. During 1997 to 2000, rainfall was close to or above normal and irrigation did not increase marketable yields. In 1999 and 2000, irrigation reduced early marketable yields relative to non-irrigated treatments. In 2000, a relatively cool year with average rainfall, there was a positive yield response to supplemental N in the non-irrigated plots, but not in the irrigated plots. In 2001, a very hot and dry season, irrigation increased early yield by 66%, marketable yield by 160% and gross...