Field test of Easter lilies transformed with a rice cystatin gene for root lesion nematode resistance.

Easter lilies, Lilium longiflorum cv. Nellie White are a staple of the floral industry. In the U.S. most of the Easter lilies are grown in Oregon and California along the coast where there is a micro climate that is favorable to growth of lilies. The main pest when growing lilies in the field is Pratylenchus penetrans, the root lesion nematode. Easter lilies are one of the most expensive crops to produce because of the cost of chemicals used to control P. penetrans and other pathogens that infect the lilies. Our previous study had shown that transgenic Easter lilies containing a rice cystatin gene (Oc-IΔD86 that has a deleted Asp86) were resistant to P. penetrans in vitro. This study examined growth characteristics of five independently transformed lines of the cystatin Easter lilies compared to non-transformed Nellie White for three seasons in the field in Brookings, Oregon. Liles grown in three soil chemical treatments 1) preplant fumigation, 2) preplant fumigation plus at plant organophosphate, and 3) at plant organophosphate were compared to those grown in nontreated soil. Growth characteristics evaluated included: time of shoot emergence, survival of plants, size of plants, visual ratings of plant health, basal roots and stem roots, weight of foliage and roots, and number and size of bulblets that developed on stems. Nematodes were counted following their extraction from the roots. While not totally resistant, when planted in the field, transformed lines demonstrated and maintained a degree of resistance to lesion nematode over two growing seasons and displayed desirable growth and quality characteristics similar to non-transformed lilies.

Deep injection and the potential of biochar to reduce fumigant emissions and effects on nematode control.

Reducing fumigant emissions is essential for minimizing the environmental impacts of pre-plant soil fumigation. Low permeability plastic films are effective at reducing emissions but have high initial purchase, installation, and disposal costs. The objective of this study was to evaluate if deep fumigant injection and biochar soil amendments can reduce emissions, improve fumigant distribution in soil, and provide acceptable control of plant parasitic nematodes. A pre-plant soil fumigation trial was conducted in a commercial orchard in the San Joaquin Valley, CA, USA. Treatments included two rates of Telone® C-35 (a mixture of 1,3-dichloropropene and chloropicrin) under totally impermeable film or with no surface seal, two injection depths (45 or 65 cm), and two biochar rates (20 or 40 ton ha-1). Emission rates were generally low due to rain events encountered during the trial, but data clearly showed that the deep injection enhanced fumigant delivery to depths below 60 cm and resulted in significantly lower peak emission compared to the standard injection depth. Biochar applied at 40 ton ha-1 had the lowest emission rates during 1-month monitoring period. Although variability in nematode survival was high, tarped, deep injection, and biochar treatment showed lower survival of nematodes at various depths. Increase in fumigant persistence, especially chloropicrin, was observed in this study, likely due to the high soil moisture and low temperature. All data indicate that biochar amendments can help reduce fumigant emissions without reducing nematode control; however, additional research is needed to optimize treatments, determine the affordability of various biochar materials, and validate results under a range of field conditions.

Reduction of root-knot nematode, Meloidogyne javanica, and ozone mass transfer in soil treated with ozone.

Ozone gas (O3) is a reactive oxidizing agent with biocidal properties. Because of the current phasing out of methyl bromide, investigations on the use of ozone gas as a soil-fumigant were conducted. Ozone gas was produced at a concentration of 1% in air by a conventional electrical discharge O3 generator. Two O3 dosages and three gas flow rates were tested on a sandy loam soil collected from a tomato field that had a resident population of root knot nematodes, Meloidogyne javanica. At dosages equivalent to 50 and 250 kg of O3/ha, M. javanica were reduced by 24% and 68%, and free-living nematodes by 19% and 52%, respectively. The reduction for both M. javanica and free-living nematodes was dosage dependent and flow rate independent. The rates of O3 mass transfer (OMT) through three soils of different texture were greater at low and high moisture levels than at intermediate ones. At any one soil moisture level, the OMT rate varied with soil texture and soil organic matter content. Results suggest that soil texture, moisture, and organic matter content should be considered in determining O3 dosage needed for effective nematode control.

Dose Response of Weed Seeds, Plant-Parasitic Nematodes, and Pathogens to Twelve Rates of Metam Sodium in a California Soil.

Metam sodium (sodium N-methyl dithiocarbamate, metam-Na) is widely used in agricultural and floricultural production for controlling soilborne plant pathogens, parasitic nematodes, and weeds. It undergoes rapid decomposition to the biocide methyl isothiocyanate (MITC) in moist soils. In this study, the efficacy of 12 concentrations of metam-Na (10 to 2,650 µmol kg-1 soil) to control seeds or tubers of five major weed species, three soilborne pathogens, and one parasitic nematode was evaluated in a sandy loam soil under controlled conditions. Soils were exposed to the fumigant in microcosms for 24 h at 10 and 20°C. Generation and dissipation curves of MITC in soil under controlled conditions showed that MITC concentrations in soils were highest 2 h after metam-Na application and decreased steadily over the 24-h incubation period. After 24 h, remaining MITC concentrations in soil microcosms at 10 and 20°C were 53 and 38% of the original amount applied, respectively, indicating a 20% reduction in MITC dissipation at the lower soil temperature. Logistic dose-response models were used to estimate the effective concentration necessary to reduce soil pest viability by 50 (LC50) or 90 (LC90) percent under both temperatures. Seed of Portulaca oleracea, with LC90 values of ≤1,242 µmol kg-1 soil, was the most sensitive to soil fumigation with metam-Na, followed by Polygonum arenastrum with LC90 values of ≤1,922 µmol kg-1 soil. At 10°C fumigation temperature, metam-Na at the highest dose tested in this study, 2,650 µmol kg-1 soil, was not sufficient to achieve adequate control of Stellaria media and Malva parviflora seed and Cyperus esculentus tubers. Weed control efficacy (average reduction in LC90 values) of metam-Na was between 25 and 60% higher if soils were fumigated at 20°C compared with 10°C, with the exception of M. parviflora. Phytophthora cactorum and Pythium ultimum were more sensitive to soil fumigation with metam-Na (LC90 ≤ 165 µmol kg-1 soil) than Verticillium dahliae (LC90 ≤ 737 µmol kg-1 soil). The nematode Tylenchulus semipenetrans was highly sensitive to soil fumigation with metam-Na (LC90 ≤ 98 µmol kg-1 soil), and the efficacy of control increased by 30% if soil was fumigated at 20°C compared with 10°C. In this sandy loam soil, metam-Na at a concentration of 850 µmol kg-1 reduced the viability of Portulaca oleracea and Polygonum arenastrum seeds, C. esculentus tubers, and all soilborne pathogens and parasitic nematodes tested by 90% at 20°C after 24 h exposure. These results indicate that metam-Na can provide effective pest and disease control at maximum label rate for the commercial formulation, but there was a reduction in efficacy at low temperature.

Sensitive PCR Detection of Meloidogyne arenaria, M. incognita, and M. javanica Extracted from Soil.

We have developed a simple PCR assay protocol for detection of the root-knot nematode (RKN) species Meloidogyne arenaria, M. incognita, and M. javanica extracted from soil. Nematodes are extracted from soil using Baermann funnels and centrifugal flotation. The nematode-containing fraction is then digested with proteinase K, and a PCR assay is carried out with primers specific for this group of RKN and with universal primers spanning the ITS of rRNA genes. The presence of RKN J2 can be detected among large numbers of other plant-parasitic and free-living nematodes. The procedure was tested with several soil types and crops from different locations and was found to be sensitive and accurate. Analysis of unknowns and spiked soil samples indicated that detection sensitivity was the same as or higher than by microscopic examination.