To: California Pepper Commission
RE: Research proposal for 2015
PI: Antoon Ploeg, Associate Nematology Specialist, Dept. Nematology, UCR, 1463 Boyce Hall, Riverside CA 02521. Tel (951) 827-3192.
Collaborator: Jose Aguiar, UCCE Farm Advisor, Riverside County, 81-077 Indio Blvd. Suite H, Indio, California 92201. Tel. (760) 342-2467.
Project Title: Establishing a root-knot nematode trial site for future field trials with bell peppers.
Statement of the problem and background.
The Southern root-knot nematode (Meloidogyne incognita) has been reported to cause serious damage to peppers. The second-stage nematodes (J2) are worm-shaped, move through the soil, and enter the plant roots. In roots of a host crop, the second-stage juveniles nematodes develop into females, while the root system responds to infection with the formation of galls. The fully developed females can produce up to 400 eggs, that are contained in clusters in a gelatinous material and "glued" to he outside of the roots. From these eggs second-stage juveniles can emerge to repeat the cycle, or eggs can remain in the soil during fallow period to serve as inoculum during the next crop cycle. The duration of the nematode life cycle depends primarily on the species of root-knot nematode and on soil temperature. Meloidogyne incognita, the most important species infecting bell-pepper, can complete its' life cycle in less than 4 weeks under an optimum soil temperature of 32C (90F), and become inactive when the soil temperature drops below 17C (62F). In most host crops, root-knot nematode infestation can easily be diagnosed because of obvious galling on the affected roots. Above-ground symptoms are however not specific, and can include chlorosis, wilting under sufficient soil moisture, stunting, and increased susceptibility of plants to fungal or bacterial root pathogens.
In the Coachella Valley of Southern California, approximately 5,000 acres are cropped with bell peppers. Root-knot nematodes are widespread throughout the Coachella Valley and growers report serious damage.
In a previous study, supported by the California Pepper Commission, we showed that a species of root-knot nematode (M. incognita) was frequently associated with stunted pepper plants in the field, sometimes in very high population levels. In greenhouse trials we demonstrated that resistant pepper varieties developed in North Carolina were also resistant against the "Coachella" population of nematodes, and that there are differences between pepper varieties with respect to their sensitivity to nematodes. Results from these studies were published in newsletter/newspaper articles (1-4) as well as in a scientific publication (5).
To control nematodes, pepper growers in the Coachella Valley commonly apply fumigant nematicides such as metam-sodium (Vapam) or 1,3-dichloropropene (Telone) as a post-harvest and/or pre-plant soil treatment.
However, allowed use of these chemicals is becoming more and more restricted, and they have adverse effects on the environment and general human health. During the last few years we have tested several potential new nematicides in field trials with other vegetables. Some of these products appear very promising, and have much fewer environmental and health hazards. For example, one product (Nimitz™) that received federal EPA registration in September 2014, and that in our field trials with tomato, carrots, and melon, showed very good efficacy, only has a CAUTION label, and a 0 hr REI. California registration is expected soon. Some other products that are under development also appear very promising in our trials.
To evaluate the potential of these products for Coachella Valley growers, it is desirable to do trials in a location/environment that is representative for the local growing conditions of the crop. Although one possibility would be to locate trials in grower fields, it is generally difficult to locate sites that have both sufficient nematode pressure and an even distribution of the nematodes. Furthermore, testing of non-registered products complicates matters with respect to worker safety and crop destruct requirements.
Therefore, we propose to initiate and maintain a root-knot nematode field site for studies on bell pepper at the Coachella Valley Agricultural Research Station (CVARS). A 0.2 acre site is available with soil conditions that are suitable for nematode establishment and maintenance.
Objectives of this project are:
- Establish and maintain a 0.2 acre field trial area with a uniform and moderately-high
infestation of a locally occurring root-knot nematode population (M. incognita).
The field site will be direct-seeded with susceptible cherry-type tomato during late February
2015 on 25, 30-inch wide(center-center) beds of 125 ft length. Watering will be through buried drip tubing (emitters 2 l/hr, 1 ft spacing). Approximately 5 wks after seedling emergence, a suspension containing root-knot nematode eggs (M. incognita) will be injected into the soil through the drip tubing at a density to give 10,000 eggs per linear ft of bed. The nematodes were originally isolated from soil at CVARS, taken to UC Riverside, and increased on susceptible tomato plants grown in a greenhouse. Infested roots from these greenhouse-grown tomato plants will be used for extraction of root-knot nematode eggs.
In June 2015, 5 plants will be dug from each bed, and roots will be examined for presence of
galls (indication of successful nematode infestation), and rated on a scale from 0-10 (0:no galls, 10:very severe galling). In July 2015, the tomato crop will be mowed, drip tubing will be removed, and the tomato crop residue incorporated. The field will be divided into 10 sections (each section 5 beds wide, 62 ft long), and soil samples will be collected from each section for nematode extraction and counting. Another nematode susceptible crop (cowpea or snap-bean) will be grown in the fall season to further increase nematode levels. Depending on soil-nematode levels detected after the tomato crop, we will decide whether or not additional nematode inoculum needs to be injected into the field. Root galling and nematode population levels after cowpea / bean will be determined as described before.
We expect that the field will have a moderately high root-knot nematode population that will be evenly distributed throughout the field after harvest of the cowpea / bean crop. The field site will be suitable for nematode-related field experiments using pepper for the spring 2016 season. In future years, the field site and nematodes will be managed, so sections of the field are available each year for experimentation.
- Ploeg, A.T., Aguiar, J. 2013. Root-Knot Nematode Damage to Bell Pepper in Coachella
Valley. Pepper News. July, 2013 p.4-5.
- Aguiar, J., Bachie, O., Ploeg, A.T. 2014. Root-knot nematode on bell pepper. Imperial
County Agricultural Briefs. Vol. May: p.2-6.
- Bachie, O., Aguiar, J., Ploeg, A.T. 2014. Root knot nematodes on bell pepper a problem
in Coachella Valley. Imperial Valley Press. Vol. 114: 18 p.1
- Aguiar, J., Bachie, O., Ploeg, A.T. 2014. Surprising spring virus wise in Coachella
Valley bell peppers. Western Farm Press. August 25, 2014 4p.
- Aguiar, J., Bachie, O., Ploeg, A.T. Response of Resistant and Susceptible Bell-pepper (Capsicum annuum) to a Southern California Meloidogyne incognita Population from a Commercial Bell-pepper Field. Journal of Nematology. (In Press).
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