Host Resistance as the Cornerstone for Managing Plant-Parasitic Nematodes in Sustainable Agroecosystems

INVESTIGATOR: McGawley, E. C.

PERFORMING INSTITUTION:
Plant Pathology & Crop Physiology
Louisiana State University
Baton Rouge, Louisiana 70803

NON-TECHNICAL SUMMARY: Plant parasitic nematodes cause yield suppression in many crop species. Host resistance suppresses nematode population densities and provides protection for subsequent susceptble crops. This project attempts to make effective use of currently available sources of resistance in sustainable cropping systems. The purpose of this project is to find effective, environmentally friendly methods to control plant parasitic nematodes.

OBJECTIVES: 1. Identification, characterization and introgression of genes for resistance and tolerance to nematodes into cotton, peanut, soybean, and major fruit and vegetable crops. 2. Development of marker-assisted selection systems for more efficient introgression of multiple resistance genes into agronomically superior crop genotypes. 3. Deployment of resistance and tolerance to nematodes in sustainable cropping systems.

APPROACH: One member of our group will focus on the bioengineering of resistance. Of particular significance are molecular signals from nematodes that are required for penetration and feeding within host plant roots. Research will focus on identifying the function(s) of nematode genes encoding paracitism factors primarily by disrupting the activity of each gene or gene product. For cotton, projects of two memebers of our group will use an existing RFLP map of cotton based on the interspecific hybrid G. hirsutum x G. barbadense to find markers linked to different resistance loci. For peanut, similar work will be done to design PCR primers that generate amplification products specific to resistant genotypes. For tobacco, RAPD markers linked to the P. parasitica nicotiana resitance locus will be evaluated for their utility as markers for the single dominant resistance gene to G. tobacum. For objective 3, field studies will include experiments on the deployment of M. arenaria resisant peanut cultivars, SCN resistant soybean, G. tabacum resistant tobacco and M. incognita resistant bell pepper. Other studies will be conducted to evaluate biological antagonists of plant parasitic nematodes, to measure the impact of various soil amendments on nematode population dynamics and to study the influence of herbicide-resistant cotton on reniform and root-knot nematodes.

PROGRESS: 2004/01 TO 2004/12
A microplot trial with Stoneville LA887 cotton was conducted using populations of the reniform nematode, Rotylenchulus reniformis, from Louisiana, Mississippi, Texas, Hawaii and Arkansas. At harvest, 122 days after planting, there were marked differences in the numbers of juveniles in soil, the numbers of eggs per gram of root, as well as dry weights of tops and roots. Among the five reniform nematode populations, the numbers of juveniles per 250 cubic centimeters of soil ranged from 2134 for the Arkansas population to 4532 for the Louisiana population; eggs per gram of root ranged from 47 for the Hawaii population to 464 for the Arkansas population. Weights of tops and roots were reduced significantly below those of controls by populations from all states except Hawaii. Subsequent studies were conducted under lab conditions to evaluate the role of egg biology in population development of these geographic isolates of reniform nematode. Over the course of two preliminary trials, hatch of eggs of isolates from 10 major cotton-producing parishes of Louisiana were determined in soil and in water. In the first trial, the percent egg hatch in water and soil, respectively, averaged 90 percent and 93 percent for the Catahoula parish isolate and 58 percent and 45 percent for the Avoyelles isolate. In trial two, the Opelousas isolate had the highest percent egg hatch, which was 91 percent in water and 94 percent in soil. The Evangeline isolate had the lowest percent egg hatch in water, which averaged 58 percent. The Avoyelles isolate had the lowest percent egg hatch in soil, which averaged 57 percent. Reproductive and genomic differences in populations of Rotylenchulus reniformis are being studied among seven populations collected from Alabama, Arkansas, Florida, Hawaii, Louisiana, Mississippi and Texas. Eight soybean lines (Lee 74, Peking, Plant Introductions (PIs) 88788, 90763, 209332, 437654, 89772, and Cloud) were each inoculated with 1,000 vermiform stages of the nematode. After 30 days, the number of eggs per egg mass and egg masses per plant were determined. Across the eight lines, the number of eggs per egg mass ranged from 0 to 66, while the number of egg masses ranged from 0 to 64. The Alabama population did not reproduce on Peking, Plant Introductions 90763, 437654 and 89772, while the Arkansas population reproduced on every line. Analysis of genomic differences among populations is based on examination of the two intergenic spacer regions (ITS1 and ITS2) by polymerase chain reactions (PCR) and restriction fragment length polymorphism (RFLP). Nematode genomic DNA is extracted from 10 swollen females dissected from tomato roots. A fragment with the size of approximately 1100 base pairs has been produced from every population.

IMPACT: 2004/01 TO 2004/12
Rotylenchulus reniformis is rapidly becoming the most economically important plant parasitic nematode in the southeastern United States. There is little, if any, commercial resistance to this nematode available to cotton and soybean producers. If, as we hypothesize, there are distinct pathotypes of this nematode found in nature, it is essential that a scheme for their identification be developed. Our research with the whole organism and its biology, as well as our molecular studies, is aimed at developing methods to distinguish between and among populations of the nematode. Research such as this will allow plant breeders to develop crop cultivars effective against the most common regional populations of the nematode.

PUBLICATIONS: 2004/01 TO 2004/12
Carter-Wientjes, C.H., J.S. Russin, D.J. Boethel, J.L. Griffin and E.C. McGawley. 2004, Feeding and Maturation by Soybean Looper (Lepidoptera: Noctuidae) Larvae on Soybean Affected by Weed, Fungus, and Nematode Pests. Journal of Economic Entomology: 14-20.

PROJECT CONTACT:
Name: McGawley, E. C.
Phone: 225-578-7145
Fax: 225-578-1415
E-mail: emcgawley@agcenter.lsu.edu  
URL: http://eppserver.ag.utk.edu

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