Raymond W. Schneider
Professor

Recent findings from this latter thrust are extremely intriguing and potentially useful for managing this recalcitrant disease.  Briefly, Schneider’s group (Brian Ward, Clark Robertson and Eduardo Chagas) found that the toxin produced by the pathogen may be involved in iron sequestration within the leaf, which would be similar to the function of siderophores (biological iron chelators) in bacteria.  This chelated iron would then be available to the fungus during its endophytic colonization phase (see below).  Given that biological chelators are induced by low iron concentrations, Schneider’s group postulated that if iron was made available to the pathogen, production of the chelator (toxin) would be inhibited, and the pathogen would lose its pathogenicity factor.  Results from in vitro and field studies confirmed this hypothesis, and a very high level of disease control was observed in field experiments in which iron was applied as a foliar spray.  These results must be confirmed, but clearly a new paradigm in disease management and host:pathogen interactions has been opened.

One of Schneider’s most recent accomplishments is the discovery that C. kikuchii infects plants many weeks before the appearance of symptoms of Cercospora leaf blight -  the so-called latent infection phase of disease progression.  This research involved the development of a real-time PCR protocol by a graduate student (Ashok Chanda) and its use in monitoring infection in the field. This novel combination of molecular protocols and practical field pathology resulted in the targeted development of a disease control strategy in which the fungicide is applied once during the season long before symptoms occur in order to suppress latent infection.  This technological achievement is now being evaluated in commercial fields, and reports from crop consultants are very encouraging.  Such a multi-year project exemplifies the classic experiment station mission of conducting fundamental research on an applied problem.

Schneider’s group (Monica Lear, Karol Elias and Michelle Warr) described for the first time the roles of root colonization by nonpathogenic strains of F. oxysporum (endophytes) and their role in disease suppressive soils.  He showed that roots that had been colonized by endophytic strains of F. oxysporum were either protected from infection by the pathogen or they were predisposed to infection.  Schneider’s publications in this area led to work by others in which they showed that Fusarium wilt of watermelon and other crops could be managed by inoculating plants with effective competitive endophytic strains.  More recent molecular work by an undergraduate student in Schneider’s lab showed that these strains were virtually indistinguishable from pathogenic strains of F. oxysporum, which suggests that pathogenic strains evolved from these endophytes.  This work could lead to novel means of cultural disease control by stimulating higher populations of these beneficial strains in order to manipulate soils to become disease suppressive.     

In other research projects, Schneider showed that chloride in association with certain cation ratios suppressed root infection by F. oxysporum.  The mechanism of disease suppression was related to root osmotic regulation and root exudation.  This work also stimulated research by others and opened new fields of discovery.  Schneider’s group (Nicole Ward, Brian Ward and Clark Robertson) recently returned to this line of investigation, and they showed that certain minor elements, including iron and aluminum, suppressed infection of soybean by the Cercospora leaf blight pathogen.  This discovery holds great promise for managing this recalcitrant disease.  Disease suppression apparently is not related optimizing plant nutrition in that minor element tissue analyses are within sufficient ranges.  Rather it appears that there is a direct effect on the pathogen possibly related to control of toxin production within leaf tissue.  Elucidating the mechanisms involved in disease suppression by these minor elements may lead to entirely new approaches to managing troublesome foliar diseases of many crop species. 

Other research projects published by Schneider’s group (Pali Kuruppu) involved providing an explanation for cultural control of red crown rot in soybean by delayed planting.  Also, he and a graduate student (Guoping Su) showed that the charcoal rot pathogen adapts to rotation crop sequences, and this provides a partial explanation of why certain crop rotation sequences are superior in managing this disease, which can be very damaging during moderate to severe drought conditions.

In recent years Schneider’s professional life has been dominated by soybean rust, which he discovered for the first time in North America in 2004.  The discovery and associated excitement were described in Science magazine by their reporter (Science, 3 December 2004. 306:1672-1673).  Schneider and his group (Nicole Ward, Clark Robertson, Paul Mumma and others) immediately began evaluating numerous fungicide chemistries for efficacy, and his work and that of his colleagues in Louisiana and other states on rates and times of application provided the soybean industry with an arsenal for combating this potentially devastating disease.  With this disease, too, molecular tools were used to demonstrate that there is an extended latent phase, and fungicide efficacy was greatly improved by spraying long before the development of disease symptoms (Nicole Ward, Clark Robertson).  Other research on soybean rust involved the development of risk models, spatial analyses (GIS) of disease development, and other pursuits. 

Schneider, a graduate student (Tomas Rush) and collaborators (Dr. Cathie Aime and others) determined that the currently used primers and probe that are used in real-time PCR detection technologies for the soybean rust pathogen (Phakopsora pachyrhizi) also detect other Phakopsora species.  This finding explains why the rust pathogen was claimed to have been found throughout the eastern U.S. and Canada.  These questionable findings were used by others to develop pathogen dispersion models and caused widespread concern about the spread of the disease into the Midwest and Ohio River Valley.  Conclusions from this work showed that these models must now be re-evaluated, and the United Soybean Board recently provided funding to conduct this investigation.

Another project was nationwide in scope in which Schneider and his group participated in a spore dispersal study.  Schneider soon realized that current spore trapping technology was not adequate for monitoring airborne populations of the soybean rust pathogen.  Schneider and an undergraduate student (Erik Durr) from Biological and Agricultural Engineering designed and tested an electrostatic particulate sampler that was far more efficient and versatile in quantifying spore populations in the atmosphere.  This device was recently awarded a patent (held by the LSU AgCenter), and a company was formed to produce and market this device under the auspices of the LSU Business and Technology Center.  The grape industry in California is currently testing this technology for management of powdery mildew, which is the most serious disease affecting grapevine worldwide. 

A graduate student in Schneider’s program (Nicole Ward) discovered that a unique fungus, Simplicillium lanosoniveum, parasitized rust spores as its exclusive food source.  The fungus was found only in association with soybean rust pustules.  She went on to show that the fungus could be grown in culture and that it could be formulated as a biological control agent that was equivalent in efficacy to the most commonly used fungicide.  This fungus is now being evaluated for commercial use by Marrone Bio Innovations, Inc.

Other achievements are briefly described below:

Collaborated with Dr. David Walker, soybean geneticist at University of Illinois, in establishing a soybean rust disease nursery in Baton Rouge to screen for disease resistance.

In collaboration with Dr. Boyd Padgett, Dr. Pat Bollich and Dr. Kurt Guidry following 6 years of field experiments in several locations, developed a yield loss calculator for three soybean diseases.  To be used as a decision aid by producers in deciding whether or not to apply fungicides.

In collaboration with several other LSU AgCenter scientists in several years of field experiments, showed that the soybean green stem disorder is related to the use of strobilurin fungicides and that there is a genetic component to this disorder.

Other achievements:

In collaboration with Dr. Jeff Hoy and postdoctoral researcher Dr. Weidong Chen, established genetic relationships among several Pythium species that infect sugarcane and rice and showed that certain Pythium species are responsible for stubble decline in sugarcane.

Determined that several Pythium species infect feeder roots of rice and coined the disease name feeder root necrosis.  Control of this disease with soil applications of metalaxyl resulted in significant enhancement of seedling establishment, early season growth and yield.

With graduate students Susan Useman and Clark Robertson and collaborators Dr. Wade Elmer and Dr. Irv Mendelssohn, provided experimental evidence that showed that the extensive dieback of Spartina alerniflora was caused by weakly pathogenic, endophytic strains of Fusarium proliferatum and other Fusarium species following predisposition by water stress.  This plant is the predominant species in coastal salt water marshes along the Gulf Coast and Atlantic Seaboard where the dieback also was documented.

Dr. Schneider has published 76 refereed journal articles, edited one book, 11 book chapters, numerous popular press articles (including Louisiana Agriculture), and more than 100 abstracts.

Teaching Experience
PLHL 4000 General Plant Pathology
PLHL 7082 Soilborne Plant Pathogens
PLHL 4014 Diseases of Economic Crops (Section of soybean diseases)

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