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IN THE UNITED STATES, SOYBEAN DISEASES RESULT IN AN ESTIMATED AVERAGE ANNUAL YIELD REDUCTION OF 11%. PLANT-PARASITIC NEMATODES ARE RESPONSIBLE FOR ANNUAL AGRICULTURAL LOSSES OF $160 BILLION, SEVERELY THREATENING GLOBAL FOOD SECURITY. ROOT-KNOT NEMATODES (MELOIDOGYNESPP.) ARE CONSIDERED THE MOST ECONOMICALLY IMPORTANT AND WIDELY DISTRIBUTED SPECIES OF PLANT-PARASITIC NEMATODE, OF WHICH SOUTHERN ROOT-KNOT NEMATODE [SRKN,MELOIDOGYNE INCOGNITA(KOFOLD & WHITE) CHITWOOD] HAS THE MOST SCIENTIFIC AND ECONOMIC IMPORTANCE. IN THE UNITED STATES, SRKN IS WIDELY DISTRIBUTED ACROSS ALL 13 SOUTHERN STATES, REPRESENTING THE SECOND MOST SUPPRESSIVE SOYBEAN PATHOGEN IN THE REGION.THE RECENT NORTHERN DISTRIBUTION OF SRKN IS HIGHLY CONCERNING CONSIDERING THAT MOST SOYBEAN VARIETIES GROWN IN THIS REGION (MATURITY GROUPS (MGS) EARLIER THAN MG 4) ARE KNOWN TO BE HIGHLY SUSCEPTIBLE TO SRKN.SRKN IS CHALLENGING TO CONTROL DUE TO ITS SHORT LIFE CYCLE AND HIGH REPRODUCTIVE RATES.THE OBSERVED SYMPTOMS OF SRKN INFECTION CLOSELY RESEMBLE THOSE CAUSED BY ABIOTIC STRESSORS, INCLUDING STUNTED GROWTH, LEAF WILTING AND DISCOLORATION, AND DEFORMATION OF THE ROOTS. THE EXTENT OF CROP LOSSES RELIES ON HISTORICAL CROP ROTATION AND FIELD USAGE, ENVIRONMENTAL FACTORS, INITIAL NEMATODE POPULATION DENSITY, SOIL TYPE, AND GENETIC BACKGROUND. STUDIES WITH CONTROLLED NEMATODE PRESSURE IN FIELD CONDITIONS HAVE SHOWN YIELD REDUCTION OF UP TO 97% IN SUSCEPTIBLE CULTIVARS WHEN EXPOSED TO HIGH SRKN PRESSURE. MANAGEMENT BASED ON CROP ROTATION IS ESPECIALLY CHALLENGING AND LIMITED SINCE MOST FLOWERING PLANTS ARE HOSTS TO SRKN. CHEMICAL APPROACHES USED TO BE AN EFFECTIVE MANAGEMENT OPTION TO CONTROL SRKN, HOWEVER, FUMIGANTS, SUCH AS 1,3-DICHLOROPROPENE ARE EXPENSIVE AND REQUIRE SPECIAL APPLICATION EQUIPMENT. NON-FUMIGANTS SUCH AS SEED-APPLIED NEMATICIDES ARE READILY AVAILABLE BUT ARE INEFFECTIVE WHEN NEMATODE DENSITIES ARE HIGH DUE TO LIMITED MOVEMENT FROM THE SEED COAT TO THE ROOT SYSTEM. THE USE OF GENETIC RESISTANCE IS THE MOST SUSTAINABLE APPROACH TO EFFICIENTLY CONTROL THE DAMAGE OF SRKN IN SOYBEANS.SINCE MOST SRKN-RESISTANT CULTIVARS ARE DERIVED FROM GENETIC RESOURCES PRIMARILY DERIVED FROM THE FORREST CULTIVAR CARRYING SOLELY THE RMI1 LOCUS (CHROMOSOME 10), IT RAISES CONCERNS REGARDING THE LONG-TERM SUSTAINABILITY OF RESISTANCE. AS PARTHENOGENIC NEMATODES, MINIMAL DIVERSITY AND EVOLUTION ARE EXPECTED. HOWEVER, RESISTANCE BREAKDOWN HAS BEEN OBSERVED IN TOMATOES AGAINST THE MI GENE. UNDERSTANDING THE MOLECULAR MODE OF ACTION RESPONSIBLE FOR THE RMI1 QTL RESISTANCE WILL HELP BETTER SAFEGUARD THAT RESISTANCE ONCE DEPLOYED IN THE FIELD. THE IMPACT OF A RESISTANCE-BREAKING POPULATION IN SOYBEANS, ALTHOUGH VERY RARE, WOULD BE DRAMATIC BECAUSE OF THE HIGH CONCENTRATION AND WIDE DISTRIBUTION OF SRKN, THE RATHER NARROW BASE OF GENETIC RESISTANCE, AS WELL AS THE LACK OF ALTERNATIVE MANAGEMENT OPTIONS. MORE EFFORTS ARE NECESSARY TO IDENTIFY AND STACK NOVEL SOURCES OF RESISTANCE IN DEVELOPING SOYBEAN L,INES WITH ENHANCED AND MORE DURABLE SRKN RESISTANCE, PARTICULARLY IN THE CURRENT SCENARIO WHERE SRKN POPULATIONS ARE BEING DETECTED IN NORTHERN SOYBEAN-PRODUCING REGIONS.THEREFORE,THE LONG-TERM OBJECTIVE OF THIS PROPOSAL IS TO PROVIDE SOYBEAN GROWERS WITH SRKN-RESISTANT CULTIVARS WITH A BROADER GENETIC BASIS FOR SUSTAINABLE SECURITY AGAINST YIELD LOSSES CAUSED BY THIS YIELD-LIMITING PLANT-PARASITIC NEMATODE. MORE SPECIFICALLY, THIS PROPOSAL IS GROUNDED IN THREE MAIN OBJECTIVES, INCLUDING I) IDENTIFICATION OF THE MAJOR GENE ON THERMI1LOCUS AND MOLECULAR CHARACTERIZATION OF ITS MECHANISMS OF RESISTANCE, II) EXPANSION OF THE GENETIC BASIS BY SCREENING AND IDENTIFYING NOVEL GENETIC SOURCES AND DIFFERENT MODES OF RESISTANCE, AND III) DEVELOPMENT OF SOYBEAN BREEDING POPULATIONS AIMING TO STACK DIFFERENT GENETIC SOURCES OF RESISTANCE.
$791.0k 7/24/24