Location: Crop Genetics and Breeding Research
2017 Annual Report
Objectives
1. Identify and characterize nematode resistance genes and work with breeders to combine them with commercially valuable agronomic traits in cotton and peanut.
1.A. Determine the phenotypic expression of Meloidogyne arenaria resistance in peanut isolines 48 (moderate resistance) and 46 (high resistance).
1.B. Evaluate the phenotypic expression of the Meloidogyne incognita resistance QTLs qMi-C11 and qMi-C14 in cotton isolines.
1.C. Identify sources of resistance to Meloidogyne incognita in cotton that differ from Auburn 623 RNR.
1.D. Identify specific Meloidogyne-resistance genes within quantitative trait loci (QTL) regions and determine their functions in cotton and peanut.
2. Evaluate antagonist-nematode interactions, and develop novel integrated strategies, including biological control methods for management of nematodes in cotton, peanuts, and biofuel crops.
2.A. Evaluate environmental factors that influence Pasteuria penetrans endospore movement in soil and attachment to nematodes.
2.B. Monitor changes in adhesion phenotypes of Pasteuria penetrans to determine the drivers of phenotypic/genetic changes occurring in a population of the bacterium and its host, Meloidogyne arenaria.
2.C. Evaluate factors that affect the general suppression of Meloidogyne spp. in field soil.
2.D. Evaluate integrated management options including resistance, suppressive cover crops, and an improved decision model for managing Meloidogyne incognita.
Approach
Field and greenhouse experiments will be conducted to develop management options for root-knot nematodes in cotton and peanut. We plan a multi-tactic approach utilizing host-plant resistance (Objective 1), crop rotation, antagonistic crops, seed treatments, and biological control (Objective 2). Host-plant resistance to nematodes is the cornerstone of our strategy. We will determine mechanisms of resistance in cotton and peanut, determine effects of nematode resistance genes on the Fusarium wilt disease complex in cotton, and try to identify new resistance QTLs in cotton. However, we cannot rely exclusively on host-plant resistance for managing nematodes. We will also investigate ecologically based control strategies that can be integrated with resistant cultivars to increase the durability of resistance and control a broader spectrum of nematodes. Specifically, we will evaluate factors that influence the ability of the nematode-parasitic bacterium Pasteuria penetrans to suppress nematodes; determine whether frequency-dependent selection occurs between the bacterium and its host; and determine whether considering P. penetrans abundance improves nematode management decisions. We will evaluate the effects of winter cover crops on the natural suppressiveness of soils to nematodes; evaluate integrated management options including combining high residue rye with resistant cotton cultivars and nematicidal seed treatments; and evaluate nematode suppression and crop damage in the novel crop rotation of cotton with double cropped sweet sorghum (summer crop) and sugar beet (winter crop).
Progress Report
This report documents progress for a new project that began in April 2017 and continues research from 6048-21220-015-00D (Host Plant Resistance and Other Management Strategies for Nematodes in Cotton and Peanut).
We completed greenhouse and laboratory studies documenting differences in the effects of two root-knot nematode resistance quantitative trait loci (QTLs) in cotton on nematode development and reproduction, as well as the relative levels of nematode penetration into the roots and subsequent emigration if they fail to establish a feeding site. The two QTLs have different effects, which is why combining the QTLs leads to more effective nematode suppression.
We have conducted multiple greenhouse tests to determine which methods work best for our planned experiments to study the interactions between root-knot nematodes and the Fusarium wilt pathogen in cotton.
The first field trial evaluating whether the nematode resistance QTLs in cotton impart any deleterious effects (linkage drag) on yield or fiber quality have been established.
We are currently collecting cotton germplasm for evaluation to identify new QTLs for resistance to root-knot nematodes. We have so far been able to acquire about 20 germplasm lines previously identified as having some level of resistance. There are approximately 20 more germplasm lines, mostly from other countries, that we are still seeking. We are seeking assistance from a collaborator in Brazil to assist with acquiring many of these lines.
We completed the first two crops in a multi-year crop rotation sequence. The first summer crop (sweet soghum) and winter crop (sugar beet) were successfully completed and the second summer crop (cotton) has been planted.
We have established the 1st year of a field study to evaluate different combinations of treatments for management of root-knot nematodes in cotton. The treatments are winter cover crop for nematode suppression (fallow, rye, and high residue rye), cotton cultivars with and without resistance to root-knot nematodes, and seed treatments with Avicta on the susceptible cotton.
The gram-positive bacterium Pasteuria (P.) penetrans is an obligate parasite of root-knot nematodes, Meloidogyne spp. We have collected a third year of data showing that there are frequently one or two dominant pathotypes of P. penetrans present at a particular location; however, the dominant pathotype differed among the locations. These preliminary data indicate that some pathotypes of P. penetrans are dominant while others are rare. We have also observed that the dominant pathotype is replaced each year by one of the rare pathotypes, presumably to adapt to changes in the nematode population.
We initiated a field experiment to determine whether information about the abundance of Pasteuria penetrans can improve predictions of nematode damage in cotton. In the fall soil samples (2016), we had a wide variation in abundance of both root-knot nematodes (RKN) and Pasteuria across the field site which should improve our chances of correlating both RKN and Pasteuria with yield losses in cotton this summer (2017).
Accomplishments
1. Root exudates modify the susceptibility of root-knot nematodes to a bacterial pathogen. The bacterium Pasteuria penetrans is an effective biological control organism for root-knot nematodes; spores of Pasteuria attach to the nematode cuticle, infect, and prevent females from laying eggs. ARS and University of Georgia researchers in Tifton, Georgia, demonstrated that when the nematodes are exposed to root exudates, they were more resistant to spore attachment than were nematodes not exposed to exudates. These results indicate that nematodes will be less susceptible to Pasteuria after they enter the root zone; therefore, seed treatments with Pasteuria spores may be less effective than in-furrow treatments.
