Progress report for GS18-194

Project Type: Graduate Student
Funds awarded in 2018: $16,471.00
Projected End Date: 08/31/2021
Grant Recipient: Louisiana State University
Region: Southern
State: Louisiana
Graduate Student:
Major Professor:
Dr. Michael Stout
Louisiana State University, Department of Entomology
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Project Information

Summary:

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most important insect pest of rice in the United States. This insect poses a global threat to rice production, having recently invaded rice-producing regions of Asia and Europe. Ideally, management of rice water weevil should incorporate combinations of control tactics. However, the current management program relies heavily on chemical control. In order to minimize the impact of insecticides on the environment while maintaining production levels, increased use of alternatives to chemical control is needed. Of the available alternative tactics, host-plant resistance may have the most potential to contribute to a more sustainable pest management program. In particular, traits that allow plants to mitigate the negative effects of herbivory will be investigated. Tolerance is a type of plant defense that allows crop plants to maintain yield in spite of herbivore injury. Susceptible rice genotypes generally suffer greater yield losses that tolerant genotypes when exposed to similar levels of injury.

This study assessed the level of tolerance in commonly grown rice cultivars in Louisiana under varying field conditions from 2017-2019 at the LSU Agcenter H. Rouse Caffey Rice Research Station in Crowley, Louisiana. The compatibility of plant tolerance with other non-chemical tactics such as early planting and delayed flooding was also evaluated in 2019-2020. Moreover, tolerance-associated traits was examined to aid in the development of rice cultivars that are tolerant to weevil injury.

The ultimate goal of the proposed research is to improve the sustainability of rice production by developing a pest management program that will reduce reliance on chemical control, reduce production costs, and increase net income.

Project Objectives:

Objective 1: Compare yield losses due to rice water weevil injury in commonly grown rice cultivars in Louisiana under varying field conditions.

Objective 2: Assess the independent and interactive effects of tolerance rice cultivars and cultural control practices against rice water weevil.

Objective 3: Elucidate tolerance-related traits to root injury in rice.

Cooperators

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Research

Materials and methods:

Objective 1: Compare yield losses due to rice water weevil injury in commonly grown rice cultivars in Louisiana under varying field conditions.

Field experiments were conducted from 2017–2019 at LSU AgCenter H. Rouse Center Rice Research Station. Eight commonly grown inbred cultivars in Louisiana were selected (Catahoula, Cheniere, CL111, CL151, Cocodrie, Jazzman-2, Jupiter, and Mermentau) and drill-planted at a seeding rate of 67 kg per ha in plots measuring 5.5m in length with seven rows spaced 18 cm apart (64 plots total per year). Infestations of rice water weevil were manipulated by treating seeds of each cultivar with Dermacor® X-100 seed treatment (a.i. chlorantraniliprole) at label rate (78.5 g a.i. per ha), low rate (7.9 g a.i. per ha), and not treated. Plots were laid out in a split-plot randomized design with four blocks. Each block contained a cultivar (whole plot) × seed treatment rate (split-plot) factorial arrangement. Fields were surface irrigated as necessary to facilitate plant emergence and to improve stand establishment. Permanent flood was applied 4 to 6 weeks after planting. Field plots were maintained following the LSU AgCenter’s recommended practices for rice production in Louisiana.

Densities of immature rice water weevils (larvae and pupae) were evaluated at 3–4 weeks after permanent flood was established, using a metal soil/root core sampler with a diameter of 9.2 cm and depth of 7.6 cm. Core sampling was conducted twice in 2017 (four cores per plot, 768 samples total), twice in 2018 (three cores per plot, 576 samples total), and once in 2019 (three cores per plot, 288 samples total). Root-soil core samples, with each core sample containing a minimum of one rice plant with intact roots, were processed by washing the soil from roots in 40-mesh screen sieve buckets that were then placed in basins of salt-water solution. Rice water weevil larvae were counted as they floated to the surface of the solution and pupae were counted by inspecting bottoms of sieve buckets.

Incidence of whiteheads resulting from stemborer infestations in the rice field was assessed by counting the total number of whiteheads in each plot. Whiteheads were collected and were dissected to identify the stemborer species.

At grain maturity, entire plots were harvested using a small-plot combine. Grain weights were adjusted to 12% moisture and converted to kg ha-1. Percentage yield losses were calculated for each cultivar in each block. Yield losses for each cultivar were calculated by taking the percentage difference between yields from plots treated with the label rate of Dermacor® X-100 and nontreated plots or plots treated with low rate of Dermacor® X-100.

Rice water weevil density, whitehead incidence, and yield loss data were analyzed using generalized linear mixed models. All analyses were carried out in SAS version 9.4.

 

Objective 2: Assess the independent and interactive effects of tolerance rice cultivars and cultural control practices against rice water weevil.

Field experiments were conducted at the LSU AgCenter H. Rouse Caffey Rice Research Station in 2019 and 2020 (ongoing). Four rice cultivars were selected (Cocodrie, Mermentau, Jupiter, and Jazzman) and drill-planted in plots measuring 5.5 m length with seven rows spaced 18 cm apart at a seeding rate of 67 kg per ha. In each year, field experiments were planted at two time points – early to mid-March (early planting) and late April to early May (late planting). At each planting date, permanent flood was established at four weeks after planting (normal flood timing) and six weeks after planting (delayed flood). Rice water weevils were excluded in half of the field plots using label rate of Dermacor® X-100 seed treatment (78.5 g a.i. per ha). Plots were laid out according to randomized block design with two blocks, each block containing two replicates of selected cultivars that were treated and not treated with Dermacor® X-100. Treated and nontreated plots of the same cultivar were planted side-by-side to reduce variation in pest infestations and yields. Field plots were maintained according to recommended production practices for drill-seeded rice in Louisiana. Weevil density, whitehead incidence, and yield data were collected similar to Objective 1.     

The combined and independent effects of rice cultivar, planting date, seed treatment, and permanent flood timing on rice water weevil densities, whitehead incidences, and yield losses will be analyzed using generalized linear mixed model in PROC GLIMMIX of SAS.

 

Objective 3: Elucidate tolerance-related traits to root injury in rice.

Ongoing experiments for 2020. Field plots were established at H. Rouse Caffey Rice Research Station to tolerance related traits to root injury by the rice water weevil. Seeds of a hybrid rice cultivar (tolerant to weevils) and an inbred rice cultivar (less tolerant to weevils) were planted at seeding rates of 28 kg per ha and 67 kg per ha, respectively, in plots measuring 5.5 m in length with seven rows spaced 18 cm apart. Weevil were excluded in half of the field plots by treating seeds with the label rate or Dermacor® X-100. Field plots were maintained similar to Objectives 1 and 2. Plant samples will be collected for phytohormone and total phenolic analyses. Stomatal conductance will be measured along with other plant traits.

Research results and discussion:

Objective 1: Compare yield losses due to rice water weevil injury on commonly grown rice cultivars in Louisiana under varying field conditions.

Weevil densities varied across years but remained high (8–22 immature rice water weevil per core). Reductions on weevil densities by 85.5% were observed in plots treated with label rate of Dermacor® X-100 and reductions of 44.4% were observed in plots treated with low rate of Dermacor® X-100 relative to nontreated plots, across cultivars and years. The popular medium-grain rice cultivar ‘Jupiter’ supported the highest numbers of weevils which suggest that this cultivar is highly susceptible to weevil, whereas weevil densities on remaining cultivars were intermediate (Fig. 1A). In 2017, stemborer injury was caused by a combination of sugarcane borer and Mexican rice borer, while in 2018 and 2019, stemborer injury was caused by mostly Mexican rice borer. Low stemborer injury was observed in ‘Cheniere’ and ‘Jazzman’ which suggest that these cultivars exhibit some levels of resistance to stemborer (Fig. 1B). High stemborer injury was observed in ‘CL151’, ‘Cocodrie’, and “Mermentau’. The combination of weevils and stemborers negatively affected rice yields with yield losses ranging from 10.4–17.9% among cultivars (Fig. 1C). Differences in yield losses among cultivars were minimal, which suggest that, in general, these cultivars do not differ in levels of tolerance. However, when yield loss × weevil relationships were considered, results revealed that ‘Cocodrie’ appeared to be more tolerant than ‘Cheniere’ indicated by significantly lower yield losses in ‘Cocodrie’ relative to ‘Cheniere’.

 

Weevil densities (A), whitehead densities (B), and yield losses (C) as influenced by cultivar. Bars within each graph accompanied by the same letter do not differ significantly (P > 0.05, Tukey’s HSD).

 

Objective 2: Assess the independent and interactive effects of tolerance rice cultivars and cultural control practices against rice water weevil.

-in progress-

 

Objective 3: Elucidate tolerance-related traits to root injury in rice.

-in progress-

Participation Summary

Educational & Outreach Activities

1 Consultations
1 Journal articles
5 Webinars / talks / presentations

Participation Summary

Education/outreach description:

Presentations

  1. Villegas, J.M., B.E. Wilson, and M.J. Stout. 2020. Tolerance to insect pests among commonly grown rice cultivars in Louisiana. 38thRice Technical Working Group Meeting, Orange Beach, Alabama, February 24 – 27, Talk.
  2. Villegas, J.M., B.E. Wilson, and M.J. Stout. 2019. Utilizing plant tolerance as an alternative management tactic against insect pests of rice (Oryza sativa L). Entomological Society of America Annual Meeting, St. Louis, Missouri, November 17 – 20, Poster.
  3. Villegas, J.M., B.E. Wilson, and M.J. Stout. 2019. Tolerance of commonly grown cultivars in Louisiana to rice water weevil infestations. 10th Annual LSU Entomology Department Graduate Student Symposium, Baton Rouge, Louisiana, October 22, PhD Poster Presentation.
  4. Villegas, J.M. and M.J. Stout. 2018. Evaluating tolerance traits to root injury in drill-seeded rice. 92nd Annual Meeting of the Southeastern Branch of the Entomological Society of America, Orlando, Florida, March 4 – 7, Talk.
  5. Villegas, J.M. and M.J. Stout. 2018. Tolerance to rice water weevil injury in rice. 37thRice Technical Working Group Meeting, Long Beach, California, February 19 – 22, Talk.

 

Journal Article

  1. Villegas, J.M., B.E. Wilson, and M.J. Stout. Assessment of tolerance and resistance of inbred rice cultivars to rice water weevil (Coleoptera: Curculionidae) and Stemborers (Lepidoptera: Crambidae) under field conditions. Entomologia Experimentalis et Applicata. (manuscript in preparation)

Project Outcomes

Project outcomes:

-in progress-

Knowledge Gained:

-in progress-

Recommendations:

-in progress-

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.