Source: UNIVERSITY OF ARKANSAS submitted to
INOCULUM AND DISEASE THRESHOLDS FOR RICE BLAST DISEASE
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
Reporting Frequency
Annual
Accession No.
0166444
Grant No.
(N/A)
Project No.
ARK01600
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Oct 1, 1999
Project End Date
Sep 30, 2004
Grant Year
(N/A)
Project Director
TeBeest, D. O.
Recipient Organization
UNIVERSITY OF ARKANSAS
(N/A)
FAYETTEVILLE,AR 72703
Performing Department
PLANT PATHOLOGY
Non Technical Summary
(N/A)
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
2121530116050%
2121530117050%
Knowledge Area
212 - Pathogens and Nematodes Affecting Plants;

Subject Of Investigation
1530 - Rice;

Field Of Science
1170 - Epidemiology; 1160 - Pathology;
Goals / Objectives
1.To establish inoculum thresholds for seedborne infection of rice. 2.To determine the relationship of the incidence of leaf, collar rot and neck rot to yield loss.
Project Methods
Approach. A total of five experiments will be conducted over 5 years. For objective 1, two experiments will be conduced. In the first, the number of seeds left on the soil surface in growers field after planting will be measured, and the second will determine direct relationship of seed infestation by the blast organism to the occurrence and incidence of seedling disease will be determined. Three experiments will be conducted for objective 2. The first experiment will determine the relationship of the incidence of leaf blast, collar rot and neck rot to yield loss by regression analysis. The second experiment, replicated over time, will determine the thresholds at which applications of fungicides will affect and increase yield and quality of harvested rice. The third experiment will determine if spores of M. grisea found within symptomatic and asymptomatic flag leaf collars can cause neck blast infections. Taken together over time, space and cultivars, these experiments will establish an effective inoculum thresholds on seed and an effective threshold for therapeutic control with fungicides.

Progress 10/01/99 to 09/30/04

Outputs
The objectives of this project were as follows: 1) to determine how blast develops over time on rice cultivars, 2) to determine if infested seeds initiate epidemics in test plots, 3) to determine if the rice blast fungus infests seed produced in Arkansas, and 4) to determine if fungicides applied at panicle cracking significantly reduce yield losses. In 2000 and 2001 artificial inoculation of plots by application of infested seed onto the surface of the soil resulted in epidemics that developed similarly to those normally found in production fields. In 2002, plots were planted in May with naturally infected seeds ranging incrementally from 0 through 5 % (as estimated by visual techniques). The results were similar to application of artificially infested seeds in that different amounts of infected seed applied to the soil surface and planting naturally infected seeds led to the development of epidemics in the field. In 2003, plots were planted with naturally infected seeds of three different cultivars estimated to contain between 0 and 4% infection. As in 2002, disease ratings for the incidence of rice blast on leaf tissues were taken periodically until harvest. In 2002 and 2003, data shows that the rate of transmission and disease incidence, as measured by the incidence of leaf blast was loosely correlated to the rate of seed infection at planting. The results of additional field tests conducted in 2004 were similar to those obtained in 2002 and 2003.Overall, our results show that rice blast is seed transmitted to the new crop. However, subsequent development of rice blast depends on a threshold for this disease which appeared to be different for each of the three cultivars used in the experiments and reflected the level of resistance to rice blast and the environmental conditions after planting. The lowest was found on the most susceptible cultivar tested. The overall rate of transmission was highest at levels of seed blast above 1%.

Impacts
Identifying infested seed as a contributing factor in the development of this disease as both a primary source of inoculum and as a vehicle for its transmission may contribute significantly to the development of a threshold concept for rice blast and effective control measures. Developments of thresholds may also aid in the development of prophylactic treatments of seeds with an appropriate fungicide because it provides a baseline upon which dosages and expectation of disease levels as a result of those treatments. It may also reduce the need for application of foliar fungicides while improving yields and seed quality in Arkansas.

Publications

  • Long, D.H., F.N. Lee, and D.O. TeBeest. 2000. Effect of nitrogen fertilization on disease progress of rice blast on susceptible and resistant cultivars. Plant Disease 84:403-409.
  • Guerber, C. and D.O. TeBeest. 2005. Infection of rice seed grown in Arkansas by Pyricularia grisea and transmission to seedlings in the field. Plant Disease. Accepted for publication.


Progress 01/01/03 to 12/31/03

Outputs
The objectives of the project are: 1) to determine how blast develops over time on rice cultivars, 2) to determine if infested seeds initiate epidemics in test plots, 3) to determine if the rice blast fungus infests seed produced in Arkansas, and 4) to determine if fungicides applied at panicle cracking significantly reduce yield losses. In 2000 and 2001 artificial inoculation of plots by application of infested seed onto the surface of the soil resulted in epidemics that developed similarly to those normally found in production fields. In 2002, plots were planted in May with naturally infected seeds ranging incrementally from 0 through 5 % (as estimated by visual techniques). The results were similar to application of artificially infested seeds in that different amounts of infected seed applied to the soil surface and planting naturally infected seeds led to the development of epidemics in the field. In 2003, plots were planted with naturally infected seeds of three different cultivars estimated to contain between 0 and 4% infection. As in 2002, disease ratings for the incidence of rice blast on leaf tissues were taken periodically until harvest. In 2002 and 2003, data shows that the rate of transmission and disease incidence, as measured by the incidence of leaf blast was loosely correlated to the rate of seed infection at planting. The relationship was less clear at harvest. In 2003, the plots planted with the most heavily infected seed lots developed blast earlier and more severely than plots planted with blast free seeds. The threshold for this disease was different for each of the three cultivars depending on the level of resistance to rice blast, and was lowest for the most susceptible cultivar tested. The rate of transmission was high at levels of rice blast above 1%.

Impacts
Identifying infested seed as a contributing factor in the development of this disease as a primary source of inoculum for rice blast may contribute significantly to the development of a threshold concept for rice blast and effective control measures. This may also reduce the need for application of foliar fungicides while improving yields and seed quality in Arkansas.

Publications

  • Long, D.H., J.C. Correll, F.N. Lee and D.O. TeBeest. 2002. Rice blast epidemics initiated by infested rice grain on the soil surface. Plant Disease 85: 612-616.
  • Long, D.H., J.C. Correll, F.N. Lee and D.O. TeBeest. 2001. Rice blast epidemics initiated by infested rice grain on the soil surface. Plant Disease 85:612-616.


Progress 01/01/02 to 12/31/02

Outputs
The objectives of the project are: 1) to determine how blast develops over time on rice cultivars, 2) to determine if infested seeds initiated epidemics in test plots, 3) to determine if the rice blast fungus infests seed produced in Arkansas, and 4) to determine if fungicides applied at panicle cracking significantly reduced yield losses. In 2000 and 2001 artificial inoculation of plots with infested seed on the surface of the soil resulted in epidemics that developed similarly to those normally found in production fields. In 2002, plots were planted in May with infected seeds ranging incrementally from 0 through 5 % (as estimated by visual techniques). Plots were inspected after planting and all surface seeds were removed manually. Seedlings were collected from plots periodically after planting and examined for the presence of the fungus after incubation on moistened filter paper. Additionally, disease ratings for incidence were taken periodically until harvest. At harvest, approximately 35 samples were collected from each plot to obtain the incidence of rice blast on flag leaves, collars, neck and panicles. Seed heads were also weighed. The fungus was detected on symptomatic and asymptomatic seedlings within 2 to 4 weeks after planting in all tests. The rate of transmission to seedlings was significantly lower when infected seeds were planted in soil rather than if placed on the soil surface. The results of this and earlier years of study suggest that infested seed remaining on the soil surface are a significant source of inoculum of the rice blast fungus in Arkansas, however, infected seeds planted in soils also produced the disease. The rate of transmission was loosely related to the rate of seed infestation early in the season, but not at harvest. Yield reductions are associated with neck rot and panicle infections.

Impacts
Identifying seed as a contributing factor in this disease as a primary source of inoculum for rice blast may contribute significantly to the development of controls for this serious disease of rice, thereby, reducing the need for fungicides and improving yields and seed quality in Arkansas.

Publications

  • No publications reported this period


Progress 01/01/01 to 12/31/01

Outputs
The objectives of the project are: 1) to determine how blast develops over time on rice cultivars, 2) to determine if infested seeds initiated epidemics in test plots, 3) to determine if the rice blast fungus infests seed produced in Arkansas, and 4) to determine if fungicides applied at panicle cracking significantly reduced yield losses. In 2000 and 2001, replicated field tests were planted at the Pine Tree Experiment Station, Colt, Arkansas. Plots were planted with rice seed naturally infected with rice blast (5.4% infested) and then were over-seeded with the same seed at rates from 0.5 to 50 seeds/ft2. Over-seeding was intended to represent seeds left on top on the soil during planting. Previously, artificial inoculation of plots in a similar manner resulted in epidemics that developed similarly to those normally found in production fields. Seedlings were collected from plots periodically after planting and examined for the presence of the fungus after incubation on moistened filter paper. Additionally, disease ratings for incidence were taken periodically thereafter until harvest. At harvest, approximately 35 heads were collected from each plot to obtain the incidence of head blast and weight measurements. The fungus was detected on seeds for as long as 4 weeks after planting and on symptomatic and asymptomatic seedlings within 2 to 4 weeks in all tests. The rate of transmission to seedlings was significantly higher when infected seeds were placed on the soil surface. Approximately 1 in 1000 seedlings were infected when seeds from a seedlot infested with blast at a 5% level were planted 1 inch deep in soil. The results of this and earlier years of study suggest that infested seed remaining on the soil surface are a significant source of inoculum of the rice blast fungus in Arkansas. Yield reductions are associated with neck rot and panicle infections.

Impacts
Identifying seed as a contributing factor in this disease and as primary source of inoculum for rice blast may contribute significantly to the control of this serious disease of rice, reducing the need for fungicides and improving yield and seed quality in Arkansas.

Publications

  • Long, D.H., F.N. Lee, and D.O. TeBeest. 2000. Effect of nitrogen fertilization on disease progress of rice blast on susceptible and resistant cultivars. Plant Disease 84:403-409.
  • Long, D.H., J.C. Correll, F.N. Lee and D.O. TeBeest. 2001. Rice blast epidemics initiated by infested rice grain on the soil surface. Plant Disease 85:612-616.


Progress 01/01/00 to 12/31/00

Outputs
The objectives of the project are: 1) to determine how blast develops over time on rice cultivars, 2) to determine if infested seeds were capable of initiating epidemics in test plots, and 3) to determine if the rice blast fungus infests seed produced in Arkansas. In 2000, replicated field tests were planted at the Pine Tree Experiment Station, Colt, Arkansas. Plots were planted with rice seed naturally infected with rice blast (5.4% infested) and then were over-seeded with the same seed at rates from 0.5 to 50 seeds/ft sq. Over-seeding was intended to represent seeds left on top on the soil during planting. Previously, artificial inoculation of plots in this manner resulted in epidemics that developed similarly to those in production fields. Seedlings were collected from plots periodically after planting and examined for the presence of the fungus after incubation on moistened filter paper. Additionally, disease ratings for incidence were taken periodically thereafter until harvest. At harvest, approximately 35 heads were collected from each plot to obtain the incidence of head blast and weight measurements. The fungus was detected on symptomatic and asymptomatic seedlings in all tests. The rate of transmission to seedlings was significantly higher when infected seeds were placed on the soil surface. Approximately 1 in 1000 seedlings were infected when seeds from a seedlot infested with blast at 5% level were planted 1 inch deep in soil. The results of this and earlier years of study suggest that infested seed remaining on the soil surface are a significant source of inoculum of the rice blast fungus in Arkansas.

Impacts
(N/A)

Publications

  • Long, D.H., F.N. Lee, and D.O. TeBeest. 2000. Effect of nitrogen fertilization on disease progress of rice blast on susceptible and resistant cultivars. Plant Disease 84:403-409.


Progress 01/01/99 to 12/31/99

Outputs
The objectives of the project are: 1) to determine how blast develops over time on rice cultivars, 2) to determine if infested seeds were capable of initiating epidemics in test plots, and 3) to determine if the rice blast fungus infests seed produced in Arkansas. In 1999, replicated field tests were planted at the Pine Tree Experiment Station, Colt, Arkansas. Plots were artificially inoculated with non- viable rice seeds (80% infested) at rates from 0.5 to 50 seeds per square foot. Previously, artificial inoculation of plots in this manner resulted in epidemics that developed similarly to those in production fields. In addition, seeds from infested commercial seed lot sources were planted in non-sterile soils in the laboratory and in small field plots at two locations. Seedlings were collected from plots periodically after planting and examined for the presence of the fungus after incubation on moistened filter paper. The fungus was detected on symptomatic and asymptomatic seedlings in all tests. The rate of transmission to seedlings was significantly higher when infected seeds were placed on the soil surface. Approximately 1 in 1200 seedlings were infected when seeds from a seed lot infested with blast at a 5% level were planted in 1 inch deep soil. The results of several years of study suggest that infested seed remaining on the soil surface are a significant source of inoculum of the rice blast fungus in Arkansas.

Impacts
(N/A)

Publications

  • No publications reported this period


Progress 01/01/98 to 12/31/98

Outputs
The objectives of the project are: 1) to determine how blast develops over time on rice cultivars, 2) to determine if infested seeds were capable of initiating epidemics in test plots, and 3) to determine if the rice blast fungus infests seed produced in Arkansas. In 1998, selected cultivars were planted in replicated tests at the Pine Tree Experiment Station, Colt, Ark. As in 1995, 1996 and 1997 rice blast did not develop continuously throughout the year. The incidence of leaf blast followed a basic pattern on all susceptible cultivars when initiated by infected transplants in 1997. Incidence and severity of leaf blast increased from initial low levels, peaked around the panicle primordia stage, then gradually declined. Infesting plots with artificially inoculated non- viable seeds at rates from 0.5 to 50 seeds/ft2 resulted in epidemics that developed similarly to those in production fields. In addition, seeds from commercial seed sources were tested in the laboratory for the presence of the fungus after incubation on moistened filter paper. The fungus was detected on several lots of susceptible cultivars. Greenhouse experiments indicated that infected seedlings were found those grown from infested seeds demonstrating that seed transmission was possible.

Impacts
(N/A)

Publications

  • TeBeest, D.O. and C. A. Guerber. 1998. Role of infested seed in the epidemiology and control of rice blast disease. In: B.R. Wells Rice Research Studies-1997. Ed. R.J. Norman and T.H. Johnston. Arkansas Agricultural Experiment Sta. Research Series 460. Pages 128-131.
  • Luo, Y., P.S. Teng, N.G. Fabellar and D.O. TeBeest. 1998. The effects of global temperature change on rice leaf blast epidemics: a simulation study in three ecological zones. Agriculture, Ecosystems and Environment 68:187-196.
  • Luo, Y. , P.S. Teng, N.G. Fabellar and D.O. TeBeest. 1998. Risk analysis of yield losses caused by rice leaf blast associated with temperature changes above and below for five Asian countries. Agriculture, Ecosystems and Environment 68: 197-205.


Progress 01/01/97 to 12/31/97

Outputs
The objectives of the project are: 1) to determine how blast develops over time on rice cultivars, 2) to determine if infested seeds were capable of initiating epidemics in test plots, and 3) to determine if the rice blast fungus infests seed. In 1997, selected cultivars were planted in replicated tests at the Pine Tree Experiment Station, Colt, Ark. As in 1995 and 1996 rice blast did not develop continuously throughout the year. The incidence of leaf blast followed a basic pattern on all cultivars for all N levels. Incidence and severity of leaf blast increased from initial low levels, peaked around the panicle primordia stage, then gradually declined. The incidence of neck blast appeared to be dependant on the incidence of leaf blast. A single application of N at very high rates significantly increased disease incidence. Artificially infesting plots at rates from 0.5 to 50 seeds/ft2 resulted in epidemics developing similar to those in production fields. Seeds from 15 commercial seed sources were tested for the presence of the fungus after incubation on moistened filter paper. The fungus was detected on several lots of two cultivars. Greenhouse experiments indicated that seed transmission was possible and resulted in infected seedlings.

Impacts
(N/A)

Publications

  • Long, D.H., D.O. TeBeest and F.N. Lee. 1997. The effect of nitrogen fertilization on the epidemiology of rice blast disease in small plots in Arkansas. In: B.R. Wells Rice Research Studies-1996. Ed. R.J. Norman and T.H. Johnston. Arkansas Agricultural Experiment Sta. Research Series 456. Pages 94- 108.
  • Luo, Y., P.S. Teng, N.G. Fabellar and D.O. TeBeest. 1997. A rice-leaf blast combined model for simulation of epidemics and yield loss. Agricultural Systems 53:27-39.


Progress 01/01/96 to 12/30/96

Outputs
In 1996, tests were continued to: 1) determine how blast develops on rice cultivars, 2) determine if blast epidemics develop continuously throughout the season, and 3) determine the effect of nitrogen fertilization on blast development. Eight cultivars were seeded in replicated tests at the Pine Tree Experiment Station, Colt, Ark with N treatments made in a split-plot design. One third of the plots received a recommended nitrogen fertilization rate (Urea) applied in a three-way split application, one third received 50% more than the recommended N rate in one treatment at preflood and one third received the recommended rate as one application at preflood. Blast was initiated by inoculation of border-spreader plots with races IB49, IC17, IG1 & IB1 of M. grisea. As in 1995, rice blast did not develop continuously throughout the year. Leaf blast follows a basic pattern on all cultivars for all N levels. Incidence and severity of leaf blast increased from initial low levels and peaked around panicle primordia then gradually declined. High N rates and application at one time significantly increased disease levels. Results suggest that nitrogen management is essential for control of this disease.

Impacts
(N/A)

Publications

  • D.H. LONG, D.O. TEBEEST AND F.N. LEE. 1996. EFFECT OF NITROGEN FERTILIZATION PRACTICES ON THE EPIDEMIOLOGY AND SEVERITY OF RICE BLAST DISEASE ON EIGHT CULTIVARS. ARKANSAS RICE RESEARCH STUDIES. EDS. R.J. NORMAN AND B.R. WELLS. ARK.AGRIC. E D.H. LONG. 1996. THE EPIDEMIOLOGY OF RICE BLAST DISEASE IN ARKANSAS. MS THESIS. UNIVERSITY OF ARKANSAS. 157 PAGES.


Progress 01/01/95 to 12/30/95

Outputs
In 1995, tests were conducted to: 1) determine how blast develops on rice cultivars, 2) determine if blast epidemics develop continuously throughout the season, and 3) determine the effect of nitrogen fertilization on blast development. Eight cultivars were seeded in replicated tests at the Pine Tree Experiment Station, Colt, Arkansas with N treatments made in a split plot design. Half of the plots received a recommended nitrogen fertilization rate (Urea) applied in a three way split application, the rest received 50% more than the recommended N rate in one treatment at preflood. Blast was initiated by inoculation of border spreader plots with races IB49, IC17, IG1 & IB1 of M. grisea. Results show that rice blast does not appear to develop continuously throughout the year. Leaf blast follows a basic pattern on all cultivars for both N levels. Incidence and severity of leaf blast increased from initial low levels and peaked around panicle primordia then gradually declined. High N rates significantly increased disease levels. Results suggest that plant age effects and environmental conditions slowed the rate of disease increase after panicle primordia stage.

Impacts
(N/A)

Publications