Source: TEXAS A&M UNIVERSITY submitted to
STRATEGIES FOR DISEASE CONTROL IN MELONS AND ONIONS
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
Reporting Frequency
Annual
Accession No.
0163302
Grant No.
(N/A)
Project No.
TEX08274
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Nov 7, 2005
Project End Date
Nov 6, 2010
Grant Year
(N/A)
Project Director
Miller, M. E.
Recipient Organization
TEXAS A&M UNIVERSITY
750 AGRONOMY RD STE 2701
COLLEGE STATION,TX 77843-0001
Performing Department
WESLACO-TAMU AGR RES CNTR
Non Technical Summary
Diseases of melons and onions result in loss of quality and production. The purpose of this project is to study diseases of these crops and to develop control measures. Unchecked, diseases can cause serious loss of quality and production. The purpose of this project is to identify disease causing agents, study the development of plant diseases and to develop effective and efficient disease control measures.
Animal Health Component
60%
Research Effort Categories
Basic
20%
Applied
60%
Developmental
20%
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
2121499106030%
2121499116035%
2121499117035%
Goals / Objectives
1)Obtain isolates of D. bryoniae from cucurbits throughout the Lower Rio Grande Valley (LRGV) of Texas and test isolates for sensitivity to fungicides commonly used to control gummy stem blight and develop fungicide control programs based on these findings; 2)Determine effects of interactions between M. cannonballus and R. vagum on vine decline development; 3) Determine cucurbit and non-cucurbit host range of R. vagum; and 4)Sample onion plants throughout the LRGV for the presence of IYSV and if present, determine the susceptibility of short-day onion cultivars grown in south Texas to the virus.
Project Methods
OBJECTIVE 1. A) D. bryoniae will be isolated on water agar plates from melon plants exhibiting symptoms of gummy stem blight. After three days of growth, hyphal tips from each fungal colony will be transferred to potato dextrose agar (PDA). To test the isolates for sensitivity to fungicides; the isolates will be grown on PDA plates and then 8mm plugs will be transferred to a series of PDA plates containing 0, 1.0, 5.0 and 50 mg/ml of the test fungicide. Each treatment will be replicated twice. Mycelial growth measurements will be taken after six days. The EC50 of the fungicide for growth of D. bryoniae isolates will be calculated using procedures in MSTAT (University of Michigan). B) Cantaloupe, cv. Primo, will be planted in a RCB design with four replications. Plants at the 3-4 leaf stage will be inoculated with 1.5 x 105 conidia/ml of an aqueous conidial suspension of D. bryoniae(DB(TX)03-11, insensitive to azoxystrobin). Initial fungicide applications will begin immediately prior to inoculation of D. bryoniae and will continue at weekly intervals for 4 weeks. The number of stem lesions and foliage disease index will be recorded. Fruit will be harvested at least four times; each fruit will be peeled and the proportion of fruit with lesions and weight of marketable and cull fruit will be recorded. Data will be analyzed using ANOVA procedures. OBJECTIVE 2. The interactions between M. cannonballus and R. vagum on root rot of cantaloupe and watermelon will be determined. Rice hull-sand medium infested with the fungi will be mixed with sand to attain 50 and 800 CFU/g of soil of M. cannonballu, R. vagum, and a combination of the two. The sand medium will be used to grow the plants in the greenhouse. The experiment will be set up as a factorial experiment with M. cannonballus as one factor and R. vagum as the other factor. Data will be gathered on plant height, root ratings and root dry weight. OBJECTIVE 3. Representative species of cucurbits (including cantaloupe, honeydew, watermelon, squash, and gourd varieties) and non-cucurbits (including corn, sugarcane, legumes, cole crops, and others) will be tested to determine the host range of R. vagum. Plants will be inoculated with 800 CFU/g of soil of the fungus grown in a rice hull-sand medium. Plants will be grown in pots in the greenhouse. Plant height, root ratings, and root dry weights of inoculated plants will be compared with noninoculated plants. Data will be analyzed using comparative tests. OBJECTIVE 4. A) Onion leaf samples will taken at least two dates (mid-season and late-season) from onion fields. Samples will be tested for IYSV using standard ELISA procedures (Agdia, Inc., Elkhart, IN). If samples test positive for IYSV, samples will be sent out for PCR diagnostic tests to confirm the ELISA tests. B) A replicated variety test with short-day onions (including yellow, white, and red varieties) grown in the LRGV will be planted to evaluate their susceptibility to IYSV. Visual evaluations for the incidence and severity of IYSV will be made on at least two dates (mid-season and late-season). Leaf tissue will be tested with ELISA to confirm the presence of IYSV.

Progress 11/07/05 to 11/06/10

Outputs
Numerous fungicides were evaluated for efficacy against powdery mildew, downy mildew, and gummy stem blight in melons, purple blotch in onions, white rust in spinach, and other foliar disease of vegetables. New fungicide chemistries were also evaluated for effectiveness where disease resistance has been noted. Integrated management systems have been developed. The etiology of iris yellow spot virus in onions continued, with work on host ranges and onion variety susceptibility. With the retirement of Dr. M. E. Miller, this project has concluded.

Impacts
Diseases of melons, onions, and other vegetable crops cause serious losses in quality and production. This project has developed efficient control methodologies, evaluated new fungicide chemistries, and identified new diseases and disease etiology of vegetable crops to ultimately enhance production and quality of vegetable crops.

Publications

  • No publications reported this period


Progress 01/01/06 to 12/31/06

Outputs
Onion plants in Uvalde, Hidalgo, and Cameron Counties in Texas exhibited necrotic lesions on leaves typical of Iris yellow spot virus (IYSV) and disease incidence approached 100% in some fields with yield loss and quality problems. Leaves of symptomatic plants were tested for IYSV and Tomato spotted wilt virus (TSWV) using DAS-ELISA, and 18 of 23 samples from the Hidalgo County area and 12 of 21 samples from the Uvalde County area were positive for IYSV. All samples tested for TWSV were negative. Virus infection is some ELISA-positive plants was verified by RT-PCR using primers derived from the small RNA of IYSV. RT-PCR gave a PCR product of expected size (approximately 1.2 kb). The DNA amplicon was cloned and sequenced (GenBAnk Accession No. DQ658242). Nucleotide sequence analysis confirmed the identity of the amplicon as that of IYSV N gene and sequence comparisons with known IYSV N gene sequences showed 95 to 98% sequence identity. Numerous weeds were tested using DAS-ELISA for IYSV and some samples of Portulaca oleracea (purslane) were positive for the virus. Several onion varieties were evaluated for their reaction to IYSV. All varieties were susceptible to the virus; however, considerable differences in symptom development occurred between varieties. 'Texas Early White' and 'Texas 1015Y' were affected the least while 'Legend' and 'Serengeti' had the most severe symptom development. Fungicides were screened for their efficacy to control downy mildew, powdery mildew, and gummy stem blight on muskmelons, purple blotch on onions, and white rust on spinach. Several new fungicides have shown promise for controlling some of these diseases.

Impacts
Powdery mildew, downy mildew, and gummy stem blight of melons, purple blotch and Iris yellow spot virus of onion, white rust of spinach, and alternaria leaf spot on cabbage can cause serious loss of quality and production of these crops. The purpose of this project is to identify disease causing agents, study the development of diseases and develop effective and efficient disease control measures for these crops.

Publications

  • Miller, M., Saldana, R., Black, M., and Pappu, H. 2006. First report of Iris yellow spot virus on onion (Allium cepa) in Texas. Plant Disease 90:1359.
  • Jifon, J.L., Crosby, K.M., Miller, M.E., and Leskovar, D.I. 2006. Physiological characteristics of grafted muskmelon grown in Monosporascus cannonballus-infested soil in South Texas. Proceedings of Cucurbitaceae 2006:23-30.
  • Jifon, J.L., and Miller, M.E. 2006. Susceptiblity to Iris yellow spot virus among sweet onion varieties in South Texas. 2006 National Allium Research Conference:40-41.
  • Miller, M.E., Saldana, R.R., and Bruton, B.D. 2006. Management of gummy stem blight of cantaloupe in south Texas. Phytopathology 96:S79.
  • Miller, M.E. and Saldana, R.R. 2006. Evaluation of fungicides for downy mildew control on cantaloupe. F&N Tests 61:V099.
  • Miller, M.E. and Saldana, R.R. 2006. Evaluation of fungicides for downy mildew control on cabbage. F&N Tests 61:V101.
  • Miller, M.E. and Saldana, R.R. 2006. Evaluation of fungicides for white rust control on spinach. F&N Tests 61:V100.
  • Saldana, R., Garza, A., Davelos Baines, A., Miller, M. and Little, C. 2006. Evaluating inoculation techniques for gummy stem blight disease of cantaloupe. Phytopathology 96:S101.
  • Miller, M.E. and Saldana, R.R. 2006. Evaluation of fungicides for gummy stem blight control on cantaloupe. F&N Tests 61:V097.
  • Miller, M.E. and Saldana, R.R. 2006. Evaluation of fungicides for purple blotch control on onion. F&N Tests 61:V098.


Progress 01/01/05 to 12/31/05

Outputs
Nine fungicides were tested for efficacy to control strobilurin-resistant isolates of Didymella bryoniae (DB(TX)03-11) on cantaloupe. There were significant differences between all fungicide treatments and controls for percent plants with stem lesions, foliar disease ratings, percent fruit with lesions, and marketable yield. There were no significant differences between Bravo Weather STIK alternated with either Pristine, Vangard, Endura, Quadris Opti, Amistar, or Switch or Bravo Weather STIK used alone. Fungicides were also screened for their efficacy to control downy mildew and powdery mildew on muskmelon, purple blotch on onions, white rust on spinach, and alternaria leaf spot on cabbage. Several new fungicides have shown promise for controlling some of these diseases.

Impacts
Powdery mildew, downy mildew, and gummy stem blight of melons, purple blotch of onion, white rust of spinach, and alternaria leaf spot on cabbage can cause serious loss of quality and production on these crops. The purpose of this project is to identify disease causing agents, study the development of diseases and develop effective and efficient disease control measures of these crops. Data from fungicide tests will be used to support requests for crisis exemptions, Section 18s, and federal registration of effective fungicides.

Publications

  • Miller, M. E. and Saldana, R. E. 2005. Evaluation of fungicides for purple blotch control on onion, 2004. Fungicide and Nematicide Tests 60:V032.
  • Miller, M. E. and Saldana, R. E. 2005. Evaluation of fungicides for purple blotch control on onion, 2004. Fungicide and Nematicide Tests 60:V033.
  • Miller, M. E. and Saldana, R. E. 2005. Evaluation of fungicides for gummy stem blight control on cantaloupe, 2004. Fungicide and Nematicide Tests 60:V029.
  • Miller, M. E. and Saldana, R. E. 2005. Evaluation of fungicides for control of downy mildew control of cantaloupe, 2004. Fungicide and Nematicide Tests 60:V030.
  • Miller, M. E. and Saldana, R. E. 2005. Evaluation of fungicides for powdery mildew control on honeydew, 2004. Fungicide and Nematicide Tests 60:V031.


Progress 01/01/04 to 12/31/04

Outputs
Cantaloupe stem isolates of Didymella bryoniae were obtained from six locations in Starr and Hidalgo Counties of Texas and tested for sensitivity to Quadris. Twenty-five of 28 isolates were insensitive to Quadris, indicating that the D. bryoniae population in this area of Texas is highly insensitive to Quadris and this fungicide should not be used in a gummy stem blight management program. Since cross-resistance within the strobilurin-based fungicides is expected, Cabrio and Flint also should not be included in a gummy stem blight management program. Additional fungicides have been evaluated for their efficacy to control D. bryoniae and new management programs for the fungus are being developed. Cucurbit powdery mildew, caused by Sphaerotheca fuliginea, was not controlled by Flint, a strobilurin-based fungicide. Since cross-resistance within the strobilurin-based fungicides is expected, fungicides within this chemical group should not be used in powdery mildew control programs.

Impacts
Unchecked, diseases can cause serious loss of quality and production. The purpose of this project is to identify disease causing agents, study the development of plant diseases and to develop effective and efficient disease control measures.

Publications

  • Miller, M. E. and Saldana, R. E. 2004. Evaluation of fungicides for powdery mildew control on honeydew, 2003. Fungicide and Nematicide Tests 59:V150.
  • Miller, M. E. and Saldana, R. E. 2004. Evaluation of fungicides for downy mildew control of cantaloupe, 2003. Fungicide and Nematicide Tests 59:V149.
  • Miller, M. E. and Saldana, R. E. 2004. Evaluation of fungicides for purple blotch control on onion, 2003. Fungicide and Nematicide Tests 59:V151.
  • Miller, M. E. and Saldana, R. E. 2004. Evaluation of fungicides for control of downy mildew control of cantaloupe. 2003. Fungicide and Nematicide Tests 59:V148.


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

Outputs
In the Spring of 2003, cantaloupe stem isolates of Didymella bryoniae were obtained from six locations in Starr and Hidalgo Counties in South Texas. Twenty-five of the 28 isolates were insensitive to azoxystrobin, indicating that the D. bryoniae population in South Texas is highly insensitive to azoxystrobin and this fungicide should not be used in a gummy stem blight management program in this area. Since cross-resistance within the strobilurin-based fungicides is expected, other fungicides within this group also should not be included in gummy stem blight management programs. The effect of cantaloupe fruit removal on root carbohydrate levels was studied under field conditions in a soil naturally infested with Monosporascus cannonballus. Individual, total, and combined root carbohydrate levels were greater in plants without fruit than in plants with fruit. Disease severity on roots of plants with fruit removed was less severe than on roots of plants with fruit. Root disease severity was associated with root carbohydrate levels.

Impacts
Unchecked, diseases can cause serious loss of quality and production. The purpose of this project is to identify disease causing agents, study the development of plant diseases and to develop effective and efficient disease control measures.

Publications

  • Miller, M. E. and Jimenez, E. 2003. Evaluation of fungicides for gummy stem blight control on cantaloupe, 2001. Fungicide and Nematicide Tests 58:V115.
  • Miller, M. E. and Jimenez, E. 2003. Evaluation of fungicides for control of downy mildew control of cantaloupe, 2001. Fungicide and Nematicide Tests 58:V114.
  • Miller, M. E. and Jimenez, E. 2003. Evaluation of fungicides for powdery mildew control on honeydew, 2002. Fungicide and Nematicide Tests 58:V116.
  • Miller, M. E. and Jimenez, E. 2003. Evaluation of fungicides for powdery mildew control on honeydew, 2001. Fungicide and Nematicide Tests 58:V117.


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

Outputs
Rhizopycnis vagum gen. et sp. nov, a recently described coelomycetous fungus isolated from roots of melons and sugarcane has been found in Costa Rica, Guatemala, Honduras, Mexico, and the USA. Root hair growth on 'Magnum 45' cantaloupe inoculated with three isolates of the fungus in microplot studies was greatly reduced or non-existant and root hairs that were present were necrotic. 'Magnum 45' plants inoculated with six isolates of R. vagum in greenhouse studies had significantly (p=0.05)higher root disease indexes and significantly smaller vine length and leaf area than control plants. Isolates TX951121, TX951120, and TX951119 obtained from cantaloupe roots were the most aggressive of the isolates tested. These data indicate that R. vagum is pathogenic on melons and likely has a role in the vine decline complex of melons.

Impacts
The purpose of this project is to study and develop control measures for diseases of melons and onion. Progress has been made on understanding the vine decline disease complex of melons and developing control measures for these destructive diseases.

Publications

  • Miller, M. E. and Hernandez, R. A. 2002. Evaluation of fungicides for gummy stem blight control on cantaloupe, 2001. Fungicide and Nematicide Tests 57:V017.
  • Miller, M. E. and Hernandez, R. A. 2002. Evaluation of fungicides for control of powdery mildew on cantaloupe, 2001. Fungicide and Nematicide Tests 57:V016.
  • Miller, M. E. and Hernandez, R. A. 2002. Evaluation of fungicides for powdery mildew control on carrot, 2001. Fungicide and Nematicide Tests 57:V020.
  • Miller, M. E. and Hernandez, R. A. 2002. Evaluation of fungicides for powdery mildew control on squash, 2001. Fungicide and Nematicide Tests 57:V093.
  • Miller, M. E. and Hernandez, R. A. 2002. Evaluation of fungicides for powdery mildew control on honeydew, 2001. Fungicide and Nematicide Tests 57:V038.
  • Miller, M. E. and Hernandez, R. A. 2002. Evaluation of fungicides for downy mildew control in spinach, 2001. Fungicide and Nematicide Tests 57:V091.
  • Miller, M. E. and Hernandez, R. A. 2002. Evaluation of fungicides for powdery mildew control in cabbage, 2001. Fungicide and Nematicide Tests 57:V015.


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

Outputs
Plants treated with alternations of CGA 173506 and Fluazinam or Quadris for control of Monosporascus root rot and vine decline on melons had significantly lower (p<0.05) root disease ratings than the untreated controls. The isolation frequency of Monosporascus cannonballus from roots was also lower from plants receiving these treatments. Plants treated with alternations of CGA 173506 and Fluazinam had the lowest foliage damage levels and longest vines (46 days after planting). Seven fungicides were tested for their efficacy to control gummy stem blight on cantaloupe. All fungicide treated plants, except for those treated with with Mankocide, had significantly lower number of stems with lesions than the control. Plants treated with F 500 alternated with Bravo WS had the fewest stem lesions. There were no significant differences in the number of fruit with lesions between treatments. Plants treated with an alternation of F 500 and Bravo or Quadris and Bravo were as effective as treatments with F 500 or Quadris alone.

Impacts
Unchecked, diseases can cause serious loss in quality and production. The purpose of this project is to identify and study the disease agents in order to develop effective and efficient control measures.

Publications

  • Crosby, K. M. and Miller, M. E. 2001. Screening melon germplasm for resistance to stem canker (Myrothecium roridum). Phytopathology 91:S19.
  • Miller, M. E. and Amador, J. 2001. Efficacy of drip irrigation applications of fludioxinil for control of Monosporascus root rot and vine decline. Phytopathology 91:S199.
  • Miller, M. and Hernandez, R. 2001. Comparison of two strobilurin-based fungicides for control of foliage diseases of vegetable crops. Phytopathology 91:S63.
  • Miller, M. E. and Hernandez, R. A. 2001. Reaction of early and mid-season muskmelon cultigens to powdery mildew, 2000. Biological and Cultural Tests. Report 2001:V94.
  • Miller, M. E. and Hernandez, R. A. 2001. Evaluation of fungicides for gummy stem blight control on cantaloupe, 2000. Fungicide and Nematicide Tests. Report 2001:V8.
  • Miller, M. E. and Hernandez, R. A. 2001. Evaluation of fungicides for control of powdery mildew control on cantaloupe. 2000. Fungicide and Nematicide Tests. Report 2001:V10.
  • Miller, M. E. and Hernandez, R. A. 2001. Evaluation of fungicides for powdery mildew control on carrot, 2000. Fungicide and Nematicide Tests. Report 2001:V17.
  • Miller, M. E. and Hernandez, R. A. 2001. Evaluation of fungicides for purple blotch control on onion, 2000. Fungicide and Nematicide Tests. Report 2001:V28.
  • Miller, M. E. and Hernandez, R. A. 2001. Evaluation of powdery mildew control on honeydew, 2000. Fungicide and Nematicide Tests. Report 2001:V18.


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

Outputs
Cantaloupe plants treated with two applications of Maxim at 0.5 and 0.25 lb/A through drip irrigation system to control Monosporascus root rot and vine decline had significantly (p=0.05) longer vine length, less vine dieback, lower root disease ratings, and higher marketable yield than non-treated plants. Vine length, vine dieback, root disease ratings and marketable yield were not significantly different on plants treated with two foliar applications of Actigard and non-treated plants. Vine length, vine dieback, root disease ratings and marketable yield were not significantly different on plants treated with a combination of two drip irrigation applications of Maxim and two foliar application of Actigard than for plants treated with drip application of Maxim only. Eight fungicides were tested for efficacy to control gummy stem blight of cantaloupe. Plants treated with an alternation of Quadris and Bravo or Pencozeb were as effective as treatments with Quadris alone. Alternations with Flint and Switch were also as effective as treatments with Flint alone. An new leaf blight of onion was found in south Texas. The symptoms were longitudinal chlorotic areas on one side of the leaf, containing sunken, elliptical necrotic lesions. Affected leaves ultimately died. Xanthomonas campestris was isolated from plants and inoculation of the pathogen to onion produced identical symptoms. This is the first report of X. campestris on onion in the continental United States.

Impacts
Unchecked, diseases can cause serious loss in quality and production. The purpose of this project is to identify and study the disease agents in order to develop effective and efficient control measures.

Publications

  • Bruton, B. D., T. W. Popham, J. Garcia-Jimenez, J. Armengol, and M. E. Miller. 2000. Disease reaction among selected Cucurbitaceae to an Acremonium cucurbitacearum isolate from Texas. HortScience 35(4)677-680
  • Batten, J. S., K-B. G. Scholthof, B. R. Lovic, M. E. Miller, and R. D. Martyn. 2000. Potential for biocontrol of Monosporascus root rot/vine decline under greenhouse conditions using hypovirulent isolates of Monosporascus cannonballus. European J. of Plant Pathology 106:639-649
  • Crosby, K., Wolff, D., and M. Miller. 2000. Comparison of root morphology in susceptible and tolerant melon cultivars before and after infection by Monosporascus cannonballus. HortScience 35(4)681-683
  • Miller, M. E., R. D. Martyn, and B. D. Bruton. 2000. Muskmelon growth and yield in response to fumigation. Acta Horticulturae 510:179-186
  • Brown, J. K., A. M. Idris, M. W. Olsen, M. E. Miller, T. Isakeit, and J. Anciso. 2000. Cucurbit leaf curl virus, a new whitefly transmitted geminivirus in Arizona. Plant Disease 84:809


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

Outputs
Twenty-one fungicide treatments were tested for efficacy to control gummy stem blight (GSB) of cantaloupe. Plants treated with an alternation of Quadris and Vangard and Bravo and Quadris had the least stem lesions (3.8%); however the percentage of stem lesions was not significantly lower than the other treatment alternations with Quadris, Quadris alone, Vangard alone, Bravo at 2.7 lbs/A, Flint at oz + Actigard, and alternations of Ridomil Bravo Gold and Flint at 3.0 oz + Actigard at 1.0 oz/A. All fungicide treated plants had significantly fewer fruit with GSB lesions than the untreated controls except those treated with an alternation of Sovran at 0.3 lbs and Bravo Ultrex at 2.7 lbs, Ridomil Bravo Gold and Flint at 3.0 oz + Actigard at 1.0 oz, and Bravo Ultrex alone at 1.8 lbs/A. Previous studies of numerous field isolates of Monosporascus cannonballus from different geographic regions revealed considerable variability in cultural growth patterns and virulence to muskmelon and the nucleic acid analysis of these isolates detected the presence of double-stranded (ds) RNAs. Plants co-inoculated with a hypovirulent, dsRNA+ isolate (Tx93-449+) of Monosporascus cannonballus and a virulent, dsRNA- isolate (Az90-33-) at an inoculum ratio of 10:1 (hypovirulent:virulent) were indistinguishable from the uninoculated control plants in greenhouse pathogenicity trials. These data suggest that dsRNA+, hypovirulent isolates of M. cannonballus may have potential for development as biological control agents to reduce disease pressure associated with Monosporascus root rot and vine decline.

Impacts
Unchecked, diseases can cause serious loss in quality and production. The purpose of this project is to identify and study the disease agents in order to develop effective and efficient control measures.

Publications

  • Zhang, J. X., B. D. Bruton, M. E. Miller, and T. Isakeit. 1999. Relationship of developmental stage of cantaloupe fruit to black rot susceptibility and enzyme production by Didymella bryoniae. Plant Disease 83: 1025-1032.
  • Zhang, J. X., B. D. Bruton, C. R. Howell, and M. E. Miller. 1999. Potential of Trichoderma virens for biocontrol of root rot/vine decline caused by Monosporascus cannonballus. Subtropical Plant Science 51: 29-37
  • Isakeit, T., Miller, M. E., Barnes, L. W., and Jones, J. B. 2000. First report of leaf blight of onion caused by Xanthomonas campestris in the United States. Plant Disease 84: (In press).
  • Batten, J. S., K.-B.G. Scholthof, M. E. Miller, and R. D. Martyn. 1999. cDNA probes for detection of specific dsRNAs from the fungal pathogen, Monosporascus cannonballus. Journal of Virological Methods (In press).


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

Outputs
Ten fungicides were tested for efficacy to control gummy stem blight (GSB) of cantaloupe. Plants treated with four applications of azoxystrobin at 224.0 g/ha had significantly less GSB lesions on fruit, higher marketable yield, lower foliar disease ratings, and fewer stem lesions than plants receiving other treatments. Chlorothalonil at 2.5 kg/ha and cyprodinil at 280.0 g/ha also effectively controlled GSB on fruit, stems, and foliage significantly better than the other fungicides or control, but to a less degree than azoxystrobin. Inoculation of cantaloupe fruit at different developmental stages with five Didymella bryoniae isolates demonstrated the greatest amount of decay on 10-day old fruit as compared to 20-, 30-, 40-, or 50-day old fruit. Each of five fungal isolates produced the greatest polygalacturonase (PG) in inoculated 10-day old fruit as compared with other age fruit. There was a positive correlation between lesion size and total fungal PG activity in decayed tissue.

Impacts
(N/A)

Publications

  • Lazcano, C. A., F. J. Dainello, L. M. Pike, M. E. Miller, L. Brandenberger, and L. R. Baker. 1998. Seed lines, population density, and root size at harvest affect quality and yield of cut-and-peel baby carrots. HortScience 33(6):972-975.
  • Bruton, B. D., Russo, V. M., Garcia-Jimenez, J. and Miller, M. E. 1998. Carbohydrate partitioning, cultural practices, and vine decline diseases of cucurbits. Proceedings of Cucurbitaceae `98: Evaluation and enhancement of cucurbit germplasm. pp. 189-200.
  • Riley, D. G, Edelson, J. V., Roberts, R. E., Roe, N., Miller, M. E., Cuperus, G., and Anciso, J. 1998. Integrated pest management in cucurbit crops in South-Central USA: Pest status, attitudes toward IPM and a plan for implementation. Journal of Extension: Volume 36, Number 4. http://www.joe.org/joe/1998august/a3.txt
  • Miller, M. E., Isakeit, T. Zhang, J. X., and Bruton, B. D. 1998. Gummy stem blight of melons. Phytopathology 88: S122.
  • Miller, M. E., Isakeit, T., Bruton, B. D., and Zhang, J. X. 1998. Fungicidal control of Didymella bryoniae on cantaloupe. Phytopathology 88: S62.
  • Zhang, J. X., Bruton, B. D., Miller, M. E., and Isakeit, T. 1998. Relationship of muskmelon fruit rot and polygalacturonase production by Didymella bryoniae. Phytopathology 88: S103.


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

Outputs
In vitro tests indicated that the EC50 for benomyl for mycelial growth was >5.0 micrograms/ml for 92% of the Didymella bryoniae isolates from south Texas, indicating a very high level of resistance in the fungal population to the fungicide. Most isolates that were resistant to benomyl were also resistant to thiabendazole. Cantaloupe plants treated with azoxystrobin at 12.3 fl oz/A had significantly less (p=0.05) fruit with GSB lesions, higher marketable yield, fewer cull fruit, lower foliar disease ratings, and fewer plants with stem lesions than plants treated with the other fungicides and the control in field studies. Chlorothalonil at 3 pts/A, and cyprodinil at 5.33 oz/A also effectively controlled GSB on fruit, stems, and foliage significantly better than most of the other fungicides and the control. Marketable yield, percentage of fruit with lesions, percentage of plants with stem lesions, and foliar disease ratings were not significantly different on plants treated with benomyl as compared with the control. A new coelomycete, Rhizopycnis vagum, was described that was isolated from melon roots in Texas, Guatemala, and Honduras. This fungus may be a contributing factor in melon vine decline.

Impacts
(N/A)

Publications

  • BRUTON, B. D. and MILLER, M. E. 1997. Occurrence of vine decline diseases of muskmelon in Guatemala. Plant Disease 81:694.
  • Bruton, B. D. and Miller, M. E. 1997. Occurrence of vine decline diseases of melons in Honduras. Plant Disease 81:696.
  • PERKINS-VEAZIE, P., COLLINS, J. K., BRUTON, B. D., MILLER, M. E., CARTWRIGHT, B. O., and EDELSON, J. V. 1996. Stored sweet onions are adversely affected by high preharvest levels of purple blotch and thrips. Subtropical Plant Science 48:38-42.
  • MARTYN, R. D., BATTEN, J. S., PARK, Y. J., and MILLER, M. E. 1996. Monosporascus root rot/vine decline of watermelon in Mexico. Plant Disease 80:1430.
  • FARR, D. F., MILLER, M. E., and BRUTON, B. D. 1998. Rhizopycnis vagum gen. et sp. nov., a new coelomycetous fungus from roots of melons and sugarcane. Mycologia (In press).
  • WOLFF, D. W. and MILLER, M. E. 1998. Tolerance to Monosporascus root rot and vine decline in melon (Cucumis melo L.) germplasm. HortScience (In press).


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

Outputs
ICIA5504, Folicur, RH-3866, & EXP10625 at 420, 560, 350, & 395 g/ha, respectively, were applied to cantaloupe cvs. Magnum 45 & Explorer either as foliar applications or through drip lines to control Monosporascus cannonballus. Fungicide, application method, & variety had a significant effect (p=0.05) on root disease severity ratings, isolation frequency of M. cannonballus, visual vine ratings & total fruit yield. Plots treated with ICIA5504 & plots receiving fungicides through drip lines had significantly lower root disease severity ratings, visual vine ratings, isolation frequency & higher yields than plots receiving other treatments. dsRNA was transferred by hyphal anastomosis from a dsRNA-plus, hypovirulent strain (TX93-449) of M. cannonballus into both a wild type, dsRNA-free virulent strain (TX90-25) & a dsRNA-cured strain (CA91-17). Phenotypic change was observed with the transfer of dsRNA between isolates & the previously pathogenic isolates exhibited hypovirulent characteristics. In greenhouse tests, Magnum 45 plants were inoculated with 400, 800, 1,600, 3,200, 6,400, & 12,800 CFU's of a Stagonospora-like fungus/g of soil. Plants inoculated with six isolates of the fungus had significantly (p=0.0001) more root necrosis & less leaf area than noninoculated plants. TX951120 isolated from cantaloupe roots was the most aggressive isolate. The Stagnospora-like fungus is pathogenic on melon, & thus, may be involved in the vine decline disease complex.

Impacts
(N/A)

Publications

  • MILLER, M. E., & MARTYN, R. D. 1996. Drip irrigation applications of ICIA5504 reduces symptom expression of Monosporascus root rot/vine decline on cantaloupe.
  • BRUTON, B. D., MILLER, M. E., & GARCIA-JIMENEZ, J., 1996. Comparison of Acremonium sp. from the Lower Rio Grande Valley of Texas with Acremonium sp. from Spain. Phytopathology 86: S3.
  • BATTEN, J. S., PARK, Y. J., SCHOLTHOF, K-B.G., MARTYN, R. D., & MILLER, M. E. 1996. Biocontrol of Monosporascus root rot/vine decline using hypovirulent Monosporascus isolates containing medium-sized (2.7-4.0 kb) dsRNA fragments. Phytopatho MARTYN, R.
  • D. & MILLER, M. E. 1996. Monosporascus root rot and vine decline: An emerging disease of melons worldwide. Plant Disease 80:716-725.
  • MARTYN, R. D. & MILLER, M. E. 1996. The role of double stranded RNA (dsRNA) in the growth & virulence of the melon pathogen, Monosporascus cannonballus. CUCURBITS TOWARDS 2000: Proc. VIth Eucarpia Mtg Cucurbit Genet. & Breed. p. 269-279.
  • MARTYN, R. D. & MILLER, M. E. 1996. Monosporascus root rot and vine decline. In Compendium of Cucurbit Diseases. APS Press, St. Paul, MN 87pp.
  • MILLER, M. E., BRUTON, B. D., & FARR, D. F. 1996 Association of a Stagonospora-like fungus on roots of melons exhibiting vine decline symptoms. Phytopathology 86: S3.


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

Outputs
A dsRNA containing isolate of Monosporascus cannonballus that exhibited degeneration in culture & was nonpathogenic on muskmelon was cured of its dsRNA by growing at 37 C for several successive generations. The "cured" isolate reverted to a wild type morphology & became pathogenic on cantaloupe when the dsRNA was eliminated. To determine if dsRNA elements could be transmitted from mycellium to ascospores through sexual reproduction, two dsRNA-harboring isolates of M. cannonballus were grown separately in a mixture of sand & wheat hulls to produce perithecia. Ascospores were homogenized in liquid nitrogen & nucleic acids extracted by CTAB protocols & visualized in ethidium bromide-stained gels & low-molecular-size fragments were observed in each isolate. The dsRNA nature of these fragments was established by digesting with Rnase, CF11 chromatography, & staining with acridine orange. The number & sizes of dsRNA fragments in ascospores were similar to those observed in nucleic acid preparations from parent mycelia. A Stagonospora-like fungus was isolated from roots of cantaloupe, honeydew, & watermelon plants exhibiting vine decline symptoms. Preliminary experiments indicate that this fungus is pathogenic on 'Magnum 45' cantaloupe.

Impacts
(N/A)

Publications


    Progress 01/01/94 to 12/30/94

    Outputs
    Isolates of Monosporascus cannonballus were obtained from two 15-acre fields of cantaloupe by employing a hierarchical sampling strategy. Of the 300 isolates collected, 65% harbored 1 to 13 dsRNA fragments that varied in length from 1.7 to 3.7 kb relative to a DNA size marker. The dsRNA pattern in individual isolates of M. cannonballus appeared to be stable in subcultures. Analysis of the spatial distribution of polymorphic types revealed no clustering in either of the two fields examined. Four isolates of M. cannonballus characterized by having different dsRNA length polymorphisms were paired in all possible combinations of water agar coated microscope slides. Hybrid dsRNA length polymorphisms could be observed in the products of all pairings. A proportion of the resulting culture produced significantly fewer perithecia than either of the parents. Transfer of dsRNA via hyphal anastomosis appeared to be associated with phenotypic change in M. cannonballus. M. cannonballus was isolated from 19% and 50% of the cantaloupe plants in two fields only two weeks after plant emergence. The frequency of plants infected reached 88% and 100% ten weeks after plant emergence.

    Impacts
    (N/A)

    Publications

    • LOVIC, B.R., MARTYN, R.D., and MILLER, M.E. 1995. Sequence analysis of the ITS regions of rDNA in Monosporascus spp. reveals its potential for PCR-mediated detection. Phytopath. 85:(Submitted).
    • LOVIC, B.R., MARTYN, R.D. and MILLER, M.E. 1995. Aggressiveness of Monosporascus cannonballus to muskmelon (Cucumis melo L.) as related to geographic origin, colony morphology, and presence of dsRNA. Phytopath. 85:(Submitted).
    • MARTYN, R.D., LOVIC, B.R., MADDOX, D.A., GERMASH, A. and MILLER, M.E. 1994. First report of Monosporascus root rot/vine decline of watermelon in Tunisia. Plant Dis. 78:(in-press).
    • MILLER, M.E., MARTYN, R.D. and BRUTON, B.D. 1994. Muskmelon yield in response to fumigation in fields infested with Monosporascus cannonballus. Plant Dis. 78: (Accepted - in revision).
    • WOLFF, D.W., MILLER, M.E., and LANDER, C. 1994. Genotype X environment interactions of muskmelon hybrids for yield and fruit size. HortSci. 29:450 (Abstract).
    • MILLER, M.E., CARTWRIGHT, B., McKENZIE, C.L., and EDELSON, J.V. 1994. Effects of thrips feeding on purple blotch severity and onion bulb yield. Phytopath. 84:1092 (Abstract).
    • LOVIC, B.R., VALADEZ, V.A. LOFLAND, D.J., MARTYN, R.D., and MILLER, M.E. 1994. Preliminary analysis of dsRNA length polymorphisms in clonal, root, and field p.