Progress 09/15/01 to 09/30/04
Outputs
The phytophthora blight disease, that is incited by Phytophthora capsici has become in a major limiting factor to squash production in south Florida, the Caribbean area and many parts of the World. The disease is causing great economic losses. The pathogen causes seedling damping off, foliar blight, stem canker, crown rot and fruit rot. The crown rot generally causes the collapse of the entire plant in a short period of time. Resistance to phytophthora blight in commercial squash lines is poor, and neither fungicides nor cultural practices provide adequate control. The pathogen is difficult to control, since no fungicides are highly effective against it and populations of the pathogen rapidly develop resistance to fungicides.The development of resistant varieties or breeding lines, is of primary importance for squash growers and the industry of Florida. A search was conducted in a number of wild and cultivated Cucurbita species to find potential sources of resistance
to phytophthora blight that could be incorporated in squash breeding lines or commercial lines. Some of the species examined include: C.ecuadorensis, C.lundelliana, C.maxima, C.moschata, C.okeechobeensis C.pepo, and C.texana. A valuable source of resistance was identified in a small fruited wild Cucurbita gourd, of the mesophytic species group. Apparently genes with additive effect to the resistance from the Cucurbita wild gourd were found in C.okeechobeensis. Segregating populations were screened for resistance to phytophthora blight, and the genetic ratios and recombinant values in heredity determined (Allard 1956). The resistance from this wild species was successfully incorporated into winter squash, Cucurbita moschata. Significant disease-resistance was found in the F1 suggesting that the resistance derived from the wild species, may be governed by dominant alleles. The minimum number of genes conditioning resistance is 1.21, estimated using the equation of Castle and Wright
(Castle and Wright, 1921 and the broad sense heritability was estimated was 43.5 percent, using the formula of Mahmud and Kramer, 1951). These findings suggest that resistance to phytophthora blight, derived from the wild Cucurbita gourd is probably governed by two dominant genes. Outstanding winter squash interspecific hybrids of (Cucurbita wild gourd x C. moschata), with incorporated resistance to phytophthora blight include F2 selections obtained by selfing and sib matting of hybrid like: 211 (111 x 111), 337 111 self and 339 111 self all with 90-100% resistance. Introgression of resistance to phytophthora blight into summer squash, C.pepo was achieved by using C. moschata with incorporated resistance to phytophthora as a bridge species. After more than one hundred inter-specific hybridizations, two hybrids of [Cucurbita wild gourd x C. moschata] x C. pepo were obtained. Three valuable interspecific hybrids of C. moschata x C.pepo have been obtained: 32 (01 x Pic-N-Pic), 128 (65 x
Gold Bar) & 363 (149 x Pic-N-Pic). Resistance to Phytophthora blight obtained by means of introgression increased from 0% in elite commercial varieties of summer squash C.pepo to 50-60% in several selections of F2.
Impacts
All commercial varieties of summer squash C. pepo are extremely susceptible to Phytophthora blight, caused by Phytophthora capsici. The pathogen is difficult to control, since no fungicides are highly effective. In addition, the pathogen rapidly develops resistance to fungicides. Therefore it is essential to develop genetic resistant lines, as an important component in the control of this devastating pathogen. Indeed this is urgent, since the industry in Florida is threatened by this pathogen. The development of resistant squash lies is of primary importance for the growers and the industry. The successful completion of this objective will result in an increase in productivity of this important crop, with corresponding decrease in the use of fungicides and benefit to the environment (Strategic Plan, Goals # 1, 2), and consequently, a contribution to a sustainable agricultural system.
Publications
- Ramos, L. J. Bryan, H. H. and R. T. McMillan Jr. 1999. Squash research at University ofFlorida-Tropical Research and Education Center. Summary of the most recent accomplishments in genetics, molecular biology and histopathology. 70th Anniversary of the Tropical Research and Education Center, Homestead.
- Bryan, H. H. and Ramos, L. J. 2001. Squash variety trial results. paage 32-33. In Vegetable variety trial results in Florida. D. N. Maynard and S. M. Olson, ed. University of Florida. Agricultural Experiment Station. IFAS.
- Bryan, H. H. and Ramos, L. J. 2002. Squash variety trial results. In Vegetable variety trial results in Florida. University of Florida. Agricultural Experiment Station (Submitted for publication).
- Ramos, L. J. Ploetz, R. C. and Bryan. H.H. 2002. FLA-HOM-04003. Annual Project Progress Report. Dec. 2002. 9 pages. with illustrations.
- Ramos, L. J.and Ploetz, R. C 2003.. Breeding for disease resistance to Phytophthora Blight caused by P. capsici. Progress Report. TSTAR.FLA-HOM 4003-R USDA, March 2003, 22 pages. with illus. Ramos, L. J. 2004 Progress Report. TSTAR, USDA.Breeding for disease reistance to phytophthora blight, caused by P. capsici Part II. Project Description.Summary of Accomplishements. 25 p with illus.Genealogy of squash advanced lines.
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Progress 10/01/02 to 10/01/03
Outputs
Objectives of the grant included: 1) Identify a valuable source of resistance to Phytophthora blight. 2) Hybridizing and selfing wild and cultivated taxa of Cucurbita.3) Determining the reaction of the above genotypes to phytophthora blight 4) Evaluating data from these and subsequent crosses to determine the heritability of tolerance to this disease in the various genetic backgrounds, and 5) investigating the introgression of tolerance from these backgrounds into commercially acceptable lines. Major Accomplishments: 1. Disease reaction of inoculated plants indicated that commercial varieties of summer squashes C. pepo are extremely susceptible to phytophthora blight, and when inoculated generally die between 4-6 days after inoculation. Some winter squashes, however, are less susceptible to phytophthora blight, but their resistance is still poor. 2. A valuable source of resistance to phytophthora blight in a small-fruited Cucurbita wild gourd was identified. This is
the first report about resistance found in this wild gourd species of Cucurbita. 3.Genes for resistance to Phytophthora blight from a Cucurbita wild source have been already successfully incorporated into winter squash of Cucurbita moschata (Calabaza), and a significant resistance to Phytophthora capsici was found in the first filial generation. Outstanding hybrids include: 144 and 247 (05 c 55mB), 171 and 238 (118x 11$), 211 (111 x 111). Several have good productivity, and fruit quality. 4. Possible mode of inheritance. The F1 hybrids using the above source of resistance have shown a significant high degree of resistance to phytophthora blight. This response suggests that the resistance to phytophthora blight is derived from wild gourd Cucurbita species and may be governed by few mainly dominant genes. 5. The minimum number of genes conditioning resistance to phytophthora blight was 1.21, estimated using the equation of Castle and Wright (Castle and Wright, 1921, and the broad sense
heritability was estimated to be 43.5 percent by using the formula of Mahmud and Kramer (1951). 6.The introgression of resistance to phytophthora blight is in progress. From more than hundred inter-specific hybridizations, and different techniques two valuable hybrids of C. moschata and C. pepo were obtained. These hybrids are: #128 (65 x C. pepo); #132 (01 x C. pepo). Selfing of F1 hybrids of # 128 and # 132 were obtained. Resistance of these two hybrids must be improved by backcrosses to more resistant non-recurrent parents as # 149 (132 x 01) and #154 (128 x 114). Considerable more work will be needed to obtain homozygous strains 7. The protocol for culture and inoculation was improved by induction of zoosporangium formation (Ploetz et al. 2002). Thus a zoospore suspension was used instead of the previously used mycelium/sporangia suspension. 8. Genetic Analysis. Extractions of DNA were initiated and will be continue for the genetic analysis. Molecular genetic assisted breeding
will be used in order to abbreviate the number of backcrosses.
Impacts
All commercial varieties of summer squash C. pepo are extremely susceptible to Phytophthora blight. The pathogen is difficult to control, since no fungicides are highly effective. In addition, the pathogen rapidly develops resistance to fungicides. Therefore it is essential to develop genetic resistant genetic lines, as an important component in the control of this devastating pathogen. Indeed this is urgent, since the industry in Florida is threatened by this pathogen.
Publications
- Ramos, 2003. Squash breeding for disease resistance to Phytophthora blight. Progress Report Page 1-22. In Project Progress Report 11/13/03.
- Ploetz, R. C., Heine, G., Haynes, J. L. and Watson, M. 2002. Investigating biological attributes that may contribute to Phytophthora capsici's importance as a vegetable. Annals of Applied Biology. 140:61-67.
- Ploetz, R. C. Haynes, J.L. 2000. How does Phytophthora capsici survive in squash fields in southestern Florida dring the off-season?. Proceeding of the Florida State Horticultural Society 113:211-215.
- Ramos, L.J. Bryan, R. T. McMillan, J. 1999. Squash research at University of Florida.A Summary of accomplishent in squash research . 70th Aniversary of the Tropical Research and Education Center, University ofFlorida, IFAS.
- Ramos, L. J., Narayanan, K. R. and McMillan, Jr., R. T. 1998. Use of chloroplast DNA polymorphism to study phylogenetic relationships among Cucurbita species p 55.In Horticultural Biotechnology Symposium. August 21-23, (Abstract). University of California, Davis.
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Progress 10/01/01 to 10/01/02
Outputs
Disease reactions of inoculated plants indicated that commercial varieties of summer squashes C. pepo are extremely susceptible to phytophthora blight, and when inoculated generally die between 4-6 days after inoculation. Some winter squashes are less susceptible, but their resistance is still poor. A few field breeding selections of winter squash used in hybridization displayed some field tolerance, and are also being used in this breeding program. The search for resistance included a rigorous screening by inoculations with Phytophthora capsici of a number wild and cultivated species of Cucurbita. This resulted in the identification of valuable sources of resistance to phytophthora blight in a wild small-fruited gourd type Cucurbita species. Genes for resistance to Phytophthora blight from this wild species have been successfully incorporated into winter squash, Cucurbita moschata (Calabaza), and significant resistance to Phytophthora capsici was found in the first
filial generation. Thus, introgression of resistance into winter squash has been achieved. Backcrosses to recurrent and non-recurrent parents are progressing. The F1 hybrids using the above source of resistance are highly resistant to phytophthora blight. Dominant resistance alleles are expressed in F1 populations, but recessive resistance genes are not detectable until homozygoyus genotypes appear later in the breeding program. This response suggests that the resistance to phytophthora blight derived from the wild Cucurbita species may be determined by one or a few mainly dominant genes. A more formal genetic analysis of phenotypes of F2 progenies is now in progress. Phenotypic variances of parents, F1 and F2 will be used to determine mode of inheritance, heritability and probable number of genes involved. The introgression of resistance to phytophthora blight is in progress. From more than one hundred inter-specific hybridizations, and different techniques two valuable hybrids of C.
moschata and C. pepo were obtained. These hybrid are: #128 (65 x C. pepo); #132 (01 x Cepo). Selfing of F1 hybrids of # 128 and # 132 were obtained. Resistance of these two hybrids must be improved by backcrosses to more resistant non-recurrent parents as # 149 (132 x 01) and #154 (128 x 114). Fertile F1 hybrids of C. moschata x wild Cucurbita # 68 (wild Cucurbita x C. moschata) and # 66 (C. maxima x wild Cucurbita) has been obtained, and F2 progenies will be inoculated to know their disease reaction and phenotypic ratios for the genetic analysis. Extractions of DNA were initiated and will be continued for the genetic analysis. Molecular genetic-assisted breeding will be used in order to abbreviate the number of backcrosses. In cases of sterile F1 hybrids, test crosses, back cross to the susceptible recurrent parent have been made, as an alternative to the genetic analysis of F2 population. The protocol for culture and inoculation was improved by induction of zoosporangium formation
(Ploetz et al. 2002). Thus a zoospore suspension was used instead of the previously used mycelium/sporangia suspension.
Impacts
This work will result in the development of both winter and summer squash cultivars with high resistance to Phytophthora blight. The causative organism has become resistant to fungicides. When released the resistant cultivars will assure that profitable production of squash can continue.
Publications
- Ploetz, R. C., Heine, G., Haynes, J. L. and Watson, M. 2002. Investigating biological attributes that may contribute to Phytophthora capsici's importance as a vegetable pathogen in Florida. Annals of Applied Biology. 140:61-67.
- Ramos, L. J, Ploetz, R. C. & Bryan, H. H. 2002.Breeding for disease resistance to Phytophthora blight, caused by P. capsici. Project Progress Report (10/01/2001-02/20/2002). 9 pp. with illustrations
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