Source: UNIVERSITY OF FLORIDA submitted to
SQUASH BREEDING FOR DISEASE RESISTANCE TO PHYTOPHTHORA BLIGHT, CAUSED BY P. CAPSICI
 
PROJECT DIRECTOR: Ramos, L. J.
 
PERFORMING ORGANIZATION
TROPICAL RESEARCH & EDUCATION CENTER, HOMESTEAD
UNIVERSITY OF FLORIDA
GAINESVILLE,FL 32610
 
NON TECHNICAL SUMMARY: This research is undertaken to find sources of resistance to phytophthora blight, a very serious disease of squash in Florida and the Caribbean. Squash plants will be crossed with wild relatives, the parents and progenies inoculated with the fungus Phytophthora, which is causing the disease, and resistant lines selected.
 
OBJECTIVES: This research is undertaken to identify sources of resistance to phytophthora blight that could be incorporated in squash breeding lines or commercial lines. Phytophthora capsici has become a major limiting factor to squash production in south Florida, the Caribbean, and many other parts of the world. Objectives of the proposal or research included 1. Hybridizing and selfing wild and cultivated taxa of cucurbita. 2. Determining the reaction of the above genotypes to phytophthora blight. 3. Evaluating data from these and subsequent crosses to determine the heritability of tolerance to this disease in various genetic backgrouds. 4. Investigating the introgression of tolerance from these backgrounds into commercially acceptable lines.
 
APPROACH: Interspecific and intraspecific hybridizations of wild and cultivated species of Cucurbita, including winter and summer squashes, will be conducted in the greenhouse and field plots. The line breeding selection will be used, preferently to the mass selection. Resistant plants will be either selfed (interpollinated), and resulting progenies will be individually screened for resistance to Phytophthora capsici. Only the resistance lines will be retained to use in successive breeding. Resistant inbreed lines can be produced on cross-pollinated species by selfing or sib-mating, that have been selected for resistance to phytophthora blight. Parents and segregating populations will be screened for resistance to phytophthora blight, and the genetic rations and recombinant values in heredity determined. By introgressive hybridization resistance genes from wild species, will be introduced into breeding lines or varieties
 
CRIS NUMBER: 0191428 SUBFILE: CRIS
PROJECT NUMBER: FLA-HOM-04003-R SPONSOR AGENCY: CSREES
PROJECT TYPE: SPECIAL GRANT PROJECT STATUS: TERMINATED MULTI-STATE PROJECT NUMBER: (N/A)
START DATE: Sep 15, 2001 TERMINATION DATE: Sep 30, 2004

GRANT PROGRAM: TROPICAL AND SUBTROPICAL RESEARCH
GRANT PROGRAM AREA: Special Research Grant

CLASSIFICATION
Knowledge Area (KA)Subject (S)Science (F)Objective (G)Percent
201142910802.240%
202142910802.235%
206142910402.215%
212402011604.210%

CLASSIFICATION HEADINGS
KA202 - Plant Genetic Resources
KA201 - Plant Genome, Genetics, and Genetic Mechanisms
KA212 - Pathogens and Nematodes Affecting Plants
KA206 - Basic Plant Biology
S1429 - Cucurbits, other
S4020 - Fungi
F1080 - Genetics
F1160 - Pathology
F1040 - Molecular biology
G2.2 - Increase Efficiency of Production and Marketing Systems
G4.2 - Reduce Number and Severity of Pest and Disease Outbreaks


RESEARCH EFFORT CATEGORIES
BASIC 30%
APPLIED 50%
DEVELOPMENTAL 20%

KEYWORDS: plant breeding; plant disease resistance; phytophthora capsici; blight; inheritance; polygenic resistance; horizontal resistance; vertical resistance; heritability; introgression; cucurbita; squash; plant genetics; hypersensitivity; plant response; pathogenicity; molecular genetics; plant improvement; plant pathology; breeding lines; hybridization; genotypes; selection systems; plant evaluation

PROGRESS: Sep 15, 2001 TO Sep 30, 2004
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.

IMPACT: 2001-09-15 TO 2004-09-30 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.

PUBLICATION INFORMATION: 2001-09-15 TO 2004-09-30
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.

PROJECT CONTACT INFORMATION
NAME: Ramos, L. J.
PHONE: 305-246-7000
FAX: 305-246-7003