host crops. Soil fumigation treatments or solarization treatments must extend far enough beyond the edge of new plantings to prevent spread of inoculum from previously infested areas ( Freeman et al., 2002 ). Colletotrichum acutatum conidia are spread
Domenico Bertetti, M. Lodovica Gullino, and Angelo Garibaldi
single-plant replications per each cultivar. Container substrate was 9 peatmoss : 1 perlite (by volume). The susceptibility trial was repeated twice. Table 1. Evergreen azalea cultivars resistant to anthracnose incited by Colletotrichum acutatum
Oleg Daugovish, Hai Su, and W. Douglas Gubler
The United States is the largest producer of strawberries in the world, with over 85% of fresh market fruit produced in California ( U.S. Department of Agriculture, 2005 ). Anthracnose, caused by Colletotrichum acutatum , is a major disease in
ANTHRACNOSE DISEASE Anthracnose, incited by the species Colletotrichum acutatum , is one of the major fungal diseases of strawberry affecting all parts of the plant during nursery and production stages ( Maas, 1998 ). Additional species of
Oleg Daugovish, Mark Bolda, Sukhwinder Kaur, Maren J. Mochizuki, Daniel Marcum, and Lynn Epstein
coastal fruit production areas in California ( Strand, 2008 ). Colletotrichum acutatum Simmonds causes anthracnose of strawberry in California and is an internationally regulated pest ( EPPO, 2004 ). The disease is generally asymptomatic in the nursery
Natalia Salinas, Zhen Fan, Natalia Peres, Seonghee Lee, and Vance M. Whitaker
Strawberry anthracnose caused by Colletotrichum acutatum is a disease of worldwide importance ( MacKenzie and Peres, 2012 ; Peres et al., 2005 ). Up to 75% yield losses have occurred in commercial fields infected with C. acutatum ( Borisova et
S. Garcés, M. Koch-Dean, J. Maas, B. Smith, and F. Hammerschlag
As part of a program to generate anthracnose (Colletotrichum acutatum) resistance in strawberry (Fragaria × ananassa Duch.) via either tissue culture or gene transfer techniques, studies were conducted to determine whether in vitro screening for resistance to C. acutatum was feasible. Six commercial cultivars (Latestar, Delmarvel, Pelican, Sweet Charlie, Chandler, and Honeoye) that differed in their response to the pathogen under field conditions were tested to see whether this response was reflected in vitro. Leaves from 4-week-old shoot cultures were soaked in a spore suspension of C. acutatum isolate Goff, transferred to 0.5% water agar, and the presence or absence of disease symptoms was evaluated on a 0-4 rating scale after 7 days. Five of the six cultivars exhibited a disease rating similar to field results. This study suggests that there is potential to use this procedure as a screening technique, and studies are in progress to screen strawberry regenerants for resistance.
Gustavo Giménez and James R. Ballington
Two half diallel mating designs were conducted to study the inheritance of resistance to Colletotrichum acutatum Simmonds on runners of strawberry. The main design included six genotypes representing a range of responses to the pathogen: `Chandler' (very susceptible); FL 87-210 (tolerant); MS/US 541 (very resistant); NC 92-01 (Fragaria chiloensis Duch.) (resistant); NCH 87-10 (tolerant-susceptible); and NCC 89-39 (susceptible). The cross `Chandler' × MS/US 541 was absent. The secondary test included `Chandler' and selections FL 87-210 and NC 85-01 (Fragaria virginiana Duch.) (very resistant) as parents. Griffing's methods 4 and 2, model I, were used to test for combining ability in the main and secondary tests, respectively. General combining ability and specific combining ability were highly significant in all analyses. This study indicated that nonadditive effects are more important than additive effects in the inheritance of resistance of runners to anthracnose. The frequency distribution of lesion lengths within progenies suggests that resistance to C. acutatum on runners is quantitative. Therefore, breeding for resistance should be accomplished using progeny testing followed by individual selection within progenies.
Mark K. Ehlenfeldt, James J. Polashock, Allan W. Stretch, and Matthew Kramer
Response to foliar infection by Colletotrichum acutatum Simmonds ex Simmonds was assayed in a diverse group of 149 blueberry cultivars and selections using a detached leaf-disk assay. Disks were inoculated and incubated for one week, then were digitally imaged, and images analyzed for percent leaf decay. Infection percentages across cultivars averaged 32%, and ranged from 8% to 79%. The lowest levels of foliar infection were seen in the cultivars, Burlington, Sharpblue, and Berkeley. Foliar responses were compared to anthracnose fruit rot susceptibility data from a previous study. Several clones were observed to have low levels of both foliar and fruit infection. Cultivars with particularly good resistance to both phases included `Sharpblue', `Sunshine Blue', `Legacy', `Little Giant', `Flordablue', `Elliott', `Blue Ridge', `Blue Rose', and `November Glow'. Little correlation was observed between foliar response and fruit response to anthracnose infection (r = 0.15). Since C. acutatum overwinters primarily in vegetative tissue, breeding new cultivars with foliar resistance may assist in reducing inoculum levels of this disease under field conditions.
Gustavo Gimenez, James R. Ballington, and Robert D. Milholland
Two experiments were designed to study components of resistance to Colletotrichum acutatum on runners of three strawberry cultivars: incubation period, latent period, length of the lesion and spore production, and infection frequency with three levels of inoculum density (104, 105, 106 spores/cc) were considered. Rate of disease development was also determined. There were significant differences in all the components among the resistant and susceptible cultivars. Both 'Chandler' and 'Sweet Charlie' expressed susceptible reactions. The length of the lesion, number of spores/cm of the lesion, incubation period, latent period, and rate of anthracnose development were statistically similar in 'Chandler' and 'Sweet Charlie'. The only significant difference among them was found in infection frequency. 'Chandler' had a greater number of infection sites with all three concentrations of spores included. The cultivar Pelican showed a high level of partial resistance associated with longer incubation and latent periods, lower number of spores/cm of lesion, shorter lesion, smaller number of infection sites, and lower rate of disease development.