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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.
Diseases affecting strawberries have been of major concern in recent years because of their widespread occurrence and potential for yield loss. Anthracnose caused by the fungus Colletotrichum acutatum is one of the most serious disases of strawberry worldwide. Although chemical controls are being used to treat anthracnose, generating disease resistant plants is a more attractive solution to the problem because chemicals can pose a health hazard, have a negative impact on the environment and may only be moderately effective. Tissue culture-induced (somaclonal) variation provides us with one strategy for generating disease-resistant genotypes. An in vitro screening system was used to evaluate several commercially important cultivars, Chandler, Delmarvel, Honeoye, Latestar, Pelican and Sweet Charlie, and shoots regenerated from leaf explants of these cultivars for resistance to C. acutatum isolate Goff (highly virulent). Somaclones with increased levels of anthracnose resistance were identified for all the cultivars. The greatest increases in disease resistance were observed for somaclones of cultivars Chandler, Pelican and Sweet Charlie that exhibited 6.8-, 12-, and 4.2-fold increases in resistance, respectively. These studies provide evidence that: 1) in vitro screening can be used to evaluate strawberry germplasm for anthracnose resistance, 2) soma-clonal variation is influenced by stawberry genotype, and 3) generating somaclonal variants may be a feasible approach to obtaining strawberry plants with increased levels of anthracnose resistance.
The chilean strawberry displays high fruit quality and tolerance to abiotic and biotic factors. Additionally, this species has a rich cultural history going back for at least several thousand years in association with aboriginal people activities and continues at a reduced level today. After its introduction to Europe during the 18th century, it formed an interspecific hybrid to become the maternal species of the commercial strawberry, Fragaria ×ananassa Duch. The objectives of the current investigation were to determine the level and patterns of partitioning of intersimple sequence repeat (ISSR) diversity. ISSR markers were used to assess the genetic diversity in 216 accessions of F. chiloensis, which represented the two botanical forms present in Chile [F. chiloensis ssp. chiloensis f. chiloensis and F. chiloensis ssp. chiloensis f. patagonica (L.) Duch.]. Our results showed high genetic diversity at the species level [polymorphic ISSR loci (P) = 89.6%, gene diversity (h) = 0.24 ± 0.17, Shannon's index (S) = 0.37 ± 0.24] and a lower genetic diversity in f. chiloensis than f. patagonica. The analysis of molecular variance (AMOVA) showed a moderate genetic differentiation among accessions (φst = 14.9%). No geographic patterns for ISSR diversity were observed. AMOVA, structure, and discriminant analysis indicated that accessions tend to group by botanical form. The impact of domestication on the genetic structure of chilean strawberry and its application to breeding and conservation are discussed.