No abstract

Diseases affecting strawberry (Fragaria  ananassa Duch.) 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 diseases of strawberry worldwide. Tissue-culture induced (somaclonal) variation provides one strategy for generating disease-resistant genotypes. As part of a program to generate strawberry germplasm resistant to anthracnose, an in vitro screening system was used to evaluate several commercial cultivars, Chandler, Delmarvel, Honeoye, Latestar, Pelican and Sweet Charlie propagated in vitro, and shoots regenerated from leaf explants of these cultivars for resistance to C. acutatum isolate Goff (highly virulent). Regenerants with increased levels of resistance were identified from all of the cultivars. The greatest increases in disease resistance were observed for regenerants from leaf explants of cultivars Pelican and Chandler that exhibited 17.5-and 6.2-fold increases in resistance, respectively. The highest levels of anthracnose resistance (2 to 6% leaf necrosis) were exhibited by regenerants from explants of cultivars Pelican and Sweet Charlie. These studies suggest that generating somaclonal variation may be a viable approach to obtaining strawberry plants with increased levels of anthracnose resistance.

No abstract

The pathogenic fungi Verticillium alboatrum and Diplodia scrobiculata were assayed for biological control of Diplodia pinea on Aleppo pine (Pinus halepensis) in Catalonia (north-eastern Spain). Young shoots were pre-treated with inoculations of either V. dahliae or D. scrobiculata, by placing colonized agar plugs on wounds made by removing a single needle fascicle. An inoculation with D. pinea was performed 15 days later. Two months after the shoot inoculations, the canker length on the stems was measured and the percentage of shoot dieback calculated. Verticillium dahliae and D. scrobiculata were found to significantly reduce the canker length of D. pinea (P<0.05) when compared with positive controls. Diplodia pinea was slightly more sensitive to V. dahliae than to D. scrobiculata, but no significant differences (P>0.05) were observed in the mean canker length between the two treatments. Trees preinoculated with V. dahliae resulted in 31.12% shoot dieback, while those pre-inoculated with D. scrobiculata resulted in 32.18% shoot dieback, compared with positive controls (42.85%).

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.