The occurrence, pathogenicity (1997 isolates only) and fungicide sensitivity of pathogens causing dry tuber rots in Scottish seed potatoes was investigated over three storage seasons between 1997 and 2000 in relation to region of production, cultivar, class and generation of seed potatoes, type of temperature control in store and earthiness of tubers. A total of 156 samples, each comprising up to ten rotted tubers, was received over the three seasons. The relative importance of each pathogen in causing rots was summarised by calculating a mean rot index that combined the prevalence of a pathogen in the samples with the incidence of tubers affected by the pathogen within those samples. Phoma foveata (gangrene) had the highest rot index, which was five times greater than for P. exigua and ten times greater than for P. eupyrena. This relationship was mirrored by the relative pathogenicities of P. foveata and P. eupyrena, as measured by size of rots developing at inoculated wounds in test tubers. Fusarium avenaceum appeared to be the greatest cause of Fusarium dry rots, having a rot index at least twice as great as that for F. solani var. coeruleum. Infection by F. sulphureum was relatively uncommon. In the pathogenicity test, F. avenaceum, F. solani var. coeruleum and F. sulphureum produced rots of similar depths and widths and larger than those of F. culmorum. The mean rot index for Cylindrocarpon spp. was slightly more than that for F. avenaceum, whereas C. destructans produced smaller rots in the tuber pathogenicity test. Region of production affected the prevalence of P. foveata and F. avenaceum, but only the occurrence of P. foveata was affected by class and generation of seed potatoes. Isolate sensitivity to thiabendazole and imazalil was examined in vitro over

The sensitivity of a bioassay in detecting soil inoculum of Colletotrichum coccodes and Helminthosporium solani was examined using potato minitubers and microplants. Tests were conducted on soils which were collected from fields in which the interval after a previous potato crop differed, and which were also artificially infested with conidia or microsclerotia. For C. coccodes , determining plant infection based on the occurrence of infected roots after 9 -12 weeks was a sensitive method for detecting and quantifying the amount of inoculum in soil. Infestations of less than 0·4 microsclerotia per g soil were detected in artificially infested soils. A semiselective medium, developed for isolating C. gloeosporioides from pepper, detected soil infestations by C. coccodes as low as nine conidia or one microsclerotium per g soil in artificially infested soil. For H. solani , infection on minitubers was a sensitive measure, with soil inoculum of fewer than 10 conidia per g soil being detected. Soil infestation could be quantified by assessing the percentage surface area of minitubers covered by sporulating lesions, which was strongly related to the amount of soil infestation. The results of these bioassay tests were compared with published results for real-time quantitative PCR assays on the same soils. The two methods were in good agreement in artificially infested soils, but the bioassay appeared to be more sensitive with naturally infested soils.

Fragaria vesca is a diploid strawberry species that produces gourmet, aromatic fruits with only limited commercial production because of its relative obscurity. Most F. vesca research focuses on genetics and fruit aroma, but yield and fruit quality data across diploid accessions are lacking. Sixteen F. vesca accessions were grown in replicated field plots in southern Florida to measure field performance and fruit quality over multiple harvests during a single growing season. Accessions 'Reine des Vallees', 'Baron Solemacher', 'Fragolina di Bosco', and 'Reugen' all had significantly higher yield (115-140 g/plot/week) and fruit number (117-139 fruit/plot/week) compared with 'Bowlenzauber', 'Attila', 'Ali Baba', and 'Pineapple Crush' (31-57 g/plot/week and 32-60 fruit/plot/week) during peak production. Total average yield ranged from 240 g ('Pineapple Crush') to 1194 g ('Baron Solemacher') per plot of 10 plants. Fruit number and fruit yield were highly correlated (R 2 = 0.96) for all accessions, and there was no significant difference in fruit weight among accessions through the entire season. Total soluble solids ranged from 10.9 to 13.5 8Brix, and fructose, glucose, sucrose, and total sugars ranged from 15.3 to 22.1, 13.5 to 20.0, 0.1 to 2.7, and 29.7 to 42.5 mg/g, respectively, fresh weight. Acidity ranged from 1.00% to 1.18% citric acid and was not consistently significantly different among accessions over multiple harvests. Forty-two aroma compounds were putatively identified over three harvests for each accession and included mostly esters and ketones with a few alcohols, terpenes, and aldehydes. The majority of these compounds were similarly abundant over harvests and among accessions with a few exceptions, including methyl anthranilate. These results are the first in-depth study of yield and fruit quality for a large number of F. vesca accessions that could lead to increased cultivation of this species for local markets.

SummaryOver 2 years, seed tubers or stems were inoculated with Fusarium sulphureum Schlecht. (F. sambucinum Fuckel f. 6 Wollenw.) and the incidence of dry rot on daughter tubers assessed by standardised wound tests. The amount of stem and soil inoculum was also measured in one year.Inoculating stem bases resulted in greater concentrations of spores on the stem bases, greater soil populations at harvest and more dry rot on tubers than inoculating the seed tuber. Overall, the incidence of dry rot and the amount of stem and soil inoculum was similar for the three methods of haulm destruction: cutting and removing the stems, applying sulphuric acid or applying diquat dibromide to the growing plants.

Botryotinia fuckeliana (de Bary) Whetzel (syn. Botrytis cinerea Pers.:Fr.) causes gray mold on the foliage of a large range of horticultural and agricultural crops, including potato (Solanum tuberosum L.). This weak pathogen may also produce pit rots on potato tubers (1). In April 1999, two lots of seed potatoes produced in Scotland were found to contain a significant number of tubers with soft rots. The cultivars were Maritiema and Charlotte, with 2.2 and 0.5% of rotted tubers, respectively. The rots on tubers of cv. Maritiema were all soft, wet, and extensive, with a distinct edge, but the proportion of this type of rot was much lower (approximately 30%) on the cv. Charlotte tubers. Gray sporangiophores developed around tuber eyes. When the tubers were cut, the affected tissue was peach to pink-gray in color but darkened on exposure to air, and was soft and water-soaked in appearance with a pale brown or, occasionally, yellow margin. A faint vinegary odor could be detected occasionally. B. fuckeliana was isolated on potato dextrose agar (PDA) from all 15 tubers of cv. Maritiema and from the three (out of 13) tubers of cv. Charlotte that had large, soft rots. Tubers produced at Scottish Agricultural Science Agency's Gogarbank farm near Edinburgh in 1998 were used for confirmatory pathogenicity tests conducted in late April and May 1999. Using a cork borer, a wound 5 mm in diameter and 5 mm deep was made in each tuber and 5-mm-diameter agar plug from either the edge of a colony of B. fuckeliana or of PDA was inserted into the wound. Nine tubers of cvs. Maritiema and Charlotte were inoculated for each treatment and tubers incubated at 5°C in boxes lined with moist filter paper. Rots, similar to those on the commercial seed tubers, developed after 28 days at wound sites inoculated with B. fuckeliana. The fungus was isolated by placing a small piece of rotted tissue from each rot on PDA. B. fuckeliana was recovered from all rots. The mean width of rots was 51 mm for cv. Maritiema compared with 40 mm for cv. Charlotte. Depth of rots was similar for both varieties. Lesions did not develop at wound sites inoculated with PDA agar only. In a second experiment, tubers of cv. Maritiema were inoculated with B. fuckeliana as described above and incubated at 5°C or room temperature (15 to 18°C). There were nine tubers for each temperature. After 21 days, no lesions had developed on tubers incubated at room temperature, but large, soft rots were present on those incubated at 5°C. The lesions produced by B. fuckeliana in these experiments were relatively large compared with the 5-m-deep rots reported previously (1) after 60 days of incubation. The appearance of these rots is similar to that for other diseases, e.g., pink rot and watery wound rot, and infections by this fungus may have been incorrectly diagnosed in the past. Moreover, the development of such rots may be favored by the recent increase in the use of low temperature storage for seed potatoes. Reference: (1) H. W. Platt. Can. J. Plant. Pathol. 16:341, 1994.