No abstract

In Argentina, more than 60 % of the tobacco crops are grown in the northwestern part of the country and where Rhizoctonia solani leads to a reduction in crop yield and quality. In this study, 35 isolates of Rhizoctonia were obtained from 32 tobacco fields in northwestern Argentina and characterized by both morphological and molecular approaches. Based on the variability in the ITS region, isolates were identified as R. solani (80 %), Waitea circinata var. zeae (Rhizoctonia zeae) (8 %) and binucleate Rhizoctonia (8 %). Most isolates of R. solani belonged to the anastomosis groups (AGs) AG 4 HG-I (44 %), AG 2-1 (41 %) and AG 4 HG-III (13 %). Isolates of binucleate Rhizoctonia belonged to AG-F and AG-P of Ceratobasidium sp. Morphological variability was higher within isolates of AG 2-1 and AG 4 HG-III than within those of AG 4 HG-I. Aggressiveness of the isolates towards tobacco seedlings was assessed in the greenhouse.Isolates of AG 2-1 were the most aggressive on leaves, causing target spot, whereas isolates of AG 4 HG-I were the most aggressive on stems and roots, causing damping-off.

flowers on plants of the orange pepper cv. Orange Glory (3). A spore suspension was prepared by flooding 5-day-old cultures on potato dextrose agar with sterile distilled water. When the plants started to flower, each flower was inoculated by placing 20 (J1 of spore suspension (1 X 10' conidia/ml) on each flower. Four isolates of F. lactis were each inoculated onto three flowers on each of seven plants. Flowers from the same number of plants inoculated with sterile distilled water were used as the control treatment. Inoculated plants were kept in a greenhouse at 25°C by day and 20°C by night. Sixty days after inoculation, mature fruits were harvested and cut open to check for internal rot. Approximately 70% of inoculated fruits showed internal rot and pinkish gray mycelial growth on the inner surface of the fruits. No symptoms were observed on the control fruits. Fungal cultures resembling F. lactis were reisolated from inoculated fruits for all four isolates, fulfilling Koch's postulates. F. lactis has been reported on sweet pepper in the Netherlands and Canada (3). To our knowledge, this is the ftrst report of internal fruit rot of sweet pepper caused by F. iactis in Korea. Although disease severity was low in this greenhouse, the economic impact on sweet pepper could be significant because the disease can reduce the quality, quantity, and market value of pepper fruits.

During March of 2006, in Famailla, Province of Tucuman, Argentina, a new foliar disease was observed on Vaccinium corymbosum L. cv. O'Neal causing severe premature leaf drop. Symptoms consisted of circular to irregular reddish brown necrotic spots varying from specks to mature lesions of 10 to 15 mm in diameter. Larger spots frequently exhibited a zonate pattern with lighter centers and darker margins that are surrounded by a black, oily halo that is consistent with target spot (3). Lesions often coalesced to form irregularly shaped necrotic areas that reached the petioles. Leaf abscission occurred soon after >50% of the foliar area was affected. No stem lesions were observed. Conidiophores were erect, brown, single or in clusters, one to seven septa, 6 to 9 × 70 to 684 μm (shorter in culture), and arose on the abaxial surface of diseased leaves; conidia were borne singly or in chains of 2 to 5, varying from cylindrical to broadest at the base and tapering toward the apex, straight to slightly curved, 3 to 20 pseudosepta, 75 to 330 × 5 to 9 μm (mean of 153 × 7 μm, shorter in culture), with conspicuous hilum. On potato dextrose agar (PDA), the rate of growth was moderate (colonies reach 25 mm in diameter after 7 days grown at 27°C) with conidia production 5 days after the culture was started. Microscopic characters and cultural patterns conformed to the description of Corynespora cassiicola (Berk & M. A. Curtis) C.T. Wei (2,4) and were identical to isolates of C. cassicola from lesions of soybean target spot. A conidial suspension (104 conidia/ml) of C. cassicola was prepared from a 2-week-old culture grown on PDA and sprayed on surface-disinfected excised blueberry stems, each with 10 healthy leaves per stem. The stems were placed in hydroponia and incubated at 27 ± 2°C with permanent light. All sprayed leaves showed symptoms within 3 days following inoculation. Within 5 days, leaves were conspicuously infected, soon followed by defoliation. C. cassicola was reisolated from the inoculated-leaves lesions and was identical morphologically to the original isolate sprayed on test leaves. Another Corynespora species, C. arctespora (Cooke & Ellis) Carris (1), was described on Vaccinium spp. stems with a distinctive feature of a phialidic synanamorph formation. This synanamorph character was not found in our isolate. C. cassiicola has a broad hosts range, but to our knowledge, has not been recorded before on V. corymbosum as the causal agent of target spot. References: (1) L. M. Carris. Mycotaxon 30:127, 1987. (2) L. S. Olive et al. Phytopathology 35:822, 1945. (3) J. B. Sinclair. Target spot. Page 27 in: Compendium of Soybean Diseases. G. L Hartman et al., eds. The American Phytopathological Society. St. Paul, MN, 1999. (4) J. A. Spencer and H. J. Walters. Phytopathology 59:58, 1969.