Gürsel Karaca

Inactivation effect of electron beam irradiation on fungal load of naturally contaminated maize seeds

BACKGROUND This work focuses on the effect of accelerated electrons (0.1-6.2 kGy) on naturally attached fungi on maize seeds. The fungal viability and corresponding inactivation kinetics were determined. The inactivation and radiosensitivity of the most abundant species in the contaminant fungi detected on maize seeds (Aspergillus spp., Penicillium spp. and Fusarium spp.) are discussed. RESULTS Fungal contamination of maize seeds decreased significantly with increasing irradiation dose. The survival curve of total fungi determined by the blotter test showed a sigmoidal pattern that can be attributed to the mixture of fungal subpopulations with different radiation sensitivities. This behaviour could be modelled well (R²  = 0.995) with a modified Gompertz equation. The predicted values for shoulder length and inactivation rate were 0.63 ± 0.10 kGy and 0.44 ± 0.04 kGy⁻¹ respectively. The sensitivity of the most common fungi to electron beam treatment followed the order Penicillium spp. > Fusarium spp. > Aspergillus spp., with total inactivation at irradiation doses of 1.7, 2.5 and 4.8 kGy respectively. CONCLUSION The effect of electron beam treatment against fungi on naturally contaminated maize seeds depended on irradiation dose, allowing the control of maize fungal load.

Identification and pathogenicity of Rhizoctonia species isolated from bean and soybean plants in Samsun, Turkey

A total of 434 isolates of Rhizoctonia belonging to 10 anastomosis groups were obtained from the roots and rhizosphere soils of bean and soybean plants grown in Samsun, Turkey. AG-4 was found to be the most common group on bean and soybean plants and AG-5, AG-6, binucleate AG-A, AG-B and R. zeae were other groups isolated from the both plant species. AG-1, AG-7 and AG-K from bean and AG-E from soybean were other groups obtained in the study. The pathogenicity tests on bean and soybean seedlings showed that the highest disease severities were caused by AG-4 isolates, whereas AG-1 and AG-6 isolates were moderately pathogenic. Binucleate Rhizoctonia AG-B isolates were also moderately pathogenic, while other binucleate Rhizoctonia were found to be weakly pathogenic. Rhizoctonia zeae isolates caused moderate disease symptoms on bean, but soybean plants were slightly affected by this group of isolates. This is the first reported observation of R. solani AG-6 and AG-7 and binucleate Rhizoctonia AG-B on bean, and R. solani AG-5 and AG-6 and binucleate Rhizoctonia AG-A, AG-B and AG-E on soybean, in Turkey.

Investigations on pests, diseases and present early warning system of apple orchards in Isparta, Turkey

As a result of three year surveys performed in the apple orchards in Isparta region, 19 pest species belonging to 4 orders were determined and it was found that the main pest was codling moth. Most of the predators and parasitoids were effective against aphids and they were mostly found in the orchards where selective pesticides were used. Apple scab and powdery mildew were the most common and important diseases. Biology of codling moth and apple scab in the region were investigated. By using the obtained data, proper application times were given and some recommendations regarding integrated pest management program in apple orchards, were summarized.

Root rot disease incidence and severity on some legume species grown in Samsun and the fungi isolated from roots and soils

Abstract Root rot disease is very common in the bean, soybean, faba bean and pea plants growing areas in Samsun province. Disease incidence and severity were detected the highest at 93.8% and 55.4% in the bean growing area, and the lowest at 64.0% and 24.3% in the faba bean growing area respectively. In this study, a total of 2714 fungal isolates were obtained from some legume plants and soil samples. The most common fungi isolated from root and soil samples were Fusarium spp., multinucleate Rhizoctonia (MNR), binucleate Rhizoctonia (BNR) and Pythium spp. respectively. Fusarium spp. were isolated at high rates from all the examined areas. MN Rhizoctonia and BN Rhizoctonia were isolated both from inner and coastal areas of the province, whereas Pythium spp. were isolated in costal areas, except for the Vezirköprü district which is situated in the inner area. When looking at the interactions among pathogens causing root rot, it was found the great majority of the samples (30.4%) isolated both Fusarium spp. and MNR-BNR group fungi, whereas Fusarium spp. and Pythium spp. were isolated together from 10.9% of the samples and MNR-BNR and Pythium spp. from only 1.5% of the samples.

Expression analysis of WRKY genes from Poncirus trifoliata in response to pathogen infection

The majority of WRKY transcription factors (TFs) play a role in the regulation of defense response in plants. Three WRKY genes, PtrWRKY1, PtrWRKY2 and PtrWRKY3, were previously identified in Poncirus and their expressions were characterized in response to cold and drought in Poncirus and Citrus. In this study, expressions of these WRKY genes were studied in response to infection with two major pathogens of Citrus, Citrus tristeza virus (CTV) and Phytophthora citrophthora, in resistant Poncirus and susceptible pummelo (Citrus grandis) plants. Northern blot analysis showed that the expression of the PtrWRKY1 gene was induced earlier and stronger in Poncirus than in pummelo in response to CTV infection. On the other hand, the expression of the PtrWRKY1 gene was not altered in response to P. citrophthora infection neither in Poncirus nor in pummelo. When the expression of the PtrWRKY2 gene was analyzed, it was repressed by CTV inoculation in Poncirus plants, whereas the expression was not changed in response to CTV infection in pummelo or in response to P. citrophthora inoculation in Poncirus or pummelo. Similarly, the expression of the PtrWRKY3 gene was repressed in Poncirus, but not changed in pummelo by CTV inoculation; however, the expression of the PtrWRKY3 gene was induced in Poncirus, but it was repressed in pummelo in response to P. citrophthora inoculation. The expression analysis of three different WRKY genes revealed that they are differentially expressed in response to CTV and P. citrophthora infection in resistant Poncirus and susceptible pummelo suggesting that they may play a role in disease resistance in Poncirus.

New hosts for Phyllactinia guttata in the Black Sea Region of Turkey

Abstract Fungi belonging to the family Erysiphaceae (Ascomycota) are obligate biotrophs causing powdery mildew disease on various host plants. Most of the species in this family are ectoparasitic while the genus Phyllactinia is known to be partly endoparasitic. Phyllactinia guttata is one of the most important powdery mildews among Phyllactinia species causing disease on deciduous trees. In this study, P. guttata was detected on 11 woody plant species belonging to 8 families of Actinidiaceae, Betulaceae, Cornaceae, Fagaceae, Moraceae, Rhamnaceae, Rosaceae and Ulmaceae in 5 provinces in the Black Sea Region of Turkey. This is the first report of P. guttata on Actinidia deliciosa, Alnus glutinosa var. barbata, A. glutinosa var. glutinosa, Cornus mas, Cydonia oblonga and Fagus orientalis in the Black Sea Region of Turkey.

Effects of some entomopathogenic fungi on Citrus Mealybug Planococcus citri (Risso) (Hemiptera: Pseudococcidae)

Citrus Mealybug Planococcus citri is an economically important pest species causing harm on citrus and some other plants. Biological control of the pest is gaining importance because of the problems caused by chemical control. In this study, effects of Beauveria bassiana, Paecilomyces fumosoroseus and Paecilomyces lilacinus against second instar larvae of mealybug were investigated. Healthy potato tubers were dipped into spore suspensions of the entomopathogens with 108 conidia/ml concentration and then infested with mealybugs. Potatoes were then kept in a climatic room with 25±1°C temperature and 60±5% humidity. Alive and dead mealybug individuals were determined 3, 5 and 7 days after applications and mortality rates were calculated. As a result, three entomopathogens caused different rates of mortality on the pest. B. bassiana isolate showed the highest effect and killed all pest individuals 5 days after the application. Mortality rates caused by P. fumosoroseus and P. lilacinus were lower in the first two observations, while they showed 96% and 82% mortality on the seventh day, respectively.