HEALTH STATUS OF CARROTS Daucus carota L. ssp. sativus GROWN IN INTEGRATED AND ORGANIC FARMING SYSTEMS

Carrot culrivars ‘Bolero’, ‘Fayette F1’, ‘Flakke, Koral’, ‘Nantes’, ‘Perfekcja’ and ‘Sukces’ were grown in integrated and organic farming systems. The severity of Alternaria leaf blight and root diseases was evaluated at harvest and after five months of storage. Fungi were isolated from carrot roots. Disease severity was affected by the years of the study, farming system and cultivar. The severity of Alternaria leaf blight was lower in the integrated farming system than in the organic system. Carrots of cvs. ‘Bolero’ and ‘Fayette F1’ were healthiest. In both production systems, the symptoms of mixed rot (soft rot, Pectobacterium carotovorum subsp. carotovorum and Sclerotinia rot, Sclerotinia sclerotiorum), dry rot (Fusarium spp.), common scab (Streptomyces scabies), crater rot (Rhizoctonia carotae) and black rot (Alternaria radicina, A. dauci) were encountered sporadically, and their severity was low on carrot roots analyzed at harvest. Disease symptoms became more severe during storage, and they were more frequently observed on carrot roots in the organic farming system. Cultivars exerted varied effects on the severity of the analyzed root diseases. The fungal pathogens isolated from carrot roots confirmed the presence of disease symptoms.

Some of the main challenges for the global society in the coming decades will be to overcome the constraints in agriculture while minimizing the adverse effects of farming on ecosystems (decrease in biological diversity, soil and water quality) and human health. The growing interest in food safety and quality stimulates the demand for crops produced in integrated and organic farming systems. Bio-based agronomic practices, breeding methods and crop protection techniques, which minimize the use of mineral fertilizers and pesticides, play a very important role in agriculture and horticulture.
The domestic carrot (family: Apiaceae) originated in Asia, and it is one of the most popular vegetables around the world. Carrots are abundant in nutrients, including antioxidants (α-and β-carotene, ascorbic acid, phenolic compounds), and they reduce the risk of cardiovascular diseases, hypertension, stroke and cancer [Leja et al. 2013]. Poland is the third largest producer of carrots in the EU after Spain and Italy. In 2018, Poland produced 726 000 tons of carrots which accounted for 14% of total vegetable production (5.271 million tons). The carrot is the third most popular vegetable after cabbage and tomatoes (fieldand greenhouse-grown). In Poland, carrots are cultivated on an area of 22 400 ha, and yields are estimated at 324 dt ha -1 [Statistics Poland 2019]. The total area under organic farming has decreased from 605 519.61 ha in 2011 to 484 676.15 ha in 2018, whereas the area under organic vegetable production has increased from 7 266 ha in 2011 to 30 049.9 ha in 2018 [IJHARS 2019].
In both farming systems, plants of the Brassicaceae family, cereals (winter wheat, winter rye, spring triticale, winter triticale, oat), and grass and legume mixtures were the preceding crops. All agronomic practices were consistent with the recommendations of the Institute of Horticulture in Skierniewice. During the threeyear experiment, certified carrot seeds were sown at 1.2-2 mln ha -1 between 26 April and 10 May. Roots were harvested between 27 September and 8 October.
Foliar disease severity scoring. The severity of Alternaria leaf blight (Alternaria dauci (Kühn) Groves & Skolko, A. radicina Meier, Drechsler & Eddy; including the symptoms of Cercospora leaf spot Cercospora carotae (Pass.) Kazn. & Siemaszko because it is difficult to differentiate between the diseases under field conditions) and powdery mildew (Erysiphe heraclei DC) was determined twice, from the stage of leaf development to the stage of root expansion, on 25 plants collected at four different sites in the field in each location, with the use of the following scale: 1° -<5% leaves infected, 3° -5-30% leaves infected, 5° -30-60% leaves infected, 7° -60-90% leaves infected, 9° ->90% leaves infected/severe defoliation [Pawelec et al. 2006]. The results were expressed as the infection index (%), according to the formula: where: (a • b) -sum of the products of the number of the analyzed plants (a) and their severity scores (b), N -total number of the analyzed plants, I -highest severity score. Root disease severity scoring. The roots of seven carrot cultivars were harvested randomly at four different sites in the field in each location. The health status of carrots was evaluated at harvest and after five months of storage in piles layered with sand. The severity of soft rot (Pectobacterium carotovorum subsp. carotovorum Hauben) and Sclerotinia rot (Sclerotinia sclerotiorum (Lib.) de Bary) -combined analysis, and dry rot (Fusarium spp.) was estimated on 5 kg root samples collected in each field. The results were expressed by the percentage of infected roots weight. The severity of common scab (Streptomyces scabies (Thaxter) Waksman et Henrici), crater rot (Rhizoctonia carotae Rader G.C., teleomorph Athelia arachnoidea (Berkeley) Jülich) and black rot (Alternaria radicina, A. dauci) was evaluated on samples of 50 roots. The severity of common scab was estimated on a 9° scale, where 1° -absence of disease symptoms, 9° -more than 50% of infected root area; of crater rot -on 9° scale, where 1° -absence of disease symptoms, 9° -more than 25% of infected root area; of black rot was evaluated on a 4° scale, where 1 -black lesions without root narrowing, 4° -black lesions with root narrowing >50% at discolored sites. The results were expressed as a percentage by calculating the infection index Ii.
Isolation of fungal pathogens. During the growing season, petioles were collected randomly at four different sites in the field in each location (a pooled sample of 30 petioles from the field in each location). Fungi were isolated from petioles and roots in the laboratory (at harvest and after five months of storage). The cubes (0.5 × 0.5 × 0.5 cm) were cut out from roots and were disinfected with 50% ethanol and 0.1% sodium hypochlorite for 30 sec, they were rinsed three times with sterile water, dried on filter paper, and cultured on the potato-dextrose-agar (PDA) medium.
Statistical analysis. The results were processed statistically by three-way analysis of variance (ANOVA) with the following factors: year, farming system and cultivar, where farming system and cultivar were fixed effects, and years and replications were random effects. The calculations were performed using STATIS-TICA 10 (2013) software (StatSoft, Tulsa, Oklahoma, USA). Mean values were compared by Duncan's test at a significance level of 0.05.
Weather conditions during the growing seasons in the analyzed locations. During the three-year experiment, mean temperatures in April-September were higher than the long-term average (Tab. 1). In all locations, mean temperatures were somewhat higher in the growing season of 2011, compared with the remaining years of the study. Temperatures in the summer (June-July) were comparable, ranging from 17.4 to 18.6°C. July and August 2010 were the warmest months during the entire experiment, and May was coldest, with temperatures below the long-term average. In all locations, total precipitation was highest in 2010 and lowest (but above the long-term average, except in Szpiegowo) in 2012. In the summer of 2010, precipitation was unevenly distributed (except in Szpiegowo), with the heaviest rainfall in August. May was cold and wet due to high precipitation levels (3-to 4-fold higher than the long-term average). July 2011 was also wet, with rainfall levels from 2.6-fold (Rywociny) to 3-fold (Taraskowo) higher than the long-term average. In the last growing season, the highest rainfall (approx. 100 mm) was recorded in June in Zgniłobłoty and Rywociny, and in June and July in the locations monitored by the Weather Station in Olsztyn.

RESULTS AND DISCUSSION
Severity of foliar diseases during the growing season. The symptoms of powdery mildew on carrot plants were observed only sporadically, therefore the results were not presented in the table. Significant differences in the average values of the infection index were noted across the years of the study, which implies that the incidence of Alternaria leaf blight (Alternaria dauci, A. radicina) - Figure 2a was considerably affected by weather conditions. The severity of the disease was lower in the integrated farming system than in the organic system. Carrots of cvs. 'Bolero' and 'Fayette F1' were healthiest (Tabs 2 and 3). In the organic farming system, the highest values of the infection index (approx. 40%) were noted on carrot cvs. 'Flakke', 'Koral' and 'Perfekcja' in 2010, which was very wet and characterized by a hot summer season (significant differences relative to cvs. 'Bolero' and 'Fayette F1'), and on cv. 'Koral' in 2012 (significant differences relative to the remaining cultivars). In the integrated farming system, the highest value of the  .6%, respectively). These cultivars were found to be healthiest in both farming systems, and significant differences were observed relative to the most infected cv. 'Koral' (Tabs 2 and 3). An analysis of infection rates in the years of the study revealed differences among locations (Tab. 4). The values of the infection index were significantly lower in Szpiegowo, compared with the remaining locations, during the last two growing seasons in the integrated farming system, and in Zgniłobłoty during the last growing season in the organic farming system. The above results were confirmed by the mean values for the years of the study in both farming systems. Alternaria dauci, A. radicina and the polyphagous A. alternata (Fig. 2b-d) are fungal pathogens of carrots Strandberg 2002, Farrar et al. 2004]. According to Irzykowska et al. [2007], cv. 'Koral' is more susceptible to infections caused by A. radicina than other carrot cultivars. Rogers and Stevenson [2010] also noted significant differences in the severity of Alternaria leaf blight between carrot cultivars, which were reflected in the total root yield. The aggressiveness of A. dauci isolates has been studied extensively in different carrot cultivars and under various environmental conditions [Courtial et al. 2018]. Grapefruit extract was effective in controlling Alternaria leaf blight during the growing season [Mazur and Nawrocki 2007b]. Töfoli et al. [2019] demonstrated that fluxapyroxad + pyraclostrobin and pyraclostrobin + metiram were more effective in controlling Alternaria leaf blight than boscalid + kresoxim-methyl, copper hydroxide and azoxystrobin.
Severity of carrot root diseases (Fig. 3a-f). In the present experiment, the severity of carrot root diseases was affected by weather conditions, farming system and cultivar (Tab. 5). The severity of disease symptoms evaluated on carrot roots at harvest was low. The symptoms of dry rot, common scab and black rot were less severe in the organic farming system, whereas the symptoms of root diseases after storage were less severe in the integrated farming system. The wet growing season of 2010 promoted the development of soft rot and black rot. The percentage of roots infected by Pectobacterium carotovorum subsp. carotovorum and Sclerotinia sclerotiorum did not exceed 5% on a weight basis in the integrated farming system (cvs. 'Perfekcja' and 'Flakke' in the first two years of the study) and 8% in the organic farming system (cvs. 'Bolero' and 'Fayette F1' during the last two growing seasons) -Tab. 6. In both production systems, the symptoms of mixed rot became more severe during storage. The weight of infected roots was significantly highest in the wettest growing season of 2010, at around 30% in the organic farming system (cvs. 'Koral', 'Nantes' and 'Perfekcja') and 26% in the integrated farming system (cvs. 'Koral' and 'Perfekcja'). After storage, cvs. 'Bolero' and 'Nantes' in the integrated farming system and cv. 'Fayette F1' in the organic farming system were characterized by the healthiest roots (Fig. 4a). The incidence of soft rot of carrots (bacterial soft rot) caused by P. carotovorum subsp. carotovorum, P. atrosepticum and Dickeya dadantii reaches epidemic proportions during prolonged spells of hot weather (20-25°C) and high soil moisture content [Nuñez and Davis 2016]. Different defense responses of carrot breeding lines to bacterial soft rot have prompted molecular analyses to investigate mechanisms of resistance to the pathogens. Pusz and Pląskowska [2008] reported that the Asahi SL biostimulant reduced the severity of infection caused by S. sclerotiorum in rapeseed stems. In a study by Tokeshi et al. [1998], Effective Microorganisms (EM) suppressed S. sclerotiorum in lettuce by reducing the number of soil sclerotia and enhancing antibiosis. A biocontrol method involving the use of Trichoderma [Geraldine et al. 2013] and Coniothyrium minitans [Bitsadze et al. 2015] isolates was effective in degrading sclerotia of S. sclerotiorum. The development of cultivars resistant to S. sclerotiorum seems promising but challenging, even with the use of genetic engineering strategies [Andrade et al. 2016]. Wang et al. [2015] found that boskalid, fluazinam, fluxapyroxad, pyraclostrobin, penthiopyrad, pycoxystrobin, prothioconazol, trifloxystrobin, tetraconazole and thiophanate-methyl were effective in controlling S. sclerotiorum.
Throughout the experiment, in both production systems, the symptoms of dry rot (Fusarium spp.) were absent or present sporadically on carrot roots analyzed at harvest (and after storage in 2010). Dry rot symptoms were observed in only 5.5% of roots in cvs. 'Bolero' and 'Fayette F1' in the integrated farming system  and in approximately 8% of roots in cv. 'Perfekcja' in the organic farming system in 2011 (Tab. 7). Disease symptoms became more severe during carrot storage in the last two years of the study in both production systems. The weight of infected roots was significantly higher in cv. 'Koral' than in the remaining cultivars in the integrated farming system (17% in 2011 and 22% in 2012). The weight of infected roots was higher in the organic farming system, accounting for 25% in cvs. 'Flakke' and 'Sukces' (2011) and 22% in cv. 'Koral' (2012); significant differences were noted relative to the remaining cultivars. The above results were confirmed by the mean values for cultivars in all years of the study (Fig. 2b) In both production systems, the symptoms of common scab (S. scabies) were absent or present sporadically on carrot roots analyzed at harvest and after storage in 2010 (Tab. 8). The values of the infection index were significantly higher in integrated and organic farming systems during the last two growing seasons, particularly in 2012 (both at harvest and after storage). In the integrated farming system, the percentage of infected roots analyzed at harvest was significantly higher in cv. 'Sukces' (9.2%), compared with the remaining cultivars. More severe disease symptoms were observed after storage, and the highest percentage of infected roots was noted in cv. 'Fayette F1' (13.2%) in the integrated farming system and in cv. 'Sukces' (15%) in the organic farming system in 2012. The mean values for cultivars point to significant differences in root infection at harvest and after storage in both farming systems (Fig. 5a). Schoneveld [1994] demonstrated that carrots were most susceptible to infection by S. scabies 4 to 5 weeks after spring sowing, and infected skin cells died rapidly during dry weather.
The symptoms of crater rot (Rhizoctonia carotae) were absent or present sporadically on carrot roots analyzed at harvest in the integrated farming system in 2010 and 2012, and in the organic farming system during the first two growing seasons. The highest value of the infection index (8%) was noted in cv. 'Nantes' in the organic farming system in 2012 (Tab. 9). Disease symptoms got worse during storage, except in the integrated farming system in 2011 and in the organic farming system in 2012. After harvest, the highest value of the infection index was noted in cv. 'Fayette F1' in the organic farming system in 2011. Differences were observed in the rates of root infection in the analyzed carrot cultivars at harvest and after storage in both production systems (Fig. 5b). Rhizoctonia carotae (= Fibularhizoctonia carotae, sexual stage Athelia arachnoidea), the causative agent of crater rot of carrots, is a soil-borne fungal pathogen. The fungus produces a white mycelium and brown sclerotia on the surface of carrot roots under conditions of high humidity and low temperatures [Punja 2002]. In a study by Dłużniewska [2018], grapefruit extract inhibited mycelial growth and sclerotium germination of Rhizoctonia solani. Nasir et al. [2018] demonstrated that a combination of Bacillus pumilus INR7 and Trichoderma harzianum suppressed Rhizoctonia root rot of common beans.
The experimental factors and their interactions significantly influenced the severity of root diseases at harvest and after storage, except for the farming system and the farming system x year interaction for common scab, and year for black rot.
Isolation of fungi from carrot petioles and roots. Species of the genus Alternaria, i.e. the most common A. alternata, followed by A. dauci and A. radicina, predominated in the fungal community isolated from carrot petioles. They had a higher share of the fungal community in the organic farming system than in the integrated system, and colonized 62.4% and 47.8% of petioles in cv. 'Koral', respectively (Tab. 12), which is consistent with the results of field analyses of the severity of Alternaria leaf blight. Species of the genus Alternaria (A. radicina followed by A. dauci) were also isolated most frequently from carrot roots at harvest and after storage in both production systems.
Most Alternaria fungi were isolated at harvest from cv. 'Sukces' in the organic farming system (more than 48%) and from cv. 'Perfekcja' in the integrated farming system (38%) - Table 13. After storage, the above pathogens more frequently colonized cv. 'Flakke' than the remaining cultivars, and organically grown carrots than carrots grown in the integrated system (more than 28% and 25%, respectively). The causative agents of dry rot were less prevalent; they had an over 20% share of the fungal community isolated at harvest (cv. 'Perfekcja' in the integrated farming system and cv. 'Sukces' in the organic farming system) and after storage (cv. 'Sukces' in the integrated farming system). The least prevalent fungal pathogens were the causative agents of crater rot, Sclerotinia rot and gray mold rot. In a study by Lima et al. [2016], A. dauci and A. alternata were isolated during emergence of carrot seedlings.

CONCLUSIONS
1. The health status of carrots was determined by the farming system, cultivar and weather conditions during the growing season. Throughout the experiment, the severity of Alternaria leaf blight was lower in the integrated farming system than in the organic system. Carrots of cvs. 'Bolero' and 'Fayette F1' were healthiest, and cv. 'Koral' was most infected. In both production systems, the wet and warm growing season of 2010 promoted the development of Alternaria leaf blight.
2. Disease severity was low on carrot roots analyzed at harvest. The symptoms of infections caused by Fusarium spp., S. scabies, Alternaria radicina and A. dauci were less severe in the organic farming system. The symptoms of root diseases, mostly soft rot and Sclerotinia rot, got worse during storage. The symptoms of infections caused by pathogens were less severe in the integrated farming system.
3. In both farming systems, significant differences were found between cultivars in the severity of root diseases caused by S. scabies, R. carotae and Fusarium spp. at harvest and after storage, and by P. carotovorum, S. sclerotiorum and Alternaria spp. after storage.
4. The isolated Alternaria species had a 50% and higher share of the fungal community colonizing carrot petioles, and they were responsible for Alternaria leaf blight. The above pathogens predominated also on carrot roots, potentially pathogenic Fusarium species were isolated less frequently, and the causative agents of the remaining root diseases were least prevalent.

ACKNOWLEDGMENTS
The experiment was financed from funds allocated for scientific research NN 310 079838 in 2010-2013. Project financially supported by Minister of Education and Science in the range of the program entitled "Regional Initiative of Excellence" for the years 2019-2022, Project No. 010/RID/2018/19. No conflict of interests.