FUNGI COLONIZING STEMS AND LEAVES OF HOT PEPPER PLANTS (CAPSICUM ANNUUM L.) CULTIVATED IN FIELD

Agnieszka Jamiołkowska
Department of Plant Protection and Quarantine, Faculty of Horticulture and Landscape Architecture, University of Life Sciences in Lublin, Poland

ABSTRACT

The species of fungi occurring in stems and leaves of hot pepper plants cultivated in the field were investigated in 2004 and 2006, in Zezulin near Lublin. The object of study were three cultivars of hot pepper: 'Rokita', 'Orkan', 'Bronowicka Ostra'. The mycological analyses showed that in stems and leaves of hot pepper predominated Alternaria alternata, Fusarium oxysporum and F. equiseti. The effect of communities on Alternaria alternata growth was evaluated with the biotic series method. The communities supported the pathogen’s growth to various extent. The structural similarity between the fungal communities investigated was evaluated with SYNTAX 5.01.

Key words: hot pepper, Alternaria alternata, Fusarium oxysporum, Fusarium equiseti, biotic series method.

INTRODUCTION

Along with trend towards healthy food, also herbal and spice plants have became more popular in Poland. Interest in hot pepper (Capsicum annuum L.), cultivated both for fresh and dried fruits used separately or in spice mixtures has grown. It makes meal's taste better, but also due to large amounts of vitamin C and flavonoids, it is a valuable component of healthy diet. Its seeds are important pharmaceutical material that is a constituent of homeopathic medicines. Hot pepper yielding depends on many factors, including its health status [20]. Hot pepper is infected by pathogens specific for Solanaceae family plants and organisms characteristic of other species. They are species of Fusarium genus that survive in the soil environment in a form of saprotrophic mycelium and chlamydospores [11]. Fusarium oxysporum Schlecht. responsible for wilting of plants as well as F. solani (Mart.) Sacc. causing stem base of rot are most frequently observed [7]. Also Botrytis cinerea Pers., Sclerotinia sclerotiorum (Lib.) de By and Alternaria alternata Keiss. were isolated from hot pepper plants [19]. Alternaria alternata is the most important pathogen above ground part of hot pepper. The fungus causes necrotic spots on leaves and fruits [10], and it's destructive a host plant results from enzymes and toxins production [17]. Due to lack of more detailed reports on disease-causing fungi that attack hot pepper in field plantations, the study aiming at evaluating the type and number of pathogens colonizing the species, that may be a threat despite of chemical control, has been undertaken.

MATERIAL AND METHODS

The experiments were conducted in 2004 and 2006 in Zezulin near Lublin (Lubelskie province). The object of study was three cultivars of hot pepper plants (Capsicum annuum L.): 'Rokita', 'Orkan', 'Bronowicka Ostra'. Manure at the rate of 40 t·ha^-1 was applied every spring before plantation setting, while mineral fertilization was used in accordance to fertilization recommendations for Solanaceae plants on a base of earlier soil analyses with subsequent ploughing. The hot pepper plants were set into the field at mid May, in 35 × 67 spacing. The experimental combination consisted of 40 plants of each cultivar (10 plants in 4 replications). Two hot pepper raws were sown around the experimental plants, and they were not used for strict study. Foliage nutrition was applied every year: once using calcium nitrate 1% and once using Florovit 0.2%. Plants were chemically protected according to Plant Protection Program for vegetables.

During full fruiting (first decade of September), 8 randomly selected hot pepper plants were sampled from each plot. Leaves and stems of hot pepper were analyzed in laboratory. Plant material was precleaned, rinsed with running tap water for 20 min and then surface disinfected with 50% ethanol and 0.1% sublimate for 1 minute. Disinfected plant material was rinsed 3 times in sterile water [5]. Next, 3 mm fragments were taken and placed on Petri dishes mineral medium: saccharose – 38 g; NH₄NO₃ – 0.7 g; MgSO₄×7H₂O – 0.3 g; KH₂PO₄ – 0.3 g; FeCl₃×6H₂O – trace; ZnSO₄×7H₂O – trace; CuSO₄×7H₂O – trace; MnSO₄×7H₂O – trace; agar 20 g supplemented with distilled water up to 1000 ml. For each experimental treatment 10 dishes with plant material, 10 plant fragments per dish, were prepared and incubated in 20-22°C for 7 days in dark. The obtained colonies of fungi were transferred to potato-dextrose medium (PDA-Difco) and identified to the species with keys and monographs [2,7,11,14,15,16].

The fungal communities obtained were compared according to numerical classification method using statistical program SYN-TAX 5.01 [8,13]. The similarity analysis bases on determination of general similarity or dissimilarity of samples, which are individual objects. In the study the analysis of communities similarity was carried out basing on similarity coefficients i.e. percent differences showed on axis in 0-1 scale. In this case 0.1 percent difference between communities corresponds to 90% similarity of these communities [8].

The effect of fungal communities on A. alternata was determined with the biotic series method [9].

RESULTS AND DISCUSSION

Meteorological conditions during 2-year experiment are presented in Fig. 1 and 2. Vegetation season 2006 was warmer and was characterized by lower precipitation than 2004, except for August 2006, when high sum of rainfall was recorded (Fig. 1, 2).

Mycological analysis resulted in 520 isolates of fungi representing 13 species, among which dominated: Alternaria alternata, Fusarium equiseti and F. oxysporum (Table 1). Greater species diversity was observed within population in 2004 than 2006. Saprotrophic fungi were: Aureobasidium pullulans, Epicoccum purpurascens, Penicillium cyclopium and Mucor spp. (Table 1).

Alternaria alternata seems to be the main pathogen that colonized stems and leaves of hot pepper. It occurred on all cultivars in both study years making up from 18.9% to 98.8% of fungal communities obtained. The species was isolated more abundantly in 2006 than in 2004 (Table 1). The pathogen is dangerous to plants, because it causes strong leaf necroses and dramatic changes in the plant photosystem [10,20]. Such weakened plants quickly fade and die [17]. The species is dangerous due to specific and nonspecific toxins produced that contribute to fast destruction of plants [17]. Development of A. alternata on plants is determined by weather conditions [17]. Warmer and drier vegetation season in 2006 favored the pathogen development on the above ground parts of plants.

Fungi of Fusarium genus are important in pathogenesis of hot pepper cultivated in field. Fusarium equiseti was abundantly isolated in 2004. It colonized 'Orkan' cv. and 'Bronowicka Ostra' cv. most numerously in 2004 making up 28.1% and 26.3% of fungal communities from tested cultivars (Table 1). Many authors [6,23] reported on strong pathogenic properties of F. equiseti towards some vegetable and spice plants. The negative effect of F. equiseti was the result of the activity of toxins and antibiotics produced by the species. Especially trichotecens and equisetin could have been involved in the pathogenesis [3,22]. Abundant population of F. equiseti on hot pepper plants needs to be verified for its pathogenicity to that plant. Among fungi isolated from stem and leaves of hot pepper, F. oxysporum is worth mentioning. It was present very abundantly on 'Rokita' cv. and 'Bronowicka Ostra' cv. in 2004. It is suggested that infestation by F. oxysporum leads to plant wilting and dying due to colonizing of the underground organs and xylem [1,4]. Wagner et al. [21] also reported on F. oxysporum harmfulness towards tomato seedlings indicating the decrease of plant's fluorescence resulting from the pathogen presence.

Chemical control reduced the number of saprotrophic fungi, only some fungi of genus Penicillium  and Mucor were isolated (Table 1). According to many authors [12,18] the presence of these fungi in habitat is always a positive fact.

Analysis of fungal communities performed by means of numerical classification using SYN-TAX software allowed determining the similarity level between studied communities. Communities isolated from stems and leaves of 'Rokita' cv. and 'Bronowicka Ostra' cv. in 2004 (70% similarity) as well as 'Orkan' cv. and 'Bronowicka Ostra' cv. in 2006 (50 % similarity) were the most similar, referring to qualitative and quantitative composition (Fig. 3).

Among fungi achieved from above ground part of hot pepper, B. cinerea, F. equiseti and Mucor spp. strongly reduced the A. alternata growth. The individual biotic effect (IBE) of B. cinerea and Mucor spp. towards the pathogen was +7, while IBE of F. equiseti was +4 (Table 2). A. pullulans, E. purpurascens, F. culmorum, F. oxysporum, F. solani and P. cyclopium did not reduce the pathogen growth showing neutral or negative IBE (Table 2). Communities originating from above ground part of studied cultivars could not reduce A. alternata growth, because their summarized biotic effects (SBE) were negative (Table 2).

CONCLUSIONS

1. Alternaria alternata is a main fungus that colonizes leaves and stems of hot pepper.

2. Colletotrichum coccodes and fungi of Fusarium genus, namely F. oxysporum and F. equiseti, are the pathogens of above ground parts of hot pepper.

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Accepted for print: 30.04.2009

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