Sansevieria trifasciata is native to west Africa.It is widely grown as a potted ornamental plant in China because it improves indoor air quality by passively absorbing toxins,such as nitrogen oxides,formaldehyde(Wolverton et al., 1989), and ozone(Papinchaki et al., 2009).S.trifasciata leaf spots are caused by Fusarium moniliforme (Jones,1940),Pythium spinosum (Takeuchi et al., 2002), and Colletotrichum sansevieriae (Nakamura et al., 2006;Aldaoud et al., 2011).

Chaetomella(Sphaeropsidaceae)is a fungus distributed worldwide that can infect numerous plant species,such as Pennisetum sp.(Sydow et al., 1916),Cycas revoluta,Ficus bengalensis,Bambusa sp.(Ramchandre et al., 1965),Rosa rugosa (Margorie,1930),sterile oak(DiCosmo et al., 1980),Cuphea spp.(Singh et al., 1999), and Eucalyptus grandis (Pérez-Vera et al., 2005).In addition,Chaetomella raphigera is an endophytic fungus that can produce anticancer drugs(Gangadevi et al., 2009).In China,a new leaf spot disease has been reported to affect S.trifasciata and constrain its growth(Li et al., 2013).We identified the pathogen as Chaetomella sp.using morphological and molecular methods(Li et al., 2013).The new leaf spot disease should be biologically characterized to establish a control method.This study aimed to control the disease by evaluating the effects of environmental factors and susceptibility of various plant species to pathogen causing S.trifasciata leaf spot disease.

A fungal culture(HPL06)was isolated from diseased leaf samples collected from S.trifasciata in Luoyang City,Henan Province,in 2011.The isolate was incubated on potato dextrose agar(PDA: 200 g of potato,20 g of glucose, and 15 g of agar in 1 000 mL of water;pH 7.0)plates.

To determine the effect of temperature on fungal growth,we placed 5 mm mycelial discs in the middle of a Petri dish containing PDA.These discs were removed from five-day-old colonies cultured on PDA plates.The Petri dish was then incubated at temperatures ranging from 5 ℃ to 40 ℃ at 5 ℃ intervals for 3 d(triplicates per temperature).Colony diameters were determined using the cross-measurement(CM)method.Triplicate measurements were averaged to obtain colony diameters.

To investigate the effect of pH on fungal growth,we adjusted the pH of PDA to various levels(pH 4-11)at intervals of 1 unit by adding an appropriate amount of 1 mol·L^-1 HCl or NaOH solution.We obtained 5 mm mycelial discs from five-day-old colonies cultured on PDA plates.These discs were inoculated onto the center of new PDA plates with different pH levels(triplicates per pH level).Colony diameters were measured three times using the CM method and then averaged.

To evaluate the effect of light environment on fungal growth,we transferred 5 mm mycelial discs onto the center of new PDA plates.These discs were removed from a five-day-old colony cultured on PDA plates.The Petri dish was placed in a chamber with an illuminating lamp at 28 ℃ at a distance of 20 cm between the lamp and dish.Four light environments were used to assess the influence of cultural conditions on fungal growth.The conditions of these light environments were as follows:1)alternating cycles of 12 h of fluorescent light(50-60 klx·m^-2 light intensity)/12 h darkness,2)natural light,3)continuous irradiation with fluorescent light(50-60 klx·m^-2 light intensity), and 4)complete darkness.Each treatment was performed in triplicate.The average of three replicates was used to determine colony diameters using the CM method.

To assess the effect of nitrogen and carbon sources on fungal growth,we inoculated 5 mm mycelial discs onto the centers of different media.These discs were obtained from five-day-old colonies cultured on PDA plates.In PDA,dextrose was replaced by sucrose,fructose,maltose, and lactose as carbon sources.Mycelial discs were placed on PDA medium as contrast.The total carbon content of these carbon sources was equal.In Richard medium(10 g of KNO₃,5 g of KH₂PO₄,2.5 g of MgSO₄,0.02 g of FeCl₃,30 g of sucrose, and 15 g of agar in 1 000 mL of water),potassium nitrate was replaced by ammonium sulfate,glutamic acid,asparagine, and ammonium chloride as nitrogen sources.Mycelial discs were placed on Richard and PDA media as contrast.The total nitrogen content of these nitrogen sources was equal.Each treatment was performed in triplicate.The average of triplicate measurements was used to determine colony diameters using the CM method.The isolates were incubated at 28 ℃ for 3 d under different pH values,light environment, and nitrogen sources, and at 28 ℃ for 5 d under different carbon sources.

The pathogenicity of the isolate was tested among 62 plant species covering 23 families.All test plants were collected from Luoyang.All fully developed leaves from the test plants collected from Luoyang were sterilized with 75% ethanol, and washed three times with sterilized distilled water.Fresh wounds were performed with a sterile needle on healthy leaves.Two methods were used for inoculation.1)A 5 mm mycelial disc cut from the margin of a five-day-old colony cultured on a PDA plate was placed on each pin-wounded leaf to ensure that the mycelium was in contact with the wound.Non-colonized PDA discs were placed on pin-wounded leaves as the control treatment.Eight leaves of one plant were inoculated.2)The isolate was grown on PDA for 5 d and then suspended in sterile distilled water to produce a suspension with a final concentration of 1×10⁵ spores·mL^-1.The isolate was spray-inoculated with a spore suspension on three leaves of one plant.Sterile distilled water was used as a negative control.The inoculated leaves were stored in a moist chamber and examined daily for symptom development.

The temperature for vegetative growth of the isolate ranged from 15 ℃ to 35 ℃, and the optimal temperature was 25-30 ℃(Tab.1).The pH for vegetative growth of the isolate ranged from 4 to 11, and the optimal pH was 4(Tab.2)The fungus could grow in four light environments,but the colony diameters of the isolate subjected to continuously irradiated fluorescent light were larger than those under the other light conditions(Tab.3).Chaetomella sp.grew well on media containing five carbon sources, and dextrose was the optimal carbon source(Tab.4).Moreover,Chaetomella sp.grew well on media comprising potassium nitrate,ammonium sulfate,glutamic acid,asparagine, and ammonium chloride as nitrogen sources(Tab.5).

Tab.1 Effect of temperature on mycelium growth

Tab.1 Effect of temperature on mycelium growth Temperature/℃ Colony diameter/mm 5 5.0 f 10 5.0 f 15 12.1 e 20 32.4 c 25 38.6 b 30 43.2 a 35 27.3 d 40 5.0 f

Tab.2 Effect of pH on mycelium growth

Tab.2 Effect of pH on mycelium growth pH Colony diameter/mm 4 81.1 a 5 77.1 b 6 56.2 c 7 32.2 e 8 36.8 d 9 27.0 f 10 25.2 f 11 13.0 g

Tab.3 Effect of light on mycelium growth

Tab.3 Effect of light on mycelium growth Light environment Colony diameter/mm 12 h of fluorescent light/12 h of darkness 35.2 b Natural light 34.6 b 24 h of fluorescent light 39.7 a 24 h of darkness 33.2 b

Tab.4 Effect of carbon sources on vegetative growth

Tab.4 Effect of carbon sources on vegetative growth Carbon source Colony diameter/mm Sucrose 56.0 d Lactose 58.4 cd Glucose 81.1 a Maltose 64.9 bc Fructose 74.1 ab

Tab.5 Effect of nitrogen sources on vegetative growth^①

Tab.5 Effect of nitrogen sources on vegetative growth① Nitrogensource Colony diameter/mm Asparagine 12.9 b Ammonium chloride 8.8 d Potassiumnitrate 8.3 de Ammonium sulfate 10.7 c Glutamic acid 7.1 d Control (PDA) 32.2 a ① Values are means of triplicate measurements. Means followed by similar letters are not significantly different.

Among the 62 plant species tested from 23 families,46 species covering 20 families were found to be susceptible to Chaetomella sp.via inoculation with mycelial discs(Fig. 1 and Tab.3).A total of 30 species covering 12 families were also determined to be susceptible to Chaetomella sp.via inoculation with conidial suspension (Tab.6).

	Fig. 1 Symptoms caused by Chaetomella sp． in selected inoculated plants a. Prunus serrulata; b. Eriobotrya japonica; c. Nandina domestica; d. Syringa oblata; e. Osmanthus fragrans; f. Distylium chinense．

Tab.6 Susceptibility of test plants to Chaetomella sp. inoculation^①

Tab.6 Susceptibility of test plants to Chaetomella sp. inoculation① No. Family Scientific name Days required for visible symptoms (method of inoculation)/d Treated with conidial suspension Treated with mycelial disc 1 Rosaceae Photinia frasery 6-7 6-7 2 Rosa chinensis 10-11 3-4 3 Eriobotrya japonica 8-9 5-6 4 Kerria japonica NT NT 5 Prunus serrulata 12-13 6-7 6 Prunus cerasifera 3-7 7-10 7 Spiraea salicifolia 11-12 4-5 8 Leguminosae Cercis chinensis 5-6 5-6 9 Wisteria sinensis 6-7 5-6 10 Dolichos lablab 8-9 5-6 11 Trifolium repens 8-9 3-4 Serial number Family Scientific name Days required for visible symptoms (method of inoculation)/d Treated with conidial suspension Treated with mycelial disc 12 Medicago falcata 6-7 3-4 13 Berberidaceae Nandina domestica 6-7 3-4 14 Berberis thunbergii 6-7 3-4 15 Berberis wangii 9-10 3-4 16 Mahonia fortunei 11-17 4-5 17 Asteraceae Dendranthema grandiflorum NT NT 18 Dahlia pinnata NT NT 19 Tagetes erecta NT NT 20 Helianthus annuus NT NT 21 Magnoliaceae Magnolia grandiflora NT 3-4 22 Oleaceae Osmanthus fragrans 7-10 3-7 23 Ligustrun lucidum 3-7 3-7 24 Ligustrun quihoui 3-7 3-7 25 Syringa oblata 3-4 2-3 26 Jasminum nudiflorum 3-4 2-3 27 Liliaceae Ophiopogon japonicus NT 3-7 28 Chlorophytum comosum NT NT 29 Lilium casablanca 7-9 5-6 30 Solanaceae Capsicum annuum NT NT 31 Lycopersicon esculentum NT NT 32 Capsicum frutescens NT NT 33 Nicotiana tabacum NT NT 34 Lycium barbarum NT NT 35 Salicaceae Salix babylonica 7-8 4-5 36 Meliaceae Melia azedarach 3-4 2-3 37 Toona sinensis 3-4 2-3 38 Hamamelidaceae Distylium chinense 7-10 7-8 39 Buxaceae Buxus sinica NT 10-12 40 Buxus bodinieri NT 11-12 41 Bignoniaceae Radermachera sinica NT 8-10 42 Gramineae Zea mays NT 8-10 43 Phyllostachys heterocycla NT 8-10 44 Papilionaceae Robinia pseudoacacia 8-10 3-7 45 Sophora japonica 3-7 3-7 46 Zephyranthes grandiflora NT NT 47 Amaryllidaceae Agave sisalana NT 11-13 48 Dracaena marginata NT NT 49 Narcissus tazetta var. chinensis NT 3-7 50 Clivia miniata NT 3-7 51 Dracaena sanderiana NT 3-7 52 Lamiaceae Salvia splendens 8-10 3-7 53 Lavandula angustifolia 7-10 3-7 54 Mentha haplocalyx NT 3-7 55 Ranunculaceae Paeonia suffruticosa 2-3 2-3 56 Paeonia lactiflora NT NT 57 Calycanthaceae Chimonanthus praecox NT 3-7 58 Pittosporaceae Pittosporum tobira NT 9-11 59 Araceae Philodendron congo NT 2-3 60 Anthurium andraeanum NT NT 61 Lauraceae Cinnamomum camphora NT 10-12 62 Oxalidaceae Oxalis corniculata NT NT ① NT denotes plants without visible symptomsat 13 d after inoculation.

Some species possess an ethnopharmacological background;in particular,S.trifasciata grown in south Africa and tropical America is used for the treatment of inflammatory conditions, and marketed as a crude drug in the market to treat victims of snakebite(Morton,1981).S.trifasciata is widely grown as a potted ornamental plant in China because it can absorb toxins(Cao et al., 2009).It also demonstrates strong ability to adapt to the environment.The new leaf spot disease caused by Chaetomella sp.affects the health and ornamental value of S.trifasciata.

Chaetomella sp.widely exists in nature, and can cause diseases in many plants.The host range experiment demonstrated that the isolate of Chaetomella sp.from S.trifasciata could infect plants from 23 families(Tab.6).The number of newly discovered plants susceptible to Chaetomella sp.comprised 74.19% of the total number of plants tested(Tab.6).We speculated that a large number of plants susceptible to Chaetomella sp.may exist in nature.Such plants may be considered as potential hosts of the pathogen.Chaetomella sp.may infect potential hosts if these plants are commercially cultivated on a large scale under conditions conducive to disease development.On the other hand ,plants not susceptible to Chaetomella sp.might be due to growth suppression of the pathogen by unknown antifungal substance.The non-host plants might be considered as promising sources for screening of botanical fungicide(s)against Chaetomella sp.

The effects of illumination,temperature,pH,carbon source levels, and nitrogen source levels on the vegetative growth of Chaetomella sp.were also characterized(Tab.1-5).The isolate could exist in various conditions and adapt to various environments.Further field studies on the occurrence of the new Sansevieria leaf spot disease are needed to establish a science-based disease management strategy.Such studies are important because Chaetomella sp.is a new causal organism of Sansevieria leaf spots and the host range of the pathogen has increased.