BREEDING, , ROOTSTOCKS, & GERMPLASM RESOURCES

HORTSCIENCE 38(1):75–76. 2003. roridum isolate 96-27. Two more Myrothe- cium isolates (98-125, 00-7) were tested on selected accessions (Ta ble 1). This Screening for Re sis tance to was done to confi rm that resistance observed in the fi rst three tests with isolate 96-27 were Myrothecium Leaf Spot Among related to horizontal resis tance in the cultivars and species of Syngonium tested rath er than Syngonium Species and Cultivars a reaction to a specifi c race or isolate of M. roridum. The three isolates (96-27, 98-125, and D.J. Norman1, R.J. Henny2, J.M.F. Yuen1, and T.A. Mellich2 00-7) were collected from Syngonium University of , Institute of Food and Agricultural Sciences, at different geographically located farms in Mid-Florida Research and Education Center, 2725 Binion Road, Apopka, Florida and were obtained in 1996, 1998, and 2000, respectively. FL 32703-8504 For inoculum production, M. roridum Additional index words. , ar row head , foliage , fungus, disease resis tance, isolates were grown on potato dex trose agar , plant breeding medium (PDA) at 25 ± 1 °C under cool-white fl uo res cent lights (9.4 µmol·m–2·s–1) on a Abstract. Commercially grown cultivars of Syngonium (Araceae) are very susceptible to 12-h day/night cycle. Fun gal cultures were Myrothecium leaf spot (incited by Myrothecium roridum Tode ex Fr.). There fore, cul ti - in cu bat ed for 2 to 3 weeks and spores were va tion of Syngonium requires rigor ous sanitation and frequent applications of fungicides har vest ed from PDA plates by fl ooding the for disease control. The goal of this research was to identify species and noncultivated ac- plates with sterile distilled water (SDW) and cessions of Syngonium re sis tant to Myrothecium leaf spot. Five commer cial cultivars and scraping with a rubber spatula. Before inoc u- 30 accessions, compris ing 16 different Syngonium species, were screened for resistance to la tions, spore con cen tra tions were ad just ed in M. roridum. All fi ve commer cial cultivars were susceptible to M. roridum. However, seven SDW with the aid of a hema cy tom e ter to 1 species (S. neglectum, S. wendlandii, S. dodsonianum, S. erythrophyllum, S. chiapense, S. × 106 conidia/mL. For inoculations, the two dodsonianum, and S. angustatum) showed the highest resistance, as did two noncultivated newest expanded leaves of each plant were accessions of S. podophyllum. The information on disease resis tance for these species and wound ed using a wood slat imbedded with accessions will be useful in future breeding work. three insect pins 2 cm apart, making a total of six wounds per plant. Spore suspen sions The genetic diversity of commercially- movement. Spread of this patho gen in a nursery were applied to leaves surfaces until runoff grown cultivars of Syngonium is very nar- can be very rapid, often resulting in extensive using a hand sprayer. High relative humidity row, with most cultivars originating from losses. In some instanc es, disposal of entire ≈100% (condu cive to infection) was provided a single clone of Syngonium podophyllum crops of young plants may be required. by placing plants inside clear polyeth yl ene bags Schott. (‘White Butterflyʼ). While many There is no published information on for 24 h. Noninoculated control plants were phenotypic differences (e.g., foliage color, the presence of genetic resistance to Myro- wound ed, sprayed with SDW, and also placed plant size, growth rate, growth habit) exist thecium leaf spot in Syngonium cultivars or in plastic bags for 24 h. Re-iso lations from between cul ti vars and have been characterized species. Such information could greatly aid in repre sen ta tive symptomatic plants in each (Henley and Robinson, 1993), no information im prov ing this important ornamental foliage experiment were made to verify presence of exists on potential genetic sources for disease plant genus. Therefore the following study was the causal disease agent. re sis tance. con duct ed to screen Syngonium species and After 7 d of incubation, a slight water- All ornamental Araceae taxa grown as cul ti vars for resistance to M. roridum. soaking was observed surround ing wounds on tropical foliage plants are susceptible to My- leaves of susceptible plants. Dur ing the next rothecium leaf spot, especially Dief fenbachia, Materials and Methods 7 d, these water-soaked lesions increased to Spathiphyllum, and Syngonium (Alfi eri et al., a diameter of ≈15 mm. By day 18, infected 1994). Of all the ornamental tropical foliage Five commercially grown Syngonium lesions had begun to dry and sporodochia plants, Syngonium is con sid ered to be one of cultivars were selected for this study as well were forming. Resis tance was documented the most susceptible taxa to Myrothecium leaf as 30 other accessions that includ ed 16 spe cies on the 18th day, by counting the total number spot (Chase, 1987). (Table 1). Stock plants were grown in a shaded of wounds on each plant exhib it ing symptoms The causal agent of leaf spot, M. roridum, green house with a max i mum ir ra di ance of 125 of M. roridum in fec tion. Data were log trans- –2 –1 is an opportunistic fungal pathogen usually in- µmol·m ·s under natural photo pe ri od and a formed (1 + log10), an a lyzed using analysis of fecting tissue-cultured plantlets or young plants temperature range of 15 to 34 °C. Plants were vari ance (ANOVA), and means were sep a rat ed during propagation and estab lish ment. Plants grown 1.6-L plastic pots con tain ing a sub strate by Tukeyʼs least sig nifi cant difference (LSD). are especially susceptible if damaged by mis- of Vergro Contain er Mix A (Verlite Co., Tampa, In addition the fol low ing rating scale was used handling, improper fer til i za tion, or pesticide Fla.) amended with Osmocote 17N–2.6P–10K to help cate go rize levels of resis tance: 0 to <2 applications. Myrothecium roridum in fec tions plus minors (The Scotts Co., Marysville, Ohio) for resistant, 2 to 3 for mod er ate ly resistant, may also occur at petiole junctions, causing at a rate of 700 kg/100 m2 per year N. Plants were and >3 sus cep ti ble. Each in oc u la tion point lateral petiole and shoot death. When leaves rooted under intermittent mist in 0.5-L pots in (wound) was rated separately. become infected, circular lesions devel op on the same medium. Cut tings were root ed with in leaves and dark black spores (sporodochia) 4 weeks, after which they were grown under the Results and Discussion form in concentric rings on infect ed tissue. same envi ron men tal and nutri tion al condi tions Thousands of spores are con tained within each de scribed pre vi ous ly for stock plants. Among the 35 accessions that were tested sporodochium. These spore structures read- Experiments were conducted on 3-month- with isolate 96-27, 10 averaged <2 infected ily dissolve in water and spores are spread by old plants using a randomized com plete-block spots and were categorized as resis tant. Of splashing irrigation, worker activ i ty, and air design (10 blocks) with one rep li cate of each these 10, three accessions were highly re- or accession per block. An eleventh sistant and developed <1 infected spot per block containing noninoculated control plants plant (Table 1). The three accessions with the Received for publication 23 July 2001. Accept ed of each cultivar and accession was isolated lowest disease rating scores were S. neglectum, for pub li ca tion 10 June 2002. Florida Ag ri cul tur al at one end of the bench to mini mize the pos- S. wendlandii, and S. dodsonianum, while S. Exper i ment Station Journal Series No. R-08612. sibil i ty of disease spread from inoc u lat ed erythrophyllum, S. chiapense, S. angustatum, 1Dept. of Plant Pathology. plants. The experiment was con duct ed three and S. macrophyllum as well as two ac ces sions 2Dept. of Environmental Horticulture. times from July through Sept. 1999 using M. of S. podophyllum were mod er ate ly resistant.

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Table 1. Resistance levels of 35 cultivars and ac ces sions of Syngonium to Myrothecium leaf spot. species. Syngonium podo phyllum S81483 Country Dis ease rating for isolatez could be especially valuable in breeding Cultivar Sourcey of origin 96–27 98–125 00–7 since there is less chance that interspecifi c S. macrophyllum Engl. (S36339) MO Cos ta Rica 5.4 q ------crossing barriers will be encoun tered. In ad- S. podophyllum Schott ‘Holly Mʼ AS Un known 4.7 p–q 4.5 e 3.4 f dition, induction of fl ower ing with gibberellic S. podophyllum Schott ‘White Butterfl yʼ AS Unknown 4.5 o–q 3.6 e 2.7 d–f acid has already been documented with this S. podophyllum Schott ‘Pink Allusionʼ AS Unknown 4.2 n–q 4.0 c 3.0 e–f species (Henny et al., 1999). S. sp. (unknown) (S71736) MO Un known 4.03 m–q ------Results from this study indicate that S. sp. (unknown) (S71734) MO Un known 3.8 l–q ------suf fi cient genetic diversity exists among S. sp. (unknown) MO Un known 3.7 k–q ------S. sp. (unknown) (S78727) MO Cos ta Rica 3.6 j–q ------Syngonium accessions to produce hybrids S. neglectum Schott (S45243) MO Mex i co 3.6 i–q 2.8 d --- resistant to M. roridum. It is important when S. sp. (unknown) (S69814) MO Un known 3.3 h–p ------testing for re sis tance to incorporate pathogen S. podophyllum Schott ‘Cream Supremeʼ AS Unknown 3.2 h–p 3.7 e 3.2 f isolates from different geographical lo ca tions. S. yurimaguense Engl. MS Peru 2.9 g–p ------This pathosystem approach increases the S. podophyllum Schott (S49759) MO Pan a ma 2.7 g–p ------like li hood that genetic variation in patho gen S. sp. (unknown) (S78727#2) MO Cos ta Rica 2.7 g–o ------isolates dif fer ing in virulence and race are S. podophyllum Schott ‘Regina Redʼ AS Unknown 2.7 f–o 3.0 e–d 2.6 d–f incorporated into the study. If this is not done S. hastiferum Croat (S79195) MO Cos ta Rica 2.6 e–n 0.9 c --- one may be testing for vertical re sis tance (oli- S. rayii Croat & Grayum MS Un known 2.6 e–m 2.3 a–c 1.1 a–b S. armigerum Standley & L.O. Williams MS Unknown 2.5 e–m ------gogenic) to a specifi c isolate or race of the S. podophyllum Schott (S53892) MO Un known 2.4 e–m ------pathogen. Va ri et ies with vertical resis tance S. podophyllum Schott (S18189) MO Hon du ras 2.3 e–m 0.5 a–c 1.7 b–d are more likely to succumb to epi dem ics of S. wendlandii Schott (S59163) MO Cos ta Rica 2.2 d–l ------new virulent races introduced from differ- S. hoffmannii Schott (S69809) MO Cos ta Rica 2.1 d–k ------ent geographic sources. Horizontal resis tance S. auritum (L.) Schott (S5676) MO Puerto Rico 2.0 d–j 0.9 b–c --- (polygenic) to multiple races is more stable S. sagittatum G.S. Bunting (S48080) MO Mexico 2.0 d–j ------and long-term allowing for multiple cropping S. steyermarkii Croat MS Gua te ma la 2.0 d–i ------before resistance is over come. Devel op ment S. macrophyllum Engl. (S47867) MO Mex i co 1.9 d–h 0.1 a --- of Syngonium cultivars resistant to M. rori- S. podophyllum Schott (S60666) MO Un known 1.7 d–h 0.1 a–b 0.9 a–b S. angustatum Schott (S69812) MO Nic a ra gua 1.6 d–g ------dum would be of major benefi t to ornamental S. dodsonianum Croat MO Ec ua dor 1.2 d–f ------tropical foliage plant producers, particularly in S. chiapense Matuda MS Mex i co 1.2 d–e ------Florida because it is one of the top ten foliage S. erythrophyllum Birdsey ex Bunting MS Unknown 1.1 c–d ------plants in wholesale dollar value (U.S. Dept. S. podophyllum Schott (S81483) MO Ec ua dor 1.0 b–d 0.9 b–c 1.3 b–c of Agriculture, 2001). S. dodsonianum Croat (Orange) MS Ec ua dor 0.2 a–c 0.03 a --- S. wendlandii Schott OG Cos ta Rica 0.2 a–c ------S. neglectum Schott (S45336) MO Mex i co 0.03 a–b ------Literature Cited Control (SDW) 0 a 0 a 0 a zMean (n =10) number of infected wounds per plant (six was the maximum possible num ber). Numbers in Alfi eri, S.A., K.R. Langdon., J.W. Kimbrough, the same column followed by the same letter are not signifi cantly dif fer ent using Tukeyʼs least signifi cant N.E. El-Gholl, and C. Wehlburg. 1994. Bul. difference pro ce dure at P ≤ 0.5. y 14. Dis eas es and disorders of plants in Florida. AS = Agri–Starts, Apopka, Fla.; MO = Missouri Botanical Garden, St. Louis; MS = Marie–Selby Botanical Div. of Plant Indus., Gainesville, Fla. Garden, Sarasota, Fla; OG = Oglesby Plant International, Altha, Fla. Chase, A.R. 1987. Compendium of orna men tal dis eas es. APS Press, St. Paul, Minn. No infected wounds devel oped on control from 1.0 to 2.7 infected wounds per plant. Henley, R.W., and C.A. Robinson. 1993. Nephthytis plants within this study. One S. podophyllum accession (S81483) dis- cultivars to know and grow. Proc. Fla. State An average of 2.7 to 4.7 infected wounds played resistance that was not signifi cantly Hort. Soc. 106:343–347. per plant were observed on the fi ve com mer cial different from the three most resistant species. Henny R.J., D.J. Norman, and M.E. Kane. 1999. S. podophyllum cultivars. Only one S. podo- S81483 was also signi fi cantly more resistant Gibberellic acid-induced fl owering of Syngon- ium podophyllum Schott ‘White But terfl y.ʼ phyl lum cultivar (‘Regina Redʼ) was moder - than the most resistant commercial cultivar HortScience 34:676–677. ate ly resistant. Among fi ve non com mer cial (S. podo phyl lum ‘Regina Redʼ) to all three M. U.S. Dept. of Agriculture. 2001. Foliage, fl ori - accessions of S. podophyllum (S49759, roridum isolates tested. These re sults indicate culture and cut greens. U.S. Dept. Agr., Stat. S53892, S18189, S60666, and S81483), the that there is a high degree of variation in dis- Serv., Agr.. Stat. Board., U.S. Govt. Printing average level of disease resis tance ranged ease response within acces sions of a single Offi ce, Wash., D.C.

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