In cross and backcross populations of Pi 292190—an accession of Cucumis metuliferus (Naud.) Mey. resistant to papaya ringspot virus (PRVS)—with a susceptible line (Acc. 2459) of the same species, resistance to thia virus was conferred by a single dominant gene. Clones of F2 and testcross plants inoculated with PRSV or watermelon mosaic virus 1 (WMV-1) reacted Identically, suggesting that the factor for resistance to PRSV is closely linked to Wmv, or may be the same factor. PRSV and WMV-1 are known to be closely related serologically. Acc. 2459 of C. , metuliferus (‘horned cucumber' or ‘jelly melon') is a valuable host for the propagation of isolates of PRS

Gonsalves, D.

Provvidenti, R.

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The Journal of Heredity 73:239-240. 1982.Resistance to papaya ringspotvirus in Cucumis metuliferusand its relationship toresistance to watermelonmosaic virus 1R. Prowldenti and D. GonsalvesABSTRACT: In cross and backcross populations of PI292190—an accession of Cucumis metuliferus (Naud.)Mey. resistant to papaya ringspot virus (PRVS)—with asusceptible line (Ace. 2459) of the same species, re-sistance to this virus was conferred by a single dominantgene. Clones of Fj and testcross plants Inoculated withPRSV or watermelon mosaic virus 1 (WMV-1) reactedidentically, suggesting that the factor for resistance toPRSV Is closely linked to Wmv, or may be the samefactor. PRSV and WMV-1 are known to be closely re-lated serotogically. Ace. 2459 of C. metuliferus (homedcucumber' or 'jelly melon') is a valuable host for thepropagation of Isolates of PRSV.PAPAYA RINGSPOT VIRUS (PRVS) occurscommonly wherever papaya {Carica papayaL.) is cultivated8. This potyvirus is transmittedefficiently by several species of aphids4 andusually spreads rapidly with destructiveconsequences3-5-610-12-13. PRSV also is able toinfect several cucurbit species and someisolates incite symptoms resembling thosecaused by watermelon mosaic virus 1(WMV-1). Although a close serological rela-tionship between PRSV and WMV-1 hasbeen demonstrated2-9, WMV-1 does not infectpapaya.Recently, we found that genotypes of Cu-cumis metuii/erus (Naud.) Mey., C. meio L.,C. sotivus L., Lagenaria siceraria (Mol.)Standl., and Cucurbila ecuadorensis Cuttlerand Whitaker, which are resistant to WMV-1,also are resistant to PRVS isolates from Ha-waii and Florida (unpublished data). Previ-ously, Provvidenti and Robinson7 reportedthat in C. metuliferus (commonly known asthe 'horned cucumber' or 'jelly melon') resis-tance to WMV-1 is governed by a singledominant gene (Wmv). The purpose of thisinvestigation was to elucidate the mode ofinheritance of resistance to PRSV in thisspecies and to determine whether the factorsconferring resistance to PRSV and WMV-1are linked.Materials and MethodsThe genetic background of the C. metulif-erus germplasm utilized in this study wasThe authors arc members of the Department ofPlant Pathology, New York State Agricultural Ex-periment Station, Cornell University, Geneva, NewYork 14456.© 1982, American Genetic Association.similar to that previously used to determinethe inheritance of resistance to WMV-17.Plants of Ace. 2459, susceptible to PRSV andWMV-1, were crossed with those of PI 292190,a line resistant to both viruses. Uniformity ingermination was achieved by placing seed onmoist blotters in plastic boxes, which wereinitially incubated at 5°C for 3-5 days andthen to 30°C. Plants of F,, F2, and those of re-ciprocal backcross populations were me-chanically inoculated when they had reachedthe two-leaf stage. To assure infection in allthe susceptible genotypes, plants werereinoculated at the four-leaf stage. Inoculumwas derived from Cucurbita pepo L. cv. Sen-eca Zucchini, or plants of Ace. 2459 system-ically infected with the Hawaiian isolatePRSV-HA2. The same hosts were used assources of inoculum for isolate NY69-49 ofWMV-17. Stock cultures of PRSV-HA and twoother isolates PRSV-HB (Hawaii) andPRSV-Fla (Florida) were maintained in apapaya cv. Solo.Clones of F2 and testcross plants were usedto determine linkage between PRSV andWMV-1 resistance factors. Thus, each plantof these populations was separately testedwith PRSV or WMV-1.Enzyme-linked immunosorbent assay(ELISA) was employed in determining infec-tivity of PRSV or WMV-1 in inoculatedplants2. An antiserum to PRSV-HA had beenprepared by Gonsalves and Ishii2, and that toWMV-1 was supplied by D. E. Purcifull(University of Florida). The work was con-ducted in an insect-free greenhouse main-tained at 27°C.ResultsPlants of PI 292190 inoculated withPRSV-HA were free of local and systemicinfection. Those of Ace. 2459, after an incu-bation period of 7-10 days, developed veinalchlorosis, mottle, reduction of leaf size andshort internodes. Severely affected plantstended to wilt and died prematurely. Plants ofAce. 2459 responded with a very prominentmosaic to infection caused by PRSV-HB, andwith a mild or moderate mottle to PRSV-Fla.Conversely, both PRSV-HB and PRSV-Flaincited only a few systemic chlorotic spots onSeneca Zucchini squash and after a longerincubation period (15-20 days). IsolatePRSV-HA caused more prominent symptomsin this same host and the incubation periodwas 12-15 days.Plants of F] behaved as the resistant parentand no virus infection was detected in inoc-ulated and uninoculated leaves. Plants of theF2 generation segregated in a ratio of 3 resis-tant to 1 susceptible. Resistant plants were freeof local and systemic infection, whereas sus-ceptible plants exhibited symptoms identicalto that of the susceptible parent. The progenyof the backcross to the resistant parent was allresistant. Plants of the testcross segregated ina ratio of nearly 1 resistant to 1 susceptible.From the data presented in Table I, it is evi-dent that resistance is conferred by a single,completely dominant gene.The segregation of clones of F2 and testcrosspopulations, which had been inoculated withPRSV or WMV-1, is reported in Table II.Plants that were resistant to PRSV also wereresistant to WMV-1; conversely, those thatwere susceptible to PRSV also were suscep-tible to WMV-1. The segregation pattern forboth populations approximated the expectedratios.DiscussionThis study has revealed that resistance toPRSV in C. metuJiferus is monogenicallydominant. Data from clones of F2 and testcrossplants indicate a close linkage between tljefactor for resistance to PRSV and Wmv, thegene for resistance to WMV-17. However, nogene symbol has been assigned to the factorfor PRVS resistance because it is possible thatWmv may be responsible for the resistance toboth viruses. PRSV and WMV-1 share anumber of common features: 1) they belong tothe potyvirus group8; 2) they are very closelyrelated serologically2-9; 3) they share a com-mon, although not identical host range913; and4) in several species, plants resistant toTable I. Segregation in F1? F2, and reciprocal backcross populations of Cucumis metuliferusfor resistance to papaya ringspot virusPopulationsPI 292190Ace. 2459(Ace. 2459 X PI292190) F,(Ace. 2459 X PI292190) F2(Ace. 2459 X PI292190) F, X PI292190(Ace. 2459 X PI29219) F, X Ace.2459resistant7504319413571No. plantssusceptible070068062Expectedratio3:11:1Goodness-of-fit(P)0.720.45Notes May / June 1982 239Table II. Reaction of clones of F2 and testcross populations of Cucumls metullferus to papayaringspot virus (PRSV) and watermelon mosaic virus 1 (WMV-1)Goodness-No. plants Expected of-fitPopulations Virus resistant* susceptible* ratio (P)(Ace. 2459 X292190) F2(Ace. 2459 X292190) FiAce. 2459PIPIXPRSVWMV-1PRSVWMV-163633939232334343:11:10.690.57Plants resistant to PRSV also were resistant to WMV-1Plants susceptible to PRSV-also were susceptible to WMV-1WMV-1 also are resistant to PRSV. A fewyears ago, Schroeder and Prowidenti11demonstrated that in Pisum sativum L. resis-tance to bean yellow mosaic virus (BYMV)and to watermelon mosaic virus 2 (WMV-2) isconditioned by the same gene [mo\. BothBYMV and WMV-2 are potyviruses, havecommon hosts, and are serologically related1.Further work on the comparison of RNA nu-cleotide sequence homologies of PRSV andWMV-1 will eventually determine howclosely related these two viruses are, andwhether they should be considered strains ofthe same virus.Wang et al.13 reported that PI 292190 wassusceptible to an isolate of PRSV from Tai-wan. The difference in reaction could be at-tributed to a different strain of the virus,mixture of viruses, or a mislabeled seed lot.The sensitivity of C. MetuJiferus Ace. 2459 toinfection with isolates of PRVS, makes this avaluable line for propagation of this virus.References1. BRANDES. I Identifizierung von gestrecktenpflanzenpathologenen vircn auf morpholog-ischcr Grundlagc. Mitteilungen Bio). Bun-desanstult Land Forstivirtschaften 100:1-130.1964.2. GONSALVES, D. and M. ISHII. Purification andserology of papaya ringspot virus Phytopatho-logy 70:1028-1032.1980.3. ISHII, M. Observations on the spread of papayaringspot virus in Hawaii. PI. Di's. Reptr. 56:331-337. 1972.4. (ENSEN, D. D. Papaya ringspot virus and its in-sect vector relationships. Phytopathology 39:212-220.1949.5. LASTRA, R. and E. QUINTERO. Papaya apicalnecrosis, a new disease associated with a rhab-dovirus. PJ. Dis. Reptr. 65:439-440.1981.6. LIMA, |. A. A. and M. N. S. GOMES Identifica-cao do 'papaya ringspot virus' em Fortaleza,Ceara. Fitossanidade 1:56-59.1975.7. PROWIDENTI, R. and R. W. ROBINSON. Inher-itance of resistance to watermelon mosaic virus1 in Cucumis metullferus. /. Hered. 68.56-57.1977.8. PURCIFULL, D. E. Papaya ringspot virus, no. 84.In Description of Plant Viruses. Comm. Mycol.Inst. Assoc. Appl. Biol., Kew, Surrey, England.1972.9. and E. HlEBERT. Serological distinctionof watermelon mosaic virus isolates. Phyto-pathology 69:112-116.197910. SANCHEZ do LUQUE, C. and G. MARTINEZLOPEZ. Reconocimiento del virus de la manchaanular de la papaya (Carica papaya L.) en Co-lombia. Rev/stu 1CA 11:205-220. 1976.11. SCHROEDER, W. T. and R. PROWIDENTI. Acommon gene for resistance to bean yellowmosaic virus and watermolon mosaic virus 2. inPisum sativum. Phytopathology 61:846-848.1971.12. SUREKA, S. K., K. MATHUR, and D. D. SHUKLA.Vims diseases of Papaya {Carica papaya) inUdaipur. Indian J. Mycol. PI. Path. 7:115-121.1977.13. WANG, H. L, C. C. WANG, R. | . CHIU, and M.SUN. A preliminary study of papaya ringspotvirus in Taiwan. PI. Protect. Bull. 20:133-140.1978.The Journal of Heredity 73:240-242. 1982.Endosperm balance numbersamong New Guinea-IndonesianImpatlens speciesToru ArlsumlABSTRACT: The results ot crosses among various plantaccessions of Impatlens species from the NewGuinea-Indonesian area support the endosperm balancenumber (EBN) hypothesis. With few exceptions, crossesamong plants with equal EBN's succeeded and thosebetween unequal EBN's failed. Existing cross data In-dicate that the present collection of New Guinea-Indo-nesian Impatlens is comprised of standard (2EBN) andtetraploid (4EBN) species.THE ENDOSPERM BALANCE NUMBER (EBN)hypothesis was proposed by Johnston et al.9 toexplain endosperm development in interploidy-intraspecific and interspecific crosses. To test thishypothesis, a species to be used as a standard isarbitrarily assigned an EBN. Other species areassigned EBN's on the basis of their crossingbehavior with the standard species. According tothis hypothesis it is the EBN's that determine theeffective ploidy in the endosperm, and for suc-cessful endosperm development the EBN's mustbe in a maternahpaternal ratio of 2:1. Johnstonand Hanneman10 used results of crosses amongtuber-bearing Solarium species to support theEBN hypothesis. The authors9-10 noted that otherinteractions also are important in determiningendosperm development and that the 2:1 EBNratio was a necessary but not sufficient conditionfor a successful cross.The purpose of this study was to test the va-lidity and predictive value of the EBN hypothesisusing results of breeding experiments with Im-patiens species from the New Guinea-Indonesianarea. This group seemed to be good material forthese tests because: 1) it was comprised of diversespecies showing cytological as well as morpho-logical differences; 2) the breeding behavior ofmost of the species and the colchicine-inducedpolyploids of their hybrids was known; and 3)some new plant accessions were available fortesting the predictive value of the EBN's.Materials and MethodsThe species and hybrids used in the presenttests and some that had been studied in the pastare listed and described in Table I. The EBN's ofthese species and the references from which theEBN determinations were obtained are alsolisted in Table 1 with the eight new species listedat the end. Seven of these species were from theNew Guinea-Indonesian area. One species, M28The author is research plant geneticist with theFlorist and Nursery Crops Laboratory, HorticulturalScience Institute, USDA, ARS, Beltsvillc, MD 20705.He thanks Dr. Gilbert McCollum for his helpful sug-gestions and for reviewing the manuscript.240 The Journal of Heredity Notes

Resistance to papaya ringspot virus in Cucumis metuliferus and its relationship to resistance to watermelon mosaic virus 1

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