Morphological and Disease Resistance Evaluation in
M.L. Gómez-Guillamón and E. Moriones
Estación Experimental "La Mayora", CSIC, 29750-Algarrobo, Málaga, Spain
M. Luis-Arteaga and J.M. Alvarez
SIA-DGA. Apdo. 177, 58080-Zaragoza, Spain
J. A. Torés, A.I. López-Sesé, I. Cánovas, F. Sánchez, and R. Camero
Estación Experimental "La Mayora", CSIC, 29750-Algarrobo, Málaga, Spain
Additional index words. melon, germplasm, Sphaerotheca fuliginea , powdery mildew, race 1, race 2, cucumber mosaic virus, zucchini yellow mosaic virus, watermelon mosaic virus 2, papaya ringspot mosaic virus watermelon strain, cucurbit yellow stunting disorder virus, melon necrotic spot virus
Abstract. Forty-two accessions of Cucumis melo and its wild related species were evaluated for 18 vegetative and fruit characters and reaction to seven important melon diseases. Leaf color and leaf shape were characters difficult to measured. The use of color charts is suggested for assessing variation in color intensities observed for fruit skin color and flesh color. Little variability was observed for reaction to the seven pathogens. Accession TGR from Zimbabwe was found to possess multiple disease resistances.
This work has been financially supported by the CICYT proposals n. AGF95-0962-C03 and BIO96-1173-C03.
Melon is an important horticultural crop widely cultivated around the world. Breeding to obtain commercial hybrids of high quality and yield for different markets is getting more important every day. For many years, breeding in melon has been focused on increased fruit quality and control of reproductive characteristics (gynoecious, monoecious, androsterility) to facilitate production of hybrid seeds. Nowadays, melon breeding emphasizes fruit quality to satisfy different melon markets. Losses in quality and yield caused by different pathogens and pests are the main problems of melon worldwide. The most suitable tools for breeders to accomplish their goals are, undoubtedly, the germplasm collections.
There are important germplasm collections in different countries where the seeds are maintained in optimal conditions to retain their viability. There is, however, very little information about the horticultural features of the accessions of those collections. Germplasm collections are then undervalued and useless since their evaluation costs much time, effort and money.
Spain is an important secondary center of diversity of melon. The possibility of genetic erosion of this species in Spain is considered to be very high by the FAO (Esquinas-Alcázar and Gulick, 1983). The Spanish government, conscious of its relevance, is financing projects to evaluate its main vegetable germplasm collections (Nuez et al., 1988; Gómez-Guillamón et al., 1985, 1994). Morphological and disease resistance evaluations have been carried out every year since 1997. Here we report the evaluations of 42 accessions from the germplasm banks of the Experimental Station La Mayora-CSIC and the Agricultural Research Service-Diputación General de Aragón. Accessions were chosen to determine the existing variability for the most important characters in C. melo and wild relatives. Some of the accessions were chosen for their known responses against different pathogens in order to standardize the artificial inoculations.
Material and methods
During Spring 1988, 32 accessions of C. melo and 10 wild relatives species of Cucumis of different
origins were evaluated (Table 1). Morphological evaluation was carried out for 18 vegetative and fruit characters known to be variable in C. melo following the suggestion of Esquinas-Alcázar and Gulick (1983), although several modifications were made for the wild related species included in the evaluations. Most of the characters have high inheritance as corresponding to a primary description. The evaluations were done in a polyethylene plastic house, in a gravel type soil. Plants were irrigated and fertilized with drip irrigation following the usual commercial practices in Almeria, Spain. Each experimental plot (acces
sion) consisted of 13 plants.
Five leaf, stem, and flowers characters were evaluated (Table 2) in each plot. Any variability observed was recorded. Thirteen fruit characters were evaluated for each accession; 30 fruit per accession (Table 3). Any variability in vegetative or fruit characters was recorded.
Artificial inoculations with six viruses and one fungal pathogen (Table 4) were done as described below. Plants were maintained in an insect-proof greenhouse at 25 to 28 oC and 16/8 h day/night with supplemental light supply when needed.
Table 1. Accessions of C. melo and wild relatives evaluated.
Bank no. Name Origin or donator
C-40 Shiroubi Okayama Japan
C-41 Freeman's Cucumber Japan
C-73 C. myriocarpus (IPK,Gatersleben, Germany)
C-76 C. metuliferus (IVT, The Netherlands)
C-87 C. melo ssp. agrestis Korea
C-101 Melón de Olor Spain
C-105 TGR Zimbabwe
C-112 Escrito Spain
C-157 PI 414723 India
C-160 Korça Russia
C-167 Sudbalkan Yugoslavia
C-170 Kreta Greece
C-173 Turkestán Turkey
C-174 Enfürter Netzmelone Germany
C-178 Short Internode Cantaloupe USA
C-181 China-3 China
C-184 Adzur (C.melo ssp. melo Flexuosus Group) India
C-189 Tokyo Giant Japan
C-192 Punjab Suneri India
C-205 C. africanus (IPK, Gatersleben, Germany)
C-211 Kogane Nashi Makuwa Far East
C-243 E-C-1 Spain
C-247 Lybian Libya
C-267 WMR 29 USA
C-277 C. zeyheri (IPK, Gatersleben, Germany)
C-279 C. anguria var. longipes (IPK, Gatersleben, Germany)
C-300 CM-C-1 Spain
C-447 Cantaloupe of Westland The Netherlands
C-453 MOO 3/89 Portugal
C-457 8/85 Yugoslavia
C-588 C. dipsaceus (IVT, The Netherlands)
C-605 WI 998 USA (Peterson)
C-633 C. prophetarum (IPK, Gatersleben, Germany)
C-635 C. meeusei (IPK, Gatersleben, Germany)
C-636 C. anguria var. anguria (IPK, Gatersleben, Germany)
C-637 C. ficifolius (IPK, Gatersleben, Germany)
C-646 Amarillo Spain
C-647 T-111 Spain
C-648 PI 161375 Korea
C-652 Charentais Fom-1 France
C-730 Charentais Fom-2 France
The isolate of papaya ringspot mosaic virus watermelon strain (PRSV-W) used in these evaluations was provided by V. Lisa, Instituto de Fitovirologia Applicata, CNR, Torino, Italy. Sphaerotheca fuliginea races 1 and 2, cucumber mosaic virus (CMV), zucchini yellow mosaic virus (ZYMV), watermelon mosaic virus 2 (WMV-2), cucurbit yellow stunting disorder virus (CYSDV), and melon necrotic spot virus (MNSV) isolates are from the authors' personal collections.
Seven plants/accession were singly inoculated with CMV (isolates B.20.2-CMV and M6-
CMV ), ZYMV (isolate C16-ZYMV, pathotype 1; and C71-ZYMV, pathotype 0). WMV (isolate M116-WMV-II), or PRSV (isolate Z43-PRSV-W). Twelve plants/accession were tested against MNSV isolate M-7-85-MNSV). The reaction of each accessions to each virus was evaluated in two separate tests. In all cases, mechanical inoculation was used. Reaction (symptom expression) was evaluated visually, and if necessary confirmed by ELISA assay.
For CYSDV, Bemisia tabaci was used as the vector for the virus transmission, following the
Table 2. Vegetative characters evaluated.
Name expressionz Shape Lobes Internodes Color
WI 998 Gynoecious Orbicular Shallow Intermediate Intermediate
Korça Andromoecious Pentagonal Absent Intermediate Intermediate
Short internode Andromoecious Pentagonal Absent Very short Intermediate
E-C-1 Andromoecious Pentagonal Shallow Long Light green
MOO 3/89 Andromoecious Pentagonal Shallow Long Dark green
Melón de olor Andromoecious Pentagonal Shallow Long Dark green
China-3 Andromoecious Orbicular Intermediate Intermediate Intermediate
Enfürter Netzmelone Andromoecious Pentagonal Intermediate Intermediate Intermediate
Freeman´s Cucumber Andromoecious Pentagonal Intermediate Long Dark green
Adzur Monoecious Elongated Intermediate Long intermediate
Agrestis Andromoecious Pentagonal Deep Long Dark green
TGR Andromoecious Pentagonal Shallow Long Intermediate
Tokyo Giant Andromoecious Reniform Intermediate Intermediate Dark green
Charentais Fom-1 Andromoecious Pentagonal Shallow Long Dark green
Cantalupe of Westland Andromoecious Pentagonal Shallow Long Intermediate
Charentais Fom-2 Andromoecious Pentagonal Shallow Long Dark green
WMR 29 Andromoecious Pentagonal Absent Intermediate Dark green
8/85 Andromoecious Pentagonal Shallow Intermediate Intermediate
Amarillo Andromoecious Pentagonal Shallow Short Intermediate
Sudbalkan Andromoecious Variability Variability Variability Variability
PI 414723 Monoecious Orbicular Absent Short intermediate
CM-C-1 Andromoecious Pentagonal Shallow Intermediate Intermediate
Punjab Suneri Andromoecious orbicular Absent Long Intermediate
Kogane Nashi Andromoecious Pentagonal Shallow Intermediate Dark green
Turkestan Andromoecious Pentagonal Intermediate Short Light green
Lybian Andromoecious Pentagonal Absent Intermediate Intermediate
Kreta Andromoecious Orbicular Absent Long Intermediate
Shiroubi Okayama Andromoecious Orbicular Shallow Intermediate Dark green
Escrito Andromoecious Pentagonal Intermediate Short Intermediate
PI 161375 Andromoecious Orbicular Shallow Long Dark green
T-111 Andromoecious Pentagonal Shallow Long Intermediate
C. dipsaceus Monoecious Orbicular Absent Intermediate Intermediate
C. africanus Monoecious Pentagonal Deep Intermediate Light green
C. anguria var. anguria Monoecious pentagonal Very Deep Short Intermediate
C. ficifolius Monoecious Pentagonal Very deep Short Intermediate
C. zeyheri Monoecious Pentagonal Very deep Intermediate Intermediate
C. prophetarum Monoecious Pentagonal Very deep Short Dark green
C. myriocarpus Monoecious Pentagonal Very deep Short Dark green
C. anguria var. longipes Monoecious Pentagonal Absent Intermediate Dark green
C. metuliferus Andromoecious Pentagonal Absent Short Dark green
C. meeusei Monoecious Elongated Deep Short Intermediate
method developed by López-Sesé, (1997), using 10 plants/accession. After 40 days of their inoculation absence or presence of symptoms was recorded.
Controlled inoculations of races 1 (isolate SF-26) and 2 (isolate SF-38 A) of S. fuliginea were done by spraying the second true leaf of each plant (9 plants/accession) with a suspension of conidia in Triton X-100 (1 µL·L1) containing 40,000 conidia/mL. After 10 days, percentage of the infected leaf tissue was recorded for each plant.
Results and discussion
Vegetative characters. Leaf shape and leaf color were difficult to evaluate although the two characters were recommended by the IBPGR to characterize C. melo (Esquinas-Alcázar and Gulick, 1983). Leaf lobes, showing high variability among the accessions, were absent, shallow or intermediate in most of the C. melo cultivars, but they were deep or very deep in most of the wild accessions (Table 2). Leaves of the plants of C. anguria var
Table 3. Fruit characters evaluated.
Skin Spot Fruit Flesh Skin Skin Cork Wt Length Width
Name Shapez colory designx ribsw colorv Abscissionu texture corkingt patterns (kg) (cm) (cm) °Brix
WI 998 Glob Yellow Striped Sprfcl Orange Easy Smooth Absent Absent 2.0 17.0 14.4 9.1
Korça Elong Yellow Spotted Absent Grnsh Intrmdt Netted Intrmdt Netted 2.0 26.0 12.0 9.4
Short Internode Flat Green Spckld Intrmdt Orange Intrmdt Netted Intrmdt Netted 0.4 9.0 9.4 9.6
E-C-1 Elong Green Spckld Absent Grnsh Difficult Netted Dense Lngtdnl 1.4 25.0 10.8 8.3
MOO 3/89 Ellip Green Spckld Absent Orange Difficult Netted Intrmdt Netted 2.6 22.8 14.2 8.7
Melón de olor Ellip Green Absent Absent White Intrmdt Netted Intrmdt Netted 2.9 22.0 16.0 10.8
China-3 Glob Green Spckstrpd Absent White Easy Smooth Absent Absent 1.0 14.5 12.0 12.8
Enfürter Netzmelone Glob Yellow Spckld Absent Orange Easy Wavy Intrmdt Netted 4.8 22.0 20.0 4.8
Freeman´s Cucumber Elong Yellow Absent Absent White Difficult Smooth Absent Absent 1.8 22.5 12.1 5.5
Adzur Elong Yellow Absent Absent Grnsh Difficult Wavy Absent Absent 2.8 47.0 11.0 8.7
Agrestis Elong Lghtgrn Striped Sprfcl Green Intrmdt Smooth Absent Absent 0.6 15.0 8.0 9.3
TGR Elong Yellow Spotted Absent White Difficult Smooth Absent Absent 0.7 14.0 9.5 4.7
Tokyo Giant Elong Yellow Striped Absent Grnsh Difficult Smooth Intrmdt Netted 2.1 30.0 11.0 7.6
Charentais Fom-1 Glob Plgrn Striped Intrmdt Orange Easy Smooth Absent Absent 1.3 13.5 13.5 13.1
Cantalupe of Westland Flat Lghtyllw Striped Deep Orange Easy Netted Dense Netted 2.5 12.6 18.0 5.2
Charentais Fom-2 Flat Plgrn Striped Intrmdt Orange Easy Smooth Absent Absent 1.4 13.0 14.0 14.0
WMR 29 Ovate Yellow Spckld Sprfcl Orange Easy Netted Dense Netted 1.2 15.0 12.0 12.0
8/85 Glob Yellow Spckld Deep Orange Easy Netted Sparse Netted 2.4 18.0 17.0 7.1
Amarillo Ellip Yellow Absent Absent Grnsh Difficult Wrinkled Absent Absent 2.0 24.0 13.0 12.1
Sudbalkan Ovate Green Spckld Absent Grnsh Difficult Netted Intrmdt Netted 2.3 20.0 15.0 9.7
PI 414723 Elongate Yellow Spotted Absent Orange Easy Smooth Absent Absent 1.7 26.5 12.0 6.4
CM-C-1 Ellip White Absent Absent White Difficult Smooth Sparse Lngtdnl 1.6 22.0 13.6 12.6
Punjab Suneri Ovate White Absent Absent Orange Easy Smooth Dense Netted 0.9 13.0 11.0 11.7
Kogane Nashi Elongate Yellow Absent Sprfcl White Difficult Smooth Absent Absent 0.7 14.5 9.3 10.2
Turkestan Glob Yellow Spckld Absent White Difficult Netted Dense Netted 1.9 16.0 16.0 11.5
Lybian Ovate Yellow Spckld Absent Orange Intrmdt Smooth Dense Netted 1.4 16.0 13.0 10.7
Kreta Ovate Yellow Absent Absent White Difficult Smooth Intrmdt Lngtdnl 0.5 14.0 9.0 11.0
Shiroubi Okayama Elong White Striped Sprfcl Green Intrmdt Smooth Sparse Lngtdnl 1.8 31.0 10.0 7.6
Escrito Ovate Yellow Absent Absent Whtrng Intrmdt Smooth Intrmdt Netted 1.6 17.0 14.0 9.2
PI 161375 Prfrm Green Spotted Absent Grnrng Difficult Smooth Absent Absent 1.2 17.0 11.0 10.5
T-111 Ellip Green Spotted Absent White Difficult Smooth Sparse Lngtdnl 2.2 21.0 14.2 14.0
C. dipsaceus Ovate Lghtyllw Absent Absent White Difficult Warty Absent Absent 0.04 6.0 3.4 5.3
C. africanus Ovate Cream Striped Intrmdt Green Difficult Spiny Absent Absent 0.05 6.4 3.4 6.1
C. anguria var. anguria Ovate Lghtyllw Absent Absent White Difficult Warty Absent Absent 0.02 4.0 3.2 5.8
C. ficifolius Ovate Yellow Absent Absent White Difficult Spiny Absent Absent 0.07 6.0 4.7 4.5
C. zeyheri Ovate Yellow Striped Absent White Difficult Spiny Absent Absent 0.05 7.0 4.0 5.2
C. prophetarum Ovate Yellow Striped Absent Green Difficult Spiny Absent Absent 0.01 4.0 2.0 4.2
C. myriocarpus Glob Cream Striped Absent Green Difficult Spines Absent Absent 0.09 2.8 2.3 8.7
C. anguria var. longipes Glob Lghtgrn Absent Absent Green Difficult Shaggy Absent Absent 0.03 4 4.0 7.6
C. metuliferus Ovate Orange Spotted Absent Green Difficult Warty Absent Absent 0.3 11.0 6.4 7.5
C. meeusei Ovate Lghtyllw Absent Absent White Difficult Warty Absent Absent 0.2 9.0 6.0 5.0
zShape: glob = globular; elong = elongate; ellip = elliptical; flat = flattened; prfrm = pyriform.
ySkin color: lghtgrn = light green; lghtyllw = light yellow; plgrn = pale green.
xSpot design: spckld = speckled; spckstrpd = speckled/striped.
wFruit ribs: intrmdt = intermediate; sprfcl = superficial.
vFlesh color: grnsh = greenish; whtrng = white orange; grnrng = green orange.
uFruit abscission: intrmdt = intermediate.
tSkin corking: intrmdt = intermediate.
sCork pattern: lngtdnl = longitudinal.
longipes, C. metuliferus and C. dipsaceus have no lobes. Variability in internode length was observed. As expected, Short Internode Cantaloupe had the shortest internodes; it carries si gene (Denna, 1962, Paris et al., 1984).
All the accessions of C. melo showed andromonoecious sexual status, except PI 414723 and Adzur (C. melo ssp. melo Flexuosus Group), which are monoecious, and WI 998 which is gynoecious. Monoecious sex type was observed in the wild species, except C. metuliferus which is andromonoecious (Table 2).
Fruit characters. Fruit shape ranged from globular to elongate in C. melo (Table 3). Elliptical fruit shape was observed in some Spanish accessions as well as in the Portuguese cultivar, as demanded by their national markets. 'Escrito' had ovate fruit and E-C-1 showed elongate fruit, related to their local markets. Accessions belonging to the cantaloupe group showed globular and flattened fruit, as well as the cultivar China-3. WMR 29 had ovate fruit. Only the fruit of PI 161375 were pyriform. Elongate fruit were observed in many accessions. Although 'Kogane Nashi Makuwa' and C. melo ssp. agrestis were classified as elongate, their fruit were made it difficult characterize their shape as elongate rather than pyriform. The fruit shape classification described by Esquinas-Alcázar and Gulick (1983) should include "others" to permit description of unusual fruit shapes. Most of the wild species showed ovate fruit except C. myriocarpus and C. anguria var longipes whose fruit were globular (Table 3).
The following colors of fruit skin were easy to distinguish in the different accessions: yellow, orange, green, gray and white (Table 3). Different intensities in yellow and green colors have, however, been observed. Fruit of C. melo cvs. Charentais Fom-1 and Charentais Fom-2 had pale green skin color. Light yellow skin was observed in the fruit of C. melo cv. Cantaloupe of Westland and in the accessions of C. meeusii, C. dipsaceus and C. anguria var. anguria although it was difficult to determine if the skin color was actually light yellow or cream. The fruit of the accession of C. melo ssp. agrestis had near-gray skin, although could they could also be also classified as light green color (Table 3). The
use of color charts are recommended as a means for reducing the subjective component of assessing fruit skin color.
Secondary color of the fruit skin was absent or present in different designs (Table 3). Secondary color was yellow mainly in speckled designs of green-skinned fruit; green in spotted or striped designs of green- and yellow-skinned fruit, and white in speckled or striped designs of yellow-skinned fruit. No distinction among different color intensities was recorded.
Fruit ribs were absent in most of the evaluated accessions (Table 3). In C. melo cultigens WI 998, WMR-29, Kogane Nashi Makuwa, Shiroubi Okayama and C. melo ssp. agrestis the fruit showed superficial ribs. Short Internode Cantaloupe, Cantaloupe Fom-1 and Cantaloupe Fom-2 had fruit with intermediate ribs. Cantalupe of Westland and the Yugoslavian cultivar, 8/85 had deep ribs (Table 3). Among the wild species, only C. africanus showed fruit ribs which were intermediate.
Variability in fruit flesh color was observed in C. melo (Table 3). White, orange and green flesh colors were easily distinguished in most accessions. In some accessions, white flesh color was not so clear, and greenish flesh or white-orange flesh was recorded in some cultivars such as E-C-1, Tokyo Giant (greenish), or Escrito (white-orange) (Table 3). In Spanish accessions, different color intensities of the fruit flesh are very common, and the use of color charts makes easy the determination of this character (unpublished data).
Accessions of the cantaloupe group had an easily separated peduncle (abscission) from the fruit when ripe. This character was recorded as intermediate in seven of the accessions, easy in 10 of the accessions and difficult in the remaining C. melo accessions. None of wild related species abscised (Table 3).
The skin texture in most of the C. melo accessions was smooth, netted or wavy. Wrinkled skin was observed in 'Amarillo', a Spanish tendral type (winter melon). Spiny fruit were only observed in wild species, as C. myriocarpus, C. africanus, C. ficifolius, C. zeyheri and C. prophetarum. Presence of warts in the fruit, although of different sizes, was recorded in C. anguria var anguria, C. dipsaceus, C. meeusii and C. metuliferus. C. anguria
var longipes showed fruit described of a shaggy texture because of the length and density of the observed hair-like protuberances (Table 3).
Fruit skin corking density was observed in accessions with fruit showing netted pattern. Some of the accessions whose fruit showed netted pattern had intermediate fruit corking as MOO3/89, Melón de Olor, Escrito, Korça, Enfurter Netzmelone, Tokyo Giant and Sudbalkan. In those cultivars, netted pattern in the fruit was wider than in the cantaloupe group. The Spanish culti
vars E-C-1, CM-C-1 and T-111 showed longitudinal corking pattern, as well as the accessions Kreta and Shiroubi Okayama. Longitudinal pattern corking when sparse or intermediate is a desired quality character for Spanish green melon market (Table 3).
The average for fruit weight in C. melo was 2.0 kg. Enfurter Netzmelone produced the heavier fruit, of 4.5 kg and Short Internode Cantaloupe the lighter fruit, with an average of 400 g per fruit. Fruit in the wild species were much more lighter
Table 4. Disease resistances evaluated.
CMV ZYMV S. fuliginea
Accession M-6 B.20.2 C-16 C-71 WMV-2 PRSV-W CYSDV MNSV Race 1 Race 2
WI 998 + + + + + + + + + +
Korça + + + + + + + + + +
Short Internode + + + + + + + + +
E-C-1 + + + + + + + + +
MOO 3/89 + + + + + + + + + +
Melón de olor + + + + + + + + +
China-3 + + + + + + + + +
Enfürter Netzmelone + + + + + + + + + +
Freeman´s Cucumber + + + + + + + +
Adzur + + + + + + + + + +
Agrestis + + + + + + + + +
TGR + + + + +
Tokyo Giant + + + + + + + + +
Charentais Fom-1 + + + + + + + + + +
Cantalupo Westland + + + + + + + + + +
Charentais Fom-2 + + + + + + + + + +
WMR-29 + + + + + + + +
8/85 + + + + + + + + + +
Amarillo + + + + + + + + + +
Sudbalkan + + + + + + + + + +
PI 414723 + + + + +
CM-C-1 + + + vz + + + + +
Punjab Suneri + + + + + + + + + +
Kogane Nashi + + + + + + + + + +
Turkestan + + + + + + + + + +
Lybian + + + + + + + + + +
Kreta + + + + + + + + + +
Shiroubi Okayama + + + + + + + +
Escrito + + + + * * + + + +
PI 161375 * * + + + + +
T-111 + + + + + + + + + +
C. dipsaceus + + + + + + + +
C. africanus + + + + + +
C. anguria var. anguria + + + + + + + +
C. ficifolius + + + + + + + + +
C. zeyheri + + + + + + +
C. prophetarum + + + + + + + +
C. myriocarpus + + + + + + + + + +
C. anguria var. longipes + + + + + + + + + +
C. metuliferus + + + + + + + +
C. meeusei + + + + + + + + +
zv = variable response.
Flowers of C. africanus were also grouped in bunches, and they had a very agreeable aroma that makes this species very suitable to be used in gardens.
Disease resistance. PI 161375, Freeman's Cucumber and Shiroubi Okayama showed resistance to the CMV-isolates used (Table 4). The genetic basis of those resistances have been already studied by different authors (Karchi et al., 1975; Risser et al., 1977, Tobías and Velich, 1983). The cultivar Tokyo Giant, as well as the accession of C. melo ssp. agrestis has exhibited complete resistance to the M-6-CMV isolate (Table 4). These data suggest an isolate-specific resistance to CMV among these accessions. The existence of isolate-specific responses among a different group of melon genotypes CMV was suggested by Lecoq and Pitrat (1982).
Among the wild species, the accession of C. zeyheri tested here was previously reported to be resistant to CMV (IVT, 1988). When inoculated with M-6-CMV, plants of C. myriocarpus showed virus symptoms and virus infection in basal leaves, but virus was not detected in ELISA assay nor were any viral symptoms observed in young leaves (Table 4). Although resistance or immunity to CMV have been observed by Horváth (1993), and IVT (1988) in C. anguria var anguria, C. anguria var longipes, C. africanus and C. myriocarpus , no resistance was observed in the accessions of those species used in our tests. Differences in the virus isolates or in the accessions of those species could explain the different results.
Partial resistance to ZYMV has been observed in PI-414723 (Pitrat and Lecoq, 1984a; Pitrat et al., 1996). In preliminary experiments, PI 161375 has also shown a resistant behavior against the ZYMV isolates used in this work (Table 4). Horváth (1993) found immunity to ZYMV in PI 161375. Variability in the responses of the cultivars CM-C-1 and Escrito was observed; when plants of these cultivars were inoculated with the pathotypes 0 and 1, respectively, half of the inoculated plants showed symptoms and were positive in ELISA assay (Table 4). Plants without symptoms were transferred to the greenhouse to obtain self-pollinated seeds for further study.
No resistance to ZYMV was found in the wild
than in C. melo. Fruit weight ranged from 10 g in C. prophetarum to 300 g in C. metuliferus (Table 4).
The longest fruit were observed in Adzur (C. melo ssp. Flexuosus Group) with fruit that were 47.0 cm long. These were followed by the fruit of Shiroubi Okayama that were 31.0 cm in length. The shortest fruit in the C. melo accessions were those of Short Internode Cantaloupe whose were an average of 9.0 cm long. The length of the fruit in wild species ranged from 2.8 cm in C. myriocarpus to 11.0 cm in C. metuliferus (Table 3).
In the C. melo accessions, the widest fruit were those of Enfurter Netzmelone (20.0 cm wide), and the narrowest fruit belonged to Agrestis (C. melo ssp. agrestis) which were 8.0 cm wide. Among the wild species, fruit width ranged from 2.0 cm in C. prophetarum to 6.4 cm in C. metuliferus to (Table 3).
Refractive index (oBrix) was higher in fruit of the C. melo accessions than in fruit of the wild species (Table 3), and ranged from a high of 14.0 Charentais Fom-2 to a low of 4.8 in Enfurter Netzmelone, similar to the two wild species C. ficifolius and C. prophetarum. Cantaloupe of Westland and Freeman's Cucumber produced fruit with very low refractive index (5.2 and 5.5 oBrix, respectively). The highest refractive index in the wild species was 8.7 oBrix, recorded in C. metuliferus (Table 3).
Other characters. Other different characters from the originally chosen were also recorded. Conspicuous blossom scars, which depreciate so much the fruit quality, were observed in fruit of Korça, Lybian and PI 161375.
Ripe fruit MOO3/89 had vitriscent-like flesh, corresponding to a quality character for the Portuguese melon market. In this cultivar, it was also observed that the external layer of the fruit skin was easily separated from the fruit. This may have been an indication of stress susceptibility to the high temperatures reached under plastic house. This type of melon is usually grown in the open field in the north of Portugal where temperatures are mild.
Plants of PI 414723 showed bushy growth habit with flowers grouped in bunches during approximately the first month of growth in the greenhouse. Later on, plants showed prostrate habit.
414723, showed resistance to races 1 and 2 of S. fuliginea as well as C. dipsaceus, C. africanus, C. anguria var anguria, C. prophetarum and C. zeyheri. Resistance to S. fuliginea in PI 414723 was also described by McCreight et al. (1987) WMR-29 and Kogane Nashi Makuwa were resistant to race 1, but susceptible to race 2. In C. meeusei and C. ficifolius, very low sporulation was observed when plants were inoculated with both races of S. fuliginea (Table 4).
Little variability was observed in C. melo for most of the pathogens considered in this work. In most cases, virus resistance was found to be isolate specific. A new accession, TGR, showed multiple virus and powdery mildew resistances. The genetic bases of the different resistances found in TGR is under way.
Although there are known sexual incompatibilities between Cucumis spp. and C. melo, the resistance found in different wild accessions could be useful when biotechnological methods for interspecific breeding are well established.
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species, although Horváth (1993) found immunity in C. anguria var anguria, C. africanus and C. ficifolius (Table 4). The different results obtained by different authors seems to indicate that resistance to ZYMV in those cultivars could be overcome depending on the virus isolate, as pointed out by Lecoq and Pitrat (1984b).
Only the accession of C. melo, TGR, showed resistance against the M-116 isolate of WMV-2. Experiments to determine the genetics of such a resistance are in progress. Although Gilbert et al. (1994) described partial resistance to WMV-2 in PI 414723, when plants of this cultivar were inoculated with M116-WMV-2, only one plant was symptomless (Table 4). Probably the different isolates used in the inoculations influence the response of PI 414723. Although PI 161375 has shown immunity (Horváth, 1993) or tolerance (Pitrat, 1978) to WMV-2 when inoculated with M116 isolate of WMV-2, plants of this cultivar were susceptible. Variability in the response of the melon cultivar Escrito was observed (Table 4).
PRSV-W resistance has been found in PI 180280 (Webb, 1979), WMR 29 (Bohn et al., 1980; Pitrat and Lecoq, 1983), and PI 414723 (Anagnostou and Kyle, 1996). Resistance to that virus was observed in the cultivar TGR from Zimbabwe (Table 4). C. africanus and C. metuliferus showed resistance against PRSV-W. Provvidenti and Robinson (1974a, 1974b) also found resistance to PRSV in C. metuliferus.
PI 161375 showed resistance to MNSV (Coudriet et al., 1981). Horváth (1993) described PI 161375 as immune to MNSV. Resistance to MNSV was observed in the C. africanus accession, but no resistance was observed in C. ficifolius accession (Table 4), in contrast to what Horváth (1993) observed.
All accessions except three expressed symptoms to CYSDV inoculation. TGR , CM-C-1 and E-C-1 that did not show any symptoms during the 40-day observation period following inoculation. Resistance to this virus has also found in C. metuliferus (Table 4). Gómez-Guillamón et al. (1994) found resistance to the yellowing virus transmitted by Bemisia tabaci in TGR and C. metuliferus; that was later identified as CYSDV (Célix et al., 1996).
Short Internode Cantaloupe, TGR and PI
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