Cucurbit Genetics Cooperative Report 13:31-33 (Article 12) 1990

Ten Interspecific Crosses in the Genus Cucumis: A Preparatory Study to Seek Crosses Resistant to Melon Yellowing Disease.

C. Soria and M. L. Gómez-Guillamón

Estación Experimental "La Mayora", Algarrobo-Costa, (Málaga), Spain

J. Esteva and F. Nuez

Universidad Politécnica de Valencia, Spain

Some wild species of the Cucumis genus show resistance to different plant pests and diseases, and consequently they may be useful experimental material for studies that seek to transfer this resistance to cultivated species.

The aim of this work was to determine the true potential of several wild species of the genus for improving melon plants Cucumis melo L. by carrying out interspecific crossing experiments. The species used in this work were selected taking into account their known resistance to melon yellowing disease shown in previous work (3,6) and also published material on this subject (1,2,4).

Four species were selected because of their resistance to melon yellowing disease in conditions of natural infection shown by several studies (3,6). They were: Cucumis anguria var. longipes, C. zeyheri, C. africanus, and C. myriocarpus. The last two species were tested against melon yellowing disease in controlled conditions to compare the results with those obtained in conditions of natural infection.

According to the literature (2,4), C. metuliferus is cross-compatible with the C. africanus wild species and also with the cultivated species C. melo. This cross-compatibility suggests that C. metuliferus could be used as a genetic bridge between these species to transfer the genes of yellowing resistance from C. africanus to the cultivated muskmelon, C. melo.

Manual cross-pollinations were carried out by using female flowers before anthesis. The plants were kept in a polyethylene greenhouse at a mean temperature of 27.4C max. and 13.7C min. with relative humidities ranging from 70% max. and 30% min.; they were cultivated in sandy soil with drip irrigation.

The following 10 interspecific crosses were studied: C. myriocarpus x C. africanus; C. africanus x C. myriocarpus; C. africanus x C. zeyheri; C. africanus x C. anguria var. longipes; C. africanus x C. metuliferus; C. zeyheri x C. africanus; C. anguria var. longipes x C. africanus; C. metuliferus x C. africanus; C. melo cv. 'Piel de Sapo' x C. metuliferus and C. melo cv. 'Bola de Oro' x C. metuliferus.

The numbers of flowers pollinated, the percentages of fruits against numbers of pollinations, and the mean numbers of embryos per fruit for the different crosses, are shown in Table 1.

Table 1. Numbers of pollinations, percentages of fruits against numbers of pollinations, and numbers of embryos.
Crosses	No. Pollinations	% Fruits	No. Embryos
C. myriocarpus x C. africanus	128	0.78	70
C. africanus x C. myriocarpus	45	86.67	131
C. africanus x C. zeyheri	23	39.13	16
C. africanus x C. anguria Lz	91	15.38	57
C. africanus x C. metuliferus	44	0.00	-
C. zeyheri x C. africanus	87	43.68	7
C. anguria L x C. africanus	85	23.53	26
C. metuliferus x C. africanus	66	21.21	415
C. melo PSy x C. metuliferus	67	7.46	0
C. melo BOx x C. metuliferus	97	7.22	3
zL: longipes variety
yPS: 'Piel de Sapo' cultivar
xBO: 'Bola de Oro' cultivar

C. myriocarpus as the female parent crossed with C. africanus, although the percentage success was very low (0.78%), and the fruits showed viable F1 seeds, but few germinated and then only with difficulty.

As the female parent, C. africanus crossed with C. myriocarpus and gave 86.67% success; with C. zeyheri, it gave 39.13%; and with C. anguria var. longipes it gave 15.38%. The fruits of these three crosses produced viable F1 seeds.

The C. africanus x C. metuliferus crosses were fruitless, but only 44 pollinations were carried out and this was less than were carried out in most of the other interspecific crosses.

C. zeyheri as the female parent crossed with C. africanus and the pollination success was 43.68%, but the viability of the F1 seeds was very small; only two seeds could be germinated in Murashige and Skoog cultivation medium (5).

C. anguria var. longipes as the female parent crossed with C. africanus to give a 23.53% success, but the F1 seed viability has not yet been tested.

C. metuliferus as female parent crossed with C. africanus to give 21.21% success. The fruits contained viable F1 seeds.

The 'Piel de Sapo' and 'Bola de Oro' cultivars as female parents crossed with C. metuliferus to give respective success rates of 7.46 and 7.22%. the first cross was fruitless. The viability of the F1 seeds of the second cross has not yet been determined.

Literature Cited

1. Custers, J.B.M. and A.P.M. Den Nijs. 1986. Effects of aminoethoxyvinylglycine (AVG), environment, and genotype in overcoming hybridization barriers between Cucumis species. Euphytica 35:639-647.
2. Esquinas-Alcazar, J.T. and P. J. Gulick. 1983. Genetic resources of Cucurbitaceae. AGPGR: IBPGR/83/48:20.
3. Esteva, J., F. Nuez, and J. Cuartero. 1988. Resistance to yellowing disease in wild relatives of muskmelon. Cucurbit Genetics Cooperative 11:52-53.
4. Fassuliotis, G. 1977. Self-fertilization of Cucumis metuliferus Naud. and its cross-compatibility with C. melo L. J. Amer. Soc. Hort. Sci. 102:336-339.
5. Murashige, T. and F. Skoog. 1962. A revised medium for rapid growth bioassay with tobacco tissue cultures. Physiologia Plantarum 15:473-497.
6. Soria, C., M.L. Gómez-Guillamón, J. Esteva, and F. Nuez. 1989. Search for sources of resistance to yellowing disease in Cucumis spp. Cucurbit Genetics Cooperative 12:42-43.