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Cucurbit Genetics Cooperative Report 17:86-87 (article 25) 1994

Resistance of Cucumis melo var. agrestis to Trialeurodes vaporariorum

C. Soria, A.I.L. Sese, and M.L. Gomez-Guillamon

Estacion Experimental "La Mayora" CSIC, 29750 Algarrobo-Costa, Malaga SPAIN

Cucumis melo var. agrestis Naud. appears to have some type of inherent resistance to greenhouse whitefly Trialeurodes vaporariorum Westwood. This work aimed to determine the possible existence of antixenosis or antibiosis by comparing the resistance of this accession to whitefly with C. melo and related species.

The experiments have been carried out. Experiment 1 was designed to determine the reproductive capacities of Trialurodes vaporariorum feeding on C. melo var. agrestis and each of two susceptible accessions of C. melo cv. 'Bola de Oro' and PI-505601, and in C. metuliferus that some authors describe as resistant (2). Five plants of each line were arranged under a fly-proof mesh box into which 800 whiteflies were introduced for 72 h. The flies had a free choice of plants to feed on and reproduce themselves during this time. At 32 days, the number of T. vaporariorum empty pupal cases on each plant and each line were counted. Three replicates were made of this experiment. Variance analysis revealed significant differences between the liens, notably C. Metuliferus on which whitefly reproduction was very high (Table 1). Possibly, this high value makes C. melo var. agrestis appear no different from the other lines, but the results show clearly that whitefly reproduction on it was quite low and this suggests that T. vaporariorum has a scale of preference and prefers other genotypes to reproduce on before C. melo var. agrestis when the others are present at the same time.,

The second experiment determined the rate of reproduction of individuals of Trialeurodes vaporariorum and their development times (eggs-adult). This experiment also included C., dipsaceus as an accession known to be resistant to whitefly (1). Twenty plants of each accession at the give-leaves-completely-developed stage were randomly selected and, by the use of clip-on cages, a recently emerged female of T. vaporariorum was placed on each low leaf of each plant. Every 48 h, each of these individual whiteflies was transferred in its cage to a younger fully expanded leaf of the same plant. Twenty-six days later, the numbers of empty pupal cases on each leaf of each plant were counted daily (total reproduction of each individual). We also counted the number of days needed to complete the development from egg deposition to emergence of the adult. analyses of variance detected significant effect of genotypes on both reproduction and development times.

The results show that T. vaporariorum reproduced well on C. melo cv. Bola de Oro, C. metuliferus and C. dipsaceus (Table 2), however, reproduction on C. melo var. agrestis and PI-505601 appeared difficult, although PI-505601 does not differ from the others. The accessions on which the whitefly development time decreased significantly were C. metuliferus and C. melo var. agrestis (Table 2).

The C. metuliferus accession used in these experiments was clearly susceptible to greenhouse whitefly. This is the same accession that was tested against the melon yellowing virus transmitted by this insect (3) and this suggests that C. metuliferus has resistance either to that virus or to its transmission.

C. dipsaceus did not really appear to be resistant to greenhouse whitefly even though its whitefly development time was longer (which apparently suggests the presence of antibiosis) because the net-rate or T. vaporariorum reproduction was the highest of all the genotypes tested and did not differ from amy of them, except that of C. melo var. agrestis (Table 2).

T. vaporariorum appeared to prefer to feed and reproduce on other genotypes before C. melo var. agrestis. The results suggest that in this accession there is an effective antibiosis mechanism against the greenhouse whitefly because its rate of reproduction on this accession is very low, however, on the other hand, the short whitefly development time contradicts this supposition; it appears that the whitefly shortens its development time to live on Cucumis melo var. agrestis, and perhaps, this could be an adaptive strategy of the insect to ensure future generations. The percentage of eggs that eventually resulted in adults with complete life cycles is not known and is the subject of on-going experiments. Perhaps, these will also determine if antibiosis is really the resistance mechanism in this accession.

Table 1. Rate of T. vaporiorum reproduction of four accessions of C. melo under free-choice conditions.

Genotypes
No. of Empty Pupal Cases
C. melo var. agrestis
55.9 az
C. melo PI-505601
101.3a
C. melo cv. Bola de Oro
355.0ab
C. metuliferus
514.2b

az Means with the same letter are not significantly different, SNK test, p>0.95

Table 2. Rates of reproduction and development times of T. vaporariorum in days.

Genotypes
No. of Empty Pupal Cases
Development Times
C. melo var. agrestis
15.73 az
30.97 b
C. melo PI-505601
26.00 ab
32.18 c
C. melo cv. Bola de Oro
69.80 b
33.26 cd
C. metuliferus
69.85 b
30.17 a
C. dipsaceus
72.67 b
33.60 d

az Means with the same letter are not significantly different, SNK test , p>0.95.

Literature Cited

  1. Esqinas-Alcazar, J.T. and P.J. Guilick. 1983. Genetics resources of Cucurbitaceaes. A.G.P.G.R.:I.B.P.G.R. 83/84:20
  2. Nijs, den A.P.M. and J.B.M. Custers. 1990. Introducing resistance into cucumbers by interspecific hybridization. In Biology and Utilization of the Cucurbitaceaes. D.M. Bates, R.W. Robinson, and C. Jeffrey (eds.), Cornell University Press, Ithaca and London, pp. 382.
  3. Soria, C., M.K. Gomez-Guillamon., J. Esteva, F. Nuez, C. Jorda, and A. Alfaro. 1991. Amarilleo del melon: causas y posibilidades de lucha a traves de la majora. Actas de Horticultura 8:125-132.
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