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Cucurbit Genetics Cooperative Report 15:55-56 (article 20) 1992

Search for Sources of Resistance to a Melon Dieback Disease in Spain

J. Esteva, F. Nuez and J. Garvia-Jimenez

Dpto. Biotecnologia. Universidad Politecnica de Valencia (UPV), Spain; Dpto. Produccion Vegetal. Universidad Politecnica de Valencia, Spain

In the Spanish Mediterranean coast a disease has appeared which brings about the sudden death of melon plants. In the Valencian area this disease has been associated with a ground fungus belonging to the Acremonium genus (2). This fungus implants itself in the plants in the early stages of development causing brownish discoloration and corky and necrotic areas in the roots and root collar (3). This deterioration at the root system brings about wilting and death of the plant a few days after hydric stress is reached. This usually occurs at first fruit set (3).

Inoculation with this fungus in hydroponic culture conditions produces root rot on melon seedlings (2). In a previous experiment (1) 45 melon accessions from the UPV germplasm bank were inoculated in this way, 35 of which were classified as susceptible, and the response of the other 10 was doubtful or variable.

Nine of these 10 accessions together with another three were tested under outdoor field conditions at two locations in Valencia (Alcudia and Paiporta). In both places plants were grown in plots where the disease had previously been noted. In Paiporta, all accessions were also grown in a plot which had previously been disinfected with methyl bromide. The number of replicates per accession was three in Alcudia and two in Paiporta. The number of plants per replicate was five.

The objective of this experiment was to test up to what point the observed response when Acremonium sp. is inoculated in laboratory is a reflection of the incidence of this disease in field conditions. The accession Pat 82 acted as a control, given that it has already shown great susceptibility to Acremonium sp. in hydroponic culture. The subterranean part of the plants were carefully inspected for signs of root rot, brownish discoloration, and corky areas. The number of wilted plants was also noted. On the basis of these characters we rated the severity of the attack using a point system (Table 1).

Wilting and sudden death of some plants were observed in Paiporta, but not in Alcudia, even though the roots were damaged in both places. Accessions Pat 46 and 81 showed little sign of disease (Table 1). In Pat 49 the symptoms were only apparent in the roots of the plants grown in Alcudia. Pat 39 and 22 showed distinct severity of the attack in both places. Plants of the accession Pat 80 grew well despite root damage in both Alcudia and Paiporta. The disease was substantial in the rest of the accessions at both places locations. However, in the plot which had been disinfected previous to planting (Paiporta), there were no signs of wilting or root damage. the presence of Acremonium sp. was confirmed in both the untreated plots.

At present, the inoculation of hydroponic cultivars does not seem to be an efficient way of selecting resistant sources.This could be due to the fact that other ground fungi, principally saprophytes, occupy the lesions produced by Acremonium sp. and cause more damage. So far we have been unable to find an accession which shows a clear resistance to Acremonium sp. in laboratory conditions. If we had one, we could confirm the usefulness of hydroponic inoculation and we would put forward more information about the part Acremonium sp. plays in the disease.

Table 1. Severity of melon dieback disease attack on accessions studied.

 
Root Appearance*
Number of withered plants
Accession
Alcudia replicates
Paiporta replicates
Paiporta replicates
1
2
3
1
2
1
2
Pat 46
0
1
1
1
1
0
0
Pat 81**
0
0
0
1
1
0
1
Pat 48**
2
3
2
1
1
0
0
Pat 39
1
2
1
4
4
5
4
Pat 22
3
3
3
1
2
0
0
Pat 80**
3
-
3
3
3
0
0
Pat 6
2
2
3
2
3
2
3
Pat 34
2
1
3
3
4
4
5
Pat 35
1
3
2
3
3
5
3
Pat 36
2
3
2
3
4
2
5
Pat 38
2
3
2
4
4
5
5
Pat 82***
3
3
3
4
-
2
-

* 0: Roots with no symptoms; 1: Slightly damaged roots; 2: Moderately damaged roots; 3: Strongly damaged roots; 4: Very strongly damaged roots.
** Accessions which were not tested by means of hydroponic culture.
*** The replicate 2 of Pat 200 in Paiporta was of 2 plants only.

Acknowledgements: This work was financially supported by the research project AGRop-816-CO2-02 held by CICYT.

Literature Cited

  1. Garcia-JimenezJ., A. Alfar,. J. Esteva, F. Nuez, and M.T. Velazquez. 1991. Resistance to Acremonium sp. in Spanish landraces of melon. Cucurbit Genetics Cooperative 14:49-50.
  2. Garcia-Jimenez, J.,M.T. Velazquez, and A. Alfar. 1989. Acremonoim sp. agente causal del colapso del melon en el levante espanol.
  3. Garcia-Jimenez, J. M.T. Velazquez, and A. Alfaro. 1989. Secuencia de sintomas en el colapso del melon. Boletin de Sanidad Vegetal y Plagas 4:333-342.
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