January 23, 2003
From: American Phytopathological Society, Plant Disease Notes [edited]

First report of Monosporascus cannonballus on melon in Brazil
R. Sales Jr., I. J. Bezerra do Nascimento, and L. de Souza Freitas, Escola Superior de Agricultura de Mossoro, ESAM, Caixa Postal 137, 59.600- 970, Mossoro-RN, Brazil; and R. Beltran, J. Armengol, A. Vicent, & J. Garcia-Jimenez, Instituto Agroforestal Mediterraneo, Universidad Politecnica de Valencia, Camino de Vera s/n, 46022-Valencia, Spain. Plant Dis. 88:84, 2004; published on-line as D-2003-1105-01N, 2004. Accepted for publication 10 Oct 2003.

Approximately 15 000 ha of melon (_Cucumis melo_ L.) are grown in the northeastern section of Brazil, mostly for export to Europe during the winter months. Surveys for melon vine decline diseases were carried out in farms in the municipalities of Mossoro (Rio Grande do Norte) and Quixere (Ceara) during 2002 and 2003.

Symptoms typical of vine decline were observed in several fields and included yellowing of crown leaves just prior to harvest and collapse of many of the vines. Affected plants exhibited necrotic root systems and lacked most of the secondary and tertiary feeder roots.

Numerous perithecia were observed on roots which, when examined with a microscope, showed characteristic asci and ascospores of the fungus _Monosporascus cannonballus_ (Pollack & Uecker, ref. 2).

Isolations were made from the crown region and primary and secondary roots of affected plants by excising 4- to 6-mm pieces that were surface-sterilized for 30 to 60 s with 1.5 percent active chlorine solution. 7 tissue pieces from each plant part were placed on potato dextrose agar (PDA) containing 0.5 g liter -1 of streptomycin sulfate.

Plates were examined daily for fungal growth for 7 days, and hyphal tips from all colonies were transferred to PDA for subsequent growth and sporulation. _M. cannonballus_ was isolated from 50 percent of the root sections. All isolates produced only one ascospore per ascus.

Pathogenicity of 4 isolates was confirmed in the greenhouse on the muskmelon cv. Temprano Rochet. Inoculum was produced in a sand-oat hulls (_Avena sativa_ L.) medium (0.5 liter of sand, 46 g of ground oat hulls, and 37.5 ml of distilled water) and incubated at 25 deg C for 1 month. Colony forming units (CFU) were quantified by serial dilution using 1 percent hydroxyethyl cellulose. A sterilized mixture of equal portions (vol/vol) of sand and peat moss was used to fill plastic pots (17 cm in diameter), and inoculum was added to produce an inoculum concentration of 20 CFU/g.

5 melon seeds were planted in each pot and after germination, were thinned to one seedling per pot. There were 5 replicated pots for each treatment with an equal number of uninfested pots. Plants were evaluated for disease 45 days after sowing. Roots were exposed by carefully washing the potting mix away.

All isolates of _M. cannonballus_ tested were highly aggressive and caused severe root necrosis compared with the noninoculated control plants. _M. cannonballus_ was reisolated from symptomatic plants, confirming Koch's
postulates.

Double-cropping in the same fields for several years has created serious problems in Brazil, which are related to this soilborne pathogen that also causes root rot and vine decline of watermelon (_Citrullus lanatus_ (Thunb.) Matsum. & Nakai) worldwide (1).

To our knowledge this is the first report of _M. cannonballus_ in Brazil and South America.

References:
(1) R. D. Martyn and M. E. Miller. Plant Dis. 80:716, 1996.
(2) F. G. Pollack and F. A. Uecker. Mycologia 66:346, 1974.

[This is the 1st report of the disease in Brazil. Management of _Monosporascus_ root rot is difficult. First reported in Arizona in 1974, it has subsequently been reported from the EPPO region: Israel (as _M. eutypoides_ [Me]), Italy, Libya (as Me) Spain and Tunisia; Asia: India, Iran (as Me), Japan, Pakistan (as Me), Saudi Arabia and Taiwan; and North America: Mexico, USA (Arizona, California, Texas) and Central America: Guatemala and Honduras. The fungus is soilborne, its ascospores are heavily walled and thus can remain viable for many years, and there are few resistant or tolerant cultivars. Management options include chemical soil treatment (which is becoming increasingly less popular because of environmental concerns) and grafting of susceptible melons and watermelons onto rootstocks of some resistant hosts ( _Cucurbita_ spp.) or bottle gourd (_Lagenaria_ spp.). Biological control is being attempted by infecting wild-type fungal isolates of the pathogen with hypovirulent isolates containing dsRNAs so as to convert wild type isolates to a less aggressive form. - Mod.DH]