Postharvest biocontrol of Colletotrichum gloeosporioides on mango using the marine bacterium Stenotrophomonas rhizophila and its possible mechanisms of action.

The marine bacterium Stenotrophomonas rhizophila was assessed in vitro and in vivo as biocontrol agent against anthracnose disease of mango fruit caused by Colletotrichum gloeosporioides. The results showed that in vitro inhibition of the colony diameter and spore germination of the phytopathogen was due to the production of VOCs, competition for nutrients, and lytic enzymes. When a concentration of 1 × 108 cells ml-1 of the antagonist bacterium was applied to the fruit, disease incidence was reduced by 95%, and the lesion diameter of anthracnose decreased by 85%, which offered greater protection than the synthetic fungicide. This is the first report of antagonistic mechanisms of the marine bacterium S. rhizophila against anthracnose disease in mango, which in this study was found to be more effective than the synthetic fungicide.

Distribution of Papaya ringspot virus and Papaya mosaic virus in Papaya Plants (Carica papaya) in Mexico.

We report the results of a survey for the presence of Papaya ringspot virus (PRSV) along the coasts of the Gulf of Mexico and the Pacific Ocean, in 15 federal states of Mexico that account for over 98% of the national papaya production. More than 80 locations were visited in 58 counties. Out of a total of 267 papaya leaf samples, 157 tested positive for PRSV. We tested for the presence of three other viruses because of the occurrence of severe, atypical symptoms in plantations. Only Papaya mosaic virus (PapMV) was detected. PRSV was present in every county. PapMV was less frequent, but its overall distribution was almost identical. PRSV and PapMV occurred in single or mixed infections of papaya and other host species that could function as virus reservoirs. We investigated the diversity of the coat protein (CP) sequences of 36 PRSV isolates. The amino acid sequence divergence among all isolates ranged from 0.4 to 9.9%, and was comparable to that found in other regions of the world. In contrast to most of these world regions, there is a clear correlation between CP sequence variation and the geographical origins of the virus isolates.

First Report of a Mexican Isolate of Papaya mosaic virus in Papaya (Carica papaya) and Pumpkin (Cucurbita pepo).

Papaya mosaic virus (PMV) is a member of the Potexvirus group and has filamentous particles of 530 nm with a positive sense single-stranded RNA of 6.6Kb. PMV was detected in Mexico in diseased papaya plants growing alone and in mixed plantations with pumpkin. Reverse transcription polymerase chain reactions (RT-PCR) and standard double-antibody sandwich enzyme linked immunosorbent assay (DAS-ELISA) procedures were used on 45 leaf samples from single plants in seven locations in southeast Mexico (States of Yucatan, Campeche, and Quintana Roo). PCR primer design was based on a GenBank sequence with accession number D13957 (1). Amplified PCR products were cloned using a TOPO TA Cloning Kit and sequenced by the dideoxy chain termination method. Twenty-six samples tested positive for PMV using one or both detection techniques: 23 of 41 from papaya and three of four from pumpkin. The two sequences reported here, YY-15 and YY-22 (from papaya and pumpkin respectively, with accession numbers AYO17186 and AYO17187), were 1180 nucleotides long and contained a fragment of ORF3, the complete ORF4 and the putative CP gene, including the 3' end untranslatable region. Within the CP gene sequence, the amino acid sequence derived had a similarity of 88% with that of D13957 from the GenBank. The similarity of the CP between the two Mexican isolates (from papaya and pumpkin) was 94% and would therefore represent two variants of PMV. A healthy papaya plant in the greenhouse, inoculated with tissue from an infected papaya plant from the field, tested positive for PMV in DAS-ELISA. (PVX was used as a negative control). These results confirmed the identity of the isolate as PMV. Reference: (1) T. L. Sit, M. G. AbouHaidar, and S. Holi. J. Gen. Virol. 70:2335-2331, 1989.

Coat protein sequence comparisons of three Medican isolates of papaya ringspot virus with other geographical isolates reveal a close relationship to American and Australian isolates.

The coat protein gene of the papaya ringspot virus was cloned and sequenced in three Mexican isolates (two from Veracruz, and one from Chiapas). The sequences of these viral isolates were compared to those of eleven isolates from other parts of the world. They had higher similarity to isolates from Australia and the United States than to Asian isolates. A region of about one hundred nucleotides neighboring the putative aphid transmission triplet of the coat protein, contained repeats of an EK (glutamic acid-lysine) motif in all the sequences. The bearing of this region on the genetic relationships and geographical distribution of the isolates is analyzed and discussed.