Anthracnose, caused by Colletotrichum truncatum (syn. C. capsici), has become a common disease of tropical crops, severely affecting the quantity and quality of fruit and seed and, therefore, reducing their market value. For years, chemical control has been extensively used for managing this disease. However, the appearance of isolates that are resistant to the most commonly employed fungicides is increasingly widespread. Twenty C. truncatum isolates from pepper, papaya, and physic nut were tested in vitro against four fungicides to determine their sensitivity. All evaluated isolates were resistant to azoxystrobin and thiabendazole and susceptible to cyprodinil + fludioxonil and mancozeb. To determine the molecular mechanism conferring thiabendazole resistance, the TUB-2 gene was characterized, revealing a glutamic acid to alanine substitution at position 198 in 6 of the 20 isolates that were tested. This work confirms the emergence of benzimidazole-based fungicide resistance in C. truncatum populations and highlights the need for monitoring fungicide sensitivity as an essential activity for the development of effective control schemes.
Colletotrichum capsici is an important fungal species that causes anthracnose in many genera of plants causing severe economic losses worldwide. A primer set was designed based on the sequences of the ribosomal internal transcribed spacer (ITS1 and ITS2) regions for use in a conventional PCR assay. The primer set (CcapF/CcapR) amplified a single product of 394 bp with DNA extracted from 20 Mexican isolates of C. capsici. The specificity of primers was confirmed by the absence of amplified product with DNA of four other Colletotrichum species and eleven different fungal genera. This primer set is capable of amplifying only C. capsici from different contaminated tissues or fungal structures, thereby facilitating rapid diagnoses as there is no need to isolate and cultivate the fungus in order to identify it. The sensitivity of detection with this PCR method was 10 pg of genomic DNA from the pathogen. This is the first report of a C. capsici-specific primer set. It allows rapid pathogen detection and provides growers with a powerful tool for a rational selection of fungicides to control anthracnose in different crops and in the post-harvest stage.
Papaya meleira virus (PMeV), causal agent of meleira or sticky disease, is a double-stranded RNA (dsRNA) virus which has been previously reported only in Brazil. A study was carried out in order to verify the presence and occurrence of PMeV in Mexico. Latex samples from symptomatic and asymptomatic papaya fruits were collected in Quintana Roo state papaya orchards, where the first symptoms of PMeV were observed, and from 29 different municipalities located in ten papaya producer states in Mexico. A molecular protocol based on nucleic acid extraction was used for the diagnosis and a virus 12 Kb dsRNA distinctive band was observed in all PMeV infected plants. Around 46% of the evaluated plants were positive for this pathogen. Presence of the virus had been confirmed in seven states indicating the potential damage that PMeV could cause in the papaya crop in Mexico. The molecular analysis used allowed the diagnosis of infected plants without symptoms and facilitated the diagnosis in flowers and small papaya fruits also. The early diagnosis of PMeV will allow papaya producers to take appropriate and timely control measures. This is the first report of Papaya meleira virus in Mexico.
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