Molecular characterization of leaf spot caused by Alternaria alternata on buttonwood (Conocarpus erectus L.) and determination of pathogenicity by a novel disease rating scale

Abstract

The buttonwood (Conocarpus erectus L.) is a mangrove shrub belonging to Combretaceae family. It mostly grows on the shorelines of tropical and subtropical regions in the world. It was introduced to Lasbela University of Water, Agriculture & Marine Sciences (LUWMS), Uthal, Baluchistan as an ornamental plant as it grows well under harsh, temperate and saline conditions. During a routine survey, typical leaf spot symptoms were observed on the leaves of buttonwood plants. A disease severity scale for alternaria leaf spot of buttonwood was developed for the first time through this study. Disease severity according to the scale was 38.97%. The microscopic characterizations was accomplished for the identification of Alternaria alternata and Koch’s postulates were employed to determine the pathogenicity. For molecular identification, 650 bp internal transcribed spacer (ITS) regions (ITS1, 5.8s and ITS2) were amplified from three representative isolates (LUAWMS1, LUAWMS2 and LUAWMS3) through polymerase chain reaction (PCR). The nucleotide sequences from ITS regions of the isolates were submitted to NCBI with GenBank accession numbers MW585375, MW585376 and MW585377, respectively. The phylogenetic tree of 22 A. alternata isolates was computed and representative isolates exhibited 99.98% genetic similarity with mangroves ecosystem isolates. This study reports the incidence of alternaria leaf spot of buttonwood at LUWMS for the first time. It is suspected that the disease may spread further. Therefore, effective management strategies should be opted to halt the further spread of the disease.

Diversity of fungal pathogens associated with loquat and development of novel virulence scales

“…lunata (1×10 4 spore/mL) and A . alternata (10 6 spores/mL) were sprayed on healthy leaves and the mean infected leaf area (mm) was recorded after 7 days [ 23 ].…”

“…The recent introduction of molecular techniques has advanced the detection, reliable identification and screening of many pathogens [ 21 ]. Sequence analysis of internal transcribed spacer (ITS) regions (ITS1, 5.8S and ITS2) has been developed for quicker and specific identification of fungi [ 22 , 23 ]. Although loquat is an important fruit crop in Pakistan, little is known about fungal pathogens causing leaf spots, fruit rot, and twig dieback in the major loquat growing areas of the country.…”

Predicting the impact of environmental factors on citrus canker through multiple regression

“…Furthermore high rainfall and wind speed accelerate the dispersion rate of the disease [ 19 ]. Extreme weather conditions such as tropical storms and hurricanes result in long-distance dissemination of the pathogen and increase disease infestation [ 20 – 23 ]. Environmental factors significantly affect host susceptibility, succulence, vigor, survival, and multiplication rate of the pathogen, pathogen dispersion, and spore penetration and germination rates.…”

Mangrove Dieback and Leaf Disease in Sonneratia apetala and Sonneratia caseolaris in Vietnam

“…Unlike for Vietnam, a range of mangrove disorders have been previously reported in other countries. Black leaf spot on Sonneratia apetala and small black leaf spot on S. caseolaris were associated with Olletotrichum lindemuthianum, Pestalotiopsis guepinii, and Phoma betae in Bangladesh [53]; Abbas et al [54] described a black leaf spot on Conocarpus erectus caused by Alternaria alternata in Pakistan. Black leaf spot disease also occurs on Ceriops decandra, Osbornia octodonta, Rhizophora stylosa, and S. caseolaris associated with Pseudocercosporella in the Philippines [38].…”

“…Fungi associated with small leaf spot of S. caseolaris were Curvularia fallax, Fusarium sp., Penicillium digitatum, and Phoma betae [53]. Alternaria alternata was considered to cause leaf spot on Conocarpus erectus in Pakistan [54].…”