Anurag Sunpapao

Corynespora cassiicola causes leaf spot disease on lettuce (Lactuca sativa) cultivated in hydroponic systems in Thailand

Lettuce (Lactuca sativa) is an annual vegetable that is widely cultivated in hydroponic systems in Thailand. In 2016, a leaf spot disease was commonly found on hydroponically-grown lettuce plants in glasshouses in Songkhla province, southern Thailand. The morphology of the fungus that was consistently isolated from the leaf spots was identical to that described for Corynespora cassiicola. The identity of the fungus was confirmed by sequencing the ITS and LSU gene regions. Koch’s postulates were satisfied, proving that C. cassiicola was the causal agent of the recent outbreaks of leaf spot in hydroponically-grown lettuce in Thailand. This paper is the first report of the disease in this country.

Disease Note: Identification of Curvularia oryzae as cause of leaf spot disease on oil palm seedlings in nurseries of Thailand

The causal agent of leaf spot disease of oil palm (Elaeis guineensis) seedling nurseries in Thailand was identified as Curvularia oryzae. The fungus was isolated from leaves with disease symptoms, characterized by morphological properties, and pathogenicity tested. The identity of the phytopathogenic fungus was confirmed through polymerase chain reaction analysis using internal transcribed spacer (ITS) primers, which amplified about a 1 kb product. Sequencing this DNA product confirmed this pathogen was C. oryzae. Furthermore, the pathogenicity test showed that C. oryzae could infect oil palm seedlings.

ALGAL LEAF SPOT OF LANSIUM PARASITICUM CAUSED BY CEPHALEUROS sp. IN THAILAND

Algal spot symptoms appeared on Lansium parasiticum (Osbeck) Sahni & Bennet leaves in late August, 2014 when rainy and warm weather favoured algal growth. The disease was found in 20% of surveyed L. parasiticum plants in Songkhla, Thailand, showing an orange to brown small, 1-4 mm circular scurf on the leaves. Thalli were sub-cuticular with sub- epidermal growth, and consequent necrosis of epidermal cells in the leaf tissue. Filamentous algal cells were short and cylindrical, 8-15×3-7 μm, with length/width ratio 1:1.1-4. Setae were short filaments with two to five cells, 100-180 × 3-7 μm. Sporangiophores, on the upper leaf surface, developed from the thalli of the algal colony. Sporangia were elliptical, 5-10×5- 8 μm. Gametangia were spherical to elliptical (8-15×3-7 μm), produced beneath the cuticle. Gametes were spheroidal (7-10×7-9 μm), zoospores were elliptical (5-10×5-8 μm). These morphometric traits were consistent with Cephaleuros sp. (Thompson and Wujek, 1997). The sequence of the 18S rDNA (GenBank accession No. LC086008), showed 94% identity to C. virescens (KM020142) and C. parasiticus (KM020146). In pathogenicity test, leaves of healthy L. parasiticum were wounded by rubbing with celite, inoculated by spraying with a suspension of algal thallus fragments (0.1 g/ml fresh thalli w/v) (Suto and Ohtani, 2011). Algal infection was evident after three months when small thalli (0.2 - 0.6 cm diameter) were observed. Reisolated algae were consistent with those originally isolated. To our knowledge, this the first report of algal leaf spot of L. parasiticum caused by Cephaleuros sp.

Cephaleuros virescens, the cause of an algal leaf spot on Para rubber in Thailand

In this study Cephaleuros virescens was found to be the causal organism of a leaf spot disease on Para rubber (Hevea brasiliensis). The algae caused circular orange to dark brown lesions on both leaf surfaces. The morphology of the algae (thallus, filamentous cells, sporangiophore, sporangia, gametangia and zoospore) were examined and found to consistently match the species Cephaleuros virescens.

Plant-Parasitic Algae (Cephaleuros spp.) in Thailand, Including Four New Records

Abstract: Recent work on species composition, taxonomy, and diversity of plant-parasitic algae in the genus Cephaleuros in Thailand has provided additional knowledge of the parasitic algae in the country. The seven previously reported species, Cephaleuros diffusus, C. expansa, C. karstenii, C. parasiticus, C. pilosa, C. solutus, and C. virescens, are shown to cause algal leaf spot on several host plants in Thailand. Four new records are reported, namely Cephaleuros druetii, C. henningsii, C. lagerheimii, and C. tumidae-setae, resulting in a total of 11 Cephaleuros species recorded from Thailand.

First report of leaf spot on lettuce caused by Curvularia aeria

In 2017, leaf spots were found on lettuce growing in fields in Songkhla Province, southern Thailand. The fungus isolated from the spot lesions on the leaves was identified as Curvularia aeria (Bat., J.A.Lima and C.T.Vasconc.) Tsuda based on morphological characteristics and DNA sequences of the ITS region of the rRNA gene. After a conidial suspension of the isolate was sprayed on lettuce seedlings, the leaf spots developed on lettuce seedlings, and the fungus was reisolated; leaves of plants inoculated with water did not develop spots. This is the first report of C. aeria causing leaf spot on lettuce.

Choanephora rot caused by Choanephora cucurbitarum on Brassica chinensis in Thailand

In July 2016, wet rot was observed on leaves of Brassica chinensis in a private greenhouse in Hatyai city, Songkhla province, Thailand. The fungal pathogen infected young and expanded leaves. The fungus was identified by morphological characterization and molecular analysis as Choanephora cucurbitarum. Pathogenicity test revealed that C. cucurbitarum could infect B. chinensis.

Cephaleuros parasiticus, associated with algal spot disease on Psidium guajava in Thailand

During 2014–2015, algal spot disease was noticed in the guava orchards of northern and southern Thailand. Symptoms of the disease occurred on the leaves and fruit. Scabs were formed on heavily infected fruits. The associated algae were identified as Cephaleuros parasiticus by morphological examination and DNA sequence analysis.

A new sudden decline disease of bullet wood in Thailand is associated with Ceratocystis manginecans

In Thailand, since 2013, sudden decline of bullet wood (Mimusops elengi) has been noted. The causal agent of this disease was identified based on both morphological and molecular properties as Ceratocystis manginecans. A portion of its ITS, β-tubulin and TEF1-α genes were amplified by PCR with the universal primer pairs PN3/PN16, βt1a/βt1b and EF1-728F/EF1-986R, respectively. Sequencing of the PCR product confirmed this pathogen was C. manginecans. This is the first report on the new sudden decline disease of bullet wood in Thailand associated with C. manginecans.