Morphological and Molecular Identification of Plant Pathogenic Fungi Associated with Dirty Panicle Disease in Coconuts (Cocos nucifera) in Thailand.

Dirty panicle disease in coconuts (Cocos nucifera) was first observed in the KU-BEDO Coconut BioBank, Nakhon Pathom province, Thailand. The occurrence of the disease covers more than 30% of the total coconut plantation area. The symptoms include small brown to dark brown spots and discoloration of male flowers. Herein, three fungal strains were isolated from infected samples. Based on the morphological characteristics the fungal isolates, they were classified into two genera, namely, Alternaria (Al01) and Fusarium (FUO01 and FUP01). DNA sequences of internal transcribed spacer (ITS), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), translation elongation factor 1-α (tef1-α), and RNA polymerase II second largest subunit (rpb2) revealed Al01 as Alternaria burnsii, whereas DNA sequences of ITS, rpb2, and tef1-α identified FUO01 and FUP01 as Fusarium clavum and F. tricinctum, respectively. A pathogenicity test by the agar plug method demonstrated that these pathogens cause dirty panicle disease similar to that observed in natural infections. To the best of our knowledge, this is the first report on the novel dirty panicle disease in coconuts in Thailand or elsewhere, demonstrating that it is associated with the plant pathogenic fungi A. burnsii, F. clavum, and F. tricinctum.

A SNP of betaine aldehyde dehydrogenase (BADH) enhances an aroma (2-acetyl-1-pyrroline) in sponge gourd (Luffa cylindrica) and ridge gourd (Luffa acutangula).

Luffa is a genus of tropical and subtropical vines belonging to the Cucurbitaceae family. Sponge gourd (Luffa cylindrica) and ridge gourd (Luffa acutangula) are two important species of the genus Luffa and are good sources of human nutrition and herbal medicines. As a vegetable, aromatic luffa is more preferred by consumers than nonaromatic luffa. While the aroma trait is present in the sponge gourd, the trait is not present in the ridge gourd. In this study, we identified Luffa cylindrica's betaine aldehyde dehydrogenase (LcBADH) as a gene associated with aroma in the sponge gourd based on a de novo assembly of public transcriptome data. A single nucleotide polymorphism (SNP: A > G) was identified in exon 5 of LcBADH, causing an amino acid change from tyrosine to cysteine at position 163, which is important for the formation of the substrate binding pocket of the BADH enzyme. Based on the identified SNP, a TaqMan marker, named AroLuff, was developed and validated in 370 F2 progenies of the sponge gourd. The marker genotypes were perfectly associated with the aroma phenotypes, and the segregation ratios supported Mendelian's simple recessive inheritance. In addition, we demonstrated the use of the AroLuff marker in the introgression of LcBADH from the aromatic sponge gourd to the ridge gourd to improve aroma through interspecific hybridization. The marker proved to be useful in improving the aroma characteristics of both Luffa species.