Somsiri Sangchote

Effect of chitosan on ripening, enzymatic activity, and disease development in mango (mangifera indica) fruit

Abstract The effects of chitosan on mycelial growth and spore germination of Colletotrichum gloeosporioides were investigated on potato dextrose agar (PDA) containing 0%, 0.5%, 1.0%, 1.5%, and 2.0% (w/v) chitosan dissolved in 0.5% acetic acid. Complete inhibition of mycelial growth and spore germination was observed in the medium containing only 0.5% acetic acid. Media containing chitosan were less inhibitory, but the highest concentrations of chitosan, at 1.5% and 2.0%, were more inhibitory than the lower concentrations (0.5% and 1.0%). Chitosan treatment (0.5%, 1.0%, 1.5%, and 2.0%) of mangoes {Mangifera indica) previously inoculated with C. gloeosporioides resulted in a lower rate of disease progression compared with the controls. Chitosan concentrations of 0.5% and 1.0% had stimulatory effects on chitinase and P‐l,3‐glucanase activities. Additionally, chitosan coatings in mangoes delayed ripening and reduced respiration rate, ethylene production, and the loss of weight, ascorbic acid, and total titratable acidity. However, the firmness of mangoes treated at concentrations above 1% caused a perceptible decline in sensory quality.

Fruit infection by Colletotrichum gloeosporioides and anthracnose resistance of some mango cultivars in Thailand

Infection of mango fruit cv Nam Dok Mai by Colletotrichum gloeosporioides was studied using artificial inoculation. Under optimum conditions (95–100% RH, 25°C), germination and appressorium formation started at 12 h and 14 h, respectively, after deposition of conidia on the peel. After 48 h, 60% of fungal propagules present were appressoria. The fungus could infect mangoes through both pedicel and peel wounds, causing stem end rot and anthracnose in ripe fruit. Inoculation of wounded peel resulted in symptom development in unripe fruit whereas un wounded peel showed no symptoms. Resistance of fruits to disease depended on cultivar. Testing of fruit resistance to the fungus could be conducted by inoculation of fruit at 24 h after harvesting. When inoculated at both pre- and post-harvest stages, mango cvv Nam Dok Mai, Nang Klang Wan and Chok Anan were found to be susceptible to anthracnose whereas Rad and Kaew were relatively resistant.

Effect of wetting period on infection of orchid flowers by Alternaria alternata and Curvularia eragrostidis

Abstract The effect of different durations of the incubation wetting period on the infection of Dendrobium flowers by two serious pathogens—Alternaria alternata (Fr.) Keissl. 1912 and Curvularia eragrostidis (Henn.) J.A. Mey. 1959—was investigated. Cut orchid flowers of the genus Dendrobium were used for the inoculation. The courses of symptom development and mycelium growth were determined. The results indicate that the infection and the subsequent development of disease on the flowers occur rapidly even if the conditions favourable for pathogen germination on the plant tissues persist for only 2 h. However, the proportion of infected flowers was significantly higher after a longer incubation period (6 h). The mycelium growth of the pathogen was also significantly influenced by the length of the incubation period.

Diversity of Colletotrichum spp. isolated from chili pepper fruit exhibiting symptoms of anthracnose in Thailand

Colletotrichum spp. are causal agents of anthracnose disease in chili fruits and other tropical crops. The disease is increasing in chili fruits in Thailand and significantly reduces fruit quality and fruit production. Forty-eight isolates of Colletotrichum spp. associated with chili anthracnose were collected from different areas of Thailand during 2010–2015. Based on morphological characteristic identification, 10 isolates were shown to belong to the C. gloeosporioides species complex, 24 isolates belong to the C. acutatum species complex and 14 isolates to C. capsici. For molecular identification, two primer sets, ITS1/ITS4 and ACT528/ACT738, were used for amplification of the internal transcribed spacer of rRNA gene (ITS1–5.8S–ITS2) and partial region actin gene (ACT), respectively. The phylogenetic analysis of individual and combined ITS region and actin nucleotide sequences identified the collected isolates into 4 species: C. gloeosporioides, C. siamense, C. acutatum and C. capsici. The pathogenicity test demonstrated that all four species were pathogenic on intact unwounded and healthy fruits. These results indicated that C. capsici, C. acutatum, C. gloeosporioides and C. siamense were the causal agents of chili anthracnose disease.