Antifungal activities of methanol extracts of some medicinal plants against germination and growth of Colletotrichum destructivum O’Gara in culture

Authors. 2021. Antifungal activities of methanol extracts of some medicinal plants against germination and growth of Colletotrichum destructivum O’Gara in culture. Asian J Nat Prod Biochem 19: 25-29. Cowpea is an important grain and leafy vegetable in many tropical locations. Anthracnose caused by Colletotrichum destructivum O’Gara is one of the several factors constraining the economic production of the crop in warm humid areas. Use of resistant varieties and synthetic pesticides for control of the disease in the crop are disadvantaged for variability of the pathogen, leading to resistance failure of cultivars in many cowpea growing areas; and pesticide residues in the treated crops which ultimately engender mammalian toxicity respectively. This study evaluated the effects of Alchornea cordifolia, Tabernaemontana pachysiphon and Lantana camara as eco-friendly fungicides against the pathogen in culture. The results showed that the extracts inhibited the fungus in a dose-wise manner. At 75 and100 % concentrations, L. camara strongly inhibited the spore germination and radial growth of the fungus better than all concentrations of T. pachysiphon and A. cordifolia; whereas A. cordifolia extracts exhibited the lowest inhibition at all concentrations. Generally, the fungitoxicity of benomyl was found higher which inhibited 90.15 % spore germination and 96.32 % radial growth of the pathogen. However, at 75%, 100% L. camara and 100% T. pachysiphon which significantly (P?0.05) inhibited (80.02%, 84.21 % and 80.91%) spore germination and (87.33%, 90.87 % and 85. %) radial growth of the fungus respectively compared well with inhibition effects recorded from benomyl. Therefore these plants can be used as viable protectants of cowpea against anthracnose (C. destructivum) in small holder farming systems of the humid tropics; to enhance its production and farm economy.

Histological aberrations and mode of damage of cowpea (Vigna unguiculata) by Colletotrichum destructivum

Enyiukwu DN, Amadioha AC, Ononuju CC. 2020. Histological aberrations and mode of damage of cowpea (Vigna unguiculata) by Colletotrichum destructivum. Nusantara Bioscience 13: 16-23. Leaf and stem of healthy 2-week old cowpea (Vigna unguiculata L. Walp.) seedlings were inoculated with spore suspension of the Colletotrichum destructivum O’Gara. Sections of the infection courts were prepared and examined under digital microscope. The results showed that the infection process began 12 hours after inoculation (hai) with the germination of spores of the fungus. Large multi-lobed primary hypha (somewhat spherical in shape) developed from the infection peg and remained inside a single epithelial cell for about 3 days. Towards the end of this time, the primary hyphae developed thin filamentous tentacles that punctured and branched into adjoining cells, initiating necrotrophic phase of the disease. During this period, typical anthracnose symptoms began to develop on the infected organs of the crop. The entire infection process lasted a maximum of 96 h, at the end of which acervulus that bore a single seta emerged on infected crop lesions. The mechanism of damage of the pathogen involved intra-cellular and inter-cellular colonization of the host tissues early and late in the disease cycle. The integrity of the affected tissues' cells was compromised by passage and colonization of Colletotrichum destructivum O’Gara evidenced by lack of clear-cut middle lamella and cell boundaries. Anthracnose affected cells dispossessed of vital nutrients became turbid, devoid of turgidity and vigor. Thus, these results have strong implications for plant health management in that effective environment-compliant control of the fungus should be initiated on or before the third day following arrival of the conidia of the pathogen on the crop. Seeds are major agents of introduction of Colletotrichum spp. to disease-free locations. Findings from this study also support that strong trans-border control of seeds of the crop should be maintained since the pathogen is known to be seed-borne and demonstrates sufficient cross-infection of crop plants. Key words: Hemibiotrophy, Colletotrichum destructivum, Anthracnose, Cowpea, Hyphal colonization

Alterations of Biochemical Composition of Leaf and Stem of Cowpea (Vigna unguiculata (L.) Walp.) by Colletotrichum destructivum O’Gara in Nigeria

Colletotrichum destructivum during pathogenesis reduced the nutrient values of cowpea leaf and stem. The protein, fat, carbohydrate, fibre contents of the leaf decreased from 34.91%, 5.42%, 43.61% and 19.46% in the uninfected leaf samples to 20.40%, 2.15%, 37.03% and 15.53% in the infected leaf respectively whereas the moisture and ash contents increased by 10.88% and 11.15% in the uninfected leaf sample to 12.51% and 11.24% respectively in the infected leaf samples. The composition of zinc, sodium, magnesium, iron, and potassium in the leaf increased whereas calcium and phosphorous decreased after inoculation with the test fungus. It reduced the protein content from 15.64% in the healthy stem tissue to 12.69% in the infected one, fat from 1.29% to 0.78%, crude fibre from 16.87% to14.62%, and carbohydrate from 31.11% to 25.39%. Also, the fungus caused a reduction of the calcium and phosphorus contents of the healthy stem tissue from 2.09 mg and 326.50 mg to 1.19 mg and 299.10 mg respectively. Infection of the stem with the pathogen led to increasing moisture, potassium, sodium, zinc, iron, and magnesium contents from 11.80%, 230.12 mg, 111. 28 mg, 1.66 mg, 0.89 mg and 0.95 mg to 12.65% , 364.21 mg, 203.64 mg, 3.02, 1.52 mg, and 2.18 mg respectively. The average loss of the major nutrients; protein, fat, and carbohydrate was more in the leaf than stem, 34.29% and 18.14% respectively 8 weeks after planting (WAP).

Biochemical Composition of Seed and Husk of Cowpea (Vigna unguiculata (L.) Walp.) Infected by Colletotrichum destructivum O’Gara in Storage

Colletotrichum destructivum was isolated from infected seeds and pods of cowpea (Var. IAR-48) with typical symptoms of anthracnose disease. The fungus during the pathogenesis, reduced the protein, fat, ash, crude fibre, carbohydrate, calcium and phosphorus, and increased the amount of iron, sodium, zinc, magnesium and potassium in the infected seed and husk. The carbohydrate, protein and phosphorus contents in the healthy husk reduced from 55.05%, 11.21% and 171.85 mg to 39.94%, 8.92% and 42.92 respectively in the infected sample whereas potassium and sodium contents in the healthy pod increased from 1.03 mg and 78.29 to 2.90 mg and 100.65 mg respectively in the infected husk. The potassium, sodium, magnesium and iron increased from 1292.25 mg, 0.19 mg, 0.09 mg and 11.00 mg in the healthy seeds to 1536.03 mg, 0.28 mg, 0.21 mg and 13.19 mg respectively in the infected seeds. The fungus caused the depletion of phosphorus from 498. 06 mg in the healthy to 430.17 mg in the infected seed, protein from 24.09% to 17.86%, carbohydrate from 57.02% to 34.35%, fat from 1.70% to 1.33% and crude fibre from 3.94% to 2.61%. The average loss of the major nutrient values; protein, carbohydrate and fat were 28.95% and 22.55% for seed and husk respectively after 8 weeks of planting.

Endophytic fungi and latent pathogens in the sedge Carex secalina (Cyperaceae), a critically endangered species in Europe

Endophytic fungi are widespread in plants and affect the host fitness and population size. We found 12 fungal taxa in C. secalina, a critically endangered species in several European countries, at two study sites in Poland. The most frequently occurring fungal taxa were Colletotrichum destructivum and Acremonium sp. Both taxa were found in half of the examined tussocks. The highest number of fungal taxa was noted in the C. secalina plants growing in the roadside area, where 7 of the 12 identified fungal taxa occurred. These fungi, inhabiting leaf tissues, are known for their pathogenicity but no visible symptoms of any diseases were observed on C. secalina leaves. This suggests that these fungi are latent pathogens.