Biological Activity of Four Antifungal Compounds in Immature Avocado

Abstract

Anthracnose caused by Colletotrichum gloeosporioides in ripe avocados originates as latent infections in the immature fruits. Concentrated ether extract of the peel of apparently healthy, immature avocados when bioassayed on thin layer chromatographic plates with conidia of either Cladosporium cladosporioides or C. gloeosporioides produced four inhibition areas at Rf 0.30, 0.32, 0.70 and 0.75 (these were denoted as AvIV, AvIII, AvII and AvI respectively). A hot chloroform extract was partitioned on a silica gel column and the four antifungal compounds were separated. Spectroscopic data revealed that one of these compounds, AvII, was similar to cis‐l‐acetoxy‐2‐hydroxy‐4‐oxo‐heneicosa‐12,15‐diene and another (AvIV) was a long chain saturated compound comprising hydroxyl group(s) having molecular weight of 268. Toxicity of AvII to C. gloeosporioides was 2 times that of AvIV and 6.5 and 7.5 times that of AvIII and AvI respectively. The amounts of these four antifungal compounds increased gradually during fruit development and reached their maxima at harvest. The concentration of AvI, AvII, AvIII and AvIV was 1300, 920, 1050 and 780 μg/g fresh peel respectively in the fruit at harvesting maturity. The amount of AvII and AvIV decreased to 53 and 64 μg/g fresh peel respectively in the fruit at the ripe stage at which neither AvI nor AvIII was detected. This took place in coincidence with the onset of progressive lesion development by the fungus.

Effect of 1-methylcyclopropene (1-mcp) treatment on postharvest quality and antifungal activity of avocado cv. ‘pollock’ under tropical storage conditions

“…According to IR and HNMR spectral studies AV II was similar to the antifungal diene previously isolated by Prusky et al (1982). It is likely that the major antifungal compound separated at Rf= 0.75 for 'Pollock' fruits is the same as AVI, reported by Sivanathan and Adikaram (1989) as we followed the same extraction procedure for compound extraction and used the same solvent system to develop the TLCs used by them. Absence of antifungal activity in 'Pollock' fruits at Rf values 0.3, 0.32 and 0.70 could be due to cultivar differences.…”

“…The antifungal activity of cultivars 'Hass' and 'Fuerte' against the anthracnose fungus Colletotrichum gloeosporiodes was attributed to the presence of a diene (1-aetoxy-2-hydroxy-4-oxoheneicosa-12, 15-diene) in the fruit peel (Prusky et al, 1982). Sivanathan and Adikaram (1989) found four compounds with antifungal activity in cultivar 'Green' fruit peel. The four compounds were denoted as AV I (Rf = 0.75), AV II (Rf = 0.70), AV III (Rf = 0.32) and AV IV (Rf = 0.30).…”

“…The peel extracts obtained were tested for the presence of antifungal compounds using Cladosporium bioassay coupled with thin layer chromatography (TLC) (Sivanathan and Adikaram, 1989). About 5 mg of the peel extract was dissolved in 1 ml of 95% ethanol and 100 µl aliquots of dissolved extracts were spotted on TLC plates (20×20 cm; Whatman 250 µm; aluminium-backed; UV fluorescing).…”

“…The two extract portions were combined and filtered through Whatman No.1 filter paper. The filtrate was collected and evaporated in vacuo at 210 rpm in a rotary evaporator (Stuart RE 300) at 40 ˚C (Sivanathan and Adikaram, 1989).…”

“…The presence of constitutive antifungal compounds in the peel of avocado fruit is one of the major attributes for the quiescence of C. gloeosporioides (Prusky et al, 1982;Sivanathan and Adikaram, 1989). There is a gradual increase in antifungal compounds with maturity, reaching a maximum level by harvesting maturity stage and then dramatically decreases upon fruit ripening enabling fungal activity in the fruit (Adikaram et al, 1993).…”