An assessment of endophytic fungi in needles of three pinus spp. cultivated in South Africa

[摘要] English: Endophytes, in the strict sense, are organisms that cause symptom less infections in plants. Assymptomless mutualists, they can act as biocontrol agents of herbivorous insects and plant diseases.They can also be indicative of host vitality and environmental pollution. Some endophytes,however, are latent pathogens with an endophytic phase.Pine needles are colonised by various species of endophytic fungi. It is well-known that theendophytic biota vary with host species, as well as with time. Therefore the aim of this study wasto qualitatively and quantitatively compare endophyte populations within the canopies of Pinas patula, P. radiata and P. elliottii, during winter and summer, and within the canopies of twoseparate P. radiata trees, over different seasons. Endophytic fungi were isolated from pine needles,sampled in different seasons from various positions within the canopy, by plating surface-sterilisedneedle sections onto cornmeal agar supplemented with antibiotics.In the first study a significant difference (P < 0.05) in endophyte numbers between samplescollected during winter and summer was observed. Pinus patula and P. elliottii were moreintensively colonised during winter than summer. In P. radiata, however, the number of fungiisolated in summer was significantly higher than in winter, but the fungal species isolated wereconsistent. Cydsneusms minus and a sterile white yeast-like fungus were most commonly isolated.Cyclsneusms minus is a latent pathogen causing autumn needle cast, and sterile yeast-like fungusis suspected to be a true endophyte. Similar endophytic fungal species were isolated in the secondstudy, performed on two eight-year-old P. radiata trees. Samples were taken during four seasonsfrom an isolated, solitary tree and one growing in an even-aged, plantation nearby. Five needlefascicles of four different age groups were collected from each tree. One needle per fascicle,including the fascicle sheath, was cut into 12 sections and used for the isolations. In general, fewerendophytes were isolated from the solitary tree than the plantation tree. Qualitative andquantitative differences in endophyte populations were observed within needles as well as betweenneedle age groups and seasons.The aim of the third study was to conduct a qualitative assay of enzyme production of 2 tpredominant fungal endophytes isolated from the pine needles. The enzymes assayed includedcellulase, pectinase, lipase, laccase, phenol oxidase, protease, B-glucosidase, cytochrome oxidase,and peroxidase. Results were consistent with attributes associated with leaf penetration and longtermresidence of fungi within pine needles. All fungi screened produced at least two of theenzymes assayed. Different substrate utilisation patterns suggest biochemical partitioning ofnutritional resources by endophytes. The ubiquitous presence of lipolytic activity in all isolatestested, suggests the ability to lyse cuticular waxes in order for penetration to occur. The toleranceof most tested fungi to tannic acid (phenol oxydase production) suggests low sensitivity to phenoliccompounds (tannins etc.) normally present in pine needle tissue.Management practices in plantations that reduce or increase the environmental stress onindividual trees, thereby influencing endophytic populations, could have distinct beneficial ornegative effects on the general vitality of trees. The most important effects of certain practiceswould be the influence they have on latent pathogens such as C minus. Further investigation offoliar endophytic fungi of intensively managed pine plantations is therefore justified with a view tounderstand the effects management practices have on their ecology.

[发布机构] University of the Free State