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3.3.1.6 Dispersed Remains and Plant Pathogens
The dispersed microfossil record yields a plethora of information on fungi and fungal interactions in the geologic past (Kalgutkar and Jansonius 2000). For example,
small ‘spherules’ that are sometimes attached to the outer surface or occurring
within the body of Carboniferous to Cenozoic land plant spores and pollen grains
obtained through palynological sampling (Fig. 3.3j) (e.g., Daugherty 1941: pg. 43;
Phipps et al. 2000: pl. 2, figs 5 and 6; Aggarwal et al. 2015: figs 2–4) are mostly
interpreted as remains of fungi and compared to modern pollen-colonizing
Chytridiomycota. On the other hand, Mesozoic and Cenozoic non-pollen palynomorph (NPP) assemblages frequently contain spores of microthyriaceous and other
fungi that are morphologically similar to the spores produced by certain present-day
fungal parasites and pathogens (e.g., Höhnel 1924; Van Geel and Anderson 1988;
Kalgutkar and Jansonius 2000; Van Geel 2002; Singh and Tripathi 2010; Kürschner
et al. 2015; Schumilovskikh et al. 2015; Roth and Lorscheitter 2016).
There are certain fungal plant pathogens such as rusts (Pucciniomycetes), smuts
(Ustilaginomycetes), and leaf spot diseases (e.g., Alternaria, Cercospora) (Agrios
2005) that are widespread today but rare or absent in the fossil record (reviewed in
Taylor et al. 2015). This is surprising since innumerable fossils of leaves are available, and one would expect to find at least some showing evidence of these fungi in
the form of lesions or galls (Callow and Ling 1978). However, there is likely a collection bias for undamaged leaves, thus probably discarding leaves with fungal
remains (Taylor and Krings 2010; Krings et al. 2012). While no convincing evidence of fossil rusts has been documented, there are several reports of dispersed
spores which are similar in morphology to extant Puccinia, Gymnosporangium, and
Uromyces (Bradley 1931; Wolf 1969; Kalgutkar and Jansonius 2000). Documented
evidence of fossil smuts is in a similar situation. Most of the reports of fossil smuts
have later been dismissed or remain inconclusive. For example, fossils interpreted
as spore clusters similar to Ustilago have been reported in degrading plant tissue
from Deccan Intertrappean cherts (Cretaceous) from India (Kapgate 2016).
However, none of the specimens figured display features of sufficient clarity to
allow assignment to any group of fungi with confidence. The dispersed spore type
Ustilago deccanii from the same beds was initially reported as a spore of a smut
fungus (Chitaley and Yawale 1976, 1978), but has subsequently been transferred to
Inapertisporites, a taxon used for fossil amerospores of Fungi Imperfecti (Kalgutkar
and Jansonius 2000). No information is available on the nutritional modes of these
fossil fungi. In yet another case, small spores in Saururus tuckerae anthers from the
Eocene of North America were initially identified as a smut fungus (Currah and
Stockey 1991; LePage et al. 1994), but are now thought to represent minute pollen
grains produced by the flower (Smith and Stockey 2007). Another important plant
pathogen today are the leaf spot fungi (Agrios 2005). There are numerous reports of
specks and dots on Mesozoic and Cenozoic plant remains (surveyed in Tiffney and
Barghoorn 1974), and even one report of a putative Paleozoic leaf spot (Wang
1997). More recently, Poinar (2018) reported well preserved pycnidia, formally
described as Palaeomycus epallelus, on an angiosperm leaf preserved in
C. J. Harper and M. Krings
3.3.1.6 Dispersed Remains and Plant Pathogens
The dispersed microfossil record yields a plethora of information on fungi and fungal interactions in the geologic past (Kalgutkar and Jansonius 2000). For example,
small ‘spherules’ that are sometimes attached to the outer surface or occurring
within the body of Carboniferous to Cenozoic land plant spores and pollen grains
obtained through palynological sampling (Fig. 3.3j) (e.g., Daugherty 1941: pg. 43;
Phipps et al. 2000: pl. 2, figs 5 and 6; Aggarwal et al. 2015: figs 2–4) are mostly
interpreted as remains of fungi and compared to modern pollen-colonizing
Chytridiomycota. On the other hand, Mesozoic and Cenozoic non-pollen palynomorph (NPP) assemblages frequently contain spores of microthyriaceous and other
fungi that are morphologically similar to the spores produced by certain present-day
fungal parasites and pathogens (e.g., Höhnel 1924; Van Geel and Anderson 1988;
Kalgutkar and Jansonius 2000; Van Geel 2002; Singh and Tripathi 2010; Kürschner
et al. 2015; Schumilovskikh et al. 2015; Roth and Lorscheitter 2016).
There are certain fungal plant pathogens such as rusts (Pucciniomycetes), smuts
(Ustilaginomycetes), and leaf spot diseases (e.g., Alternaria, Cercospora) (Agrios
2005) that are widespread today but rare or absent in the fossil record (reviewed in
Taylor et al. 2015). This is surprising since innumerable fossils of leaves are available, and one would expect to find at least some showing evidence of these fungi in
the form of lesions or galls (Callow and Ling 1978). However, there is likely a collection bias for undamaged leaves, thus probably discarding leaves with fungal
remains (Taylor and Krings 2010; Krings et al. 2012). While no convincing evidence of fossil rusts has been documented, there are several reports of dispersed
spores which are similar in morphology to extant Puccinia, Gymnosporangium, and
Uromyces (Bradley 1931; Wolf 1969; Kalgutkar and Jansonius 2000). Documented
evidence of fossil smuts is in a similar situation. Most of the reports of fossil smuts
have later been dismissed or remain inconclusive. For example, fossils interpreted
as spore clusters similar to Ustilago have been reported in degrading plant tissue
from Deccan Intertrappean cherts (Cretaceous) from India (Kapgate 2016).
However, none of the specimens figured display features of sufficient clarity to
allow assignment to any group of fungi with confidence. The dispersed spore type
Ustilago deccanii from the same beds was initially reported as a spore of a smut
fungus (Chitaley and Yawale 1976, 1978), but has subsequently been transferred to
Inapertisporites, a taxon used for fossil amerospores of Fungi Imperfecti (Kalgutkar
and Jansonius 2000). No information is available on the nutritional modes of these
fossil fungi. In yet another case, small spores in Saururus tuckerae anthers from the
Eocene of North America were initially identified as a smut fungus (Currah and
Stockey 1991; LePage et al. 1994), but are now thought to represent minute pollen
grains produced by the flower (Smith and Stockey 2007). Another important plant
pathogen today are the leaf spot fungi (Agrios 2005). There are numerous reports of
specks and dots on Mesozoic and Cenozoic plant remains (surveyed in Tiffney and
Barghoorn 1974), and even one report of a putative Paleozoic leaf spot (Wang
1997). More recently, Poinar (2018) reported well preserved pycnidia, formally
described as Palaeomycus epallelus, on an angiosperm leaf preserved in
C. J. Harper and M. Krings