Fungi Associated with and Influence of Moisture on Development of Kernel Mold of Hazelnut

Abstract

Kernel mold on hazelnuts is defined by the United States Department of Agriculture, U.S.A., as any visible fungal growth either on the outside or inside of the kernel. Only one yeast and one filamentous fungus have been associated with kernel mold of hazelnut in Oregon. In this report, fungi were isolated from kernels with mold and identified using morphological and molecular characters. Penicillium spp. were isolated most often from kernels with mold, but species of Aspergillus and Cladosporium and Diaporthe rudis were also frequently isolated. Additional fungi from three other genera were also isolated. All of the same fungi were also isolated from symptomless kernels. Eremothecium coryli or Ramularia sp. previously associated with kernel defects in Oregon were not found associated with symptoms of kernel mold. Incidence of mold was the highest when nuts were incubated in moist chambers on wet, nonautoclaved orchard soil and was significantly higher than kernel mold found in nuts incubated on either air-dried soil or wet, autoclaved soil. Preventing hazelnuts from coming in contact with wet soil in the field using elevated wire screens resulted in significantly less mold development in two out of three years evaluated. Nuts on screens had a greater chance to dry out between rainstorms as measured by significantly lower nut moisture levels at harvest.

Molecular Characterization of Diaporthe Species Associated With Hazelnut Defects

“…Only three strains were identified at the species level in the study, but this suggested that D. eres was responsible for the visible brown spots on the kernel surface and the internal discoloration observable after the nut was cut in half (Battilani et al, 2018). D. eres was also recently reported by other authors as associated with hazelnut trunk cankers in Oregon (Wiman et al, 2019), while D. foeniculina was mentioned by Guerrero et al (2019) as causing black tip and necrotic spots on hazelnut kernels in Chile and D. rudis was detected in hazelnut kernels with visible mold in Oregon (Pscheidt et al, 2019).…”

“…When comparing the hazelnut taxonomic composition with that of other nuts (mainly walnuts and almonds), it is interesting to see that each study reports slightly different Diaporthe species present in the considered matrix, with D. rostrata, D. amygdali, and D. eres being more recurrent. D. foeniculina has been reported in sweet chestnuts from Italy and hazelnut kernels from Chile (Annesi et al, 2016;Guerrero et al, 2019), D. rudis in hazelnut kernels from Oregon, United States (Pscheidt et al, 2019), and D. australafricana from Chilean hazelnuts (Guerrero and Pérez, 2013); among these species, only D. eres was found to be related to the hazelnut strains studied here.…”

“…Several fungal genera were isolated in this survey; they may have been influenced by the hazelnut varieties, as previously stated for D. rudis (Pscheidt et al, 2019), but this factor cannot be discussed in this study because a mix of different hazelnut varieties were grown in the sampled orchards. Among the isolated fungi, the key role of Diaporthe spp.…”

Draft Genome Sequence of a New Fusarium Isolate Belonging to Fusarium tricinctum Species Complex Collected From Hazelnut in Central Italy

“…In Oregon, Pscheidt et al (2018) , studying the fungi involved in kernel mold on hazelnut, found out that Penicillium spp., Aspergillus and Cladosporium spp., and D. rudis were frequently isolated, together with F. lateritium (identified by ITS and EF-1α).…”

Data_Sheet_1.PDF

“…This should be studied deeper in order to find out eventual interaction between Diaporthe and related defects with Aspergillus; this genus includes well-known fungi that can lead to severe economical and health impacts due to mycotoxin production (Ozay et al, 2008;Kabak, 2016;Houshyarfard and Javadi, 2018). The most isolated genus was Penicillium, in agreement with Pscheidt et al (2019), but relations between this fungus and defects were not found. Nevertheless, Penicillium also includes mycotoxin producing fungi and merit to be studied deeper for possible health issue implications.…”